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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, California and Barbers Point Naval Air Station, Hawaii during late-January and early-February 1996. The mission was sponsored by NASA's Office of Mission to Planet Earth and Office of Aeronautics.
This STRAT flight series began 22 January 1996 and concluded on 15 February 1996. The specific objectives of this flight series were to: 1) extend the times series of trace gases, including H2O, CO2, N2O, NOy, and ozone, from approximately 60 N to the equator; 2) intercompare the ER-2 and DC-8 in situ instruments, and intercompare the ER-2 in situ instruments with the DC-8 lidar instruments; 3) perform stacked flights in the upper troposphere and lower stratosphere to provide full samplings of the trace gases in these regions; and 4) integrate the ER-2 spearpod instruments into the superpods. Flights covering the latitude range from 2 S to 59 N give almost the full range of tracer observations in the lower stratosphere, comparable to those measurements made during the Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE) test flights in November 1992, the follow-up SPADE flights in November 1993, and the October/November 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign. All of the instruments were reintegrated onto the platform and performed well. Three stacked flights were conducted (two over Ames and one over Barbers Point) which comprehensively sampled the upper troposphere and the lowest portion of the stratosphere.
The ER-2 instrument complement for studying ozone depletion and transport processes, initiated under UARP and currently operated under a UARP-AEAP partnership, has continued to evolve. New instruments continue to be developed and flown, keeping constant pressure on the carrying capacity of the flight platform. To alleviate the payload space limitation imposed by using the older and smaller spearpods, and because the spearpods were no longer being maintained by the Air Force fleet, a decision was made in late 1994 to transition the wing pod instruments from the spearpods into the larger superpods. This year-long effort of configuration decisions, detailed engineering and final fit-check and integration culminated in the first use of the superpods for the STRAT experiment on this latest deployment. This was a team effort with significant contributions by all of the pod instrument PIs, Lockheed engineering, and instrument coordinators.
Date Flight Pilot Hours Sortie Comments 01/26 Test Flight B. Collette 1:30 96-062 ER-2 ADC 01/29 Stacked Flight R. Williams 5:05 96-063 FCAS, MTP 01/31 Planned Flight J. Barrilleaux 0:00 Icing conditions 02/01 Northern Survey J. Barrilleaux 7:55 96-064 FCAS, MTP 02/02 Stacked Flight B. Collette 4:50 96-065 None 02/04 Attempted Transit J. Nystrom 0:00 Lightning 02/05 Transit to Hawaii J. Nystrom 5:55 96-066 MTP, C-141 CDC 02/08 Stacked w/ DC-8 K. Broda 3:30 96-067 CPFM, ER-2 AC generator 02/10 Planned Flight K. Broda 0:00 Runway x-winds 02/11 Attempted Flight K. Broda 0:00 Runway x-winds 02/12 Test/Stacked Flight K. Broda 3:00 96-068 None 02/13 Southern Survey J. Nystrom 8:00 96-069 None 02/15 Transit to Ames K. Broda 6:05 96-070 ALIAS Total Flight Hours : 45:50
The January/February 1996 STRAT deployment began on 22 January 1996 and concluded on 15 February 1996. Including transit and test flights, there were a total of nine flights over the course of this deployment.
This deployment had some significant results. This was the first time that measurements from the ER-2 were made in the inner tropics during midwinter. The vertical propagation of the seasonal cycles of both water and CO2 were observed in the inner tropics during this period. This vertical lifting is strongest during midwinter; hence, this is a first check on the transport rate of tropospheric constituents into the stratosphere. A nearly complete "latitudinal" scan of trace gases was made during this deployment, since the ER-2 was able to penetrate the polar vortex on 960201, and then flew into the inner tropics on 960213. The polar vortex flight showed evidence of heterogeneous chemistry via HCl loss and via NOy denitrification and redistribution. Aerosol measurements showed the continued decay of the Mt. Pinatubo-injected aerosols. The stacked flights provided increased knowledge of the distribution and variability of trace gases in the upper troposphere and lowest-most stratosphere (i.e., stratospheric middleworld). These regions are key to understanding how strat-trop exchange takes place, determining the rates of transport into and out of the stratosphere, and initializing models. The STRAT stacked flight of 960208 just slightly north of Oahu was coordinated with the NASA DC-8 and provided key data from: 1) DC-8 and ER-2 in situ instrument intercomparisons, 2) ER-2 intercepts of the DC-8 engine exhaust, and 3) upper tropospheric radical measurements during sunrise.
The STRAT instrument integration was extremely smooth with one exception, and the ER-2 completed a 1.5-hour test flight on 960126. The superpod integration went extremely well, thanks to the preliminary work of the instrument teams, project management, and the Lockheed crew. A problem occurred during the integration of the HOx instrument, since the HOx lasers were damaged in shipment from Harvard to Ames. The HOx group put in some very long hours to fix the lasers, which were repaired and back in the instrument by 960128.
The first week of the Ames portion of the deployment was somewhat difficult because the surface weather was poor and the polar vortex was just within range near Hudson's Bay in Canada. Initial plans included an 8-hour flight towards Canada, but were changed to a stacked flight on 960129 when the inclement weather appeared to be closing in. We planned flight legs at 35, 37, 39, 41, 47, 53, and 65 kft, and estimated that the tropopause would be at ~33 to 37 kft. The ER-2 took off at 8:00 a.m., and returned at approximately 1:05 p.m. local time (pilot: Ron Williams). The plan was to fly 7 legs (37, 39, 41, 43, 49, 59, and 67 kft) just off the California coast. Three legs were flown for 20-30 minutes per leg, with the 59-kft leg shifted to 57 kft for air traffic control reasons. All of the instruments worked successfully, with a couple of fail lights from the FCAS and MTP instruments. The pilot reported thin cirrus at the 39- and 41-kft levels, suggesting that the tropopause altitude forecast near 37 kft was in error. The science objective was to make measurements of trace-gas values in the upper troposphere and the stratospheric middleworld. The first two legs of the flight were below the tropopause as indicated by the MTP and MMS data (below 336 K in potential temperature). The next two legs at ~340 K and 355 K were clearly stratospheric middleworld legs, while the final three legs were in the overworld part of the stratosphere above 375 K.
After trying to get off a flight towards the polar vortex on 960131 which was scrubbed because of icing conditions, we were able fly to the polar vortex on 960201. The ER-2 took off at 8 a.m. PST (pilot: Jim Barrilleaux) on an 8-hour flight, and returned a few minutes early. Specifically, the plane flew northeastward towards Canada and Hudson's Bay to ~53 N and 95.5 W. This flight profile was expected to provide 1) an optimal scan of trace gas measurements over the northern mid-to-high latitudes, 2) values of trace gases inside and at the edge of the polar vortex, and 3) measurements in air that was below the NAT saturation limit over the last five days. FCAS and MTP experienced problems on the flight, but both instruments were able to recover a good fraction of their data. PV charts and RDF calculations from NCEP, GSFC/DAO GEOS-1, and UKMO data indicate that the polar vortex was within range, consistent with MMS observations. Wind speeds fell off as the plane passed over Lake Winnipeg, suggesting that the plane passed beyond the jet core into the edge region of the polar vortex. UGAMP model predictions of N2O were on the order of 160 ppbv. ALIAS, ATLAS, and ACATS observations were consistent with these low numbers, suggesting some penetration into the polar vortex. Extremely low-N2O air also was sampled in the dive, consistent with low Harvard CO2 data. ACATS measurements of SF6 confirm that this air, with low CO2 and N2O, was older air contained by the vortex. NOAA NOy measurements indicate some degree of denitrification inside the vortex.
The third flight of the deployment was a stacked flight. The ER-2 took off at 11 a.m. PST (960202) on an 5-hour flight (pilot: Bill Collette), and returned a few minutes early. Seven legs were flown (35, 37, 39, 41, 47, 53 kft, and then up to maximum altitude) just off the California coast. Each leg was somewhere between 20 and 30 minutes long. The tropopause should have been ~36 kft, with some probability of cirrus on the first leg at 35 kft. However, the pilot reported some light cirrus at both the 35- and 37-kft layers. The subtropical jet was just to the south, so winds were very strong in the lower legs as reported by the pilot. It was clear from a number of instruments that aircraft plumes were encountered on the first three legs. In particular, a very strong plume was seen at 39 kft. Water measurements show that the 35- and 37-kft legs were probably tropospheric, because of water vapor measurements over 50 ppmv. The third leg had intermediate values of water, and the rest of the legs had low water characteristic of the overworld. The sixth leg at 53 kft was extremely interesting insofar as water, ozone, and NOy were quite low while N2O and F-11 were quite high, suggesting that the air in this part of the stratosphere was of recent tropical origin. The air above the 53-kft level was more characteristic of that typically sampled in the mid-latitudes of the stratosphere.
The STRAT transit flight to Hawaii was flown on 960205 by Jan Nystrom. The flight was originally planned for 960204; however, heavy rains, gusty winds, and a thunderstorm forced the pilot to scrub as he was taxiing to the runway. The flight took off at about 10 a.m. PST, and was a straight course from Ames to Hawaii, with a dip down to about 50 kft about halfway across. The flight was interesting insofar as the temperatures in the dive were extremely cold, and the water vapor mixing ratios dropped to ~2 ppmv.
The STRAT ER-2/DC-8 coordinated flight was flown on 960208 from Barber's Point, Hawaii (ER-2) and Fairbanks, Alaska (DC-8). The ER-2 took off at ~6:55 a.m. HST from Barbers Point (pilot: Ken Broda). This was 25 minutes later than expected because of DC control panel failure. Fortunately, Jeff Cohen and the rest of the ground crew did some quick work and corrected the problem. The ER-2 rendezvoused with the DC-8 shortly before 7:30 a.m. (sunrise was at 7:08 a.m.) at a point just to the north of Oahu. The ER-2 was in visual range of the DC-8 over the entire course of one 30-minute leg flown westward at 39 kft, and a second leg flown for ~30 minutes at 35 kft. The ER-2 pilot noted that he felt the DC-8 wake turbulence a number of times, and visually identified the DC-8 contrail. The first leg occurred at ~347 K (39 kft), and the second leg of the intercept was at ~345 K (35 kft). After flying these two coincident legs, the DC-8 landed at Barbers Point and the ER-2 continued to higher altitudes to complete a stacked flight. The ER-2 completed stacked legs at 357 K (46 kft), 370 K (51 kft), and 385 k (56 kft). Additional legs were originally planned at 61 kft and 65 kft, but the ER-2's AC generator failed at 9:40 a.m. HST, forcing the pilot to abort the mission during the 56-kft leg. Temperatures on this last leg were less than 192 K, with MTP reporting that we were approximately 100 meters below the tropopause at 17.15 km. Most of the instruments functioned properly with the exception of the CPFM UV/VIS instrument, which failed at power-up. Because nearly all of the instruments (with a couple of exceptions) use the AC power, there is very little data after the AC generator failure. Since the flight was aborted at that stage, data for the descent into Barbers Point is not available. Consistent with these tropospheric legs, ozone values from the Proffitt/Margitan instrument were quite low (less than 0.12 ppmv). Similarly, NOy was quite low. The HOx data clearly show the sunrise under conditions of fairly clean upper tropospheric air.
Approximately 10 separate intercepts of the DC-8 wake were made by the ER-2 on 960208. The DC-8 exhaust was observed in NOy, NO, CN counter, and HOx measurements. It is not clear that all of the plumes encountered were from the DC-8; two of the plumes did not seem to have originated from the DC-8 when using MMS winds to backtrack to the DC-8 from the ER-2. Tropospheric levels of variability in the trace gases preclude a clear identification of the DC-8 exhaust. This is clear from the CO2 data, where the variability is such that the CO2 emissions from the engines do not stand out clearly against the tropospheric background. This implies that relatively quiescent regions are required for plume sampling. Strong winds preclude a clear identification of plumes (even in the mid-Pacific). Based on the 8-Hz data from the HOx instrument, it is evident that the plumes are highly structured, implying that only fast-response instruments can be used for calculating emission indices.
Because of the aircraft problems on 960208, a 3-hour test flight was flown on 960212 (pilot: Ken Broda). Three legs at 55 kft, 60 kft, and maximum altitude were originally planned, but the altitudes were increased by 1000 ft because of the relatively high tropopause from the Lihue radiosonde at 1200 GMT. Data from the Proffitt/Margitan instrument show that ozone levels were very small on the 56-kft leg. The ACATS F-11 data were also near tropospheric levels on this lowest leg, and the ALIAS CO measurements were relatively high. According to the MMS data, we were just above the troposphere by ~250 meters on this 56-kft leg. The three legs were at 383 K, 426 K, and 479 K. Minimum temperature measured by MMS was ~189.6 near the tropopause. The ER-2 reached a maximum altitude of ~66.7 kft, and made a slow descent into Barbers Point, landing at ~12:50 p.m. HST.
An 8-hour southern survey flight to the equator was flown on 960213 (pilot: Jan Nystrom). The primary objectives were to survey stratospheric tracers down to the equator, obtain a vertical profile to the tropopause at the equator, and to intercompare the ER-2 in situ instruments with the DC-8 lidar data. A secondary objective was to intercompare the ER-2 instruments with the Mauna Loa NDSC instruments. The ER-2 performed a "box maneuver" over the Mauna Loa NDSC station, and then headed directly south to ~1 S. The aircraft turned and dove to ~51.5 kft, penetrating the troposphere by a few thousand feet at the equator. CO values shot up to tropospheric values, ozone was quite low, and a minimum temperature of ~186.3 K was observed at 16.6 km at ~0.75 N. The plane returned to Barbers Point by a slightly more direct route than previously planned, bypassing Mauna Loa on the return leg. The pilot also reported very thin cirrus on the horizon near the equator that is probably the subvisible cirrus observed by the DC-8 during the TOTE/VOTE mission. CO2 showed an equatorial minimum at 19 km that was a result of the upward propagation of the CO2 from the tropospheric fall minimum. Extremely low water values were observed in the equatorial dive that were consistent with the cold temperatures. The O3/NOy ratio showed that the we penetrated the inner tropics by a few degrees.
The transit flight back to Ames was flown on 960215. The flight was again a direct flight with a dip down to ~50 kft at the midpoint in the transit (31 N). While cold temperatures were observed on takeoff from Barbers Point, the dive exhibited much warmer temperatures. The ER-2 dove down to ~405 K on the return leg, still substantially in the stratosphere. A great deal of structure was observed during the dive in N2O, NOy, CO2, and ozone.
The main objective of the Whole Air Sampling (WAS) investigation is to measure a suite of organic molecules of different chemical lifetimes in order to examine mixing rates and transport time scales between the upper troposphere and lower stratosphere. Target molecules include: C2-C5 alkanes, HCFCs and HFCs (22, 141b, 142b, 134a), C2Cl4, CH2Cl2, CHCl3, methyl halides, and a full suite of organic bromine molecules (e.g., Halons, CHxBryClz). The January/February 1996 STRAT flights were the first full deployment for WAS on the ER-2 for this mission. The instrument was reconfigured in a temporary location in the left superpod nose. Because of additional weight allowance in this location, WAS collected a maximum of 49 samples during each flight. This number of samples allowed a unique opportunity for high-density sampling of the tropopause region during each of the stairstep profiles.
WAS performed well and collected samples during all flights. Samples were pressurized to 3 atm in electropolished stainless steel containers, and these containers were returned to the laboratory in Boulder for detailed chemical analyses. A total of 334 samples were collected during the mission. Analyses are currently underway.
Measurements of stratospheric and mid- to upper tropospheric CO2 were obtained and archived for all nine flights of the January/February 1996 STRAT deployment. These new measurements, particularly when combined with simultaneous measurements of N2O, fulfill a number of important goals:
The MMS instrument operated successfully on all flights. All archived MMS data used the best calibration obtained from the October 1995 STRAT mission. Navigation data as well as ground-speed data to compute wind were obtained from the aircraft INS (92INS). Data calibration and data integrity will require further detailed analysis because the 92INS data have been "updated" and are unavailable to characterize their performances.
The MMS installed a new dedicated Embedded-GPS-INS (EGI) to provide independent navigation and ground-speed data. The first EGI arrived one week before the start of the STRAT mission and we are just beginning to interface to the new data stream. MMS sampled EGI data on five out of the nine flights. We are planning to correlate the data from the 92INS and the EGI and will reprocess the flights in the near future.
We had a fairly successful STRAT deployment for the Airborne Chromatograph for Atmospheric Trace Species (ACATS-IV). Data were collected on all nine flights. Our precisions for SF6, H2, and CH4 have continued to improve since the beginning of the second STRAT deployment. The precision improvement for H2 and CH4 (channel #4) is attributed to changing the injection order of the four channels, where channel #4 is now first. This problem was caused by contamination from channel #2, N2O and SF6, which uses P-5 (with 5% CH4 in Ar) as a carrier gas. Our improved SF6 precision narrows the uncertainty on the age of air calculation. SF6 mixing ratios have increased since the ASHOE/MAESA mission because of its rapid growth in the atmosphere. We have confirmed the separation of tropical data from mid-latitude data on Halon-1211 vs. N2O correlation plots that were seen on earlier STRAT and ASHOE/MAESA deployments. Preliminary analysis shows that 30 to 50% of the tropical air is mixed with extra-tropical air. Our improved H2 precision confirms the ASHOE/MAESA result of an inverse correlation with long-lived tracers such as CFC-11. We observed polar vortex air with low tracer gas mixing ratios at one point on the northern survey flight (960201).
Mixing ratios of stratospheric CCl4 continue to be higher than expected from ASHOE/MAESA. This result indicates a source of contamination within ACATS-IV or a source of CCl4 or similar compound within the Q-bay. The problem is difficult to troubleshoot because our tropospheric CCl4 data are unaffected. All ambient N2O values appear to have increased by 3% after the ferry flight from Ames to Hawaii during deployment #2 (951102). A preliminary comparison of our bulk flight standard vs. primary and secondary standards indicate that the N2O mixing ratio in our flight standard has dropped. With the exception of N2O and stratospheric CCl4, data from all flights have been submitted to the archive on cloud1. We expect to submit N2O data once our calibrations are complete.
Measurements of NO and NOy in the upper troposphere and lower stratosphere were successful for all flights. An intercomparison of ER-2 and DC-8 NO/NOy instruments was performed during the coincident flight (960208). Although ambient NO and NOy concentrations were at the detection limit of both instruments (7 and 45 pptv, respectively), the differences of measured values between the two instruments were only 5 and 7 pptv, respectively.
Extensive HCN interference tests for NOy were carried out in the field. A preliminary upper limit of the interference for each stacked flight has been determined. For the October/November 1995 deployment, the typical value is 10 pptv. Values for the January/February 1996 deployment vary from flight to flight, ranging from 20 to 40 pptv.
The preliminary data indicate that the NOy-N2O correlation slope in this deployment increased 5% from the last deployment. Although the measured change is on the order of the combined instrument precision, it is consistent with the NOy-N2O seasonal cycle in the lower stratosphere at mid-latitudes as predicted by 2-D models.
On 960129, an NOy/O3 ratio of 0.002 was measured at 20 km above Ames. This is significantly lower than the typical mid-latitudinal value of 0.003. In Hawaii, however, only 0.003 was measured except near the equator during the southern survey flight.
Denitrification and NOy redistribution were observed at 53 N during the northern survey flight on 960201.
The Microwave Temperature Profiler (MTP) flew on eight of the nine January/February 1996 STRAT mission flights. The California-based flights require extensive calibration corrections made necessary by a faulty local oscillator for Channel 1. Frequent "fail-light" stoppages occurred during these flights; however, there was negligible data loss because MTP resumed operating each time its power was recycled. Three of these four flights have been recalibrated and the data appear to be acceptable. MTP did not fly on the ferry flight to Hawaii (960205), as it was undergoing repair at JPL at that time. The repair fixed both problems, and normal data was obtained on the subsequent Hawaii-based flights.
The principal role for MTP during STRAT is to determine tropopause altitude from the temperature field on those occasions that MMS data is unable to do so - such as during dives, level-flight legs, or ascents and descents through air that has strong horizontal temperature gradients. There were 21 tropopause "proximity events" in which the ER-2 either crossed the tropopause or dipped close to it, and MTP has data for 19 of these. A table of tropopause altitudes is in preparation. This table, which will combine the MTP and MMS estimates in a subjectively weighted manner, will be submitted to the STRAT archive with the name TR960126 (where 960126 denotes the first flight date of the deployment summarized by the table).
Four tropopause "proximity events" for this deployment should provide especially good resolution of tracer profiles in the tropopause vicinity: (1) legs 2 and 3 of the Ames-based stacked flight (960129) straddle the tropopause with tropopause-referenced altitudes of -300 and +300 meters; (2) the Ames-based stack flight (960202) straddled the tropopause during legs 3 and 4, being very close during leg 3; (3) the Hawaii-based stacked flight (960208) never crossed the tropopause, but was a mere 200 meters below during the last leg; and (4) leg 1 of the stacked flight on 960212) was 300 meters above the tropopause, yet tracers (ozone, water, etc.) were tropospheric! It is possible that this condition exists only in the tropics, where air has recently entered the stratosphere.
Two MTP/ER-2 and MTP/DC-8 intercomparisons have been filed in the combined VOTE and STRAT archives: DC960208/ER960208 and DC960213/ER960213. The first of these comparisons has not been studied yet, but a preliminary review of the second one shows good agreement. The MTP/DC-8, while flying at 11 km at the south end (near the equator), showed a tropopause at 16.5 to 17.0 km with temperatures of 186 or 187 K. MTP/ER-2 flew in the same region 12 hours later and measured a tropopause at 17.2 km with coldest temperatures of 186 K. This agreement is excellent.
The water vapor instrument produced good-quality data for all the January/February 1996 STRAT flights. Problems from the October/November deployment related to the quartz chopper (to measure background) were successfully solved. The seasonal cycle of water vapor entering the stratosphere continued to be observed in the tropics. The southern flights from Hawaii were particularly important. In contrast to the 951105 flight, where water vapor at the tropical tropopause was comparatively high (~3.5 ppmv), water vapor on the flight of 960213 was ~1.7 ppmv at the tropopause, consistent with the extremely cold temperatures there. This extremely dry air was also observed on ascents and descents into Barbers Point during the February deployment. On both of the southern survey flights (951105 and 960213) flights, the ER-2 appeared to briefly enter the troposphere near the equator, based on an increase in water vapor after the minimum. The stacked flights were also quite interesting, with very different water vapor amounts observed on the various flight levels. Analysis is ongoing to determine the origins of the air observed and how it mixes from the troposphere to the stratosphere and from the tropics to mid-latitudes and vice versa.
All flights of the ATLAS instrument returned quality data. There are some detailed issues which affect data quality for some flights; however, the effect is no more than to reduce accuracy from a nominal 3% to possibly 4% absolute. All data currently in the archive are preliminary and are subject to recalibration and revision for a final archive. Nonetheless, the following conclusions are firm and will be minimally affected by any future revision of the archived data.
The survey and ferry flights produced new and valuable enhancements of our picture of the Northern Hemisphere and tropical CO2:N2O correlation. They reveal the expected seasonal and secular variations in this tracer correlation. As these new data and those of future STRAT campaigns are integrated into the "big picture," we will have a good view of the behavior of the surf zone and the "pipe" over the quasi-biennial oscillation, as well as over the course of the seasons. Similar comments can be made for NOy:N2O; we now are working on a carefully focused study of this correlation in the Northern Hemisphere surf zone over the seasonal cycle. The STRAT data has a special status as it encompasses, along with the October 1994 ASHOE/MAESA flights in the Northern Hemisphere, the epoch in which for the first time ATLAS achieved an absolute measurement accuracy of 3% or better. (We now believe that this is about the accuracy limit we can expect to achieve routinely with the current edition of ATLAS.)
The stacked flights provided interesting vertical profile data on N2O. The flight of 960208 is especially interesting as it provides several legs flown entirely in the troposphere. The data return from this flight illustrates the accuracy of ATLAS since we have a direct comparison with NOAA CMDL (ACATS IV) measurements of N2O in the troposphere. Preliminary analysis indicates that our estimate of 3% uncertainty in ATLAS data is borne out by this comparison.
The UV-Vis spectrometer per se performed well and produced excellent spectral data. However, the absolute radiometric calibration was compromised by the continuing malfunction of the filter wheel assembly. This problem causes apparent gain shifts at data block boundaries. Work is in progress to develop procedures and computer codes to correct these shifts in the final STRAT data to be archived and to do a reanalysis of earlier data. At the same time, an aggressive investigation program is underway to isolate the root cause of the problem so that future flights will produce more accurate data and permit faster data processing in the field. It is hoped that applying the corrections to the data will not produce a large increase in the final uncertainties calculated for the absolute intensities and the J-values which depend on these data.
Information from the CPFM instrument concerning the column ozone above the aircraft appears to be of very good quality for all flights. These data are being reprocessed, taking into account comparison data from the ground-based observations made by Brewer Ozone Spectrophotometer #009 at Moffett Field and Barbers Point, and with observations reported from the Dobson instrument at Mauna Loa Observatory (MLO). For the first time, a close comparison between the MLO instrument and the CPFM was obtained when the ER-2 made a box turn around the island of Hawaii on its return from the southern survey flight (960213). In addition, the observatory staff made a special effort to launch an ozonesonde at about the time the ER-2 was in the vicinity. The analysis of these data should provide a useful benchmark to tie the ER-2 observations to the long-term record from Mauna Loa. In addition, the GSFC ozone DIAL was operating at MLO during this STRAT deployment.
As was the case during the October/November 1995 campaign, ground-based column ozone data were made available in near-real-time through the cooperation of John Rives at the University of Georgia, who collects data from the EPA Brewer Spectrophotometer network; Gloria Koenig at NOAA in Boulder, who reported Dobson data; and Jim Kerr at the AES who provided data from the Canadian Brewer network.
Albedo data produced by the CPFM instrument also has been affected by the gain variations in the system. For this reason, the current release of the data should be used with caution. Final reprocessing in the next few weeks should produce a much larger proportion of reliable values, and regions where there are problems will be identified in the exchange files. There were regions during a number of flights where the albedos show substantial variations and considerable differences between the CPFM-derived values and the satellite results. These differences are mostly the result of poor time matching between the ER-2 overpass and the time the satellite image was recorded.
The northern survey flight (960201) from Ames was quite interesting. The ozone record shows a change corresponding to the boundary of the Arctic vortex. The ozone values become quite variable in the vicinity of the edge and there is a decided drop in ozone amount across the boundary. These features correlate with other species measurements made during the flight.
On the fall (October/November 1995) deployment, the O3/NOy ratio value was 300, independent of theta (390 to 510 K) at mid-latitudes (26 to 58 N), but increasing dramatically in the tropics and showing a strong theta dependence, ranging from 300 at 390 K to 800 at 490 K.
The stacked flight on 960129 found the O3/NOy ratio values ranging from 280 at theta = 390 K to 480 at 490 K over the 35 to 38 N latitude range, suggesting the influence of tropical air. On the 960201 survey flight, the ratio showed some theta dependence, ranging from near 300 at theta = 390 K to 400 at 510 K, again suggesting some tropical influence. As the ER-2 crossed the polar jet (wind max near 51 N), the ratio decreased from 350 to 400 down to the 300 range that was typical during fall (when the vortex was forming).
The deployment to Hawaii provided an interesting contrast. The tropical edge (in O3/NOy ) was only encountered southward of 8 N on the southbound flight (the boundary had been at 18 to 26 N in the fall). The ferry to Hawaii (960205), the stacked flight at Hawaii, and the first 10 degrees southward all showed air with mid-latitude character in O3/NOy : values near 300, with very little theta dependence. Thus, the Ames stairstep encountered more "tropical" air than the Hawaii stairstep. This raises an interesting issue for the OMS balloon flights, which most probably will rely on a single flight profile at mid-latitudes compared with a single profile in Brazil: were we to do this with the Ames and Hawaii stairstep flights, we would come to exactly the opposite view of tropical vs. mid-latitude signatures.
The O3-N2O correlation plots for 960129 generally fell along the AASE II ("vortex exterior") reference line except at 470 and 490 K, which showed substantially higher ozone (> 500 ppbv higher), but with the same slopes (490 K even higher than 470 K). On the 960201 flight, the points fell along the AASE II line for N2O > 230 ppbv. Below 230 ppbv of N2O, the spread increased both above and below the line, with ozone values at N2O = 200 nearly 1000 ppbv higher than the line. Also, at the northern end, ozone values fell dramatically relative to N2O, hitting 2300 ppbv at N2O = 110, nearly 2000 ppbv below the correlation line value.
The Aircraft Laser Infrared Absorption Spectrometer (ALIAS) instrument produced simultaneous measurements of N2O, CH4, CO, and HCl from 40 N to 2 S, sampling the region from the upper troposphere to the lower stratosphere in flights out of Moffett Field, California, and Barbers Point, Hawaii.
The ALIAS instrument performed well during the January/February 1996 STRAT deployment. ALIAS N2O and CH4 data were collected on all nine ER-2 flights. ALIAS CO data was collected on seven flights, although the CO dataset is only partial for the northern survey flight (960201) and mid-latitude stacked flight (960202). No CO data were collected on the transit flight (960205) or the first Hawaii stacked flight (960208). Excellent HCl data were obtained for the test flights and first northern survey, but HCl data collection was not possible on subsequent flights in order to ensure the priority of the CO and CH4 data collection.
ALIAS CO exhibited a strong positive correlation with Harvard CO2 (R = 0.9898) in the mid-latitude flights. The correlation has a continuous linear trend from the upper troposphere through the stratospheric middleworld and into the lowest overworld. As the air gets progressively older, CO decreases due to reaction with OH, and CO2 decreases due to its seasonal cycle. However, for potential temperature > 480 K, CO is in photochemical steady state and is independent of CO2 mixing ratio. In mid-latitudes, the average CO mixing ratio was 85 ppbv at the tropopause, 40 ppbv at the 380-K isentropic surface, and 12.5 ppbv above the 480-K isentropic surface. In the tropics, there was less CO than at northern mid-latitudes due to smaller tropospheric CO source terms. The average CO mixing ratio was 55 ppbv at the tropical tropopause and 50 ppbv at 380 K.
ALIAS and ATLAS N2O measurements agree to within 4.5%, with ATLAS N2O tending to be systematically higher than ALIAS N2O. ACATS CH4 is systematically higher than ALIAS CH4, especially at low pressures. However, ACATS CH4 shows much larger scatter than ALIAS CH4 and has a poorer correlation with N2O. The correlation of ALIAS N2O and CH4 during this deployment was consistent with ALIAS correlations from the October/November 1995 STRAT deployment and northern mid-latitude ASHOE/MAESA flights. During sampling of the Arctic vortex on the northern survey flight (960201), N2O and CH4 mixing ratios plummeted to 117 ppbv and 910 ppbv, respectively, indicating descent of air from the middle stratosphere. The correlation of N2O and CH4 in the Arctic vortex is consistent with ALIAS data collected during SPADE.
Excellent HCl data were obtained on the Ames test flight and northern survey, from which HCl vs. N2O correlation was captured for the low background aerosol conditions, and large HCl losses (up to 1.5 ppbv) inside the vortex region were observed. The STRAT HCl measurements at mid-latitudes show HCl/Cly values of about 80%, somewhat higher than the October/November 1995 STRAT values, and higher than the November 1994 ER-2/ATMOS intercomparison flights. The January/February 1996 STRAT observations by FCAS show lower surface areas of less than 1 µm2/cm3. These measurements extend and are consistent with the 1993 SPADE, 1994 ASHOE/MAESA, and 1995 STRAT datasets, which show an HCl/Cly ratio increasing with time as the particle surface area from the eruption of Mt. Pinatubo slowly diminishes.
The 1996 HCl vs. N2O correlations add consistency to the picture of a recovering HCl/Cly fraction with time from 1991 through 1996 as the Mt. Pinatubo aerosol loading diminishes.
After initial difficulties with laser failures, the HOx instrument performed very well. OH and HO2 measurements were obtained on all science flights and preliminary datasets have been archived.
These measurements substantially expand the upper tropospheric HOx observations. The morning rise of OH and HO2 was observed on the Hawaii stacked flight (960208), which will provide clues for OH sources in this region. OH Observations in the DC-8 exhaust plume will provide evidence for the photochemical evolution of the exhaust plume. Together with the other measurements made onboard the ER-2, these new observations will allow study of the role of NOx, hydrocarbons, and HOx in determining the photochemical budget of ozone in the upper troposphere.
The condensation nucleus counter (CNC) measures the total concentration of particles with diameters from ~0.08 to ~3 mm with no size discrimination. A second channel on the instrument measures the concentration of particles that survive heating to 190 degrees C. The FCAS measures the concentration of particles with diameters from 0.1 to 2 µm in 31 size bins. Particle surface area and volume concentrations are calculated from the measured number size distribution.
Problems with the FCAS data system plagued the instrument during the early stages of the deployment. The latter 2/3 of the FCAS data from 960201 are lost, and data from 960129 may or may not be recoverable from a damaged hard disk. The failure of an optical element in the sensing cavity resulted in complete data loss during the latter 3/4 of the short stacked flight on 960212.
The Ames-based flights showed that the decay of Pinatubo aerosol surface and volume concentrations continued, with mid-latitude "overworld" values of ~0.7 µm2 cm-3 and ~0.05 µm3 c-3. These values are within the range of measurement uncertainties for pre-Pinatubo conditions, but may be expected to continue to decline slightly. Particle number concentrations remain at pre-Pinatubo levels as they have since 1993, maintained by the tropical source. Consistent with previous measurements, particle number concentrations in the tropics exceed those at similar q levels in mid-latitudes, both in the lower stratosphere and upper troposphere. These measurements support the conclusion that the near-tropopause region in the tropics is a major source for stratospheric particle number.
Several aircraft plumes were intercepted during lower legs of the stacked flights over Ames and Barbers Point. The particles were clearly seen in the CNC data but were not detectable by the FCAS, indicating that the particles were < 0.1 mm diameter. Impactor samples were collected during two plume intercepts (one by the DC-8); these samples will be analyzed by scanning transmission electron microscopy for information on the size and composition of plume particles. The DC-8 appears to be a prodigious producer of particles. One plume showed peak concentrations of ~105 particles cm-3, typical of the Concorde intercepts during ASHOE/MAESA, despite apparently higher plume dilution for the DC-8 case.
FCAS measurements show a response to apparent Ci cloud penetrations during the stacked flight of 960202. Such a response was not seen during the dive during the southern survey flight on 960213, despite the pilot's reports of Ci that was visible slantwise.
In addition to providing meteorological support to the Project Scientists jointly with Leslie Lait (NASA GSFC), our team is responsible for providing meteorological satellite data to the project and analyzing its significance for STRAT goals. Clouds are important to STRAT in four ways. First, they serve to transport material upward (and downward) rapidly within the troposphere, in many cases bringing it up to the tropopause. In some cases, such as penetrative tropical convection, the clouds inject material directly into the stratosphere. The relationship of convection to upward troposphere-to-stratosphere mass transfer in the tropics is a question of major scientific interest. In mid-latitudes, there is some evidence from previous STRAT missions that mid-latitude clouds determine the water content of air transferred into the middleworld by condensation and subsequent ice removal in excess of cloudtop saturation mixing ratios. Second, knowing the cloudtop heights is important in experiment operations, since some aircraft instrumentation performs poorly (or is actually harmed) by prolonged flights through clouds. Third, clouds change the UV and visible radiation fields in the stratosphere through reflection of solar radiation, thus affecting the chemical balance. Finally, convective clouds generate vertically propagating gravity waves which can affect the momentum balance at all levels in the middle and upper atmosphere.
During the January/February 1996 STRAT deployment, water (from the Harvard instrument) showed ice saturation up to the tropopause for the two stacked flights at Ames (960129 and 960202), and on descent at the end of the northern survey mission (960201). For the flight of 960129, cloudtop temperatures from the GOES-9 window channel in the coldest clouds (upwind of the aircraft) were roughly consistent with the lowest temperatures of ice saturation (which corresponded roughly with cloud location). However, for the 960201 northern survey and 960202 stacked flights, ice saturation or clouds were observed at temperatures from 5 to 10 degrees colder than the coldest cloudtop temperatures. More refined use of the two window channels on GOES-9 may reduce this discrepancy. However, it may be that there is a region of very thin clouds above the main body that is not detectable by the satellite. If so, this has implications for using cloudtop temperatures from global satellite imagery for evaluating the water content of air entering the bottom of the stratospheric middleworld. A complication for the 960202 stacked flight was that the clouds were observed just above a stable layer near 11 km, a stable layer that coincided with a significant vertical increase of ozone (to 85-90 ppbv). It should be noted that the observed clouds at 11.3 km (37 kft) for the flight of 960202 can be related to a passing feature in the satellite data. All of these cases involved storm systems to the west of Ames accompanied by moist air from low latitudes being advected northward and rising to form clouds in advance of the storm center.
Over Hawaii, low water vapor to about 400-410 K was observed along with tropospheric values of N2O. This air appeared to originate in the western equatorial pacific, where GMS imagery showed persistent, widespread, deep convection throughout the STRAT period (from 80 E to 150 E). In fact, the outflow from this region appears to dominate the lowest stratosphere to 400 K throughout much of the Pacific south of the subtropical jet. The dip south of Hawaii at the equator on 960213 showed low water vapor up to about 400 K. The lowest values corresponded to potential temperatures of 365 K, probably related to outflow from deep convection in the SPCZ south of the equator. The coldest brightness temperatures from this convection were -84, while minimum temperatures measured by the aircraft (over a relatively cloud-free region) were almost 3 degrees colder. Again, more refined use of the two window channels on GOES-9 will reduce this discrepancy.
It appears that the visible albedos from GOES-9 and those from the UV/VIS instrument agree only qualitatively, with GOES values being lower. Calibration issues will be explored by comparing with NOAA AVHRR satellite instrumentation.
No flights over deep convection occurred, so there were no observations of convectively generated gravity waves in this deployment.
For much of the Ames deployment, the polar vortex had a strong wave number two component, with a lobe dipping down over North America. This put the vortex within range of the ER-2 for the northern survey flight of 960201, but the wind patterns over the western U.S. were such that there was potential for strong gravity-wave turbulence. To avoid this, the stacked flights on 960129 and 960202 were run along the California coast. According to the meteorological analyses produced by the Goddard Data Assimilation Office (DAO), both of these stacked flights had several legs in the upper troposphere, the stratospheric middleworld, and the stratospheric overworld, which was the desired sampling.
The dive on the 960205 ferry flight to Hawaii was located over a feature with relatively low potential vorticity. The legs of the stacked flight on 960208 that were coincident with the DC-8 were oriented roughly parallel to the forecast winds to facilitate sampling the same air masses as the DC-8. According to the DAO analyses, this worked well; however, because of the generator failure on the ER-2, the higher, stratospheric legs of the stack were not flown until the test flight on 960212. On this later flight, the tropopause was high enough that the first leg was just barely above the tropopause at 56 kft. The southern survey flight of 960213 encountered westerly winds, as expected from the phase of the quasi-biennial oscillation, although the winds measured by MMS were stronger (15-20 m/s) than those from the DAO analyses (~9 m/s). Temperatures on the dive were 186 K as measured by MMS, 194 K according to the DAO analyses. By the time of the 960215 transit flight back to California, warmer stratospheric temperatures had moved south closer to Hawaii, ruling out a dive to sample the tropopause.
The NASA/GSFC Data Assimilation Office (DAO) continues to provide forecasts and meteorological analyses as the principal flight planning tools for the STRAT mission, and during January/February 1996, for the TOTE/VOTE mission as well. The data products are near real-time analyses and five-day forecasts. The assimilation system used is the GEOS-DAS vc5.4/oi1.5, which uses rotated poles. There were two runs each day; the early run starts about 9:30 EST, and the final run begins at 18:30 EST.
Unlike the 1995 deployments, the analyses and forecasts during this mission were carried out on the J916 computer rather than the C98. As a result, the time required to complete the runs was more than doubled. This problem was handled by creating a new queue on the J916 exclusively for DAO production runs during the mission, and delays due to queuing should not be a problem during future deployments. In spite of these computing facility constraints, DAO provided near-timely and high-quality products to the mission scientists.
The final forecast for the stacked flight of 960129 did a very good job of predicting the temperature field, with an RMS error between forecast and MMS data of 2.1 K. The wind predictions were not as good because the jet stream passed over the flight route, creating a large wind error for a small spatial error. The assimilation (analysis), however, did a much better job. The forecast and analyzed fields were even better for the northern survey flight of 960201. While the assimilation provided the smallest RMS error when compared to MMS temperature and wind (u and v) fields, both the early (ERL) and final (FNL) forecasts had only slightly greater error. Because of the high quality of these data products, mission scientists were able to sample air masses chosen during the flight planning. For example, N2O concentrations predicted with the UGAMP model were consistent with the ALIAS measurements, suggesting penetration into the polar vortex on 960201, as intended.
During the three STRAT deployments conducted to-date, we have provided (via ftp) high-resolution trajectory calculations using the Australian Bureau of Meteorology's Global ASsimilation and Prediction (GASP) system to on-site personnel for flight planning. These three- to five-day forecasts agree well with subsequent calculations using analyses, and generally provide good guidance for flight planning.
We also have performed 3-D chemical-transport model simulations of several long-lived tracers (e.g., N2O, CH4, and SF6) and of the "age spectrum" using winds from the NCAR MACCM2 model. Preliminary comparisons of model results and measurements made onboard the ER-2 (from STRAT and previous mission deployments) are very encouraging. The latitude variation of zonal-mean tracers within the model agrees well with ER-2 measurements. Also, the model simulations show a large difference between the mean age and the phase lag of an annually oscillating signal, consistent with time scales inferred from the SF6 and CO2 measurements. We currently are examining the tracer-tracer scatter plots from the model and STRAT measurements.
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Last Updated: 17 May 1996
Content Editor: Kathy Wolfe