Statistical analysis of thermospheric gravity waves from Fabry-Perot Interferometer measurements of atomic oxygen

Abstract

Abstract. Data from the Fabry-Perot Interferometers at KEOPS (Sweden), Sodankylä (Finland), and Svalbard (Norway), have been analysed for gravity wave activity on all the clear nights from 2000 to 2006. A total of 249 nights were available from KEOPS, 133 from Sodankylä and 185 from the Svalbard FPI. A Lomb-Scargle analysis was performed on each of these nights to identify the periods of any wave activity during the night. Comparisons between many nights of data allow the general characteristics of the waves that are present in the high latitude upper thermosphere to be determined. Comparisons were made between the different parameters: the atomic oxygen intensities, the thermospheric winds and temperatures, and for each parameter the distribution of frequencies of the waves was determined. No dependence on the number of waves on geomagnetic activity levels, or position in the solar cycle, was found. All the FPIs have had different detectors at various times, producing different time resolutions of the data, so comparisons between the different years, and between data from different sites, showed how the time resolution determines which waves are observed. In addition to the cutoff due to the Nyquist frequency, poor resolution observations significantly reduce the number of short-period waves (<1 h period) that may be detected with confidence. The length of the dataset, which is usually determined by the length of the night, was the main factor influencing the number of long period waves (>5 h) detected. Comparisons between the number of gravity waves detected at KEOPS and Sodankylä over all the seasons showed a similar proportion of waves to the number of nights used for both sites, as expected since the two sites are at similar latitudes and therefore locations with respect to the auroral oval, confirming this as a likely source region. Svalbard showed fewer waves with short periods than KEOPS data for a season when both had the same time resolution data. This Correspondence to: E. A. K. Ford (eakf@bas.ac.uk) gives a clear indication of the direction of flow of the gravity waves, and corroborates that the source is the auroral oval. This is because the energy is dissipated through heating in each cycle of a wave, therefore, over a given distance, short period waves lose more energy than long and dissipate before they reach their target.

Thermospheric mass density: A review

“…The presence of gravity waves in the ionosphere and thermosphere was first demonstrated by Hines (1960). Recent observational studies of gravity waves in the thermosphere include Ford et al (2008), Nicolls (2009), andYang et al (2010). Theoretical studies include Hickey et al (2009), and Yiğit et al (2014.…”

Multi-instrument observations of large-scale atmospheric gravity waves/traveling ionospheric disturbances associated with enhanced auroral activity over Svalbard

“…or FPI (e.g. Innis et al, 2001;Ford et al, 2006Ford et al, , 2008Nicolls et al, 2012;Shiokawa et al, 2012) or satellite data (e.g. Johnson et al, 1995;Idrus et al, 2013;Momani et al, 2010) or data from radars such as ionosondes and EISCAT (European Incoherent SCATter) (e.g.…”

The phases and amplitudes of gravity waves propagating and dissipating in the thermosphere: Application to measurements over Alaska

“…Errors in line‐of‐sight (LOS) wind determination have decreased significantly with the switch to imaging CCD detectors in recent years [ Aruliah et al , 2005; Ford et al , 2006, 2008; Meriwether et al , 2011; Makela et al , 2011]. The advantage of these imaging FPI observations over imaging all‐sky FPI observations [e.g., Conde and Smith , 1995; Conde et al , 2001; Aruliah et al , 2010] during times of auroral activity is the ability to detect small Doppler shifts with errors of only several ms −1 in a given direction.…”