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The Second Airborne Arctic Stratospheric Expedition (AASE-II) on CD-ROM

Entry ID: AASE9192

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Summary

Abstract: This CD-ROM contains the final data pertaining to the Airborne Arctic Stratospheric Expedition II (AASE-II) which was based in Bangor, Maine between October 1991 and March 1992, with ER-2 flights from Ames Research Center, Moffett Field (California), Fairbanks (Alaska), and Bangor (Maine), along with and DC-8 flights from Ames, Bangor, Anchorage (Alaska), Stavanger (Norway), and Tahiti. The data ... consist of measurements collected onboard the NASA ER-2 and DC-8 aircraft, ozonesonde soundings from six Canadian stations, global grid point values of Nimbus 7 TOMS ozone, and selected radiosonde soundings from stations in the region of the experiment. Theory teams provided calculations of potential vorticity, temperature, geopotential, horizontal winds, parcel back trajectories, and concentrations of short lived species along the aircraft flight tracks; and northern hemispheric analyses of potential vorticity, temperature, geopotential, horizontal winds, and radiative heating rates.

All files within this release are standard ASCII files with variable length records terminated by a carriage return/line feed pair (, ASCII decimal values 13 and 10). Therefore, MS-DOS users should be able to read them as they are, but UNIX and MAC users will have to strip off either the or the from each line to convert them to standard UNIX or MAC files. Commercially available software, such as dos2unix and Apple File Exchange, exists to convert MS-DOS files to both UNIX and MAC files. VMS users can define the files to have STREAM record formats.

In general, the file naming convention uses a two-character prefix to identify the measurement, followed by a six digit number (yymmdd) giving the year, month, and day (UT) of the flight, balloon launch, or model result. To identify the measurement platform, a three character extension of EA1, DA1, Bhh, or Ghh is used to denote the data is from the ER-2, DC-8, balloon, or grid point model output (hh denotes the UT hour of balloon launch or model result). Exceptions to this convention are the SFyymmdd.Enn files which use the extensions E00, E01, E05, E30 to denote aerosol loading factors; the TOMS data files which have the extensions N7; and the chemical modelling result MA911006.H00.

The NASA ER-2 and DC-8 aircraft and balloons were employed to carry a suite of instruments into the lower stratosphere. Many of these were used in the 1989 AASE-I. New instruments included a gas chromatograph to measure CFC-11, a diode laser spectrometer to measure CH4, N2O, and HCL, and spectrometers to measure in situ CO, CH4, N2O, and CO2. The ER-2 was deployed from Ames Research Center, California (37N, 122W), to Fairbanks, Alaska (65N, 147W) in October 1991, so that air could be observed at the highest possible latitudes before it was incorporated into the forming polar vortex. In November 1991, the ER-2 was moved to Bangor, Maine (45N, 69W) where it would have a high probability of encountering air in the arctic vortex, but could still have acceptable weather for aircraft operations. The ER-2 missions involved flights to Greenland, 20N, 25N, 55N, 65N, 70N, 85N, and 90N. The DC-8 missions involved flights to Tahiti, Norway, Wyoming, 15N, 20N, 65N, and 90N.

On March 11, 1992, a balloon launched from Greenland (67.0N, 50.6W) carried instruments to measure O3, NO, and CLO. The objective of the balloon launch was to extend the aircraft measurements to higher latitudes. The Canadian Ozone Experiment (CANOZE-7) launched balloons from December 1991 to March 1992 from Alert, Canada (82N, 62W). The nitric acid measurements made from these balloons are also reported here.

The AASE-II data set provides the first seasonal perspective on polar ozone chemistry in the northern hemisphere. It also provides the first detailed investigations of the chemistry occurring on volcanic sulfuric acid aerosols. The data show clearly the important counterbalance between dynamical resupply of ozone in the arctic vortex and ongoing chemical destruction. The aircraft measurements also show the important role of nitrogen oxides, produced by nitric acid photolysis, in destroying CLO after temperatures become too high for polar stratospheric clouds to form. These results highlight the fact that large ozone losses in the arctic spring require either extensive denitrification of the vortex, which could occur if temperatures fell below that at which ice clouds form, or long lasting polar stratospheric clouds, that will occur if temperatures remain low enough for nitric acid to condense for extended periods of time. Neither extremely low temperatures, with extensive denitrification, nor a prolonged period of low temperatures occurred in 1992. Therefore, although very high levels of CLO were present in the arctic vortex in January 1992, the ozone loss that occurred was limited by the rapid decline of CLO in February. Other winters, such as 1992-1993, which had much more persistent low temperatures, may have conditions more conducive to significant ozone loss. It is also clear from the AASE-II data set that volcanic aerosols do significantly perturb stratospheric chemistry. However, some of the reactions are saturated at aerosol surface areas only slightly greater that ambient, and others depend strongly on temperature. Therefore, an assessment of the impact of the Pinatubo eruption on global ozone requires careful treatment of the entire thermal, dynamical, aerosol and chemical evolution of the stratosphere.