Overflights of a tropical cyclone during the Australian winter monsoon field experiment of the Stratosphere‐Troposphere Exchange Project (STEP) show the presence of two mesoscale phenomena: a vertically propagating gravity wave with a horizontal wavelength of about 110 km and a feature with a horizontal scale comparable to that of the cyclone's entire cloud shield (wavelength of 250 km or greater). The larger feature is fairly steady, though its physical interpretation is ambiguous. The 110‐km gravity wave is transient, having maximum amplitude early in the flight and decreasing in amplitude thereafter. Its scale is comparable to that of 100‐to 150‐km‐diameter cells of low satellite brightness temperatures within the overall cyclone cloud shield; these cells have lifetimes of 4.5 to 6 hours. Aircraft flights through the anvil show that these cells correspond to regions of enhanced convection, higher cloud altitude, and upwardly displaced potential temperature surfaces. A three‐dimensional transient linear gravity wave simulation shows that the temporal and spatial distribution of meteorological variables associated with the 110‐km gravity wave can be simulated by a slowly moving transient forcing at the anvil top having an amplitude of 400–600 m, a lifetime of 4.5–6 hours and a size comparable to the cells of low brightness temperature. The forcing amplitudes indicate that the zonal drag due to breaking mesoscale transient convective gravity waves is definitely important to the westerly phase of the stratopause semiannual oscillation and possibly important to the easterly phase of the quasi‐biennial oscillation. There is strong evidence that some of the mesoscale gravity waves break below 20 km as well. The effect of this wave breaking on the diabatic circulation below 20 km may be comparable to that of above‐cloud diabatic cooling.

Simultaneous, in situ observations of ClO, BrO, O3, N2O, pressure, and temperature are used to examine the kinetics of ozone destruction within the Antarctic polar vortex. The high azimuthal symmetry of the vortex is used to simplify the problem such that the time rate of change of ozone on isentropic surfaces between 450 and 360 K (18.3‐ to 13.5‐km geometric altitude) can be calculated based on proposed catalytic cycles involving ClO, BrO, HO2 and O(3P). The availability of simultaneous, spatially resolved data on N2O, pressure, and temperature is used to reduce scatter in observed O3; this clarifies the quantitative analysis of ozone loss rates on isentropic surfaces. The kinetics of ozone destruction is thus cast in an N2O‐potential temperature coordinate system to suppress atmospheric variability. We conclude, based upon observed radical concentrations and the most recent laboratory kinetics data, that the chlorine dimer mechanism (Molina and Molina, 1987) rate limited by ClO + ClO + M → ClOOCl + M, referred to herein as mechanism I, constitutes the largest single contribution to the integrated rate of ozone destruction within the vortex on isentropic surfaces between altitudes of 14 and 18.3 km. We find that approximately 40% of the observed ozone loss rate in this altitude interval results from this mechanism, using the recently established pressure and temperature dependence for the rate of dimer formation reported by Sander et al. (1989). The coupled bromine‐chlorine catalytic cycle (McElroy et al., 1986) rate limited by ClO + BrO → Cl + Br + O2 (herein mechanism II) constitutes approximately 20% of the ozone loss rate integrated over the course of the mission, August 23 to September 22, 1987. Mechanism III, suggested by Solomon et al. (1986), which is rate limited by ClO + HO2 → HOCl + O2 (in close competition with OH + O3 → HO2 + O2), constitutes 4% of the observed ozone loss rate based on observed ClO, but calculated HO2 concentrations. We find that the time‐honored catalytic coupled ClO + O → Cl + O2 followed by Cl + O3 → ClO + O2, identified by Molina and Rowland (1974) as the key reaction linking chlorofluorocarbon release to middle‐ and low‐latitude stratospheric ozone depletion, constitutes 3% of the observed loss in the Antarctic vortex. The sum of all four mechanisms thus constitutes 65% of the observed O3 loss with an experimental uncertainty of ±30%. An array of other halogen‐oxygen radical catalytic cycles are considered. The manifold of possible catalytic cycles is large, particularly when the temperature and pressure regime characteristic of the Antarctic lower stratosphere is considered. Quantitative analysis is impeded primarily by the absence of laboratory data on key reaction rates. For example, a potentially critical alternative channel, designated herein as mechanism V, is the termolecular process ClO + O3 + M → ClO · O3 + M, followed by photolysis, for which no kinetic data exist. Explicit note is also taken, in the quantitative conclusions, of the ozone flux divergence within the ch...

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.

During the 1987 Airborne Antarctic Ozone Experiment we estimated the NO3, Cl, and SO4 contents of stratospheric aerosols by testing for the presence of condensed nitric, sulfuric, and hydrochloric acid. In various segments of the ER‐2 sample flights, aerosol particles were impacted on four 500‐mm‐diameter gold wires, strung across aluminum rings. The wires were pretreated to give results specific to certain physical and chemical aerosol properties. One wire was carbon coated and used for aerosol concentration and size analyses by scanning electron microscopy. Simultaneous X ray energy dispersive analyses permitted the detection of S and Cl in individual particles. Three more wires were coated with Nitron, barium chloride, and silver nitrate to detect nitric, sulfuric, and hydrochloric acids, respectively, in the aerosols. Wires were exposed at a number of geographic locations at altitudes near 18 km. Immediately after collection, the acids were fixed as ammonium salts by exposing them in flight to NH3. Results show that condensed nitrate is found below a threshold temperature of 193.6±3.0 K, generally encountered at latitudes exceeding 64°S. A negative correlation exists between condensed nitrate and ozone concentration. This is consistent with theories that postulate removal of gas‐phase NOy as a necessary step in allowing active chlorine‐ozone reactions to occur. Condensed H2SO4 is present at concentrations between 0.2 and 0.9 parts per billion by mass. The mass of condensed HCl is estimated to be approximately 3% of the mass of sulfuric acid.

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