Spatial structure in the thermospheric horizontal wind above Poker Flat, Alaska, during solar minimum

Abstract

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.

Thermospheric winds and temperatures above Mawson, Antarctica, observed with an all-sky imaging, Fabry-Perot spectrometer

“…See Conde and Smith (1998) for a detailed discussion of this vector fitting method. The vector fit describes the two-dimensional wind field as a superposition of uniform wind terms (mean meridional and zonal winds, calculated separately in each annulus) and the gradients of these winds in each of the meridional and zonal directions.…”

“…That is, the software first determines to which zone a pixel belongs, and then determines which spectral channel that pixel maps to at that point in the scan. As described by Conde and Smith (1998), the latter determination is based on both the position of the pixel and on the current spacing of the plates. A scan over one interference order thus produces N individual camera frames, with a typical integration time for each frame being 0.1 s. N is configurable; it was set to 128 for the observations reported here.…”

“…Recently, evidence has been growing that structures exist in the thermospheric wind field at spatial scales of several hundred kilometers or less (Conde and Smith, 1998;Aruliah and Griffin, 2001;Aruliah et al, 2004). Ongoing development of all-sky imaging Fabry-Perot spectrometers (Rees and Greenaway, 1983;Rees et al, 1984;Batten et al, 1988;Sekar et al, 1993;Biondi et al, 1995;Griffin et al, 2008) has resulted in instruments capable of recording independent spectra from many tens of locations across the sky simultaneously, making it possible to investigate this structure directly.…”

Spatial sampling of the thermospheric vertical wind field at auroral latitudes

“…It is capable of acquiring spectra at many tens of locations (referred to as "zones") simultaneously across an approximately 144°full-angle field of view of the sky. Measurements of Doppler shift of the 630.0 nm airglow emission of atomic oxygen in each zone were converted into line-of-sight wind speed, from which an estimate of the two-dimensional horizontal vector wind field was obtained using the method of Conde and Smith [1998]. In addition to, and concurrently with, spectral acquisition, the SDI is able to generate a low-resolution, spectrally unmodulated, monochromatic image of the sky at the same wavelength as the spectra and over an identical field of view.…”

Numerical simulations of thermospheric dynamics: divergence as a proxy for vertical winds

“…These instruments have been utilised in numerous studies at both high and mid latitudes - Rees et al (1984b), Crickmore et al (1991), Aruliah (1995), Price et al (1995), Innis et al (1996), Dyson et al (1997), Conde and Smith (1998), Ishii et al (1999) and Greet et al (2002) for example. Since they only measure the component of the wind parallel to their look direction, a single ground-based Doppler spectrometer can unambiguously measure vertical wind only when observing directly overhead.…”