Measurements of total water were made with Lyman α resonance fluorescence hygrometers mounted on the ER‐2 and DC‐8 aircraft. Direct evidence was obtained for dehydration of the lower stratosphere over Antarctica; minimum values were about 1.5 parts per million by volume (ppmv), compared with values of 3.0 4.5 ppmv immediately outside the region high potential vorticity gradient in the potential temperature range 420<θ<460 K. On one flight, ice crystals large enough to have appreciable sedimentation velocities were observed. The DC‐8 data at 300<θ<320 K frequently showed extensive belts of dry, ozone‐rich air between 60° and 75°S latitude, with the equatorward “edge” in water well correlated with that observed by the ER‐2 some 8–9 km higher. Data from near Punta Arenas and from the ferry flights are used to argue that the effects of dehydration over Antarctica were visible at mid‐latitudes.

The amount of organic chlorine and bromine entering the stratosphere have a direct influence on the magnitude of chlorine and bromine catalyzed ozone losses. Twelve organic chlorine species and five organic bromine species were measured from 12 samples collected near the tropopause between 23.8°N and 25.3°N during AASE II. The average mixing ratios of total organic chlorine and total organic bromine were 3.50 ± 0.06 ppbv and 21.1 ± 0.8 pptv, respectively. CH3Cl represented 15.1% of the total organic chlorine, with CFC 11 (CCl3F) and CFC 12 (CCl2F2) accounting for 22.6% and 28.2%, respectively, with the remaining 34.1% primarily from CCl4, CH3CCl3, and CFC 113 (CCl2FCClF2). CH3Br represented 54% of the total organic bromine. The 95% confidence intervals of the mixing ratios of all but four of the individual compounds were within the range observed in low and mid‐latitude mid‐troposphere samples. The four compounds with significantly lower mixing ratios at the tropopause were CHCl3, CH2Cl2, CH2Br2, and CH3CCl3. The lower mixing ratios may be due to entrainment of southern hemisphere air during vertical transport in the tropical region and/or to exchange of air across the tropopause between the lower stratosphere and upper troposphere.

No abstract

The U‐2 aircraft was instrumented and flown in the stratosphere during the Stratosphere‐Troposphere Exchange Project's experiments of April 1984 to provide a set of simultaneous measurements by fast responding sensors that would aid in the identification of the modes of cross‐jet transport. The measurements confirm the preexperimental deductions that transport is dominated by waves, not by large‐scale circulations. Monotonic gradients of trace constituents normal to the jet axis, with upper stratospheric tracers increasing poleward and tropospheric tracers increasing equatorward, are augmented by large‐scale confluence as the jet intensifies during cyclogenesis. These gradients are rotated, intensified, and significantly increased in area as their mixing ratio surfaces are folded by the differential transport of a very low frequency, transverse wave. The quasi‐horizontal transport produces a laminar structure with stable layers rich in upper stratospheric tracers alternating vertically with less stable layers rich in tropospheric tracers. The transport proceeds toward irreversibility as higher frequency, shear‐gravity waves extend the folding to smaller horizontal scales. It becomes irreversible when these short waves actually fold the isentropic surfaces and small‐scale mixing develops. The progression to higher wave numbers is a discrete, not a continuous, cascade with major gaps in the observed horizontal wavelengths. The wave modes are identified by matching the observed amplitudes and phases against those obtained by linear perturbation theory. Prior to mixing, the wave‐generated perturbations maintain the correlations produced by advecting the larger‐scale mean gradients; thus the high resolution measurements support the linear turbulence closure assumption.

Fundamentally, the hypotheses that have been presented to explain the late winter loss of Antarctic ozone fall into two broad categories. One is that it is essentially chemical in origin, the other that it is caused by dynamically induced ingress of ozone‐poor air from the troposphere. Whole‐air samples collected aboard both the NASA ER‐2 and DC‐8 aircraft as part of the Airborne Antarctic Ozone Experiment (AAOE) were analyzed in a field laboratory set up at Punta Arenas, Chile. Mixing ratios obtained from gas chromatographic analyses of these samples are presented for CH4, CO, N2O, CFCl3, CF2Cl2, C2F3Cl3, CH3CCl3, and CCl4. Variations in the mixing ratios of these trace gases provide valuable information for both categories of postulation as indicators of the presence, motions, and history of air masses in the Antarctic atmosphere. Evidence of sustained subsidence is clearly indicated by comparison of CFCl3/N2O mixing ratios from the flights of September 16–29, 1987.