Gravity wave propagation through a large semidiurnal tide and instabilities in the mesosphere and lower thermosphere during the winter 2003 MaCWAVE rocket campaign

摘要

The winter MaCWAVE (Mountain and convective waves ascending vertically)rocket campaign took place in January 2003 at Esrange, Sweden and the ALOMARobservatory in Andenes, Norway. The campaign combined balloon, lidar, radar,and rocket measurements to produce full temperature and wind profiles fromthe ground to 105 km. This paper will investigate gravity wave propagationin the mesosphere and lower thermosphere using data from the Weber sodiumlidar on 28–29 January 2003. A very large semidiurnal tide was present inthe zonal wind above 80 km that grew to a 90 m/s amplitude at 100 km. Thesuperposition of smaller-scale gravity waves and the tide caused smallregions of possible convective or shear instabilities to form along thedownward progressing phase fronts of the tide. The gravity waves had periodsranging from the Nyquist period of 30 min up to 4 h, verticalwavelengths ranging from 7 km to more than 20 km, and the frequency spectrahad the expected –5/3 slope. The dominant gravity waves had long verticalwavelengths and experienced rapid downward phase progression. The gravitywave variance grew exponentially with height up from 86 to 94 km, consistentwith the measured scale height, suggesting that the waves were notdissipated strongly by the tidal gradients and resulting unstable regions inthis altitude range.