Solar Diurnal Tides in the Horizontal Winds between 90 and 110 km as Observed by WINDII/UARS and Simulated by CMAM
Abstract
The annual mean fields and annual/semi-annual (A1/A2) variations of a number of solar diurnal tide components are derived from horizontal winds in the mesosphere and lower thermosphere from several years of observations with the Wind Imaging Interferometer (WINDII) and com-pared to those diagnosed from a run of the extended Canadian Middle Atmosphere Model (CMAM). The most significant tidal motions are in meridional (v) winds between 90-105 km around 20 degrees of latitude for the migrating mode (1,1), standing mode (1,0), and west-ward propagating non-migrating mode (1,2), and in zonal (u) winds near 105 km around the equator for the eastward propagating non-migrating mode (1,-3). The total (annual mean plus A1/A2 variations) amplitudes of modes (1,1) and (1,2) show significant A2 variation peaking in March/April and September/October. The magnitudes are 60 -80 m/s in v and 20-30 m/s in for mode (1,1), and 20-35 m/s for both components of mode (1,2). The hemispheric phases differences (HPD) of both modes are 8-14 hrs in v and less than 2-3 hrs in u, suggesting a dominance of the first symmetric Hough mode. The WINDII and CMAM data show some similarities below 100 km, but the amplitude maxima have a time shift of one month or more and differ by as much as 15-20 m/s around September/October. The total amplitudes of mode (1,0) are comparable to those of mode (1,2), and show a significant A2 variation in WINDII, but the variation in the CMAM data is A1 peaking in July/August. The HPD are 4-6 hrs in v in both datasets, but 10-12 hrs and 4-6 hrs in in CMAM and WINDII, respectively. For mode (1,-3), the amplitudes show significant A1 variation with a maximum of 30 -35 m/s around 105 km in July/August in WINDII, but an A2 variation with a maxima of 20 -25 m/s around 107 km in March/April and September/October in CMAM. It is anticipated that differences such as these will provide insights into issues with model tidal sources in the future.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.1314W