[1] The new Horizontal Wind Model (HWM07) provides a statistical representation of the horizontal wind fields of the Earth's atmosphere from the ground to the exosphere (0-500 km). It represents over 50 years of satellite, rocket, and ground-based wind measurements via a compact Fortran 90 subroutine. The computer model is a function of geographic location, altitude, day of the year, solar local time, and geomagnetic activity. It includes representations of the zonal mean circulation, stationary planetary waves, migrating tides, and the seasonal modulation thereof. HWM07 is composed of two components, a quiet time component for the background state described in this paper and a geomagnetic storm time component (DWM07) described in a companion paper.

Observations of the mesosphere and lower thermosphere winds obtained by the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) during 1991 to 1995 reveal a semiannual variation in the amplitude of the (1, 1) diurnal tide. The global‐scale wave model (GSWM) represents the first numerical modeling attempt at simulating this seasonal variability, and a preliminary comparison of the GSWM tidal results with HRDI measurements is presented. The results of the comparison and of numerical tests point to some vital and unresolved questions regarding tidal dissipation and tropospheric forcing. In addition to the seasonal variability, HRDI has revealed a strong interannual modulation of the diurnal tide with amplitudes observed to change by nearly a factor of 2 from 1992 to 1994.

The high resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) has provided measurements of the horizontal wind field in the stratosphere, mesosphere, and lower thermosphere since November 1991. This data set, which spans a period of more than 3 years, has facilitated an investigation of the long‐term behavior of the background circulation on a nearly global basis. At middle and high latitudes the zonal circulation is characterized by an annual oscillation. At low latitudes (±30°) the most prominent long‐term variation above the stratopause is the mesosphere semiannual oscillation (MSAO), which maximizes near the equator at an altitude of between 80 and 85 km. Further analysis of the time series reveals an additional strong variation, with an amplitude near 30 ms−1 and a period of about 2 years. This feature shows the same altitude and latitude structure as the MSAO and exhibits a phase relationship with the stratospheric quasi‐biennial oscillation (QBO). Observations from the Christmas Island MF radar (2°N, 130°W) confirm the presence of this mesospheric QBO (MQBO). These observations support recent findings from a modeling study which generates an MQBO via the selective filtering of small‐scale gravity waves by the underlying winds they traverse.

[1] Using the TIMED Doppler interferometer (TIDI) mesospheric and lower thermospheric neutral-wind multiyear data set (2002)(2003)(2004)(2005)(2006)(2007) and NCAR TIME General Circulation Models (GCM) 1.2 annual run results (2002)(2003)(2004)(2005) at the TIDI sampling points, we study the migrating diurnal tide's global distribution, interannual, and seasonal variations in connection with the mean zonal wind interannual variations. A strong quasi-biennial oscillation (QBO) effect on the diurnal tide was observed in the TIDI data and reproduced to a lesser degree in the TIME-GCM run. The migrating diurnal tide amplitude is larger during the eastward phase of the stratospheric QBO and weaker during the westward phase. Westward mesospheric equatorial mean zonal winds appeared during the eastward phase of the stratospheric QBO (in 2002, 2004, and 2006). The strongest QBO effect on both the migrating diurnal tide and mean zonal winds was observed during the March equinox. The stronger tides may be related to the weaker gravity wave filtering in the stratosphere during the eastward phase stratospheric QBO. The TIDI data also exhibit large interhemispheric asymmetry. The westward mean zonal winds in the mesosphere appeared to be associated with the enhanced diurnal tide. The TIME-GCM 1.2 diurnal tide amplitudes are in general smaller than those observed by the TIDI instrument. Limited vertical spatial resolution for the TIME-CGM 1.2 is suggested as the cause. Future improvements are expected with a higher spatial resolution in the model.

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A strong westward traveling oscillation, with a period of 2 days and zonal wave number 3, is observed in the mesospheric and lower thermospheric winds from the High Resolution Doppler Imager on the Upper Atmosphere Research Satellite. The important events happen in January, July, and September/October, of which the occurrence in January is the strongest with an amplitude over 60ms−1. Detailed analyses for the periods of January 1992 and January 1993 reveal a cause‐and‐effect relationship in the wave developing process at 95km. The global structures of the wave amplitude and phase are also presented.

The 5‐day planetary wave has been detected in the winds measured by the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) in the mesosphere and lower thermosphere (50–110 km). The appearances of the 5‐day wave are transient, with a lifetime of 10–20 days in the two‐year data set. The structures of selected 5‐day wave events are in generally good agreement with the (1,1) Rossby normal mode for both zonal and meridional components. A climatology of the 5‐day wave is presented for an altitude of 95 km and latitudes mainly between 40°S and 40°N.

The high‐resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) is a triple‐etalon Fabry‐Perot interferometer designed to measure winds in the stratosphere, mesosphere, and lower thermosphere. Winds are determined by measuring the Doppler shifts of rotational lines of the O2 atmospheric band, which are observed in emission in the mesosphere and lower thermosphere and in absorption in the stratosphere. The interferometer has high resolution (0.05 cm−1), good offband rejection and excellent stability. This paper provides details of the design and capabilities of the HRDI instrument.