Inna Fedulina

ABSTRACT Nighttime volume emission rates and rotational temperatures, obtained from simultaneous observations of molecular oxygen and hydroxyl airglow at Almaty (43.25°N, 76.92°E) and Sierra-Nevada (37.2°N, 356.7°E), along with ionospheric density derived from foF2 in the vertical sounding ionograms over Almaty are analysed to study the variability and coupling of parameters observed in the upper mesosphere and ionosphere during the period of February – April, 2000.Ionospheric critical frequency measurements and airglow observations by the Mesopause Rotational Temperature Imager (MORTI) at Almaty and the Spectral Airglow Temperature Imager (SATI) at Sierra-Nevada Observatories show an increase in long-period planetary wave (PW) activity from the end of February until the middle of March, 2000.Very good agreement was found in the temporal variations of emission rates and rotational temperatures from March 1–15, 2000 measured at the Almaty and Sierra-Nevada sites. Similar perturbations could also be seen in the ionospheric critical frequency (ΔfoF2) obtained as a difference between current foF2 values and an ionospheric background level.The perturbations observed have been interpreted employing the Met office stratospheric model results. Latitudinal structure of a quasi 5-day wave was identified, for which the first-symmetric-mode amplitude and symmetric behaviour of phase are in good agreement with theoretical prediction. The analysis of the Met office stratospheric data indicate the presence of westward-propagating PW with periods of ∼5 and 10 days during the period of interest. The temporal correlation between planetary scale oscillations observed in the datasets examined (ionospheric, optical and meteorological) suggest dynamical coupling with the stratosphere. A negative disturbance in ΔfoF2 of ∼25% observed 1 day before a sharp increase in the MORTI mesospheric rotational temperature registered on March 10 at Almaty, is also discussed in the context of the possible stratosphere/mesosphere/ionosphere coupling.

ABSTRACT Hourly values of the F-region critical frequency, foF2, obtained by ground-based ionosonde method at Alma-Ata station during 1988–1999 are used to study the F2-layer variability in terms of ΔfoF2 obtained as a relative deviation of the current foF2 values from their background level. It has been found that in comparison with summer and equinox the winter ionosphere is more variable with an increase in the night time ionosphere day-to-day variability. Usually, the relative deviations ΔfoF2 occurred in the ±20% range, with about 80% of them occurring in the ±10% range. The winter nighttime ΔfoF2 values usually occurred in the range from -30% to 25%. Examples of the emission rate and rotational temperature for the O2 (0–1) atmospheric band obtained at Almaty using the MORTI instrument over nights of January and May 1999 show that the range of the ΔE and ΔT deviations like those in the ionosphere are maximum in winter like those in the ionosphere suggesting that the winter mesosphere is also more variable than summer mesosphere. Ionospheric data indicate episodic events of pronounced planetary wave (PW)-like oscillations observed in winter ionosphere. Two of the events, which occurred in the period of December 1994–January 1995 and December 1998, are analysed and revealed planetary-wave (PW) like oscillations in foF2 with periods of 5–14 days. The midnight ionospheric data were compared with available optical data obtained at Almaty employing the MORTI instrument for the period of December 1998–January 1999. The comparison showed that the F2-layer electron density, O2 emission rate and rotational temperatures over the entire period of observations tend to behave similarly, indicating oscillations with a period of about 9 days. NCEP/NCAR-reanalysis temperature and zonal wind at 40N and at 10 hPa pressure level as well as geopotential heights at 1 hPa pressure level (UKMO assimilated data) were analysed to interpret the observed perturbations in the mesosphere and ionosphere. A good coincidence between PW-like oscillations in foF2 and those of geopotential heights for periods of about 5 and 9–14 days has been obtained. The number of geomagnetic storms registered at Alma-Ata has been analysed as a plausible source of the ionosphere variability. Potential mechanisms linking the PW-like activity in the ionosphere with the wave events in the stratosphere/mesosphere have also been discussed.

The analysis of UKMO data shows that these assimilated fields can be used to study a long-term variability of planetary waves in the stratosphere (Fedulina et al., 2002). However, this daily data set can not be used to consider the planetary waves with periods shorter then of about 4~days. The ECMWF operational analysis 6-hourly data set gives us a possibility

The foF2 data obtained at Alma-Ata [43.250° N, 76.920° E] during winter/spring periods of 2004-2006 are analyzed to investigate the upper ionosphere variability in relation with stratospheric warming and springtime transition events. The geomagnetic activity and the middle stratosphere dynamics, involving planetary wave (PW) activity, analyzed for understanding the physical conditions and processes that can explain the observed ionospheric variability.