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This study examines the properties of inertia-gravity waves observed in the lower stratosphere over Macquarie Island, how these properties vary with season, and the likely source of the waves. The waves are observed in high-resolution upper-air ozonesonde soundings of wind and temperature released from Macquarie Island during the 1994 ASHOE-MAESA program. The properties of the inertia-gravity waves observed in the soundings are quantified using hodograph and rotary spectral analyses. The analyzed waves have horizontal wavelengths between 100 and 1000 km, vertical wavelengths between about 1 and 7 km, intrinsic frequencies between f and 2 f, and horizontal trace speeds between Ϫ50 and 30 m s Ϫ1. There appears to be a seasonal cycle in the inertia-gravity wave activity in the lower stratosphere, the minimum being in the austral winter when the background zonal flow is strong and westerly and its vertical shear is positive. In contrast, the variance of the horizontal perturbation winds does not show a similar seasonal cycle. Inertia-gravity waves are detected over Macquarie Island on days with a common synoptic pattern. Two features define this synoptic pattern: 1) an upper-level jet and associated surface front lying upstream of Macquarie Island, and 2) a 300-hPa height field with Macquarie Island located between the inflection axis and the downstream ridge. This common synoptic pattern is observed on 16 of the 21 days on which inertia-gravity waves were detected. Moreover, the pattern is not observed on 15 of the 21 days in which inertia-gravity waves are not identified. This common synoptic pattern shows a seasonal cycle similar to that found for the inertia-gravity wave activity. Analyses of the ozonesonde soundings suggest also that the source of the inertia-gravity waves is in the troposphere. Using GROGRAT, the ray-tracing model developed by Marks and Eckermann, a cone of rays is released 21 km above Macquarie Island and traced backward in time. These rays suggest that the inertiagravity waves are generated in the jet-front system southwest of Macquarie Island.

Efficient and flexible algorithms for the retrieval of atmospheric constituent and aerosol profiles from a limb‐sounding satellite radiometer are presented. The radiative transfer scheme ( “forward model”) has been generalized to cope with departures from local thermodynamic equilibrium (LTE), modelling emission from fundamental bands as well as hot bands. Its formulation makes possible a fast method of accurately calculating the radiance derivatives (“weighting functions”) required for the nonlinear optimal estimation algorithms. The retrieval schemes can be used with a wide variety of signal to noise ratios and with measurements from more than one wavelength. Multiple retrieval products are possible. A complete error analysis method emerges naturally from the theory, permitting an extensive prelaunch characterization of the retrieval products. The algorithms have been implemented for the improved stratospheric and mesospheric sounder (ISAMS), an infrared limb sounder on the Upper Atmosphere Research Satellite. The retrieval algorithms and error analysis are illustrated with some of the prelaunch tests performed for ISAMS. The O3 retrieval exemplifies those using measurements with a very high signal to noise ratio for which the quality of the retrieved product will be limited by spectroscopic and other forward model deficiencies. Preliminary calculations indicate that it should be possible to perform retrievals of daytime CO in the mesosphere and lower thermosphere because of rather than in spite of the strong non‐LTE emission in that region due to solar pumping at 4.6 μm. The “optimal onion‐peeling” algorithm used in the joint retrieval of CH4 and N2O is a very accurate means of solving strong cross contamination problems and proves to be much quicker than any iterative sequence of single‐product retrievals.

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