First results of ground-based optical measurements of the ion-neutral coupling within the polar region.
Authors: Meriwether John , Cooper Matthew , Gerrard Andrew , Trondsen Trond 
Published: February 2023

&lt;div dir=&quot;auto&quot;&gt;Ground-based imaging Fabry-Perot interferometer (FPI) optical measurements of the ion-neutral coupling between the F-region plasma and the polar thermosphere were made during the 2022-2023 northern winter season at the Kjell Henriksen Observatory (78.2 N, 15.6 E). By observing in sequence with a filter wheel located in front of the etalon, measurements of the spectral profiles of both the O&lt;sup&gt;+&lt;/sup&gt; 732 nm emission and the O 630 nm emission for each direction selected by a double axis mirror system were used to determine Doppler shifts and Doppler broadenings. The 732 O&lt;sup&gt;+&lt;/sup&gt; results were analyzed to determine the averaged line-of-sight F-region drift speed and ion temperature for a typical exposure time of 120 s.&amp;#160; For the 630 nm O emission, the averaged line-of-sight wind speed and neutral temperature were determined for an exposure time of 30 s. The FPI clear aperture was 120 mm, the FPI etalon gap separation was 1.4925 cm, each filter bandwidth was ~0.8 nm, and the focal length for an apochromatic lens assembly was 300 mm enabling the imaging observations of 12 rings for the 630 nm O emission and 11 rings for the 732 nm O&lt;sup&gt;+&lt;/sup&gt; emission. The primary production excitation source of the observed 732 nm O&lt;sup&gt;+&lt;/sup&gt; emission was that of solar EUV photoionization but the soft particle energetic precipitation associated with the polar cusp region also contributed significantly to the production of both emissions, especially during the noon sector period. Contamination by the 1PG molecular band emission of N&lt;sub&gt;2&lt;/sub&gt; was generally non-existent. It was found there was sufficient O&lt;sup&gt;+&lt;/sup&gt; emission for almost all directions chosen to determine the line-of-sight ion drift and ion temperatures with reasonable accuracy. Contamination of the O&lt;sup&gt;+ &lt;/sup&gt;732 emission by the 731.6 nm OH doublet&amp;#160; associated with the OH hyperfine structure caused by lambda splitting was always present in each O&lt;sup&gt;+&lt;/sup&gt; observed spectral profile. Removal of this emission in the analysis proved to be straightforward as one of the two OH peaks is seen clear of the O&lt;sup&gt;+&lt;/sup&gt; spectral profile, and its intensity could be used after the step of annular summing to normalize the OH structure for removal from the composite ring-integrated interferometric spectral profile. The two peaks of the O&lt;sup&gt;+&lt;/sup&gt; 732 nm doublet were almost coincident within each interferogram order. Results will be analyzed: 1), to search for indications of anti-sunward drift of the F-region plasma, 2) to determine the degree of variability of the observed plasma drifts, and 3) to determine the extent of Joule heating creating differences between the ion and neutral temperatures. The data obtained in the magnetic zenith direction will be examined to search for evidence of possible ion outflow.&lt;/div&gt;
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