WACCM-X Simulation of Tidal and Planetary Wave Variability in the Upper Atmosphere

A 20 year climate simulation using Community Earth System Model 1/Whole Atmosphere Community Climate Model with thermosphere extension has been made under constant solar and low geomagnetic conditions, and the simulation is analyzed to study the tidal variability in relation to the variability of mean state and planetary waves. On interannual scales, the migrating diurnal and semidiurnal tides (diurnal westward propagating wave 1 (DW1) and semidiurnal westward propagating wave 2 (SW2)) and the nonmigrating diurnal eastward propagating wave 3 component (DE3) in the mesosphere/lower thermosphere (MLT) are modulated by the quasi-biennial oscillations. Correlation analyses are performed between deseasonalized tidal wave amplitudes with winter stratospheric state anomalies for solstitial periods. The correlation between DW1 amplitude at midlatitude and low latitudes and the winter polar stratospheric temperature anomalies is negative in the winter hemisphere and alternates signs over altitudes in the summer hemisphere. SW2 shows a significant positive correlation with the winter polar stratospheric temperature anomalies in the summer stratopause, low latitude and midlatitude in the mesosphere, and lower thermosphere. The correlation alternates signs with altitudes at midlatitudes to high latitudes in the winter hemisphere. The nonmigrating SW1 in the MLT region correlates positively with the planetary wave 1 in the winter stratosphere. DE3 in the equatorial MLT region, where it peaks, does not show any significant correlation with the winter stratosphere anomalies. The shortterm variability of these tidal components have time scales of several days, much shorter than the typical time scales of stratospheric planetary wave variability (10-20 days). The magnitude of the day-to-day tidal variability is significant and is persistent throughout the year.