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The May 1995 STRAT test flight series began May 1, 1995 and concluded on May 18, 1995. The specific objectives of this test flight series were to: 1) extend the times series of H2O, CO2, N2O, and ozone, 2) re-integrate instruments onto the ER-2 with the new interface box, and 3) test the ability to perform stair-step flights down to 40 Kft.
Instruments: JPL Microwave Temperature Profiler (MTP): B. Gary NASA Meteorological Measuring System (MMS): P. Bui NOAA Ozone: M. Proffitt, J. Margitan NASA/Ames ATLAS N2O: M. Loewenstein, J. Podolske Harvard CO2: K. Boering NCAR Whole Air Sampler (WAS): E. Atlas Harvard H2O, O3: E. Hintsa, E. Weinstock STRAT Flight Log: May 1995 Series: Limited Payload Nose - WAS or H2O/O3 QBay - MMS, O3, MTP L Wing - CO2 R Wing - N2O Date Flight Pilot Hours Sortie 950324 WAS Recertification B. Collette 1.30 95-068 950427 MMS Recertification D. Krumrey 0.00 95-074 950503 May Recertification K. Broda 1.50 95-086 950505 Canceled Flight (WX) 950508 North Survey Flight D. Krumrey 8.00 95-088 950510 Canceled Flight (WX) 950511 South Survey Flight R. Williams 8.00 95-090 950512 WAS Flight B. Collette 1.50 95-091 950515 Stair-Step Flight D. Krumrey 5.45 95-092 950516 WAS Flight J. Barrilleaux 3.05 95-093 950517 Stair-Step Flight J. Nystrom 5.15 95-094 950518 WAS Flight D. Krumrey 2.20 95-096 Total Flight hours: 37:35
The certification flight occurred on May 3, 1995 (WAS certification on March 24, 1995). The payload was certified, albeit Harvard water failed because of a software glitch. A northern survey flight was flown on 950508, and the southern survey was flown on 950511. A Whole Air Sampler (WAS) flight was flown on 950512, and was followed by a stair-step flight on 950515. A second WAS flight was flown on 950516, a stair-step on 950517, and the final flight for WAS occurred on 950518. The third week of the mission involved flights on 4 consecutive days!
The second flight (950508) was an 8 hour flight north to approximately 60N. The objective of this northern survey flight was to: A) continue the high latitude N2O-CO2-H2O-O3 data time series from the SPADE, and ASHOE/MAESA flights, B) observe northern hemisphere constituent values following the breakup of the polar vortex (i.e. observe possible ozone losses and dehydration), and finally C) observe filaments of material, both meteorological parameters and constituent parameters. A filament that had broken off of a vortex fragment was forecast by NMC, GASP, GEOS-1 data, and reverse domain filling techniques to be to the north of Ames at approximately 55N. This filament was observed by the ER-2 payload. While unambiguous ozone loss was not established, it was clear from the N2O data that the filament had descended from high altitudes, and had remained relatively unmixed with mid-latitude air for a substantial period. Further, based on the Harvard water data, the filament was not dehydrated. Both the MMS and MTP data provide clear-cut information on the vertical and horizontal structure of the filament, and the Harvard CO2 data provide a reasonable estimate of the the age of the air.
The scientific yield from this northern survey flight was somewhat limited by the lack of other tracers and radical measurements. The lack of measurements (radicals, HCl, chlorine species) in this filament precluded stating how the vortex recovered from the chemically perturbed 94/95 winter conditions. Further, we cannot definitively detect dehydration without methane measurements.
The northern survey flight was extremely successful in sampling the range of trace gas values in the northern lower stratosphere. Measured values of N2O as low as 40 ppb at 60 N during May are unprecedented, and provide a real challenge to models simulations over seasonal time scales. The low N2O and high water values in the filament present 3 challenges to model transport: 1) bring high altitude air down to approximately 500K (3-D and 2-D), 2) preserve the mixing ratios of N2O and water over the course of the winter and spring via the isolation of the polar vortex (3-D and 2-D), and 3) produce similar filamentation to the measured structure (3-D). The CO2 observations continue the time series obtained during the SPADE campaign (1993), and the ASHOE/MAESA campaign. These CO2 observations challenge the 2-D and 3-D models with a 3 year data set that both exhibits a temporal trend, and an annual cycle. The meteorological data challenge lower stratospheric assimilation data sets in their ability to accurately represent both the broad scale features, and to simulate the thermal structure of the low N2O filament. MTP observations clearly reveal the thermal structure of the low N2O filament. This is the third time that MTP has sampled the structure of a filament, and the first time that MTP has sampled the structure of a vortex filament in the northern hemisphere.
The southern survey flight (950511) goals were to: A) continue the low latitude N2O-CO2-H2O-O3 data series, B) observe tropical material being transported into the northern mid-lats, and vice versa, C) verify tropical transport calculations, D) observe trace gases near the tropical tropopause, and D) make coincident measurements of H2O and O3 with the HALOE instrument aboard the NASA UARS satellite. The tropical survey flight from Ames is generally not adequate for penetrating the inner tropics. With the exception of the tropical tropopause altitude, the forecasts in the tropic were not particularly credible. Further, the meteorological analyses of the tropical stratosphere were not particularly good, calling into question the tropical transport calculations. We need the tropical deployments to achieve the STRAT goals.
The southern survey was somewhat successful in sampling the range of trace gas values in the northern tropical lower stratosphere. The ER-2 can reach latitudes of 15N from NASA/Ames, whereas a latitude of about 5N is optimal for crossing into the inner tropics (as defined by the O3/NOy ratio). Low values of O3 and high values of N2O were observed equatorward of 19N. The dive to approximately 50,000 ft on the southern end of the flight just touched the troposphere, as indicated by MTP and MMS data.
Two 5.5 hour stair-step flights that sampled altitudes extending from about 40 Kft to approximately 70 Kft were attempted during this deployment. The stair-step (950515 and 950517) goals were to: A) test the basic format for stair step flights, B) get feedback from the ER-2 pilots on the basic outline of the stair-steps in order to optimize safety and the sampling strategy, C) observe upper tropospheric values of trace gases over extended periods, and D) determine the structure of lower stratosphere trace gas fields. The stair-step flights were difficult to plan, and required close collaboration with the ER-2 pilots. Airspace restrictions, and air traffic control requirements conflicted with an optimal sampling of the evolution of the meteorological and trace gas fields. Preliminary modeling suggested that 4000 foot increments in altitude was necessary for resolving trace gas structures in the lower stratosphere, and this was validated by both stair-step flights. The flight of 950515 established the need to configure the flight plan well in advance of the actual flight, and this was implemented in the planning for the stair-step flight on 950517. Restricted airspace forces the aircraft to fly in the quadrant of airspace to the northeast of Ames.
The stair-step flights proved to be extremely useful. High resolution observations near the tropopause provided an unprecedented wealth of information for assessing transport rates. Further, these observations provide cross sections of trace gas measurements that are extremely fine in detail, and show layering of trace gases in the lower stratosphere. On the flight of 950515, air was observed near 400 K that had been injected into the stratosphere at the tropical tropopause, and then advected into the mid-latitudes. High values of N2O, and CO2 identify this air as having recently come from the troposphere, while the dry characteristic of the air (3-4 ppm of water) identified it as having come through the tropical cold trap. Simulation of the two stair-step flight observations will prove to be extremely challenging for 3-D chemical transport models.
Three flight were attempted using the Whole Air Sampler (WAS) during this deployment. The 950512 flight failed to obtain samples as a result of differences among instrument switches in the cockpit. This problem was resolved, and a second attempt was made on 950516. The second attempt also failed because of a power glitch in the WAS instrument that reset the WAS scheme. Hence, only two observations were made by WAS. The 950518 WAS flight was fully successful, and made measurements from 69 Kft to 41 Kft. Analysis of the WAS data from the certification flight of 950324 show very good results. This suggests that WAS would be extremely useful for use on stair-step flights. Further, investigations into intergrating the WAS instrument onto the superpods would make possible the use of WAS on future flights. Analysis of the 950518 WAS samples should be completed within the next few weeks.
An issue that arose during the second week of the deployment was the surface weather forecasting at Moffett Field, and the implications for flying during the Fall and Winter deployments. The ER-2 has tight constraints on take off and landing wind conditions (15 knot crosswind, 30 knot total wind). Therefore, timely and accurate surface weather forecasts are essential, especially when the overall weather conditions are marginal.
Because the Navy forecasters are no longer located at Moffett, a terminal forecast (TF) for Moffett is no longer provided. At present, operations must either wait on a TF for the San Jose airport (available between 7:20 and 8:00 AM), or use the San Francisco TF (available at a very early hour). Generally the early SF TF is a poor forecast for Moffett, while the San Jose TF is too late for an 8:00 AM takeoff decision. Hence, during the May deployment, the STRAT flights generally had 10:00 AM takeoffs to insure that operations had useful NWS forecast wind information. During October, the 8 hour survey flights need to be flown in daylight, and a 10:00 AM takeoff would require a landing around 6:00 PM, approximately 30 minutes after sunset.
Since the weather situation at Moffett is generally excellent, this forecasting issue should not have a major effect on the STRAT flights. However, with the tight STRAT schedule, any canceled flight can potentially diminish our science return. Flight cancellations are inevitable because of the many factors involved (weather, instrument health, airplane health, people health), but it is important that we minimize the risk due to factors that are within our control, i.e., access to timely weather information.
Currently, Steve Hipskind and Lenny Pfister are working this issue with the weather service and with operations to improve the situation for subsequent field campaigns.
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