Sodium lidar observed variability in mesopause region temperature and horizontal wind: planetary wave influence and tidal-gravity wave interactions

Abstract

The CSU sodium lidar system at Fort Collins, CO (40.6N, 105W), after a decade of mesopause temperature observation was upgraded in 1999 from a one-beam system to a two-beam system, capable of simultaneous and continuous observations of mesopause region temperature, zonal wind, and meridional wind, over full diurnal cycles, weather permitting. The regular observation under this operation mode started in May 2002. The valuable datasets could be used to study not only the tidal day-to-day variability but also planetary waves and gravity waves. Analysis of our longest dataset near fall equinox in 2003 (September 2003 campaign) reveals the dramatic tidal day-to-day variability with 2-fold increase in tidal amplitudes in all three fields during UT day 267 and 268. Further TIME-GCM (Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model) study and comparison between lidar observed temperature and the SABER observed global temperature field suggest that both tidal/planetary wave interactions and tidal/gravity wave interactions play an important role for the tidal amplitude enhancement. Though detailed causes for tidal variability require further study, we have demonstrated that substantial information on MLT dynamics may be obtained from a comprehensive long-period data set. Three near 80hr continuous datasets in consecutive summers of 2002, 2003, 2004 give us the opportunities to study summer quasi-two-day waves (QTD) with the possible modulation of Quasi-Biannual Oscillation (QBO) on QTD wave amplitude. Comparisons between the QTD wave amplitudes of temperature observed by lidar and SABER for all three campaigns show very good agreement. A strong winter mesospheric temperature inversion layer (MIL) was observed by our sodium lidar in December 2004 campaign. Studies of this event reveal the strong MIL which is consistent with mean state and tidal/gravity wave interactions. The observed dramatic tidal amplitude increase in day 338 is the result of such wave-wave interactions.