Mesospheric wind diurnal tides within the Canadian Middle Atmosphere Model Data Assimilation System

Abstract

The horizontal wind data from the standard version of Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS) have been analyzed to obtain the diurnal wind structures in the mesosphere. In the standard version of CMAM-DAS, meteorological observations from radiosondes, aircraft, surface measurements, and satellites are assimilated only in the troposphere and stratosphere (below 1-hPa) with no increments applied in the mesosphere. Results for the years 2006–2008 are being used here as part of the Canadian International Polar Year (IPY) program and the Canadian Network for the Detection of Atmospheric Change (CANDAC) Research Program. The CMAM-DAS shows good overall agreement with radar observations for the seasonal characteristics of the diurnal tides at single stations from low-middle latitudes. The most prominent nonmigrating diurnal tides revealed by the CMAM-DAS winds at 88 km include the westward propagating component with zonal wavenumber 2 (DW2), the standing oscillation (D0), and the eastward propagating wavenumbers 3 (DE3) and 2 (DE2). A detailed discussion of the latitudinal and seasonal variations and Hough modes is provided for these predominant nonmigrating components and the migrating tide (DW1). The modeled nonmigrating diurnal tides, on both monthly (60-day windows) and annual time scales, are generally in good agreement with those determined from TIDI (TIMED Doppler interferometer) and from UARS-HRDI (High Resolution Doppler Imager)/WINDII (Wind Imaging Interferometer). This work provides further evidence for the tidal forcing from below.