HR: 0800h
AN: SA41A-1058    [Abstracts]
TI: A Data assimilation model for determining the mean state and migrating tide structures in the mesosphere and lower thermosphere using TIMED measurements of wind and temperature
AU: * Ortland, D A
EM: ortland@nwra.com
AF: NorthWest Research Associates, 14508 NE 20h St, Bellevue, WA 98007
AB: One of the main goals of the TIMED mission is to characterize the structure of the mean winds and the migrating tides in the mesosphere and lower thermosphere (MLT). This task is made difficult by the fact that the zonal mean and migrating tides are aliased in satellite measurements of any dynamic or constituent field. The typical approach to separating the mean and tidal components in a single measured field is to use the satellite precession to scan in local time and then use harmonic analysis on the local time dependence of the measured field. This approach assumes that the tide and mean components are steady during the time it takes for the satellite to complete a full yaw cycle, but this assumption is far from true in light of the 60 day yaw cycle of TIMED. Attempts to use data from a partial yaw cycle will run into other difficulties. A new approach to the tidal analysis of satellite data has been developed and shown successful on data from HRDI/UARS. Our approach relies on the simultaneous measurement of wind and temperature fields to separate the mean and tidal components and incorporates data assimilation techniques into a steady-state model of the mean winds and migrating tides. This technique can be applied to obtain results from only a single day's measurements of winds from TIDI and temperatures from SABER. Unlike assimilation techniques used in weather forecasting, which rely on slow manifold balance conditions, this new technique relies on the assumption of geostrophic balance for the mean winds and the ageostrophic balance implied by the tidal equations. The fact that different balance conditions apply to the mean and tidal components enables their separation if wind and temperature measurements are used simultaneously. The tidal model uses the theory of generalized Hough modes developed by the PI to incorporate the effect of mean winds and damping (from gravity waves and molecular diffusion) on tidal structure. The sensitivity of tidal structure to damping enables information to be derived on the magnitude of damping effectively applied to the tides.
DE: 3332 Mesospheric dynamics
DE: 3384 Waves and tides
DE: 3394 Instruments and techniques
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting