[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.

[1] Since 1958, over 400 chemical tracer measurements have been made of the wind profiles in the upper mesosphere and lower thermosphere. The measurements cover a wide range of latitudes, longitudes, seasons, and local times. The results from the analysis of the data set show that a wind maximum in the altitude range between 100 and 110 km is a consistent feature of the observations at midlatitudes and low latitudes. The wind speed associated with the maximum exceeds 100 m s À1 in over 60% of the observations. Large shears are found, especially on the bottomside of the wind maximum, and the observed shears are often large enough to be either unstable or approaching instability. The wind maximum and shear features are characteristics of the overall data set and are not tied to particular observation sites, particular seasons, or special conditions. INDEX TERMS: 3369

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The observations were made at the same time that ionospheric electric fields and plasma number densities were measured in situ by instruments on sounding rockets. Neutral wind profiles were also measured during the campaign from triangulation of chemiluminescent trails from rocket releases. Aperture synthesis radar imaging techniques permit the sorting of the coherent backscatter into small azimuth and range bins and the determination of the scattering altitude. Individual Doppler spectra could thereby be unambiguously associated with in situ electric field measurements in the same small volume. We find that the Doppler shifts of the auroral echoes correspond to the ion acoustic speed times the cosine of the flow angle, where the former is predicted according to an empirical wave heating law. Type I echoes are only observed for very small flow angles regardless of the convection speed.

Abstract. Common-volume observations of sporadic Elayers made on 14-15 June 2002 with the Arecibo incoherent scatter radar and a 30 MHz coherent scatter radar imager located on St. Croix are described. Operating in dualbeam mode, the Arecibo radar detected a slowly descending sporadic E-layer accompanied by a series of dense E-region plasma clouds at a time when the coherent scatter radar was detecting quasi-periodic (QP) echoes. Using coherent radar imaging, we collocate the sources of the coherent scatter with the plasma clouds observed by Arecibo. In addition to patchy, polarized scattering regions drifting through the radar illuminated volume, which have been observed in previous imaging experiments, the 30 MHz radar also detected large-scale electrostatic waves in the E-region over Puerto Rico, with a wavelength of about 30 km and a period of about 10 min, propagating to the southwest. Both the intensity and the Doppler shifts of the coherent echoes were modulated by the wave.