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This summary is a compilation of research performed by the investigators of the Stratospheric Tracers of Atmospheric Transport (STRAT) aircraft campaign which was based at the NASA Ames Research Center, Moffett Field, CA, and Barbers Point Naval Air Station, HI, during late-October and early-November 1995. The mission was sponsored by NASA's Office of Mission to Planet Earth and Office of Aeronautics.
Date Flight Pilot Hours Sortie Comments 10/17 ARGUS Test Flight J. Barrilleaux 2:05 96-017 None 10/20 Full-up Test Flight B. Collette 2:00 96-018 ALIAS, ACATS, and CPFM 10/23 Attempted Flight R. Williams 0:00 96-019 Pressure Suit 10/24 Northern Survey R. Williams 8:05 96-021 ALIAS 10/26 Stair-Step Flight K. Broda 5:10 96-023 None 10/27 Planned Flight J. Nystrom 0:00 96-024 Instruments 10/28 Planned Flight R. Williams 0:00 96-025 Oil Sump Tank 10/31 Stair-Step Flight K. Broda 5:00 96-026 FCAS 11/02 Ferry to Hawaii J. Barrilleaux 6:05 96-030 Nav. Recorder 11/04 Planned Flight B. Collette 0:00 96-031 Hawaii Storm 11/05 Southern Survey B. Collette 7:50 96-031 Flaps failure 11/07 Stair-Step Flight J. Barrilleaux 5:25 96-032 MTP 11/09 Ferry to Ames B. Collette 6:00 96-033 Flaps failure Total Flight Hours: May Balance: 4:45 Approved: 180:00 Flown: 47:40 Balance: 137:05
The certification flight occurred on 951020. The payload was certified, albeit CPFM, ACATS, and ALIAS failed because of a cut wire on the interface plug, a software glitch, and a hung computer, respectively. These problems were successfully resolved. Our second flight was a northern survey on 951024. The third flight, our first attempt at a full payload stacked flight, was successfully completed and followed up with another stacked flight on 951031. The ER-2 departed for Hawaii on 951102. An attempt was made to fly a southern survey on 951104, but was thwarted by torrential rains on the evening of 951103 which flooded the hangar and inundated the circuit breakers providing power to the hangar. The southern survey flight was successfully flown on 951105. This survey was followed up with the first Hawaii stacked flight on 951107. The ER-2 returned to Ames on 951109.
The second flight (951024) was an 8-hour flight NNW to approximately 59 N. The objective of this northern survey flight was to: 1) continue the high-latitude N2O-CO2-H2O-O3 data time series from the SPADE, ASHOE/MAESA, and May 95 STRAT flights; B) observe Northern Hemisphere constituent values early in the development phase of the northern polar vortex; and 3) observe filaments of material. The flight was vectored to the NNW to intercept the relatively weak vortex as it rotated eastward. The lowest values of N2O observed on this flight were seen at the northern end of the flight track, dropping down to 170 ppbv. These N2O values were comparable to those observed one year earlier on 941104 during ASHOE/MAESA, and substantially greater than the low of 40 ppbv seen during the 950508 flight. Ozone values were also comparable to those observed during ASHOE/MAESA on 941104. The CO2 and H2O annual cycles were once again observed in the lower stratosphere, although the water data from this flight were of relatively low quality. (High-quality data for water were obtained on all subsequent flights).
The first stacked flight with the full payload was successfully flown on 951026. Flight legs were flown at 41, 43, 49, 55, and 57 kft, and maximum altitude for approximately 30 minutes on each leg. During this period, an anticyclone (geopotential high) had pushed in from the southwest into the California region. These anticyclones are associated with high tropopause altitudes, and characteristically contain air advected from subtropical latitudes. The MMS and MTP data confirmed that this high tropopause was at approximately 45 kft. The relatively high concentrations of CO, NOx, N2O, CO2, and other tracers, combined with the low values of ozone, indicate that the first two legs were clearly in the troposphere. Potential vorticity analyses combined with trajectories indicate that this upper tropospheric air was tropical in character.
The second stacked flight with the full payload was successfully flown on 951026. Flight legs were flown at 37, 39, 41, 50, and 57 kft, and maximum altitude for approximately 30 minutes on each leg. During this period, the anticyclone sampled on 951026 had pushed off to the west, and a second anticyclone had moved onto the west coast of the US. Embedded in this anticyclone was a cut-off low (COL) that had developed in the Pacific between 25 and 27 October. This COL moved into the California region, and was sampled by the ER-2 on the 951031 stacked flight. In addition to the COL, aircraft plumes were sampled by the ER-2 at the lower altitudes of this stacked flight.
The transit flight on 951102 illustrated the differences between subtropical air and mid-latitude air. During the takeoff, the aircraft climbed through a tongue of mid-latitude air extending down the coast (~350 K), did a dive through air that was more characteristic of tropical air, and descended into Barbers Point in air that was very similar to that seen in the dive.
The southern survey flight on 951105 was very successful in sampling the range of trace-gas values to the equator in the lower stratosphere. The ER-2 dipped into the troposphere during the dive over the equator. Ozone values compared to 1994 ASHOE/MAESA measurements are slightly lower for similar values of theta. This is in agreement with the phase of the quasi-biennial oscillation, since the lower stratospheric westerlies should slow the vertical lifting, allowing ozone production via photolysis to increase the local ozone concentrations in the lower stratosphere. However, if transport of ozone-rich air into the tropics was somewhat stronger during 1994 than 1995, then ozone mixing ratios would also have been somewhat larger.
The third stacked flight of the deployment occurred on 951107 slightly to the west of Oahu. The flight legs of this second flight were at 37 43, 49, 53, 57, and 61 kft, and maximum altitude for approximately 30 minutes on each leg. The lowest two legs of this flight were clearly in the troposphere, while the third leg was near the tropopause. This Hawaii stacked flight occurred slightly to the west of a decaying COL.
Measurements of stratospheric and mid to upper tropospheric CO2 were obtained from all eight flights of the October/November 1995 STRAT deployment. CO2 concentrations in the atmosphere vary on both monthly and annual time scales; as part of a continuing time series of observations beginning in 1992 with the SPADE campaign, these new measurements will add significantly to our understanding of stratospheric transport, testing both our qualitative understanding of how rapidly air moves through the stratosphere and quantitative results from computer models of the atmosphere. The additional capability of prolonged flight in the upper troposphere and the stratospheric "middle world" for STRAT allowed a significant amount of CO2 data to be collected by the ER-2 in these regions for the first time. Correlations between CO2 and CO, CH4, ozone, and particles in both the upper troposphere and lower stratosphere were distinctly different between air masses originating in the tropics versus mid-latitudes; meteorological analyses were remarkably good at predicting these air mass differences along the ER-2 flight tracks. In addition, because these lower altitudes coincided with flight corridors for commercial air traffic, in situ sampling of commercial subsonic aircraft exhaust was achieved with the same set of instrumentation used in the ER-2 and Concorde plume encounters during previous missions, potentially allowing a direct comparison of the emission indices for NOx and particles of commercial subsonic, high-altitude subsonic, and commercial supersonic aircraft.
The MMS instrument worked on every flight between 951020 through 951107. The preliminary field data are reasonably within the stated accuracy at cruise-level flight. Further calibration and improvement are needed for the profiles and stair-step flights where the aircraft operates outside the preferred Mach envelope. The southern survey flight reveals an enticing inertia gravity wave between 6 and 8 degrees latitude and between 18 and 19 km pressure altitude. Further analysis will answer the questions: 1) what is the source of this perturbation (forced vertical displacement or horizontal wind shear), and 2) is there any mixing horizontally and vertically ?
ACATS-IV was operated onboard the ER-2 aircraft during the second STRAT deployment. ACATS-IV measures CFC-11, -12, -113, chloroform, methyl chloroform, carbon tetrachloride, Halon-1211, hydrogen, and methane once every 180 seconds, and nitrous oxide and sulfur hexafluoride once every 360 seconds. We have had a total of seven successful science flights. We tested 60-second chromatography for CFC-11 on the test flight of 951022 and the science flight of 951026. This permits three times as much data per flight as the original configuration, and is necessary for the OMS balloon component of STRAT. We will evaluate the results at our home laboratory and determine whether we will install the shorter period on ACATS-IV during the next STRAT deployment. While our results at this time are very preliminary, we again observed distinctively different correlations in the tropics versus the mid-latitudes for the correlation of a short-lived tracer, Halon-1211 (16 years) vs. a longer lived tracer, CFC-12 (140 years). Measurements of sulfur hexafluoride showed that the mean age of the air over the tropics at ER-2 altitudes was shorter than 1.5 year, while air over the mid-latitudes was older (as high as 3.5 years old).
NOy has been measured successfully between 0 and 60 N latitude. The NOy/ozone ratio gradient at the edge of the inner tropics observed during the Airborne Antarctic Ozone Expedition (AAOE) and ASHOE/MAESA has been seen again. The gradient location and magnitude varies with altitude and time. Observed NOy/N2O ratios form a tight and nearly linear curve and are in excellent agreement with ASHOE/MAESA results.
Measurements of NO and NOy in the upper troposphere in both the tropics and mid-latitudes have been successful. Improved precision and accuracy of the NOy instrument have been demonstrated for the stacked flight pattern. High NO/NOy ratio (~0.5) events have been observed in the upper troposphere.
MTP produced scientific quality data for all seven flights of the deployment. The fail light alerted outages on 2 flights, leading to a total data loss of 8 and 15 minutes, respectively, for flight time above 40 kft.
Altitudes of the "temperature field tropopause" were determined for all flights. The flight on 951031 exhibited a double tropopause, with the higher one being a 2-km thick region. The ferry flight from Ames to Barbers Point dipped to an altitude 1.0 km above the tropopause. The southern survey flight on 951105 dipped below both altitudes of a double tropopause pair (at 17.4 and 16.1 km). The Hawaii stair-step flight on 951107 penetrated a 15.6-km tropopause between legs 3 and 4 (most of leg 4 was within 100 meters of the tropopause).
On this deployment of the STRAT mission, we continued to learn about the distribution of water vapor and other tracer molecules in the stratosphere and the transport processes that control them. While data validation and analysis are still proceeding, we are continuing to observe the seasonal cycle of water vapor in the stratosphere. Right now, air which has recently entered the stratosphere (i.e., during the past summer) is wetter than air which entered the stratosphere during the past winter, when the tropopause was higher and colder. Also, the stair-step or "stacked" flights have been very successful, and are crucial to understanding chemistry and transport in the "middle world," close to the tropopause. In this region, we have observed mixing of stratospheric and tropospheric air. It is expected that these data will help in understanding the atmospheric effects of both supersonic and subsonic aircraft.
The ATLAS instrument performed very well during this campaign, accurate to about 2% for the preliminary data, with the accuracy expected to be improved to about 1.5% within the next two months with the addition of a small pressure correction. No failures or data loss occurred during the test or science flights.
The correlation plots of N2O with ozone and theta proved useful for characterizing the air masses encountered. There are robust N2O vs. ozone and N2O vs. theta correlation curves that exist in the tropics, the best examples of which are from the flight of 951105. The low scatter of these curves indicates that the tropics region is horizontally well-mixed. The mid-latitudes show more variation. A good example of the canonical mid-latitude correlations is the 951026 flight. The high-latitude correlations can be inferred from the asymptotic behavior of the correlation plots of 951024 (the flight north out of Ames). The transitions from tropical to mid-latitude (or at least subtropical) air masses were fairly abrupt during all three November flights, supporting the notion of the "tropical pipe" inhibiting free diffusive exchange between the tropics and mid-latitudes. The tropical to mid-latitude edges occurred at different places for different altitudes. Between the mid-latitudes and the high latitudes, the flight data shows a more or less continuous transition. The flights of 951024 and 951031 show this mid- to high-latitude transition behavior.
The UV-VIS instrument operated throughout all of the STRAT science flights and provided excellent ozone column data. The preliminary data from several flights are already usable in all product forms (spectra, fluxes, and J-values ), but some error recovery will be needed during reprocessing for the data from 951024 and 951102. These data were compromised because of apparent gain shifts from an unidentified source during the flights. The equatorial flight of 951105 has provided particularly interesting information on the influence of albedo and overhead ozone column on the J-value for the production of O(1D) from ozone. These effects are clearly identifiable when data from the OH instrument is compared with the J-values estimated from the CPFM experiment data. Brewer Ozone Spectrophotometer number 009 was operated at both Ames and Barbers Point to provide total column ozone, Umkehr profiles and ultraviolet radiation measurements. The ground-based column measurements are used to verify the calibration of the CPFM instrument. The ground-based and airborne ozone column data are of particular importance for this STRAT mission since there are no TOMS ozone data available.
Unlike the May 1995 flight series, tropospheric weather and clouds were not the limiting factor in getting ER-2 flights off the ground during the October 1995 flight series. However, as the ER-2 science community becomes more interested in tropospheric radical chemistry and tracer transport within the troposphere, clouds and tropospheric weather become more of a factor both in flight planning (to protect the instruments from the water soaking of flying through clouds) and in the interpretation of the tropospheric measurements. Clouds are also important to processes in the stratosphere: first, to the radical chemistry as reflectors of solar radiation, especially as regards NO2 dissociation rates and, to a lesser extent, HOx chemistry; and second, as generators of gravity waves, especially in the tropics. Both of these aspects were demonstrated during this deployment.
The Ames deployment consisted of one northern survey flight and two stacked flights. The first stacked flight on 951026 surveyed a near-tropical upper troposphere, with a very high tropopause (near 100 mbar) and extremely cold temperatures. A convective system north of Hawaii produced enhanced water in the 500- to 200-mbar layer, but this did not extend to the lowest sampled level at 41 kft (12.5 km). The second stacked flight was in more typical mid-latitude conditions (at least as regards tropopause height), so lower altitudes were flown. Unfortunately, an upper level disturbance was over northern California at the time, so cloud tops to 35 kft were seen in the satellite imagery (and verified by the ER-2 pilot). Thus, the lowest altitude flown was 37 kft to protect instruments from cloud soaking. Still, some data within the troposphere was obtained.
Our arrival in Hawaii on 951102 coincided with the arrival of a deep trough west of the islands. This trough was able to bring moist air northward, producing a line of deep convection (to 50 kft in some cases) just west of the islands. The next day heavy rains resulted in prolonged power, phone, and network outages through 951104. Thus, the next flight, a southern survey flight, was postponed to 951105. This flight featured a flight over the ITCZ, with minimum brightness temperatures under the aircraft of 208K, implying cloud tops of 150 mbar. Albedos reached 88%, nicely consistent with aircraft-measured values from CPFM. Impacts on both the NO and OH concentrations were noted. Enhanced gravity wave activity above the clouds was noted in the MMS data (but no turbulence). The final flight on 951107 was in near-clear conditions, with only low-level cloudiness. There was a weak upper-level trough over the islands (essentially left over from the trough producing the storm on 951103). The flight stacks were oriented east-west across the PV gradient (at near-tropopause (15 km) levels) formed by this low.
Mid-latitude correlations of ozone vs. N2O were well-defined and tight. In the tropics, significantly larger amounts of ozone were observed for similar N2O abundances; e.g., at an N2O of 285 ppbv, ozone was 1700 ppbv in the tropics vs. 700 ppbv at mid-latitudes. This behavior is similar to that seen during ASHOE/MAESA in October/November 1994, but shows somewhat better defined differences between mid-latitudes and tropics.
Plots of the ozone/NOy ratio vs. latitude show a marked difference between mid-latitudes and the tropics. At latitudes above 30 N, the ratio is in a narrow range around 270-300, independent of theta. On the transit flight to Barbers Point, a sharp edge was encountered near 26 N, on the 490K surface, where ozone/NOy increased to over 700. On the southbound flight from Barbers Point, this edge was located near 18 N. In the tropics, a strong theta dependence in ozone/NOy is evident, with the ratio increasing from 320 at theta = 390, to 750 at theta = 470, and over 800 at theta = 490.
The northern survey flight from Ames on 951024 was directed towards high potential vorticity (PV) air associated with the early beginnings of the polar vortex. Analyses from the Goddard Data Assimilation Office (DAO) indicate that the aircraft reached the edge of this air mass. The dive during the transit flight to Barbers Point on 951102 was designed to partially intersect a forecast air mass with relatively high PV; the analyses indicate this was partly successful. The southern survey flight from Barbers Point was flown on 951105; as expected from the current phase of the quasi-biennial oscillation, the MMS zonal winds show westerlies over the equator, although easterly winds were seen as far south as 5 N. The cold tropical tropopause was also sampled on this flight (MMS shows 190K; the DAO analyses show ~196K). The stacked flight on 951026 was flown in a feature with an anticyclonic circulation and its associated raised tropopause. The stacked flight on 951107 was flown in northerly winds south of air lanes, in hopes that aircraft exhaust plumes might be seen at low altitudes. Telecommunications problems prevented generation of trajectories during the deployment, but upon returning to Goddard, we expect to be able to use reverse domain filling analyses and back trajectories from the flight track to investigate some of the features seen in the tracer data (e.g., the filament of high-ozone, low-N2O air seen in the 951102 transit flight).
The NASA/GSFC Data Assimilation Office (DAO) provided meteorological analyses which were the principal flight planning tools utilized during the October STRAT deployment. These analyses, comprised of near real-time analyses and five-days forecasts, were used for the flight planning and subsequent analyses. The assimilation system is GEOS-DAS vc5.4/oi1.5, which uses rotated poles. There are two runs each day; the early run starts about 9:30 EDT and the final run starts at 19:30 EDT.
During the 951024 flight (north bound), both temperatures and winds matched very well with the flight measurements, although the assimilated data do not show the perturbed structure along the flight routes. No systematic bias was found in the comparison of these analyses with the MMS measurements. This flight did catch the high potential vorticity air mass associated with the weak polar vortex as intended during the planning. The assimilated data also compared very well with the stacked flight data of 951026; however, there was a cold bias in the southbound flight and a warm bias in the returning flight in the assimilated data. The wind fields also showed discrepancies, especially in the boundaries of easterlies and westerlies.
Both the early and final forecasts were very close to the final assimilation fields, which provided assurance for the flight route planning.
ALIAS produced simultaneous measurements of N2O, CH4, CO, and HCl from 40 N to 2 S, sampling the region from the upper troposphere to lower stratosphere during flights out of Moffett Field, CA, and Barbers Point Naval Air Station, HI.
Although ALIAS experienced data collection difficulties during the test flight (951020) and first science flight (951024) which produced only a partial data set for the latter northern survey flight, the instrument performance has been excellent during the subsequent flights. Measurement precision for N2O, CH4, and CO has been typically 0.5% (1 sigma) or better, a significant improvement over earlier missions and within the goal of 1% set by the STRAT mission requirements. Measurement accuracy of about 3 to 5% for CH4 and N2O is now based upon pre-flight and in-flight comparison with gas standards provided by the NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) group.
Agreement between the ALIAS and ATLAS laser measurements of N2O has been excellent, with maximum differences limited to the 3% level. During the October 1995 STRAT flights, N2O mixing ratios between 320 and 170 ppbv were sampled, with an associated range of CH4 measurements between 1.8 and 1.0 ppmv. The correlation plots of CH4 vs. N2O are tight, with slope values similar to the mid-latitude correlations of ASHOE/MAESA. At ER-2 altitudes in the tropics, the correlation plots are not expected to separate greatly, and the differences in the CH4 vs. N2O correlation between the northern mid-latitudes and the tropics are not apparent in the high mixing ratio data sampled. Although large systematic differences are sometimes seen between the ALIAS CH4 and the ACATS CH4, the latter data set shows much larger scatter than that of ALIAS and a poorer correlation with N2O.
A large decrease in tropospheric CO levels is seen going south from northern mid-latitudes, reflecting the decreasing tropospheric source terms in the cleaner Southern Hemisphere. Tropospheric CO has a seasonal cycle with a peak in local spring and a minimum in local early fall, this cycle being driven by seasonal variations in OH through the CO + OH reaction. Tropospheric CO levels of about 100 ppbv near Ames and about 80 ppbv near Barbers Point seen during the transit flight are consistent with earlier ALIAS measurements during ASHOE/MAESA and with NOAA CMDL measurements.
Mid-latitude stratospheric CO levels of about 12 ppbv are somewhat higher than those seen in the November 1994 ER-2/ATMOS intercomparison flights. When the measured CO is used with measured NO and ozone to calculate HO2/OH ratios, the calculated ratio agrees very well with direct measurements of OH and HO2 over a factor of 5 change in the ratio [Wennberg et al., Science, 266, 398-404, 1994].
STRAT measurements of HCl at mid-latitudes show HCl/Cly values of 70%, somewhat higher than the November 1994 ER-2/ATMOS intercomparison flights, and consistent with the lower surface areas of about 1 µm2 cm-3 measured by FCAS. These measurements extend and are consistent with the 1993 and 1994 SPADE and ASHOE/MAESA data sets which show an HCl/Cly ratio increasing with time as the particle surface area from the eruption of Mt. Pinatubo slowly diminishes.
The "stair-step" or "stacked" flights during this deployment have produced the first series of HOx measurements in the free troposphere. Combined with the simultaneous measurements of NO, NOy, CO, and ozone, these observations should help further our understanding of the photochemistry of ozone in the upper troposphere - a key goal of the Subsonic Assessment (SASS) component of the Atmospheric Effects of Aviation Project (AEAP). The HOx instrument performed very well - high-quality data sets were obtained for all flights. The precision of the OH measurements in the troposphere is nearly equal to that obtained in the stratosphere - 0.1 pptv in 2 sec. HO2 concentrations in troposphere are very elevated because of the small ratio of CO to ozone.
The ER-2 CNC II instrument measures the concentration of aerosol in the 0.008- to 2-micron diameter range. It has two channels; one measures the total aerosol concentration and the other measures the concentration of particles surviving heating to 190 degrees C. CNC II also includes a multiple aerosol sampler which permits 22 samples to be collected per flight for later analysis by electron microscopy. FCAS measures size distributions in the diameter range from 0.08 to 2 microns.
The FCAS, heated CNC, and unheated CNC channels acquired data reliably on all science flights during this deployment. Data are missing for occasional, brief time periods for a variety of reasons. The aerosol sampler collected far more samples than can be analyzed. Occasional operator failures resulted in loss of particular samples, but the reliability of this sampler has been improved significantly.
Preliminary data analysis shows significant differences between aerosol typical of the tropics and of mid-latitudes. This was true in both the upper troposphere and lower stratosphere. Evidence of the transport of air from the upper tropical troposphere to the mid-latitudes was observed. In addition, several plumes from aircraft were detected in the upper troposphere. These plumes showed evidence of volatile (presumably sulfuric acid) and non-volatile (presumably soot) particles. Grid samples may permit these presumptions to be validated.
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Last Updated: 27 February 1996
Content Editor: Kathy Wolfe