The wintertime two-day wave in the polar stratosphere, mesosphere and lower thermosphere

[摘要] Recent observations of the polar mesosphere have revealed that waves withperiods near two days reach significant amplitudes in both summer andwinter. This is in striking contrast to mid-latitude observations wheretwo-day waves maximise in summer only. Here, we use data from a meteor radarat Esrange (68° N, 21° E) in the Arctic and data from the MLSinstrument aboard the EOS Aura satellite to investigate the wintertime polartwo-day wave in the stratosphere, mesosphere and lower thermosphere. Theradar data reveal that mesospheric two-day wave activity measured byhorizontal-wind variance has a semi-annual cycle with maxima in winter andsummer and equinoctial minima. The MLS data reveal that the summertime wavein the mesosphere is dominated by a westward-travelling zonal wavenumberthree wave with significant westward wavenumber four present. It reacheslargest amplitudes at mid-latitudes in the southern hemisphere. In thewinter polar mesosphere, however, the wave appears to be aneastward-travelling zonal wavenumber two, which is not seen during thesummer. At the latitude of Esrange, the eastward-two wave reaches maximumamplitudes near the stratopause and appears related to similar wavespreviously observed in the polar stratosphere. We conclude that thewintertime polar two-day wave is the mesospheric manifestation of aneastward-propagating, zonal-wavenumber-two wave originating in thestratosphere, maximising at the stratopause and likely to be generated byinstabilities in the polar night jet.

[学科分类] 大气科学