Vertical wind distribution in the polar thermosphere during HorizontalERegion Experiment (HEX) campaign

Abstract

Vertical winds in the thermosphere were measured with two Fabry‐Perot Interferometers at the Poker Flat Research Range (PFRR) and Eagle observatory, Alaska during the Horizontal E Region Experiment (HEX) campaign (Feburary and March 2003). Since these two observatories have almost the same geomagnetic latitude, we could deduce vertical wind distributions along the same auroral arc. The OI557.7‐nm and OI630.0‐nm emissions were separated using a dichroic mirror, which enabled us to estimate temporal variations in vertical winds in the E and F regions simultaneously. To measure the optical auroral distribution, we used all‐sky imagers at the PFRR. We had 13 clear nights out of a total of 23. We obtained the following results from the observations. (1) The temporal variations in vertical wind observed at OI557.7 nm at the two observatories had a high degree of correlation, despite being ∼300 km apart. The correlation coefficients exceeded 0.6 on six of the 13 nights. The chance of exceeding a correlation coefficient of 0.6 on an individual night is about 0.1%. (2) The correlation was relatively low in the OI630.0‐nm observation. (3) Some low‐correlation cases for both wavelengths indicated that the location of the auroral arc with respect to the observatory was different for the two sites, namely, whether the auroral arc was poleward or equatorward of the observational area. These results suggest that the vertical wind structures along one auroral arc are uniform at least 300 km apart. This wind distribution was consistent with previous works in most cases, but some exceptions were also found.