Data from the Midcourse Space Experiment Tilere is evidence (R. H. Picard, J,'unes H. Brown (MSX) has provided the first observations of thunderstorm-personal communications, 1997) that gravity wave generated gravity waves imaged from space. Gravity wave structures are present in a number of MSX MWIR images. theory predicts that isolated, sufficiently convective This evidence is based on morphology, length scales, thunderstorms can launch waves mid create a unique power specUa and MWIR mdimive properties. The present intensity pattern of concentric circles on a radiating sinface paper shows that in particular cases the sources of these of constant altitude above such a storm. banong the MSX waves can be established as thunderstorms. This source constant-nadir-angle mid-wave hlfmred (MWIR) identification was prompted by the work of Taylor anti observations, two instances of such patterns have been Hapgood [1988] who showed that a pattern of concentric identified. It was conf'mned frown •neteorological satellite circles in ground-based observations of nightglow images that highly convective isolated thunderstorms emissions in the mesopause region was caused by va• occurred at the locations and ti•nes expected. isolated thunderstorm that occurred six hours prior to the nightglow observation.

Abstract.Distinctive structure in the 4.3-/•m spectral region has been imaged by the SPIRIT 3 radiometer on the MSX satellite observing the cloud-free atmosphere. We show nadir, high-nadir-angle (NA) sublimb, and limb images which, coupled with radiative transfer analysis, indicate that this structure originates from internal gravity waves (GWs). Such structure occurs in a significant fraction of both below-the-horizon (BTH), or sublimb, and above-the-horizon (ATH), or limb, obser-

[1] Spatial Infrared Imaging Telescope (SPIRIT) III radiometer on the Midcourse Space Experiment (MSX) satellite measured highly structured infrared, IR, emission from polar mesospheric cloud (PMC) ice particles at northern latitudes above 51 degrees on 22 July 1996 in the 11.1 to 13.2 and 18.2 to 25.1 mm radiometer channels, bands C and E, respectively. Measurements of the PMC thermal emissions included the observation of an extended cloud at 84.8°N and 325.6°E at 0313:25 UT, a local solar time of approximately 0056. In this Earth limb observation, the radiance due to the PMC has been isolated from other sources-atmospheric emission, nonrejected off axis radiation from the terrestrial surface and zodiacal radiance-and inverted to determine the volume emission rates of the ice particles at a spatial resolution of 0.3 km in the altitude range from 83.4 to 86.4 km. The band C PMC volume emission rate profile has a maximum value at 84.0 ± 0.3 km and decreases to one half the peak value at 85.0 and 83.5 km. Temperatures in the range from 143 ± 7 to 130 ± 8 K and ice volume densities from 1.5 to 0.5 Â 10 À13 cm 3 per cm 3 were determined from the LWIR volume emission rates at altitudes from 83.4 to 86.4 km. The PMC ice densities are equivalent to an enriched gas phase water mixing ratio of 8 to 16 parts per million by volume, ppmv, and a vertical column mass density of 3.3 Â 10 À8 gms cm À2 in this observation.

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