Dynamics of Neutral Wind in the polar region observed with two Fabry-Perot Interferometers

Abstract

Optical observations were made at Ramfjord, Norway from January 10 to February 14, 1997. Two types of FabryPerot interferometers (FPIs), Doppler-imaging and scanning, were installed at the EISCAT radar site and were used to acquire data simultaneously with radio instruments. Both FPIs can observe emissions of two different wavelengths simultaneously. We can estimate the horizontal and vertical wind in different emission layers simultaneously with high time-resolution (∼1 min). The observations on February 8 and 9, 1997, show some notable characteristics: (1) large-scale perturbations (≈ ±150 m/s) are observed in the upper thermospheric wind. They seem to begin 30 min after the onset of a magnetic substorm and to stop when the next substorm begins. (2) Clear wave-like structures are found in the horizontal wind variations. Some of them can be seen over the entire sky, and one of them is found in a restricted regions. (3) A clear wave-like structure is also found in the vertical wind in the upper thermosphere. A similar structure can be seen in the lower thermosphere, but these structures are not always in phase. This phases difference starts at the same time that horizontal winds between the two layer has their phase difference. (4) The relation between the vertical wind and the divergence of horizontal wind seems to change with time. The correlation coefficient between them changes one-hours before and on-time of a substorm on-set. This sign of the coefficient is negative in most of the time, with considering about time-lag. It means the vertical morion is caused by divergent flow of horizontal wind.

Evidence for thermospheric gravity waves in the southern polar cap from ground-based vertical velocity and photometric observations

“…A third possibility is that gravity waves (if that is what they are) are prevented from propagating into the region of the auroral oval. Ishii et al (1999) note such an effect in their FPI observations, where wave-like events disappear from the wind time series when the aurora moves into the instrumental field-of-view. They speculate that the wind field generated by auroral heating disrupts the wave.…”

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

“…The neutral temperature may be estimated from the spectrum analysis of the vertical wind data, if vertical oscillations at the Brunt-Väisälä frequency are obvious in the data (Revathy et al, 1996;Mohan et al, 2001). However, according to previous observations with the Fabry-Perot interferometer (FPI) (Peteherych et al, 1985;Price and Jacka, 1991;Price et al, 1995;Ishii et al, 1999Ishii et al, , 2001Ishii et al, , 2004, external forces associated with geomagnetic activity may vertically accelerate the air parcel in the lower thermosphere at high latitudes. These observations suggest that dissipation of the Joule and particle-heating energies in the lower thermosphere is relevant to generation of Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Thermospheric temperature and density variations

“…The Fabry-Perot interferometer (FPI), which can detect the Doppler shifted and broadening emissions from the atmospheric species, is one of the most important instruments to observe the neutral temperature and wind in the thermosphere (e.g., Aruliah et al, 1991;Ishii et al, 1999;Shiokawa et al, 2003;Ford et al, 2007). In addition, the radar techniques enable us to obtain information of the thermospheric wind and temperature.…”