CEDAR Postdoc: Seasonal Variations in Mesopause Region Temperatures, Zonal and Meridional Winds: Climatology and Variability of Mean-State, Diurnal and Semidiurnal Tides

Colorado State University, Fort Collins CO

Investigators

Abstract

This is a study of seasonal variations of temperatures and meridional winds in the mesopause region. The Colorado State sodium lidar has been upgraded to a two-beam system capable of simultaneous measurements of mesopause region temperature and winds, over full diurnal cycles, weather permitting. Regular observations in this mode of operation began in May 2002, and by the end of April 2003, one full year of data acquisition was completed giving a total of 1,388 hours of observation with 634 hours under sunlit conditions. The salient feature of a dataset with full-diurnal-cycle coverage lies in its ability to decompose the vertical profiles of dynamical fields (temperature, zonal and meridional winds) into a unique linear superposition of diurnal-mean and oscillations with different tidal periods, plus a residual. In this manner, the diurnal-mean and the amplitude and phase of tidal period oscillations can be determined solely from experimental data. The coherence of tidal excitation and of mean solar forcing prevails over the variability, leading to the convergence of the climatological mean in a multi-day observation. The 6-day composite yields means and diurnal tides that resemble model predictions very well. Preliminary analyses on data acquired in other months have generally shown similar variability and coherent convergence to climatological means, though the behavior in each month depends on the availability of full-diurnal-cycle data and the occurrence frequency of atypical profiles. Though the results of the first year of observation have exceeded expectations, at the present rate, it would require three years of data acquisition to produce a reliable study of climatology and variability. This study will continue the observations and associated science study as a post-doctoral program.