The 8-h tide in the mesosphere and lower thermosphere over Collm (51.3° N; 13.0° E), 2004–2011

[摘要] The horizontal winds in the mesosphere and lower thermosphere (MLT) atheights of about 80–100 km have been measured continuously since summer 2004using an all-sky 36.2 MHz VHF meteor radar at Collm, Germany (51.3° N,13° E). A climatology of the 8-h solar tide has been constructed fromthese data. The amplitude shows a seasonal behaviour with maximum valuesduring the equinoxes, and it is generally increasing with altitude. Thelargest amplitudes are measured in autumn, partly reaching values up to 15 m s⁻¹.The phase, defined as the time of maximum eastward or northward wind,respectively, has earlier values in winter and later ones in summer. Exceptfor summer, the phase difference between the zonal and meridional componentsis close to +2 h, indicating circular polarization of the tidal components.The vertical wavelengths are short in summer (~20 km) butsignificantly longer during the rest of the year. The terdiurnal tide isgenerally assumed to originate from either a terdiurnal component of solarheating or nonlinear interaction between the diurnal and semidiurnal tide.Analysing monthly means reveals positive correlation during the springmaximum, but negative correlation in autumn.

[学科分类] 电子、光学、磁材料