The Horizontal Wind Model (HWM) has been updated in the thermosphere with new observations and formulation changes. These new data are ground-based 630 nm Fabry-Perot Interferometer (FPI) measurements in the equatorial and polar regions, as well as cross-track winds from the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite. The GOCE wind observations provide valuable wind data in the twilight regions. The ground-based FPI measurements fill latitudinal data gaps in the prior observational database. Construction of this reference model also provides the opportunity to compare these new measurements. The resulting update (HWM14) provides an improved time-dependent, observationally based, global empirical specification of the upper atmospheric general circulation patterns and migrating tides. In basic agreement with existing accepted theoretical knowledge of the thermosphere general circulation, additional calculations indicate that the empirical wind specifications are self-consistent with climatological ionosphere plasma distribution and electric field patterns.

Abstract. A new all-sky imaging, wavelength scanning Fabry-Perot spectrometer was used to record high-resolution (R ___ 200,000) spectra of the A630 nm thermospheric optical emission above Poker Flat, Alaska. These spectra were used to derive spatially resolved maps of the horizontal wind vector at approximately 250 km altitude. We describe the procedure used to infer vector winds from hue-of-sight Doppler shifts, along with its limitations. We present the time evolution of the vector wind fields obtained from this method for 6 nights of observation. Five of the 6 nights contained periods when we inferred the existence of significant curvature, divergence or shear in the thermospheric wind across our instrument 's 001000 km diameter field of view. The sixth night exhibited little spatial structure and is shown for comparison. We compare these results with a "generic" solar minimum winter time run of the National Center for Atmospheric Research's Thermosphere, Ionosphere, and Electrodynamics General Circulation Model. While agreement was good at the start and end of the night, considerable differences were found in the late evening and midnight sectors. Some possible origins for these discrepancies are proposed. In particular, we suggest that the F region horizontal wind may be deflected by upwelling vertical winds, which are in turn driven by E region heating in the auroral zone. We note that both the instrument used and our high-latitude implementation of the analysis procedure are new experimental techniques. Thus the data presented here should be regarded as prehminary and, if possible, be vahdated by comparison with results from other techniques.

We present three case studies that examine optical and radar methods for specifying precipitating auroral flux parameters and conductances. Three events were chosen corresponding to moderate nonsubstorm auroral activity with 557.7 nm intensities greater than 1kR. A technique that directly fits the electron number density from a forward electron transport model to alternating code incoherent scatter radar data is presented. A method for determining characteristic energy using neutral temperature observations is compared against estimates from the incoherent scatter radar. These techniques are focused on line‐of‐sight observations that are aligned with the local geomagnetic field. Good agreement is found between the optical and incoherent scatter radar methods for estimates of the average energy, energy flux, and conductances. The Pedersen conductance predicted by Robinson et al. (1987) is in very good agreement with estimates calculated from the incoherent scatter radar observations. However, we present an updated form of the relation by Robinson et al. (1987), ΣH/ΣP=0.57〈E〉0.53, which was found to be more consistent with the incoherent scatter radar observations. These results are limited to similar auroral configurations as in these case studies. Case studies are presented that quantify auroral electron flux parameters and conductance estimates which can be used to specify the magnitude of energy dissipated within the ionosphere resulting from magnetospheric driving.

This paper investigates the large‐scale seasonal dependence of geomagnetically quiet time, northern high‐latitude F region thermospheric winds by combining extensive observations from eight ground‐based (optical remote sensing) and three space‐based (optical remote sensing and in situ) instruments. To provide a comprehensive picture of the wind morphology, data are assimilated into a seasonal empirical vector wind model as a function of season, latitude, and local time in magnetic coordinates. The model accurately represents the behavior of the constituent data sets. There is good general agreement among the various data sets, but there are some major offsets between GOCE and the other data sets, especially on the duskside. The assimilated wind patterns exhibit a strong and large duskside anticyclonic circulation cell, sharp latitudinal gradients in the duskside auroral zone, strong antisunward winds in the polar cap, and a weaker tendency toward a dawnside cyclonic circulation cell. The high‐latitude wind system shows a progressive intensification of wind patterns from winter to equinox to summer. The latitudinal extent of the duskside circulation cell does not depend strongly on season. Zonal winds show a mainly diurnal variation (two extrema) around polar and middle latitudes and semidiurnal variation (four extrema) at auroral latitudes; meridional winds are primarily diurnal at all high latitudes. The strength of zonal winds channeling through the auroral zone on the duskside is strongest in the summer season. The vorticity of the wind pattern increases from winter to summer, whereas divergence is maximum in equinox. In all three seasons, divergence is weaker than vorticity.

[1] Doppler-shift measurements of the thermospheric 630.0 nm emission recorded by two spatially separated imaging Fabry-Perot spectrometers in Alaska have been combined to infer F region horizontal wind vectors at approximately 75 locations across their overlapping fields-of-view. These "bistatic" horizontal wind estimates rely only on an assumption regarding the local vertical wind (and assume a common observing volume), and thus represent a more direct measurement of the wind than do the monostatic (single-station) vector wind fields routinely inferred by these instruments. Here we present comparisons between both the independently derived monostatic wind fields from each instrument and the bistatic wind estimates inferred in their common observing volumes. Data are presented from observations on three nights during 2010. Two principal findings have emerged from this study. First, the monostatic technique was found to be capable of estimating the actual large-scale wind field reliably under a large range of geophysical conditions, and is well suited to applications requiring only a large-scale, 'big picture' approximation of the wind flow. Secondly, the bistatic (or tristatic) technique is essential for applications requiring detailed knowledge of the small-scale behavior of the wind, as for example is required when searching for gravity waves.