Gravity waves in the mesopause region observed by meteor radar, 2: Climatologies of gravity waves in the Antarctic and Arctic

A simple technique has been used to investigate gravity waves in the Antarctic and Arctic mesosphere. Data from two meteor radars are used, one at Rothera in the Antarctic (68 degrees S) and one at Esrange in the Arctic (68 degrees N). Observations have been made from 2005 to 2008 in the Antarctic and from 2000 to 2008 in the Arctic. The results reveal a seasonal behaviour with a semi-annual cycle. Over both sites wave activity maximises at the solstices and minimises at the equinoxes. Monthly-mean gravity-wave activity increases with height in all seasons except in summer when gravity-wave variances show little or no increase with height at heights below about 90 kin. Above about 90 km in summer there is a rapid increase in wave activity. We suggest that this summer-time behaviour is a consequence of rapid wave growth as gravity waves ascend into the more stable air of the lower thermosphere. Differences between the Arctic and Antarctic gravity-wave field are also evident. In particular, a higher level of gravity-wave activity is observed in the Antarctic spring compared to the Arctic spring. We suggest that these inter-hemi spheric differences may be the result of differences in the generation of gravity waves in the polar troposphere and stratosphere.