The interannual variability of a 5-7 day wave in the middle atmosphere in autumn from ERA product data, Aura MLS data, and meteor wind data

The interannual variability of a 5-7 day wave was investigated on the basis of Obninsk meteor wind data (1979-2010), Microwave Limb Sounder geopotential heights (2004-2011) and ERA project data (1958-2011) for August-September. Several points of evidence were found indicating that the wave variabilities in the mid-latitude mesosphere/lower thermosphere (MLT) and in the lower stratosphere are significantly connected in the Northern Hemisphere. Statistically significant correlations between the year-to-year variability of the wave period (+0.86) and the date of the amplitude maxima (+0.71) estimated from the Obninsk meridional wind data and the ERA project geopotential heights (at 1 hPa) are obtained if the years 1980, 1989, 2006 and 2008 are excluded as years with a significant difference between the wave periods at the two levels. There is also a possible influence of the wave activity from the Southern Hemisphere. According to the MLS geopotential heights, the wave could not have readily propagated into the mid-latitude MLT from the stratosphere in 2006 and 2008, though we found that it can propagate from the Southern Hemisphere through the equator into the Northern Hemisphere. For other MLS years, the statistically significant coherent behaviour of geopotential height oscillations is observed in the mid-latitude MLT and upper stratosphere during August-September. In turn, the interannual variability of the wave amplitudes in the mid-latitude upper stratosphere are significantly anti-correlated (−0.8) with the variability of the Northern Annular Mode index at upper troposphere heights under eastward quasi-biennial equatorial winds taken at 50 hPa. There is no significant correlation under the opposite phase possibly because of some leakage of the wave activity from the Southern Hemisphere into the Northern Hemisphere through the equator.