Interannual variations of the quasi-16-day oscillation in the polar summer mesospheric temperature

Abstract

Nighttime measurements of the hydroxyl Meinel (4,2) rotational band have been used to infer the mesospheric temperature over Scandinavia from June to August during the years 1992-1995. While the nightly averaged temperatures show a statistically significant, quasi-16-day oscillation in the 1992 and 1994 summer data, none is observed during 1993 and 1995. When present, the period, amplitude, and temporal behavior of this oscillation agree with both model predictions and previous wind measurements of the (1,3) Rossby normal mode in the summer mesosphere. Thus this temperature oscillation appears to correspond to the thermal signature of the 16-day Rossby mode. Its appearance in the summer mesosphere is shown to occur when the oscillating zonal flows in the upper stratosphere near the equator are in an eastward phase, while it appears to be blocked during the westward phases. This correspondence of the 16-day wave in the summer mesosphere with the eastward equatorial wind would favor the explanation that it is generated in the winter hemisphere and propagates vertically and toward the summer pole following the westerly mean winds.