.[1] This paper compares results from a whole atmosphere-ionosphere coupled model, GAIA, with the COSMIC and TIMED/SABER observations during the 2008/2009 northern winter season. The GAIA model has assimilated meteorological reanalysis data by a nudging method. The comparison shows general agreement in the major features from the stratosphere to the ionosphere including the growth and decay of the major stratospheric sudden warming (SSW) event in 2009. During this period, a pronounced semidiurnal variation in the F region electron density and its local-time phase shift similar to the previous observations are reproduced by the model and COSMIC observation. The model suggests that the electron density variation is caused by an enhanced semidiurnal variation in the E Â B drift, which is probably related to an amplified semidiurnal migrating tide (SW2) in the lower thermosphere. The model and TIMED/SABER observation show that the SW2 tide amplifies at low latitudes from the stratosphere to the thermosphere as well as the phase variation. Possible mechanisms for the SW2 variability in the low latitude stratosphere could be the change of its propagation condition, especially the (2, 2) mode, due to changing zonal background wind and meridional temperature gradient, and/or an enhancement of its source due to redistribution of stratospheric ozone. Present results also show a prominent long-term variation of the terdiurnal migrating component (TW3) in the ionosphere and atmosphere.

No abstract

[1] The midlatitude sporadic E layers form when metallic ions of meteoric origin in the lower thermosphere are converged vertically in a wind shear. The occurrence and strength of sporadic E follow a pronounced seasonal dependence marked by a conspicuous summer maximum. Although this is known since the early years of ionosonde studies, its cause has remained a mystery as it cannot be accounted for by the windshear theory of E s formation. We show here that the marked seasonal dependence of sporadic E correlates well with the annual variation of sporadic meteor deposition in the upper atmosphere. The later has been established recently from long-term measurements using meteor radar interferometers in the Northern and Southern Hemispheres. Knowing that the occurrence and strength of sporadic E layers depends directly on the metal ion content, which apparently is determined primarily by the meteoric deposition, the present study offers a cause-and-effect explanation for the long-going mystery of sporadic E layer seasonal dependence.

[1] The present paper is focused on the global spatial (altitude and latitude) structure and seasonal and interannual variability of the migrating diurnal tide derived from the Sounding of the Atmosphere using Broadband Emission Radiometry/ThermosphereIonosphere-Mesosphere-Energetics and Dynamics (SABER/TIMED) temperature measurements for 6 full years (January 2002 to December 2007. The tidal results are obtained by a new analysis method where the tides (migrating and nonmigrating) and the planetary waves (zonally traveling and stationary) are simultaneously extracted from the satellite data. It has been found that above 70 km height the SABER migrating diurnal tide reflects mainly the distinctive features of the first symmetric propagating (1,1) mode, while below this height it reflects the features of the first symmetric trapped (1,À2) mode. The trapped component amplifies near 50 km, and its phase is close to $1600 LT. The seasonal behavior of the diurnal tide over the equator is dominated by semiannual variation with a primary maximum in February-March (18 K, average amplitude for 6 years) and a secondary maximum in August-September (15 K). The tidal amplitude grows rapidly in the mesosphere/lower thermosphere; however, it undergoes some decay near $90 km, defining ubiquitous double-peaked vertical structure. A very rapid reduction in amplitude is detected at heights near 115 km; however, above this level the diurnal tide amplifies again. The vertical wavelength of the propagating diurnal tide is $20 km over the equator; at middle latitudes it is not very different from that over the equator, but its magnitude depends on the season. In the winter it is longer than that in summer. The interannual variability of the diurnal tide indicates a clear correlation with the stratospheric quasi-biennial oscillation.Citation: Mukhtarov, P., D. Pancheva, and B. Andonov (2009), Global structure and seasonal and interannual variability of the migrating diurnal tide seen in the SABER/TIMED temperatures between 20 and 120 km,

[1] Vertical coupling in the low-latitude atmosphere-ionosphere system driven by the 2-day wave in the tropical MLT region has been investigated. The problem is studied from an observational point of view. Three different types of data were analyzed in order to detect and extract the 2-day wave signals. The 2-day wave event during the period from 1 December 2002 to 28 February 2003 was identified in the neutral winds by radar measurements located at four tropical stations. The 2-day variations in the ionospheric electric currents (registered by perturbations in the geomagnetic field) and in the F-region electron densities were detected in the data from 23 magnetometer and seven ionosonde stations situated at low latitudes. Two features for each kind of wave were investigated in detail: the variation with time of the wave amplitude and the zonal wave number. The results show that the westward propagating global 2-day wave with zonal wave number 2 seen in the ionospheric currents and in F-region plasma is forced by the simultaneous 2-day wave activity in the MLT region. The main forcing agent in this atmosphere-ionosphere coupling seems to be the modulated tides, particularly the semidiurnal tide. This tide has a larger vertical wavelength than the diurnal tide and propagates well into the thermosphere. The parameter that appears to be affected, and thus drives the observed 2-day wave response of the ionosphere, is the dynamo electric field.

No abstract

A new meteor radar has been deployed at Esrange (68°N, 21°E) near Kiruna in Sweden. The radar has been used to measure winds and tides in the Arctic mesosphere/lower thermosphere region over the interval August 1999 to July 2000. Conspicuous features of the measured mean winds include a strong shear of up to 5 m s−1 km−1 in the summer zonal flow, resulting in eastward flows of in excess of 30 m s−1 at the upper heights observed (97 km). An equatorward meridional flow is observed in summer and winter, which reaches maximum values of ∼13 m s−1 in a summer jet. Poleward flow in comparison is weak and only occurs at the equinoxes. The monthly mean and seasonal mean behaviors of the amplitudes and phases of the 12‐ and 24‐hour tides are examined and compared to the Global Scale Wave Model‐98. The observations are generally very close to the model predictions for the 24‐hour tide and for the 12‐hour tide in winter. In other seasons, particularly summer, the observed 12‐hour tidal amplitudes are significantly larger than those predicted. In spring and summer the wavelength of the 12‐hour tide is significantly larger than that predicted.

Abstract. The "Scandinavian Triangle" is a unique trio of radars within the DATAR Project (Dynamics and Temperatures from the Arctic MLT (60-97 km) region): Andenes MF radar (69 • N, 16 • E); Tromsø MF radar (70 • N, 19 • E) and Esrange "Meteor" radar (68 • N, 21 • E). The radar-spacings range from 125-270 km, making it unique for studies of wind variability associated with small-scale waves, comparisons of large-scale waves measured over small spacings, and for comparisons of winds from different radar systems. As such it complements results from arrays having spacings of 25 km and 500 km that have been located near Saskatoon. Correlation analysis is used to demonstrate a speed bias (MF smaller than the Meteor) between the radar types, which varies with season and altitude. Annual climatologies for the year 2000 of mean winds, solar tides, planetary and gravity waves are presented, and show indications of significant spatial variability across the Triangle and of differences in wave characteristics from middle latitudes.