Thermospheric vertical winds in the subauroral and polar latitude regions

A 15 cm imaging narrow field Fabry Perot interferometer (designated as

the Hot Oxygen Doppler Imager - HODI) was operated in a first-light

campaign at the Jenny Jump Observatory (40.9 N, 74.9 W) in the

northwestern corner of New Jersey. This effort was followed up with

the deployment of HODI to the Kjell Henriksen Observatory (78.15 N,

16.08 E) in Longyearbyen, Norway for the 2022 summer months and the

2022-2023 winter, respectively. Analysis of the 12 ring interference

pattern for the 630 nm OI emission determined Doppler shifts and

Doppler widths. Typical exposure times for each direction were 120

seconds, and the typical error bars for vertical winds and

temperatures were 1-2 m/s and 3 to 5 K, respectively. Frequent laser

calibrations to define the instrumental Doppler reference normalized

by the averaged nighttime vertical wind were obtained. The primary aim

of these measurements was to observe the vertical winds throughout the

night in a search for gravity wave activity. Lomb-Schargle periodogram

analysis processing was applied to establish the dominant periodicity

of the vertical wind data.  The results for geomagnetically active

periods show vigorous vertical wind activity with fluctuations of the

order of 20 to 30 m/s, and even for quiet periods there was indicated

vertical wind fluctuations of a few m/s. One instance on 25 July, 2022

showed evidence for a monochromatic wave fluctuation of ~±25 m/s for

the wind and ~± 20 K for the temperature. The phase difference between

the temperature and vertical wind oscillation was ~90 degrees in

agreement with theoretical expectation.  Examination of the

differential TEC map for this night showed a strong indication of a

correlation with a valley of negative TEC fluctuations propagating

through the JJO region in the southwest direction. The KHO vertical

wind results showed strong vigorous activity from night to night.

These results suggest that thermospheric gravity wave structures exist

continually from night to night. The next step in studying the

thermosphere gravity wave activity is to determine the direction and

speed of propagation of these GW structures, which can be done with a

tri-static Fabry-Perot observatory, i.e. a Gravity Wave Tracker (GWT)

system. HODI will be operated at KHO for the 2023-2024 winter season

and then returned for installation at JJO in March, 2024.