Abstract
Abstract. Product spectra of ground pressure variation and seismic oscillations have been calculated in the period sub-ranges of 42–90 min and 2.5–5 h, based on synchronous, co-located microbarograph and seismograph measurements at St. Petersburg (60° N, 30° E). The 200 records of 2–3.5 days in length and a combined duration of 525 days have been used. The product spectra have been computed for winter, spring, summer, and autumn, both individually and in combination. The spectra of different seasons are distinct from each other for both microbarograph and seismograph measurements; this can be caused by a seasonal variation in both frequency and amplitude of free oscillations of the atmosphere. There are pressure and seismic oscillations with close frequencies in the spectra for both, for each season and when all seasons are combined. At present, suggestions may only be made regarding the origin of most of these common oscillations. Once again, the penetration of the Earth’s free oscillation 0S2 with a period of about 54 min into the atmosphere has been confirmed. A common pressure and seismic oscillation with the 206 min period has been detected and has attracted considerable interest. The 159-min periodicity revealed in pressure variations may be associated with the well-known solar oscillation of the 160.01 min period.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
Highlights
Quasi-periodic fluctuations of wind, pressure, density, and temperature in the ∼ 1–5 h period range are observed ubiquitously in the lower and middle atmosphere
We have restricted our consideration to two frequency subranges of the ∼1–5 h period range, namely those in the 55.55–110.72 μHz and 185.15–396.5 μHz subranges (2.5– 5 h and 42–90 min periods, respectively)
We searched for statistically significant oscillations among the spectral peaks which exceed the 10% probability level
Summary
Quasi-periodic fluctuations of wind, pressure, density, and temperature in the ∼ 1–5 h period range are observed ubiquitously in the lower and middle atmosphere. Microbarograph observations of ground pressure variation have shown atmospheric oscillations with steady frequencies in the ∼1−2 h period range (Garmash et al, 1989; Lin’kov et al, 1989; Shved et al, 2000). These frequencies coincide with those observed in seismic oscillation spectra. Among the above atmospheric oscillations the 54-min periodicity is the only oscillation with a known physical source (Shved et al, 2000) This pressure oscillation is forced by the fundamental spheroidal mode 0S2 of the Earth’s free oscillations (Aki and Richards, 1980). As for other oscillations with steady frequencies, those can be caused by both the free atmospheric oscillations (Petrova and Shved, 2000) and tectonic effects (e.g. Petrova, 1994)
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