[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.

/pdf/an-empirical-model-of-the-earth-s-horizontal-wind-fields-vm989vom4t.pdf

An empirical model of the Earth's horizontal wind fields: HWM07

On the importance of gravity waves in the middle atmosphere and their parameterization in general circulation models

Thermospheric winds measured by the Wind Imaging Interferometer (WINDII) on the upper atmosphere research satellite are analyzed for migrating solar tides. The data cover a 2-year period commencing February 1992 and are obtained from the atomic oxygen O(1S) 557.7-nm emission, which provides observations of the 90- to 200-km altitude range during daytime and the 90- to 110-km range at night. The subtropical lower thermosphere is dominated by the diurnal propagating tide which exhibits a vertical wavelength of approximately 22 km, grows in amplitude up to 95 km, and decays rapidly above where molecular diffusion greatly reduces the vertical shears. Although the phase remains fairly uniform throughout the year, a pronounced semiannual oscillation is observed in the diurnal tide amplitude. At both 20°N and 20°S the meridional and zonal wind components attain their maximum values at equinox of approximately 70 and 40 m/s, respectively, while the solstitial minima are nearly a factor of 2 smaller. At 35°N the diurnal tide semiannual amplitude oscillation is still present in the lower thermosphere, but above 100 km it is replaced by an annual cycle with a maximum in July and August. This contrasts with 35°S where the July/August peak is absent and the semiannual oscillation extends to 110 km. At midlatitudes the zonal and meridional winds are of similar magnitude, and no significant hemispheric asymmetries in amplitudes are observed. In the lower thermosphere the semidiurnal tide amplitude exhibits an annual oscillation, with maximum values of 30 to 40 m/s occurring in June/July near 100 km at 35°N, 35°S, and the equator. A bimodal structure in the seasonal variation of the semidiurnal phase is observed. This feature is characterized by rapid equinoctial transitions and is particularly well defined at the equator. Examination of the equatorial middle thermosphere indicates that the semidiurnal tide attains its maximum amplitude at 140 km and exhibits a vertical wavelength of approximately 60 km. These findings indicate the predominance of the antisymmetric (2,3) Hough mode in the tropics.

Satellite observations of thermospheric tides: Results from the Wind Imaging Interferometer on UARS

[1] A semidiurnal oscillation with zonal wave number s = 1 has been observed over the South Pole, and longitudinal variations of the semidiurnal tide at northern midlatitudes have been ascribed to the presence of nonmigrating tides. A three-dimensional nonlinear spectral model is used herein to study nonlinear wave-wave interaction as a possible mechanism for the generation of nonmigrating tides in the mesosphere and lower thermosphere. In particular, the s = 1 and s = 3 nonmigrating semidiurnal tides are studied as a by-product of the nonlinear interaction between the semidiurnal s = 2 migrating tide and a stationary s = 1 planetary wave in the lower and middle atmosphere. This process is found to yield significant amplitudes (∼10–30 m s−1) of the nonmigrating semidiurnal components with s = 1 and s = 3 in the upper atmosphere. Comparisons with monthly nonmigrating tidal amplitudes and phases at 95 km derived from High Resolution Doppler Imager and Wind Imaging Interferometer wind measurements from UARS show good agreement with the model simulations. The effect of the dissipating nonmigrating tides on the zonal mean circulation is found to reinforce that of the migrating component, contributing ∼10–20 m s−1 to the zonal wind field and ∼5–10 m s−1 to the mean meridional wind field. Several other wave components are generated through nonlinear interactions, including 6-hour tides with zonal wave numbers s = 0, 1, 4 and a semidiurnal oscillation with s = 6. These wave components have amplitudes in the range 6–30 m s−1 in the 110–150 km height regime. The combination of all nonmigrating tides together with the migrating component suggests significant longitudinal variations in the semidiurnal tide in the E region which may be important for studies of the quiet-time generation of ionospheric electric fields by the dynamo mechanism.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JA900179

Nonlinear interactions in the upper atmosphere: The s = 1 and s = 3 nonmigrating semidiurnal tides

[1] The aim of the UARS (Upper Atmosphere Research Satellite) Reference Atmosphere Project (URAP) is to provide a comprehensive zonal mean reference description of the stratosphere using measurements from instruments on board the UARS. A data set has been produced which describes the monthly zonal mean zonal winds from the surface to the upper mesosphere. Wind measurements from the High Resolution Doppler Imager (HRDI) were combined with results from the Met Office stratospheric data assimilation system. Balanced winds derived from the URAP temperature data set were used to bridge the gap between the stratospheric winds and HRDI mesospheric winds.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JD003135

Compilation of wind data for the Upper Atmosphere Research Satellite (UARS) Reference Atmosphere Project

The WIND imaging interferometer (WINDII) was launched on the Upper Atmosphere Research Satellite (UARS) on September 12, 1991. This joint project, sponsored by the Canadian Space Agency and the French Centre National d'Etudes Spatiales, in collaboration with NASA, has the responsibility of measuring the global wind pattern at the top of the altitude range covered by UARS. WINDII measures wind, temperature, and emission rate over the altitude range 80 to 300 km by using the visible region airglow emission from these altitudes as a target and employing optical Doppler interferometry to measure the small wavelength shifts of the narrow atomic and molecular airglow emission lines induced by the bulk velocity of the atmosphere carrying the emitting species. The instrument used is an all-glass field-widened achromatically and thermally compensated phase-stepping Michelson interferometer, along with a bare CCD detector that images the airglow limb through the interferometer. A sequence of phase-stepped images is processed to derive the wind velocity for two orthogonal view directions, yielding the vector horizontal wind. The process of data analysis, including the inversion of apparent quantities to vertical profiles, is described.

/pdf/windii-the-wind-imaging-interferometer-on-the-upper-v44lqcecm2.pdf

S. Brune

Papers

WINDII, the wind imaging interferometer on the Upper Atmosphere Research Satellite