SUBSONIC AIRCRAFT: CONTRAIL AND CLOUD EFFECTS SPECIAL STUDY END-OF-MISSION REPORT
Dave Starr-Mission Scientist
Steve Hipskind-Project Manager
TABLE OF CONTENTS
- OVERVIEW OF MISSION GOALS AND RESULTS
- MAJOR RESULTS OF PI GROUPS
- CLOUD MICROPHYSICS
- MASP; Baumgardner, Barr, and Gandrud
- PVM; Gerber
- CVI; Twohy, Gandrud
- P-Nephelometer; Lawson
- VIPS; Heymsfield
- Cloudscope; Hallett
- AEROSOL PROPERTIES
- UNH AEROCOMP; Talbot, Dibb, Loomis
- Real-time aerosol characterization; Coggiola
- CCN; Hudson
- Ice nucleating aerosols; Kreidenweis, Rogers, and DeMott
- Replicators; R. Pueschel
- ATMOSPHERIC CHEMISTRY
- Chemical ionization mass spectrometer; Ballenthin
- T-39 Highlights; Anderson
- ATHOS; Brune, Tan, Faloona
- In situ NO, NOy, O3; Weinheimer, Campos, Ridley
- In Situ CO2, CO, CH4, N2O and H2O; Sachse, Collins, Anderson
- METEOROLOGY AND DYNAMICS
- RADIATION AND REMOTE SENSING
- RAMS; Valero, Bucholtz
- DC-8 scanning lidar; Uthe, Nielsen
- HIS and MAS; Moeller, Ackerman, Revercomb
- TSCC, CLS, MIR and MAS; Spinhirne
- Satellite Observations; Minnis
- CART GROUND BASED OBSERVATIONS
- Ground based spectroscopy-Pilewski
- Cloud Infrared Doppler lidar - Eberhard
- Contrail-Cirrus Studies at FARS-Sassen
- THEORY TEAM
- CLOUD MICROPHYSICS
- FUTURE ANALYSIS AND REPORTING OF DATA
The SUCCESS project was conducted from the Kansas State
University airport facilities in Salina, Kansas from April 8, 1996 until
May 10, 1996, with an extension from May 10 until May 15, 1996 at
NASA's Ames Research Center in Moffett Field, Ca.
SUCCESS had several objectives. We planned to better
determine the radiative properties of cirrus clouds and of contrails so
that satellite observations can more reliably measure their impact on
Earth's radiation budget. We hoped to determine how cirrus clouds
form, whether the exhaust from subsonic aircraft presently affects
the formation of cirrus clouds, and if the exhaust does affect the
clouds whether the changes induced are of climatological significance.
We also planned to develop and test several new instruments.
Finally, we expected to better determine the characteristics of
gaseous and particulate exhaust products from subsonic aircraft and
their evolution in the region near the aircraft.
In order to achieve our experimental objectives we used the
NASA DC-8, and T-39 aircraft as in situ sampling platforms. We also
employed the NASA ER-2 aircraft as a remote sensing platform. The
NASA 757 was used as a source aircraft for studies of contrails and
exhaust. Table 1 lists the flights that were made by these aircraft.
Many of the flights were made over the Department of Energy's
Climate and Radiation Testbed (CART) site in Northern Oklahoma,
where a suite of ground based remote sensing instruments was
located. The DOE also operated an Egret and a Twin Otter aircraft,
mostly using remote sensing instruments. The dates on which we
flew over the CART site, and those on which the Egret or Otter flew
are also noted in Table 1.
Table 2 list the targets of the various flights, as planned and as
flown. We were able to find meteorological opportunities for most of
the planned missions in the vicinity of Salina, Kansas. However, the
cirrus-over-water flight could not be done from Salina, but instead
was done over the Pacific Ocean using Ames Research Center as a
base of operations. Although we attempted a diurnal chemistry
flight, weather conditions prevented it from being done. That was
the only objective for which a research flight was not completed. As
described below by the various PI groups most of the instruments
functioned for the majority of the mission.
There were a large number of interesting science results from
the SUCCESS project. Preliminary discussions of these are outlined by
the PIs below. Although it is too early to determine if every
question posed for SUCCESS was answered, it is clear that
considerable progress was made.
We learned a great deal about the radiative properties of cirrus
clouds and contrails. We made a number of multiple-aircraft flights
with aircraft making radiative as well as in situ measurements over
the well-instrumented CART site. We had several coincident flights
with satellite overpasses. We obtained the most complete set of ice
cloud particle size distributions and cloud optical properties to data
which should help resolve long-standing debates about the role of
small particles in ice cloud radiative properties, and the shape of the
scattering phase function for ice particles of various shapes. We
made numerous flights in which we obtained vertical profiles of
cloud properties. We also performed several flights in which we
were able to help calibrate ground-based and aircraft-based remote
sensing instruments.
We obtained much data which should shed light on the
formation mechanisms of cirrus clouds and contrails. We measured
the supersaturations at which ice nucleation occurs which will aid in
the prediction of ice formation, we observed contrails at
temperatures where existing theories did not predict their
occurrence so new theories may be needed. We made the first
extensive measurements of ice nuclei (IN), cloud condensation nuclei
(CCN), and condensation nuclei (CN) concentrations as well as
compositions in the upper troposphere. We observed the swelling
and pre-activation of aerosols providing insight into the nucleation
process, we observed the scavenging of aerosols by ice crystals, and
we collected data on the (surprising) composition of the aerosols in
the upper troposphere over the US. We also found much evidence
for significant mixing between the surface and upper troposphere,
and possibly on the alterations of aerosol properties which occur in
convective cloud systems. We also observed a number of interesting
dynamical phenomena associated with the tropopause.
One of our goals was to develop and test a series of new
instruments. We were fortunate in that each of the new instruments
on the DC-8 performed very well. A new suite of instruments for gas
phase chemistry, aerosol chemistry and microphysics is now
available to the community. In addition, we performed numerous
instrument intercomparisons. For instance, we had at least 5
independent air temperature measurements, 4 independent water
vapor measurements, as well as multiple CN, ice water content, IN
and particle size measurements. These already indicate not only
good agreement in some cases, but reveal problems with some
measurements previously thought to be reliable.
Our goal of obtaining new Near Field data was clearly met and
exceeded. We were able to obtain both gas and particle data from
very close to the engine (< 50m) to far from the aircraft (>10 km) for
a variety of aircraft. Data were obtained in persistent and not-
persistent contrails, in exhaust which did not form a contrail, at a
variety of altitudes and for fuels with a large range of sulfur
contents. Unique data on concentrations of sulfur, nitrogen, and odd-
hydrogen species, as well as on particles were obtained. Numerous
emission indices were determined for a variety of aircraft and flight
conditions.
Table 1: SUMMARY OF SUCCESS FLIGHTS
_____________________________________________________________
Date DC-8 ER-2 T-39 757 CART* Purpose
_____________________________________________________________
4/4 X Test flight
4/8 X Ferry flight
4/10 X Test flight at Ames
4/11 X Transit flight
4/13 X X X DC-8 transit and
contrails, ER-2
Cart site for clear sky
Radiation
4/15 X X X X Coordination practice,
near field sampling and
clear sky radiation
4/16 X X X X Near field sampling by
T-39 Cirrus profiling by
DC-8 radiation
observations of
contrails and cirrus by
ER-2
4/18 X X Xe Near field sampling
without contrails. DC-8
sampled supercooled
water cloud.
4/20 X X X Xe,o T-39 inst. test flight.
ER-2 and DC-8 observed
cirrus clouds with
multiple vertical profiles.
4/21 X X X Vertical profiling of
Cirrus clouds observed
from the top. Contrail
sampling by DC-8.
Studies of convective
clouds
4/23 X ER-2 overflew wave
clouds
4/24 X X X T-39 did near field
sampling of DC-8
exhaust. DC-8 did
vertical profile in cirrus.
4/26 X X T-39 followed
commercial aircraft, ER-2
did satellite underflight.
4/27 X X X Xe,o DC-8 sampled contrail of
T-39, and profiled cirrus
that were observed by
the ER-2
4/29 X X X DC-8 profiled stratus
clouds at CART site for
radar calibration. T-39
sampled DC-8 exhaust.
4/30 X X X DC-8 studied wave cloud
and practiced finding
757 exhaust. T-39
sampled 757 exhaust.
5/2 X X ER-2 and DC-8 studied
wave cloud over Boulder.
5/3 X X X X Xe Sampling of 757 contrail
by the DC-8 and T-39.
5/4 X X X X Xe,o Sampling of the 757
contrail by the DC-8 and
T-39.
5/7 X X X X Sample persistent
contrails over Nebraska
5/8 X X X study convection, T-39
studies DC-8 exhaust.
5/10 X X X transit to Ames or
Langley
5/12 X X Persistent contrail.
5/15 X X Cirrus over water.
_____________________________________________________________
Total 19 18 15 4 11
Flight
hours 110 85
*e=Egret, o=Twin otter
Table 2: SUMMARY OF FLIGHT OBJECTIVES DURING SUCCESS
______________________________________________________________
Missions Flights Flights
Proposed Flown
______________________________________________________________
Contrails 3 6
Cirrus 2 7 (+1 stratus)
Lenticular Clouds 2 2
Cirrus over water 2 2
Near Field 3 3 (757) (parts of 11)
Second Priority Missions:
Outflow from Convective Clouds 2 2
Diurnal Chemistry in Clear Skies - 0
Clear sky aerosols - many
______________________________________________________________
Back to TOC - Overview of Mission Goals & Results
The SUCCESS research flights offered a unique opportunity to evaluate aerosol/cloud interactions in upper tropospheric cirrus and mountain induced wave clouds. Preliminary results show that number concentrations measured with the NCAR Multiangle Aerosol Spectrometer Probe (MASP), that measures particle size from 0.35 mm to 20 mm, increased by factors of 10-100 above ambient number concentrations (typically 1 cm-3). The in-cloud concentrations are roughly of the same order as the number concentration reported for the CN measurements outside cloud. This result implies that for both the wave cloud and cirrus events the majority of environmental condensation nuclei are being activated and grow to sizes detectable by the MASP. More careful analysis is required to better quantify this observation. The penetrations of the 757 exhaust provide a comparison of particle sizes in conditions where contrails either did or did not form. Preliminary analysis indicates the MASP saw little increase in number concentrations over background values in exhaust plumes where visible contrails were not formed. In visible contrails, however, the measured concentrations were several orders of magnitude above ambient values. This observation indicates that contrail particles are much larger than non-contrail particles and, with the accompanying gas measurements, will provide data needed to understand the contrail formation process and the underlying microphysics. Finally, the wave cloud study of Flight 12, on May 2, had the DC-8 making multiple passes through the tropopause while flying along and across the front range of the Rocky Mountains. The size, number, surface and volume of the particles showed significant changes when transitioning between troposphere and stratosphere. Studies of these transitions will provide insight into particle transport processes across the tropopause and will help better define particle lifetimes in these two regions of the atmosphere. Once the refractive index information available from the MASP is processed, it will also give us a clue as to differences in particle composition between the troposphere and lower stratosphere and possibly these composition differences or similarities will indicate the degree of particle transport across the tropopause.
A new aircraft instrument, the PVM, was deployed for the first time on a jet aircraft, and operated for the first time above the boundary layer and at temperatures as cold as -60 C. The probe operated exceptionally well; although, its interaction with its fairing caused some loss of data. A unique high-frequency data set was collected for ice water content (IWC) and ice crystal effective radius in cirrus, mountain- wave, and contrail ice clouds. Analysis of this data will give an unprecedented high-resolution look at ice cloud structure. The most significant highlight is the apparent close agreement between IWC measurements made with PVM and the NCAR CVI for ice clouds with small crystals. Confidence in the measurements made with both experimental techniques is thus generated, and suggests that the CVI is also properly measuring IWC when crystals are large (barring aerodynamic effects caused by the aircraft's fuselage.) Another highlight is the surprisingly low IWC (several mg m-3) and effective radii (between 1 mm and 2 mm) found in the 757 contrail on the May 4 flight.
In SUCCESS, the CVI system measured the properties of cloud droplets/crystals with aerodynamic diameters larger than about 3 mm, and was also used at times as a more standard aerosol inlet to sample ambient aerosol particles. Number concentration and volatility of the ambient aerosol in the upper troposphere was variable, with the percentage of particles volatilized at 250 C ranging between about 10 and 80% for particles larger than 15 nm. Quality high-rate (1-5 Hz) measurements of number and ice water content of particles larger than 3 mm were obtained in T-39, DC-8, and 757 contrails, with typical measurements in the 757 contrail being 10-20 particles cm-3 and 1-2 mg m-3 of water. Volatility of the residual particles from the contrail ice was substantially higher when low-sulfur fuel was used. Particles larger than 3 mm that were not associated with any water were also sometimes seen in aircraft exhaust plumes. Ice water contents of cirrus near the CART site varied between a few to more than a hundred mg m-3. The CVI ice water content measurements agreed within 25% of those measured by the PVM in wave clouds, where both instruments efficiently measured relatively small crystals. Residual particle concentrations measured with the CVI were as expected (a few cm-3) for short-lived contrails and wave clouds. However, for cirrus clouds, residual particles were present in unexpectedly high concentrations (up to 100 cm-3), and were not usually volatilized at 250C. Further analysis will be required to determine whether these observations are real or due to measurement artifact.
The P-Nephelometer digitally images particles from 10 mm to 2 mm and simultaneously measures the scattering phase function. The intense eight-month design and fabrication of this new instrument was completed within only a few days of the start of SUCCESS. The field project served as both a shake-down and an opportunity to collect unique data. Much has been learned about the operation and performance of the probe. The instrument suffered from occasional hardware failures and some software bugs, but, by in large, it collected unique measurements in cirrus, contrails and wave clouds. Several gigabytes of digital images were collected along with scattering phase function measurements. We have already seen some tantalizing tidbits of exciting new measurements from the P-Nephelometer. Samples of the digital images were presented at one of the science meetings held during SUCCESS. A histogram of particle size distribution in thin cirrus and contrail showed that most of the ice crystals were < 50 mm in size. The smaller particles were mostly plates, columns and spheres while the (few) larger particles were typically rosettes. The scattering phase function measurements were collected but can not be analyzed without post-calibration work that must be performed in the laboratory. (There was insufficient time to do the calibrations prior to the field project.) There is considerable processing and analyzing of the collected data that must be performed before the data set is in suitable form to distribute to other investigators. This is mainly to recover data, which, due to hardware failures, was not handled properly in real time by the image processing hardware, and, to develop new analysis software to automatically size particles, determine concentration, crystal habit and scattering phase function.
Our suite of microphysical instruments focused on several of the key scientific questions defined in the SUCCESS mission statement by coupling continuous measurements of key state parameters with the collection of particle size spectra. The four state parameter instruments (cryogenic hygrometer, UV hygrometer, temperature, liquid water content) provide an independent, corroborative set of measurements available to SUCCESS investigators. We added three Particle Measuring Systems (PMS) probes sizing from 15 mm to 6 mm and our Video Ice Particle Sampler (VIPS) imaging data above 5 mm to increase the overall range and quality of the ice particle size spectra data available to the group. The hygrometers indicated highly ice-supersaturated environments in virga (ice streamers) produced by ice crystals sedimenting from contrails; at the leading edges of wave clouds sampled at temperatures between -38 and -64 C; and, numerous times, at the tops of cirrus ``generating cells'' (convective cirrus elements). Surprisingly large ice crystals were observed within and below the precipitating contrails, with the largest sizes increasing from 50 mm within to as large as 300 mm below the visible contrails, although ice crystals of order 10 mm diameter dominated throughout. In cirrus, ice crystal sizes increased from order tens of mm near cloud top to hundreds of mm near base, but throughout size spectra were broad and concentrations were dominated by the sub- 100 mm ice crystals. Particle sizes in the leading edges of the wave clouds (10 mm diameter) were larger than might be expected at low temperature when there is only a few seconds for ice particles to grow. Synthesis of our state parameter and micro-physical data will increase the SUCCESS project team's understanding of the response of ice particles (both in contrail and natural cirrus) to the environmental relative humidity field and help characterize the conditions which lead to contrail initiation and development.
The following instruments were employed in SUCCESS. The DRI cloudscope - an imaging microscope with field of view 0.5 X 0.5 mm and resolution down to 1-2 mm obtained data (as a video record) on 15 flights. The DRI/Ames replicator - obtained permanent replica record for subsequent optical and SEM analysis on 8 flights and nitron doped replica for nitrate analysis on 3 flights. Key information: simultaneous measurements of a wide dynamic range of particle sizes (few mm to mm) and particle phase with time resolution of a few tenths second. Results:
- High concentrations (few/ml) of 5/10 mm ice particles in fresh contrails.
- Cloudscope gives zero concentration on the evaporating tail of a contrail which still appears visually white, showing that the particles are less than a few mm in size but greater than approx. 1 mm or alternatively of low density.
- Cloudscope shows the presence of a few particles in contrails which evaporate to leave a soot-like residue.
- Shows the presence of particles at low temperatures <-65C which evaporate more slowly as the size becomes smaller suggesting the presence of a component other than ice with a lower vapor pressure.
- There is some evidence of particle conversion to a liquid phase as they evaporate suggesting the presence of a soluble component which is reluctant to evaporate.
- It is highly noticeable that in natural cirrus and in cirrus with contrail regions of 'small' ice crystals 5/10 mm occur dimension 100m; also regions of mixed size (small and large, few 100mm); also regions of only large crystals. This observation suggests local growth and evaporation possibly in a gravity wave.
- Early contrail differs significantly from natural cirrus; aged contrail may differ depending on dynamical history with likelihood of increased opacity from excessive numbers of small particles, consistent with Hudson's CCN measurements.
- Old contrail and natural cirrus appear to contain multi-habit crystals in the same air parcel - extreme habit plates and columns - suggesting a defect controlled growth regime and a low prevailing supersaturation.
We have been fully operational throughout the deployment. Through Flight 14 (4 May) we collected 180 filter samples for determination of water soluble ionic compounds in the particle phase (no filters were collected on the test flight out of Ames). All filters through flight 12 have been successfully returned to the lab at UNH, analyzed there, and the data has been made available to the science team. We expect that results for Flights 13 - 15 should be available by 8 May and that all samples from subsequent flights will be turned around at a similar rate. Our sampling has been restricted to legs at constant flight level; the flight plans have resulted in a data set biased toward the upper troposphere, with quite a few lower stratosphere samples included. All but 6 of the samples were taken in the 4 - 13 km (pressure altitude) range, with at least 75% above 8 km. Our samples have shown no enhancements of aerosol SO4= or NO3- in any of our encounters with the plume or contrail from the T- 39 or DC-8. (Samples collected behind the 757 have not yet been analyzed.) In many cases the time in-plume was quite short relative to our sample integration time, but even when we maintained good contact with T-39 exhaust on Flight 9 (27 April) we did not find elevated aerosol SO4= or NO3- concentrations. The lack of a signal on our filters would appear to imply that the volatile ultra-fine particles measured in the near-field by the T-39 remain very small during the 10s to 100s of seconds of aging before sampling from the DC-8. It should be noted that our longest time "in-plume" behind the T-39 was on a day when the contrail was so short-lived that the DC-8 could not get into it before the visible contrail was gone. The 4 May flight (number 14) behind 757 represents the only time so far that we may have gotten good samples of contrail. It will take quite a lot of effort (and time) to correlate our sample intervals to fast response instruments measuring cloud microphysical properties in order to determine how much time we were in or out of cloud during each period. (This will also require access to these other data sets after they have been released by the various PIs.) However, a qualitative assessment of our own data suggests that any effects of cloud processing on the chemical composition of aerosols have been quite subtle and may not be possible to verify above spatial and temporal variability in clear air. On the larger scale, our samples reveal some interesting aspects of free tropospheric aerosol composition over the study area. We find no evidence for H2SO4 in the condensed phase below 7 km and only a small fraction of the samples at higher levels seem to be dominated by H2SO4. Abundant NH3 throughout the troposphere partially to completely neutralized the H2SO4, resulting in NH4+/SO4= equivalence ratios in the majority of our samples in the range of 0.5 - 1.0. About 10% of our samples show NH4+ to be in excess of SO4=, in most of these there is ample aerosol NO3- to balance the excess NH4+ (implying NH4NO3 aerosols in the upper troposphere). We were also surprised to find that the measured cations often exceed the measured anions (implying a basic aerosol, since we do not measure H+ or anything in the CO2 system). High levels of Ca2+ (and occasionally Mg2+) derived from surface soils join with NH4+ to overwhelm the acid anions. Given the altitudes we have been sampling, there must be very vigorous mixing through nearly the entire depth of the troposphere. On the past several flights over Kansas and Oklahoma we have seen a tendency for a more acidic aerosol, perhaps reflecting weaker sources of surface dust after the rains of past week or so (though it is not clear that the source regions are local and we are not yet aware of temporal variations of soil conditions in potential sources upwind to the west). In more of a case study mode, we have sampled several combustion plumes, perhaps reflecting the frequent stubble burning that was pervasive in Kansas and Oklahoma early in the mission. We also feel we have evidence of convective pumping of boundary-layer air up to flight level, though it was not apparent during the intentional circling of the isolated anvil on Flight 7 (21 April). Our samples collected just above 6 km near 16:00 (local time) on 27 April (Flight 9) showed 2- to 6-fold enhancements of NO3-, SO4=, NH4+ and Ca2+ relative to those on the identical track about 3 hours earlier. Even higher concentrations of these same tracers were encountered at 11 km on Flight 7 as we flew along the line of convection that was touching off tornadoes in western Arkansas.
As a new instrument, the SRI real-time aerosol characterization instrument performed well during the SUCCESS mission, acquiring aerosol mass spectra on all flights with an average uptime of 95%. More than 25,000 spectra were acquired during the mission. Although the external sampler was not optimized for larger aerosols (> 0.5 microns), our sampling rate corresponded well with that reported by others. In general, our aerosol detection rate was highest during cirrus cloud transit, and significantly lower during contrail penetration. Higher rates were observed when flying below the contrails than when flying in the contrails, and very few aerosols were observed when above the contrails. At flight levels above approximately 39,000 feet in clear air, the aerosol sampling rate was essentially zero. After examining the bulk of the mass spectra, we have found numerous examples of aerosols containing a variety of chemical species, including ammonium sulfate (and/or bisulfate), ammonium nitrate, sodium sulfate (and/or bisulfate), sulfuric acid (most notably while following the 757), calcium nitrate, and sodium bicarbonate. Additional laboratory calibrations are planned to confirm these assignments, as well as to establish the approximate sizes of these aerosols. The vast majority of the aerosol spectra appear to consist of water only, either because the core was too small to be detected by the instrument, or it did not volatilize at 600 deg C. Back to TOC - Real time aerosol characterization
There were much higher CCN concentrations in the 757 exhaust at high (>35k') altitudes than has been the case for our previous measurements in jet exhausts. Preliminary cursory comparisons with CN measurements by other investigators indicate that the CCN/CN ratio is much higher than the 1% we have previously measured (e.g. Pitchford et al. 1991). The 757 appeared to produce much fewer CCN at the lower altitude (30k'). The CCN may be a function of the amount of sulfur in the fuel. As in previous projects there seems to often be a middle atmospheric layer that is depleted of particles. This may be the result of cloud scavenging processes (Hudson and Frisbie 1991). In these layers there seems often to be high concentrations of CN suggesting that small particles are produced where there is less surface area. This in fact is similar to the preliminary results from the recent ACE-1 experiment in the tropics and southern Hemisphere. At the higher altitudes near the tropopause the CCN concentrations were rather high and they had a rather low volatility temperature characteristic of sulfuric acid rather than ammonium sulfate (100 C rather than 200 C). This might be characteristic of the aircraft exhaust plumes, which seemed to also be as volatile. This points to the possibility that aircraft are a significant source of CCN in the upper troposphere. If so this might have important climatic implications. A large collection of high altitude CCN measurements were made for the first time. This will provide the beginnings of a climatology of CCN at high altitudes. Back to TOC - CCN
Our aerosol instrumentation operated every flight on the NASA DC-8 during the SUCCESS project. We measured ice nucleating aerosols (IN) over a wide range of temperature (-15 to -40C) and humidity (ice saturation to 20% water supersaturation). We also collected IN and ambient aerosols for later analyses using single particle electron microscope techniques, and we made continuous measurements of condensation nuclei (CN). The real-time IN and CN measurements have fast enough response that it may be possible to estimate profiles of aircraft exhaust plumes, atmospheric layers and cloud structure. To our knowledge, this is the first attempt to obtain relatively fast response continuous measurements of IN concentrations, in real time, from an airborne platform. At this early stage of analysis, we can make some general conclusions. The CN data clearly identify aircraft exhaust penetrations, and will be used to segregate IN concentrations and chemical composition data into background and contrail-influenced subpopulations. Typical background IN concentrations are on the order of several per liter, with a range from 0 to several tens per liter. Large increases in freezing nuclei (at ~-30C) are not apparent in jet exhaust regions. Initial results from electron microscopy and x-ray analyses show that silicates and metals are detected in the IN fraction, with a wider range of chemical composition in samples from the full aerosol spectrum. However, definitive statements with regard to the chemical composition of the IN and non-IN fractions require analyses of a much larger number of samples, currently in progress. Back to TOC - Ice nucleating aerosols
The atmospheric aerosol behind an aircraft appears distinctly different from the "background" aerosol. The distinctions are: 1. Occasional high concentrations of small (D<0.1mm) spherical (combustion-produced) particles; 2. Appearance of large (D>1mm) crystal-like particles. These particles could either be generated by aircraft, or their origin is the background aerosol that is modified during the combustion process. Morphological and elemental composition analyses are in progress to identify the mechanisms of formation. Similar to tropical cirrus investigated in TOGA-COARE, continental cirrus also contain an abundance of small (micrometer- size) particles that might dominate the clouds' radiative properties. Replicator tapes need to be analyzed to quantify their appearance. The first intercomparison of Goodman replicator samples between contrail ice and cirrus ice indicates that natural cirrus particles are larger but less abundant than are contrail ice particles. Back to TOC - Replicators
On May 3rd and 4th the T-39 participated in an aircraft chase of the B-757 under conditions where the B-757 was burning low sulfur fuel in one engine and high sulfur fuel in the other. The concentrations of the target exhaust products, NO2, HNO2, HNO3, SO2 and H2SO4 were measured within the individual plumes and near field wakes at separation distances ranging from 0.1 km to 10 km. The signature of the exhaust gases in the mass spectrum were clearly discernible with either fuel relative to the ambient concentrations of the measured species. Sampling of the low sulfur exhaust trail indicated a substantial reduction (~x5) in the observable gas phase SO2 and H2SO4 relative to that found in the high sulfur exhaust trail under identical sampling conditions. The concentrations of the NOy species were found to be essentially invariant with respect to fuel sulfur content. Back to TOC - Chemical ionization mass spectrometer
Observations of aerosol/trace gas emissions and wake/plume dynamics were obtained from the T-39 on 14 separate flights during the SUCCESS mission. On 10 of the flights, data were recorded within the wake of the NASA DC-8 or B757 aircraft at separation distances ranging from < 50 m to > 10 km and at altitudes ranging from the surface to near 13 km. Two of the flights were devoted to sampling the B757 exhaust as it alternately burned fuel of high (~700 ppm) and low (< 20 ppm) sulfur content. Important new information gathered in these flights include:- Modern aircraft engines appear to generate 1-5 x 1015 >20 nm diameter soot particles per Kg fuel burned at cruise altitudes. This emission index (EI) may be slightly pressure/temperature dependent as most altitude profiles suggest values increase a factor of 2 between the surface and 12 km. -Aircraft, when burning nominal sulfur level Jet A fuel, generate an aerosol fraction volatile at < 290¡C which is 10-20 times more abundant than the soot component. These aerosols typically are < 20 nm in size and exhibit an EI which increases somewhat with decreasing atmospheric pressure/ temperature. They are present within 50 m (plume age of 0.25 seconds) behind the source aircraft engine and appear to grow in size with age and in high humidity/contrail producing situations. Their numbers are significantly reduced in heavy contrail cases and by decreasing the level of fuel sulfur, suggesting they are both soluble and most probably composed of sulfuric acid or sulfate. Back to TOC - T39 Highlights
Of the 14 flights to date, ATHOS has observed OH on all flights and HO2 on 5 flights. All data are recorded at 5 Hz, and statistically significant OH signals are produced in 0.2 seconds in aircraft contrails. Although ATHOS is not yet well-calibrated, preliminary looks at the data suggest the following observations. First, the HO2 to OH ratio was generally in the range of 10 to 50 for mostly clear-sky conditions. Its dependence on altitude, solar UV, water vapor, NO, and other factors has not yet been determined. Second, in the near- field contrails of both the 757 and the T-39, OH was enhanced above ambient by a factor of 5 to 10, while HO2 was decreased a factor of 2 to 3. The anticorrelation between OH and HO2 was strong, although it is not yet clear if the increase in OH was equal to the decrease in HO2. Third, in the DC-8 contrails, which were older when observed than the 757 contrails were, the enhancement in OH was typically only a factor of two or three. Laboratory studies will be necessary to guarantee that these enhancements are not instrument artifacts. Fourth, OH was not enhanced in clouds, and after more analysis, may be shown to actually decrease. Last, while determination of OH and HO2 mixing ratios awaits post-flight calibrations, estimates using a preliminary calibration suggest that the OH mixing ratio is in the range of a few tenths of a pptv and the HO2 mixing ratio is in the range of a few pptv. Back to TOC - ATHOS
We measured NO, NOy, and O3 with 1-sec time resolution. We made two measurements of NOy, one through an aft-facing inlet to provide gas-phase NOy (plus aerosols smaller than a micron or so), and the other through a forward-facing inlet to sample particulate NOy with an enhancement by up to a factor of 50 relative to the gas phase. With measurements of the gas phase NO/NOy ratio, and in combination with the numerous aerosol measurements on board, we will look for heterogeneous effects on NOy partitioning arising from reactions on contrail particles, natural cirrus particles, or other aerosols. With measurements of particulate NOy we will look for the presence of NOy in the condensed phase. If much NOy is present in larger particles, then sedimentation will transport NOy downward. We have yet to determine the effects of particles on the NO/NOy ratio, but we saw numerous cases in which NOy was present on particles in amounts comparable to, and, in some cases, in excess of gas phase amounts. Very large amounts of particulate NOy were generally seen in low-level stratus near the airport, while the amounts detected in cirrus were more variable, though cases of significant amounts (10%) were not rare. Indeed on most flights we saw some particulate NOy, ranging from a few percent to amounts comparable to simultaneously measured gas phase amounts (about 1 ppb in one case). Particulate NOy was not associated with comparable deficits in the gas phase abundance. Little or no particulate NOy was seen in the relatively young contrails behind the 757, while larger amounts were seen in the relatively older DC-8 contrails sampled over the Pacific on 960512. This suggests an increase with time in particulate NOy in contrails. On two flights we saw enhanced NO and NOy in association with convection that may have resulted from lightning. On 960421 we saw enhanced NOy, most of which was NO, in turbulent air at the edge of a convective storm with tops to 55 kft. On 960508 we flew in the anvil of a mesoscale convective system where we saw more sustained high levels of NO, with two cases with values as high as 500 to 1000 pptv for 10 minutes each in contrast to ambient levels under 100 pptv. The exhaust measurements are critical to the measurement of emission indices (in conjunction with DACOM measurements of H2O, CO2 and CO) and will also contribute to inferences on plume chemistry. During the 757 sampling we saw sustained high levels in the 10s of ppbv range of NOy (nearly all of which was in the form of NO) with peaks to larger than 100 ppbv at times. When sampling DC-8 exhaust, short-duration peak values were in the 1 to 10 ppbv range. Back to TOC - NO, NOy & O3
The Langley airborne spectrometer package performed well throughout SUCCESS, providing fast-response, high precision measurements of the above five tracer species with duty cycles generally >90% on all missions. The data are currently undergoing Quality Analysis and 1-second averaged data will be archived well in advance of the first data workshop in October. The quality of the water vapor measurements are of particular note, as SUCCESS was only the second deployment of the new LaRC open-path tunable diode laser (TDL) hygrometer and its performance characteristics were not previously well-documented. Preliminary analysis of SUCCESS data recorded above 5 km altitude indicates this instrument had a precision approaching 0.1 ppm for 1-second averages of 20 Hz-response data. Its absolute measurements were also in good agreement with mixing ratios calculated from the aircraft dew/frost hygrometer data within the instruments' range of overlap. Field analysis of the LaRC tracer species data revealed a number of interesting findings and observations: Large combustion plumes with chemical signatures typical of biomass burning and containing significant aerosol enhancements were observed on a number of flights over the ARM site. Crossings of the T-39, DC-8, and B757 plumes were easily identifiable in the CO2, CO, and H2O records as most encounters produced enhancements well above the instruments' precisions and below their saturation. The CO2 and/or H2O data from these crossing can be used in calculating the emission indices (EI) of trace chemical/aerosol species and, when coupled with the fuel analyses of H/C ratios, to evaluate the fraction of emitted water condensed on contrail particles. The CO data from the crossings, in the form of EIs, provide insight into the aircraft engine's combustion efficiency. Preliminary analyses suggest the T-39 engines produced an order of magnitude more CO per Kg fuel burned than the DC-8 and B757, both of which have more modern and efficient engines. Enhanced mixing ratios of the combustion tracers (CO, CO2, and CH4) were observed in the outflow regions around convective clouds on flight 960421. These data should be examined in concert with the NCAR reactive nitrogen measurements to delineate the source of the NO and NOy enhancements observed on the same flight. Stratospheric air was sampled on several flights as indicated by reduced mixing ratios of N2O and CH4. These data might be useful to discriminate any changes due to vertical mixing from those related to aircraft emissions in cases of plume sampling in the stratosphere. Water vapor mixing ratios smaller that of the surrounding background air was documented in several contrail crossings, suggesting contrail formation might, in some cases, have a dehydrating effect on the upper troposphere. Back to TOC - CO2, CO, CH4, N2O, & H2O
The DC-8 MMS is a new instrument, flight-tested for the first time on 4/10/96. The MMS performed very well during SUCCESS, which began its deployment mission on 4/13/96. Except for 100 minutes of data on 4/21/96 (blockage of the dynamic pressure probe by ice when the DC-8 circuit breaker providing power to transducer heaters popped out), the MMS captured all data during the science flights. The measurements were processed with a set of preliminary calibration constants, determined in the field (Salina, Kansas) by using many induced aircraft maneuvers during flights. Analysis of the three sets of temperature data (two sets from the Tslow probe and one set from the Tfast probe) indicates that the self-consistency of the temperature measurement is within about 0.3 K of the MMS design specifications. However, we have great concerns that the impactors mounted on the DC-8 nose could adversely affect the MMS measurements. The assessment of the possible adverse effect by the impactors requires a careful comparison of the MMS measurements with the impactors on (performed during the transit flight on 4/13/96) and with the impactors off. A preliminary set of the MMS products (p, T, theta, u, v, w, latitude, longitude, pressure altitude) has been submitted to the Project. A final set of the MMS data products will be provided for the archive after the MMS is re-calibrated and the data reprocessed within four to six months after the end of the mission. Back to TOC - MMS
The MTP aboard the DC-8 measured vertical movements of two types during this mission: 1) mountain wave uplift, causing the tropopause to be displaced upward where lenticular clouds form, and 2) non-orographic generated thickening and thinning of a shallow layer immediately above the tropopause. The tropopause and isentrope surface uplift is the more dramatic of the two, especially considering that the tropopause above lenticular clouds was observed to fall 600 feet before rising to 2000 feet above the undisturbed level near the lenticular cloud, and finally fall to 600 feet below the undisturbed altitude on the downwind side before returning to the normal altitude. Cooling rates of 10,000 K/day were measured. I believe these are the first mesoscale measurements of the two-dimensional topography of the tropopause! Isentrope surface cross-sections verify that the tropopause displacements are correlated with isentrope displacements, which is an expected result. However, if lenticulars are formed from air that has first been heated, as the present measurements indicate, then it is natural to ask if this pre-heating in any way pre-conditions the aerosols to favor only a few for subsequent condensation, thus accounting for the significant number of large particles found in lenticulars. Possibly of greater significance, I believe, are the measurements of a subtle oscillation of the thickness of a layer of stratospheric air bordering the tropopause. During a 40-minute period of flight in air that was remote from convective storm systems, isentrope surfaces within a 1-km thick region immediately above the tropopause were observed to separate and come together quasi-periodically for two cycles. The associated adiabatic heating and cooling caused the "temperature field tropopause" to briefly jump into the stratosphere, to the top of the dynamic layer. Meanwhile, the main tropopause moved upward and downward, crossing isentropic surfaces in phase with the overlying layer's changes. Such behavior might possibly lead to the exchange of air between the stratosphere and troposphere, and warrants further study in the context of understanding mechanisms for the redistribution of aircraft exhaust throughout the atmosphere. Back to TOC - MTP
During the SUCCESS Field Campaign the Atmospheric Research Laboratory from the Scripps Institution of Oceanography, University of California-San Diego operated a suite of radiometers, collectively known as RAMS, which were mounted in zenith and nadir viewing ports on the NASA DC-8 and ER-2 aircraft. Upwelling and downwelling hemispheric broadband solar flux (0.3-4.0 microns), near- IR flux (0.7-2.8 microns) and narrow-band (0.1 microns wide) spectral solar and near IR flux (0.5, 0.862, 1.064, 1.25, 1.5, 1.65, and 1.75 microns) were measured on each flight from both platforms. In addition, the spectral optical depth at 0.5, 0.862, 1.064, 1.25, 1.5, 1.65, and 1.75 microns, and the upwelling radiance at 4-40 microns, and 8-12 microns were measured from the DC-8 aircraft. Similar instruments were located at the ARM-CART site and on the Twin Otter and Egrett DOE aircraft flying out of Blackwell, OK, making for a total of 28 radiometers operating simultaneously during SUCCESS. A good coordinated cirrus flight over the ARM-CART site was obtained on the 20th of April. All aircraft flew on this date, including the DOE planes, allowing us to obtain the radiative flux properties and optical depth of the cirrus deck from multiple altitude levels above and below the clouds. On the 29th of April the DC-8 flew by itself both in and over a low altitude broken stratus deck centered on the CART site. The DC-8 radiative measurements at a range of altitudes above the broken clouds will let us explore the affect of 3-dimensional cloud fields on our flux measurements. On the 4th of May all the airplanes were once again flying over the CART site as the NASA 757 generated a short-lived contrail. The DC- 8 flew flight legs above and below the 757's contrail in order to measure its radiative properties. On all of these, and other flights it is hoped that our radiative measurements can be compared to the in situ particle measurements from the DC-8. In addition, throughout SUCCESS our radiometers have been cycled onto the zenith viewing ports of the ER-2 in order to calibrate our instruments against the known solar flux. Back to TOC - RAMS
A compact airborne lidar was installed on the NASA DC-8 to support in-situ aerosol and gas chemistry measurements during SUCCESS. The most notable features of the lidar were its capability to automatically scan in directions from vertically upward to forward to vertically downward and real-time displays of atmospheric structure. Therefore, the lidar determined the presence, altitude and thickness of particulate layers above and below the DC-8 to help establish optimum in-situ sampling altitudes. Once the sampling altitude was selected, the lidar was mostly used in forward-looking angular-scan patterns to map structure of clouds and contrails that the DC-8 was about to penetrate. This data can be used with the in- situ measurements to help establish quantitative constituent profiles. The lidar and its associated scanning mirror pod performed well during SUCCESS and relatively large database of cirrus cloud and contrail observations was collected for later analyses. Notable observations include clouds observed above indicated tropopause, 757 contrails above and at the DC-8 altitude, the height distributions of contrails below the DC-8 altitude, and clouds above the possible flight altitude of the DC-8. A variety of lidar transmitter and receiver configurations including visible and infrared wavelengths and linear, logarithmic (40dB), and extended logarithmic (60dB) amplifiers were investigated for input to design of future missions. SUCCESS also identified several lidar limitations that can at least be partially resolved if other similar field studies are conducted. For example, the laser transmitter can be modified to emit selectable lower energy pulses. This will benefit short-range observations without detector saturation and reduce eye-safety requirements. An eye hazardous range of 5 km rather than 9 km (IR only) or 13 km (IR and visible) would have resulted in much greater usage of the lidar during SUCCESS. More flexible real-time display programs would benefit SUCCESS type missions. The lidar will be of greater use on DC-8 missions that are conducted without the numerous aircraft employed on SUCCESS. It should also be noted that the scanning mirror pod may be of use with other passive and active remote sensors providing directional observation capability. In summary, the DC-8 Scanning lidar performed well during its first mission, a large database of cloud and contrail observations was collected for analysis, and several system limitations were identified that will be addressed if the system is used on future SUCCESS type missions. Back to TOC - DC8 Scanning Lidar
The MODIS Airborne Simulator (MAS) and High resolution Interferometer Sounder (HIS) on the ER-2 have collected observations of cirrus (thin to thick), contrails, convective activity, and clear conditions during SUCCESS. MAS and HIS have flown 15 missions together during SUCCESS. MAS flew 3 additional missions (ferry to NASA ARC, 2 Pacific ocean missions). Radiometric measurements of cirrus, contrails, and the background environment are of particular interest. Analysis of MAS radiometric data from April 20 differentiates the contrail signal from the surrounding cirrus. This is related to contrail particle characteristics (size, shape, phase, content). Unanticipated large spectral variations of radiometric temperature (20 to 30 K) were observed for certain clouds on April 13 and 21. MAS and HIS collocated data will be used to explore microphysical signals from this and other ER-2 flight dates (e.g. April 26, May 7). The combination of high spatial resolution MAS and high spectral resolution HIS data provides a far more detailed depiction of cloud and atmospheric conditions than is available separately from either instrument. Observations during SUCCESS have shown that the particles that make up "young" contrails are typically smaller and more numerous than cirrus cloud particles. The microphysical signal of contrail particles may contain clues to the evolution of contrails, and their interaction with cirrus cloud. Comparisons between in situ data collection (DC-8 and T-39) and the radiometric data (ER-2 and CART) will be made to further this investigation. HIS and AERI (CART site) retrieved temperature and moisture profiles will provide background atmospheric conditions. Observations of convective activity by HIS on April 21 also demonstrate a possible microphysical signal. Analysis of the 11 minus 12 micron brightness temperature shows the difference becomes negative over vigorous convective activity. This signature has previously been observed in GOES-8, AVHRR, and MAS data; however, this is the first such observation with the excellently calibrated HIS instrument. The HIS observations will be compared to collocated satellite observations for corroboration; once the observations are corroborated, investigation will focus on defining the microphysical and thermal properties which produce the negative difference signature. Information on these and other MAS/HIS SUCCESS investigations is available on the World Wide Web CIMSS homepage (http://cimss.ssec.wisc.edu/success/sucsum.html) Back to TOC - HIS & MAS
The TSCC, MAS and CLS on the ER-2 are a single experiment in that analysis applications have typically involved the combination of data from instruments. It is difficult to determine immediately after the SUCCESS flight missions what has been learned since the imager data is not yet available in a meaningful format, and won't be for sometime. However, we can contrast the SUCCESS observations from cirrus and contrail observations we have previously analyzed from FIRE and other previous field missions. The major justification of further observations of cirrus and contrails in SUCCESS was that there hopefully would be a much larger sample of observational cases with a larger variations of conditions. More importantly we needed much better and more extensive comparisons to in situ measurements of cloud radiation and microphysical parameters than what had come out of previous field experiments. The participation with the DC-8 experiment was to provided the improved radiation and microphysical comparisons. An initial view of the overall flight data from SUCCESS indicates that these objectives may have been met, at least to a degree. Project SUCCESS produced an extensive and unique aggregation of observations from the ER2 remote sensing instruments. Judging from CLS quick look products, the observations included many hours of views of mid-latitude cirrus with a wide range of optical depths in single and multilayer patterns. Of special importance, the remote sensing observations contained contrails verifiable from observations of the other SUCCESS aircraft. The contrails were observed in conditions extending from clear sky to multilayer optically opaque situations. The contrails ranged from fresh, newly produced variety to those which were quite old and persistent and well into the transformation process. An advantage of the SUCCESS contrail observations compared to those found in other deployments is that the contrails are of a more known origin which permits an easier quantitative analysis of observations of contrail properties and eases the tasks of comparisons with theoretical model computations. Based upon preliminary and qualitative comparisons of CLS observations with those from some of the other ER-2 remote sensing instruments, such as MAS and HIS, cases from four flight days have been identified as potentially rich sources for contrail remote sensing radiative transfer studies. These days are April 16, April 20, April 21, and May 7. On each of these days, contrails are evident in the MAS imagery and corresponding contrail signatures appear in the CLS data. Also, the last three of these days were flights where the ER2 was coordinated with the DC-8 so that useful in situ microphysical and chemical data will be available. Although we have not done the necessary interpretation of the DC-8 and ER-2 flight coordination, it is also hoped from the DC-8 that there will adequate flux radiation data to determine the radiative forcing of the cloud layers. The variety of documented contrail observations should permit construction of contrail categories. New elements of our ER-2 cloud remote sensing work was attempted during the SUCCESS flights. These were the higher resolution and wider field-of-view capabilities for the TSCC instrument and the 325 Ghz remote sensing of cirrus from the MIR instrument. For the flight of May 7, initial looks indicate that we should have for the first time high resolution TSCC BRDF measurements of contrail cirrus in conjunction with DC-8 microphysics and radiation measurements. For MIR, signal effects from cirrus were seen in some 325 Ghz microwave data. However, similar to what we found for 220 Ghz measurements, the cirrus signal for 325 Ghz is at the extreme range of sensitivity. These results call into question the ultimate utility of high frequency microwave measurements as a method to determine the IWC of cirrus, at least optically thin cirrus, but more study is needed. One of the goals for these instrument applications was to have some measurements over a uniform water background in order that thin cirrus scattering characteristics could be distinguished from surface effects. The move of the base for the SUCCESS mission from Texas to Kansas made the operational problem to obtain such flights extremely difficult. One such flight with some coordinated measurements between the ER-2 and DC-8 for thin cirrus over water was obtained on May 15. Initial looks indicate that the data from the TSCC and other instruments is of good quality. The investigator appreciates the strong effort that was made by the project personnel in the attempt to carry out the overwater flights. Back to TOC - TSCC, CLS,MIR & MAS
Satellite data were collected in real time and provided in video loops and hard copies to the mission forecasting and planning teams throughout SUCCESS. The Geostationary Operational Environmental Satellites, GOES-8 at 75 deg W and GOES-9 at 135 deg W, and the NOAA-12 and 14 Advanced Very High Resolution Radiometer (AVHRR) provided the bulk of the satellite data. GOES-8 was the workhorse for the Great Plains portion of the experiment while GOES- 9 served as the primary satellite for the Pacific flights. Four-km imager (0.65, 3.9, 6.7, 10.8, & 11.9 um) data from the primary GOES were taken on a 15-min basis during flight days and every 30 minutes during the remaining days of the mission. One-km visible data were also collected during flight days. One-km AVHRR (0.67, 0.86, 3.7, 10.8, & 11.9 um) data were acquired for most flight days, while 4-km AVHRR data were obtained for the remaining days when the viewing angles were favorable. Additional 1-km AVHRR data are being acquired. GOES gif images are available on the NASA Langley SUCCESS homepage for every experiment day. The GOES collection was extremely successful with acquisition of more than 95% of the possible images archived. The weather conditions were the most favorable for cirrus remote sensing ever encountered in a NASA cirrus experiment. A variety of excellent cirrus systems were observed with in situ sampling which will provide verification of the remotely sensed cloud properties. The satellite data are being analyzed for cloud amount, phase, altitude, and particle size with separate estimations of cirrus and contrail properties when possible. Estimates of albedo and outgoing longwave radiation will also be include in the cloud products. These results will be provided on a 0.5-deg grid for use in modeling and diagnostic studies. The cloud microphysical properties will be related to the density of contrails as determined from visual and objective methods. Both ER-2 lidar and the ground-based radar and lidar at the CART site will be used to verify the satellite-derived cloud structure. Several cases of cirrus and contrails over broken and overcast low-level clouds were encountered. These cases will be used to evaluate and develop retrieval methods for multilayer cloud conditions. Although the number of cases with satellite-detectable contrails and coincident in situ data were relatively small, at least one extensive, uniquely shaped, contrail system was detected with GOES-8 and tracked for 6 hours as it spread and finally dissipated around sunset. This system should yield valuable information about the lifetime characteristics of contrails. Other contrails observed in the vicinity of the CART area and the various flight tracks will be identified with the AVHRR and tracked with GOES when possible. The results of these analyses will be used in our ongoing SASS study to help assess the total impact of contrails on the radiation budget. Back to TOC - Satellite Ovservations
An Ames Research Center Solar Spectral Flux Radiometer (SSFR) was deployed at the SGP CART site during the 1996 SUCCESS mission. The SSFR was used to measure downwelling solar spectral radiance or irradiance in the region 250-2500 nm with 9nm resolution at wavelengths less than 1000nm and 15nm at wavelengths greater than 1000nm. Operating dates were every day from 12-29 April, with 18000 thousand spectra collected (40-60 second time integration). From 23-25 April the SSFR was co-located with an ASDI FieldSpec spectrometer. Spectra obtained by the two instruments agree very well, suggesting that the moderate resolution solar irradiance spectra will also provide reliable values for band- integrated solar irradiance. Retrieved cloud properties using the SSFR radiance spectra include cloud thickness, particle size, integrated water path, and liquid/ice water content. The SUCCESS mission on April 29 will be particularly interesting because the DC-8 sampled in stratocumulus and cumulus congestus over the CART site. This will provide an ideal case to test new SSFR cloud parameter retrieval algorithms. Back to TOC - Ground based spectroscopy
The cloud infrared Doppler lidar, an ARM/NOAA developmental system, performed well during its maiden field campaign. After calibrations and Doppler intercomparisons are complete, we will assess to what extent dependable microphysical retrievals can be made for the observed cirrus cases using combined lidar and radar data. Back to TOC - Cloud Infrared Doppler lidar
In support of all NASA SUCCESS aircraft missions into the vicinity of the DOE Southern Great Plains CART site (36.605 degrees N, 97.488 degrees W) near Lamont, OK, ground-based remote sensing measurements were collected by a mobile remote sensing platform from the University of Utah, including the dual-wavelength scanning Polarization Diversity Lidar (PDL), coaligned midinfrared radiometer and video recorder, and all-sky video and 35-mm photography. Additional data were obtained at other times during periods of cirrus cloudiness and from extensive fields of contrails generated by local commercial jet aircraft. A radar-based laser safety shutdown device for automatic aircraft identification was successfully tested using a variety of aircraft, allowing PDL scans of cirrus and contrails to be made for the first time. Exceptionally high resolution PDL data were also obtained at 1.5-m range and 0.1-s time resolutions, revealing a surprising amount of fine scale structures in cirrus clouds and contrails. A preliminary inspection of our SUCCESS dataset reveals that although portions of contrails created by the participating NASA aircraft were sampled, the extensive fields of contrails from nearby commercial jet corridors, including subvisual sheets of spreading contrails, were the most notable and extensively studied. Back to TOC - Contrail-Cirrus Studies at FARS
The measurements taken during SUCCESS open new perspectives on the chemistry of the upper troposphere and the role of heterogeneous chemistry. For example, the Penn State measurements provide the first extensive data set of OH and HO2 concentrations in the upper troposphere. These observations will be compared to photochemical model calculations of OH and HO2 concentrations constrained with the measurements of O3, H2O, NO, CO, and UV fluxes. The NO/HNO3/NOy ratios measured by NCAR and Phillips Lab will similarly be compared to model calculations of chemical cycling of the NOy family. Based on these comparisons and the detailed data for aerosol microphysics and chemistry collected during SUCCESS, it will be possible to investigate the role of heterogeneous chemistry in perturbing the HOx and NOx budgets in the upper troposphere. The increased understanding of upper troposphere chemistry resulting from the SUCCESS mission will enhance considerably our ability to assess chemical perturbations associated with aircraft emissions. The UNH measurements of aerosol chemistry indicate relatively low sulfate concentrations in the upper troposphere (typically 25-50 pptv), which suggest that sulfate transported from the boundary layer is efficiently scavenged by deep convection; this hypothesis must be tested further by investigation of correlations of sulfate with tracers of boundary layer air (CO, methane). Efficient scavenging of sulfate originating from surface sources implies a correspondingly larger role of aircraft emissions as a source of sulfate in the upper troposphere. Another interesting result from the UNH data is the lack of correlation between nitrate and sulfate in the upper troposphere, suggesting that these two species originate from different sources (correlation would be expected if both originated from surface sources). Sulfate and nitrate in the upper troposphere aerosol appear to be largely neutralized by ammonium and soil dust, a surprising finding that has important implications for the chemical and microphysical properties of the aerosol. Back to TOC - Upper Tropospheric Chemistry
From the Near-Field modeling perspective, the mission was able to collect a large amount of relevant data due to excellent flight planning and superior mission execution. Data were obtained at ranges closer to the wake generating airplane than was initially thought possible on board the T-39 as the chase plane. Wake encounter durations were maintained for periods also exceeding expectations for both the T-39 and DC-8 as chase aircraft. Thus the statistical reliability of the data for the various altitude, separation, and ambient conditions will allow excellent opportunities for data analyses. The measurement of gas phase species allows the calculation of emission indices for H2O, CO, (Sachse) NO, NOy (Ridley), NO2, HONO, HNO3, SOx [SO2 and H2SO4] (Ballenthin) by referencing to CO2 (Sachse). Preliminary results indicate that the fuel sulfur level affects the measured gas phase SOx emissions, while the CO and NOy emissions are not affected by fuel sulfur changes, but these emissions do vary among the measured airplanes (T-39, B757). The oxidative state of the exhaust gases as measured by the above species is complemented by measurements of perturbations to the OH and HO2 levels (Brune), which also clearly indicate the presence of exhaust gases. T-39 aerosol measurements have indicated a clear aircraft emission signature. Ultrafine particles counters (> 4nm) show a large volatile component that is not measured in the fine particle (>20nm) channel. The fine particle channel acquires a volatile component at very cold, near-tropopause temperatures and perhaps to some degree with downstream distance. When contrails form, ultrafine aerosols appear to decrease, implicating scavenging by contrail particles. An apparent non-volatile component of the ultrafine particles that appears at the lowest temperatures is tentatively attributed to larger volatile aerosol that has not completely evaporated, since it varies with both ambient temperature and volatilization temperature. The ultrafine volatile component essentially disappeared when the low sulfur fuel was used, suggesting a sulfate origin for this volatile component. DC-8 aerosol measurements to date [May 6 am] have only been made in non-contrail and non-persistent contrail formation conditions. CN and CCN counts increase dramatically within the wake. IN appear at much smaller levels and may be localized near the edges of the non-persistent contrail wake structure. Compositional data and large particle measurements are expected to be most useful when measured in persistent contrails. Back to TOC - Near Field observations
The necessary measurements needed to answer questions about formation of contrails and cirrus clouds were successfully collected. DC-8 temperature and humidity measurements will be used to determine the environmental conditions required for contrail formation. Contrails did sometimes form at temperatures above the theoretical threshold, especially in patchy cirrus. On several occasions, the lifetime of the DC-8 contrail was determined from the aft video, ER-2, T-39, or ground observations. These observations will allow us to determine what environmental conditions are required for contrail persistence. Finally, in situ microphysics measurements of persistent contrails will be analyzed to understand contrail evolution. Several key measurements were made that will clarify upper tropospheric ice nucleation processes. Clear-sky temperature and humidity measurements will indicate what humidities are required for ice nucleation. Preliminary humidity results indicate that substantial supersaturations frequently exist in the upper troposphere. The leading-edge region of wave-clouds (where ice nucleation occurs) was sampled extensively at temperatures near - 40 and -60 C. Numerous samples of aerosols in ice crystals were taken, as well as measurements of the ice nucleating activity of ambient aerosols. Finally, measurements of aerosols and ice crystals in contrails should indicate whether aircraft exhaust soot particles are effective ice nuclei.Back to TOC - Clouds & Contrails
In order to facilitate the analysis of the SUCCESS data a science team meeting will be held at NCAR in Boulder Co. on Oct 23-25, 1996, as part of the FIRE science team meeting. This meeting will be focused on forming groups to address the questions originally posed for the SUCCESS mission. A special issue of a journal, probably Geophysical Research Letters, will be devoted to SUCCESS with a deadline for paper submission of May 15, 1997.