[1] Planetary waves drive the mean meridional circulation of the stratosphere and at the same time facilitate quasi-horizontal mixing of trace gases. This paper presents significant day-to-day variability of stratospheric trace gas fields associated with large planetary wave activity observed during the second mission of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment. Geopotential height data of the UK Met Office show that the CRISTA-2 observations in the Southern Hemisphere winter were made during a period of extremely large amplitudes of both wave-1 and wave-2. The planetary wave-1, usually a quasi-stationary feature, moved eastward with the traveling planetary wave-2. The large amplitudes of both wave-1 and wave-2 led to a significant displacement of the edge of the polar vortex toward the tropics (down to 30°S). As a result of the large wave amplitudes and favorable phase alignment, the anticyclone drawing up tropical air was unusually strong, and thus considerable wave-induced trace gas flux from the tropics toward midlatitudes was observed, mainly in the form of a pronounced planetary-scale tongue advected out of the tropics around the vortex and into the anticyclone. Quantitative transport calculations based on a sequential data assimilation system highlight the importance of such transport events for trace gas eddy-flux in the Southern Hemisphere winter stratosphere.

Data from the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) showed three narrow streamers of air with tropical mixing ratios of HNO3 and N2O pointing from the tropics toward middle latitudes in the middle stratosphere on November 6, 1994. By means of the mechanistic prognostic model, the diagnostic chemical transport model (CTM) and the combined nudged model, which are all versions of the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA), the hypothesis is checked of whether these streamers are due to adiabatic transport processes on a timescale of days. Whereas the prognostic model reproduces the northern hemisphere streamers only qualitatively in their position, the CTM and the nudged model show a good agreement between their simulated tracer structures and the observed streamers. Because of the clear streamer signal in the nudged model compared to the CTM, its data are used for the investigation of isentropic tracer deformations. They show that the northern hemisphere streamers are mainly built by adiabatic transport on a timescale of days. Rossby wave breaking plays a role in the dissolution of the streamers. In the southern hemisphere, the production of Ertel's potential vorticity (EPV) and the net heating rate is large, and the observed streamers are therefore not reproduced in the EPV. Moreover, the isentropic deformations of the EPV due to the horizontal flow are that strong during a minor warming in the end of October that the reproduction of the southern hemisphere streamer by means of artificial tracers fails.

[1] The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured a variety of trace gases globally with high spatial resolution during two Space Shuttle missions. This paper concentrates on members of the NO y family and highlights differences between CRISTA 1 (November 1994) and CRISTA 2 (August 1997). A sequential assimilation technique is used to combine the CRISTA measurements of total NO y fields with corresponding model forecasts based on the National Center for Atmospheric Research Research for Ozone in the Stratosphere and its Evolution (ROSE) model. For this study we use a model version driven by wind and temperature data provided by the UK Met Office. NO 2 and N 2 O show large-and medium-scale structures caused by dynamical processes. N 2 O 5 shows a strong dependence on the aerosol load and solar zenith angles. N 2 O 5 and NO 2 changes from CRISTA 1 to CRISTA 2 are consistent with a reduction of aerosol concentrations in the Southern Hemisphere and minor aerosol changes in the Northern Hemisphere. For both missions the model reproduces well the measured diurnal cycles of the NO y family members. Measured diurnal variations of N 2 O 5 and NO 2 are consistent with the nighttime production of N 2 O 5 from NO 2 . Compared to the effect of heterogeneous chemistry, the influence of ozone and temperature changes on the NO y partitioning is rather small. A model run based on a three-dimensional aerosol field derived from CRISTA observations indicates that zonal asymmetries in the background aerosol have strong local effects on the N 2 O 5 and NO 2 distribution.

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