Long period wind oscillations in the 80–110 km altitudes observed by the Kyoto meteor radar in 1983–1985

During the MAP period, the Kyoto meteor radar has almost continuously monitored the wind fields in the 80–110 km altitudes. Wind oscillations with various periods ranging from 2 to 20 days are detected. The period of the quasi 2-day wave in 1983 was 2.2 days in summer months but became as short as about 2.0 days in autumn. Antisymmetry in phase profiles is detected by comparing the behavior of the quasi 2-day wave simultaneously observed at Adelaide and Kyoto.     

Longitudinal MLT wind structure at higher mid-latitudes as seen by meteor radars at central and Eastern Europe (13°E/49°E)

The mid-latitude mesosphere and lower thermosphere (MLT) wind speeds measured by two SKiYMET meteor radars (MRs) at Collm (51°N, 13°E) and Kazan (56°N, 49°E) during 2016–2017 were analyzed to study longitudinal wind structures. The differences between monthly mean prevailing wind speeds and tidal amplitudes were compared with the corresponding differences obtained from TIMED/TIDI satellite winds and gradient wind speeds from the AURA/MLS instrument. It is shown that the MR wind difference between the two sites is statistically significant. The difference of the horizontal prevailing winds can be explained by a superposition of the background zonal flow, which is different at the two latitudes, with stationary planetary waves of different origin. Non-migrating tides contribute significantly to the difference of the semidiurnal tidal winds between the two sites.     

Global structure,seasonal and interannual variability of the eastward propagating tides seen in the SABER/TIMED temperatures (2002–2007)

The present paper is focused on the global spatial (altitude and latitude) structure, seasonal and interannual variability of the most stable in amplitude and phase eastward propagating diurnal and semidiurnal tides with zonal wavenumbers 2 and 3 derived from the SABER/TIMED temperatures for full 6 years (January 2002–December 2007). The tidal results are obtained by an analysis method where the tides (migrating and nonmigrating) and the planetary waves (zonally travelling, zonally symmetric and stationary) are simultaneously extracted from the satellite data. It has been found that the structures of the eastward propagating diurnal tides with zonal wavenumbers 3 and 2 change from antisymmetric with respect to the equator below ∼85 km height, to more symmetric above ∼95 km. The seasonal behavior of the DE3 is dominated by annual variation with maximum in August–September reaching average (2002–2007) amplitude of ∼15 K, while that of the DE2 by semiannual variation with solstice maxima and with average amplitude of ∼8 K. These tides revealed some interannual variability with a period of quasi-2 years. The seasonal behavior of the eastward propagating semidiurnal tide with zonal wavenumber 2 in the southern hemisphere (SH) is dominated by annual variation with maximum in the austral summer (November–January) while that in the northern hemisphere (NH) by semiannual variation with equinoctial maxima. The SE2 maximizes near 115 km height and at latitude of ∼30° reaching an average amplitude of ∼6 K. The seasonal behavior of the eastward propagating semidiurnal tide with zonal wavenumber 3 in both hemispheres indicates a main maximum during June solstice and a secondary one during December solstice. The tide maximizes near 110–115 km height and at a latitude of ∼30° reaching an average amplitude of ∼4.8 K in the SH and ∼4 K in the NH. The tidal structures of the two eastward propagating semidiurnal tides are predominantly antisymmetric about the equator.     

Ionospheric parameters in the European sector during the magnetic storm of August 25–26, 2018

Variations of ionospheric parameters Total Electron Content (TEC) by GNSS, critical frequency (foF2) by vertical sounding and electron density (Ne) by low-altitude satellite were studied at high, mid and low latitudes of the European sector during the magnetic storm of August 25–26, 2018. During the main phase of the storm the ionospheric F2-layer was under the positive disturbance at mid and low latitudes. Then the transition from the positive to negative ΔfoF2 values occurred at all latitudes. The recovery phase was characterized by negative ionospheric disturbance at all latitudes. This is due to the decrease of thermospheric O/N2 ratio during the recovery phase of the storm. The intense Es layers screened the reflections from the F2-layer on August 26th at high and at low latitudes but at different times. Some blackouts occurred due to the high absorption level at high latitudes. In general, foF2 and TEC data were highly correlated. The major Ne changes were at the low latitudes. In general, Ne data confirmed the ionospheric dynamics revealed with foF2 and TEC.     

Mean winds of the upper middle atmosphere (∼70–110 km) from the global radar network: Comparisons with CIRA 72, and new rocket and satellite data

A substantial quantity of wind data have been assembled from radar systems since CIRA-72 was formed: most of these radars include height ranging, and operate on a regular and even continuous basis. Systems include meteor and MF (medium frequency) Radars: an MST (mesosphere-stratosphere-troposphere) Radar (meteor mode); and an LF (low frequency) drift system. Latitudes represented are near 20° N/S, 35° N/S, 45° N/S, 50°N, 65° N/S. In all cases tidal oscillations were calculated so that corrected mean winds (zonal, meridional) are available - the meridional was not included in CIRA-72. Means for groups of years near 1980 are available, as well as individual recent years (1983, 1984) to allow assessment of secular trends: revised and improved analysis has been completed for several stations.Height-time cross-sections have been formed for each observatory: heights are typically ∼75–110 km, with time resolution of 7–30 days. Such detailed cross-sections were almost unknown before 1972. Comparisons with CIRA-72 are shown, and these emphasize the differences between hemispheres (NH, SH) in the radar winds. Other new winds from rockets and satellite radiances are contrasted with the radar set. There are important differences with the satellite-derived geostrophic winds (1973–78): possible explanations involve secular trends, longitudinal variations, and ageostrophy.