Variability of the semidiurnal tide due to fluctuations in solar activity and total ozone

Abstract

An attempt was made to investigate some variations of the semidiurnal tide observed in the mesosphere/lower thermosphere (MLT) region by meteor radar above the UK in the time interval 1 January 1989–6 May 1993, which are possibly due to the variability in the total ozone and solar activity. The total ozone is used here mainly as a proxy for stratospheric planetary wave information in the extra tropics. A positive correlation between the solar activity and the variability of the semidiurnal tide and total ozone was found for the investigated interval. During winter the semidiurnal amplitude modulations with periods: ∼10, ∼16 and 25–28 days were found to be present simultaneously with similar variations in the total ozone. They strengthen significantly during stratospheric warmings and the amplification of the stratospheric height wave 1. The amplitude modulations of the semidiurnal tide observed in the MLT region during winter are mainly produced by non-local coupling between the semidiurnal tide and planetary waves in the stratosphere. The influence of the planetary wave activity in the lower stratosphere on the variability of the semidiurnal tide observed in the MLT region indicates the non-negligible effects of the tropospheric tidal forcing. A strong response of the total ozone and the semidiurnal tide to solar radio flux variations on the time scale of the solar rotation period was found especially in the beginning of 1991. There is some provisional evidence for a response of the semidiurnal tide and the total ozone to the variations in the solar radio flux at intermediate periods of 50–80 days.