Abstract
Abstract. The horizontal winds in the mesosphere and lower thermosphere (MLT) at heights of about 80–100 km have been measured continuously since summer 2004 using 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 from these data. The amplitude shows a seasonal behaviour with maximum values during the equinoxes, and it is generally increasing with altitude. The largest 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. Except for summer, the phase difference between the zonal and meridional components is close to +2 h, indicating circular polarization of the tidal components. The vertical wavelengths are short in summer (~20 km) but significantly longer during the rest of the year. The terdiurnal tide is generally assumed to originate from either a terdiurnal component of solar heating or nonlinear interaction between the diurnal and semidiurnal tide. Analysing monthly means reveals positive correlation during the spring maximum, but negative correlation in autumn.
Highlights
The dynamics of the mesosphere and lower thermosphere (MLT) are strongly influenced by atmospheric waves, including the solar tides with periods of a solar day and its harmonics
The terdiurnal tide (TDT) has been considered to play an important role as well, because occasionally their amplitudes are as large as the ones of DT and semidiurnal tide (SDT)
Observations in the Arctic mesosphere showed a relationship between the vertical wavelengths of the TDT, SDT and DT when the TDT had large amplitudes
Summary
The dynamics of the mesosphere and lower thermosphere (MLT) are strongly influenced by atmospheric waves, including the solar tides with periods of a solar day and its harmonics Their wind amplitudes usually maximise around 100–120 km Observations in the Arctic mesosphere showed a relationship between the vertical wavelengths of the TDT, SDT and DT when the TDT had large amplitudes This indicates, at least to a certain degree, the existence on nonlinear coupling (Younger et al, 2002). Huang et al (2007) used a nonlinear tidal model and concluded that the migrating TDT can be significantly excited by the nonlinear interaction between the diurnal and semidiurnal tides in the MLT region. This data represents an update of the one presented by Fytterer and Jacobi (2011) and Jacobi (2011)
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