Comparison of neutral winds in the thermosphere at altitudes of ~120km and ~240km over Alaska using an overlapping network of 4 all-sky implemented Fabry-Perot Interferometers

A network of four all-sky viewing Fabry-Perot interferometers, called scanning Doppler Imagers (SDIs), regularly observe Doppler spectra of optical emissions from the thermosphere at green-line (5577A at ~120km altitude) and red-line (6300A at ~240km altitude) wavelengths. Numerical fitting of model spectra then produces estimates of thermospheric line-of-sight winds over Alaska, with each instrument viewing 115 sub-fields within a circular region covering roughly one million square kilometers. Each instrument has a temporal cadence typically of a few minutes per observation. The instruments combined observed fields overlap so that many regions are viewed along two or more lines of sight, allowing all three vector wind components to be reconstructed with minimal assumptions. We present a new method for deriving these winds using the technique of geophysical inversion to infer three vector (zonal, meridional, vertical) wind components at both heights. Using this technique we compare the fields for two nights of contrasting geomagnetic activity. The night of the March 2nd, 2016 is examined in conjunction with the JETS sounding rocket mission out of Poker Flat Research Range (Chatanika, Alaska). Additionally the night of November 20th, 2016 is examined to compare and contrast altitude dependent thermospheric responses to forcing. Over time scales of an hour or more, winds in the lower thermosphere are seen to respond in kind with upper thermospheric winds. Over time scales of tens of minutes during times of dynamic forcing, the lower thermosphere and upper thermosphere wind speed can become uncorrelated, indicating differing altitude dependent responses to forcing in the thermosphere.