oa Low Latitude Mesospheric Gravity Wave And F-Region Plasma Depletion Studies From Cachoeira-Paulista, Brasil

An all-sky, monochromatic CCD imaging system has been used to investigate the<br>occurrence and properties of short-period (<1 hour) gravity waves in the mesosphere and<br>lower thermosphere (MLT) region at low latitudes. Novel measurements of several<br>visible and near infrared nightglow emissions (spanning the altitude range ~80-100 km)<br>were made from the INPE site at Cachoeira-Paulista, Brasil (23°S) during 1998-2000 and<br>have revealed a wealth of wave structure. Measurements of gravity waves at low<br>latitudes, particularly in the Southern Hemisphere, are rare and these data provide new<br>information on their characteristics and occurrence frequency important for quantifying<br>their seasonal signatures and variability. In addition to the MLT studies measurements<br>of the thermospheric (~250 km) OI (557.7 nm and 630 nm) emission signatures of FRegion<br>depletions were conducted during this period. A number of events were<br>measured exhibiting unusually complex and detailed features. A summary of these<br>results together with a statistical and case study of the mesospheric wave data will be<br>presented.