Abstract
Longitudinal dependences of stratospheric gravity wave (GW) fluctuations and lower ionospheric irregularities (sporadic E) at midlatitudes are studied by means of radio occultation data of the Global Positioning System/Meteorology Experiment (GPS/MET) satellite mission. The zonal average of temperature variance of GW fluctuations with vertical scales less than 7 km at northern midlatitudes is observed to be similar to that at southern midlatitudes, but there is a significant interhemispheric difference in the longitudinal dependence of GW fluctuations. The GPS/MET data at northern midlatitudes show a rapid change of the gravity wave distribution from 25 to 35 km height, resulting in a broad maximum of temperature variance located over the Atlantic and Eurasia. We only find in the wave distribution at h = 25 km some weak traces of possible orographic effects. On the other hand, the distribution of GW fluctuations at southern midlatitudes has a strong and sharp maximum over Andes, which is obviously due to orographic wave generation by the interaction of surface wind with the Andean mountain ridge. This observation of the new GPS radio occultation technique is in agreement with previous measurements of spaceborne microwave and infrared limb sounders. The amplitude of the average wave field increases with height over Andes, while the amplitude maximum moves westward, against the prevailing wind. The temperature fluctuations have an apparent, dominant vertical wavelength of around 6 km. In situ measurements by a balloon‐borne rawinsonde at Ushuaia, Argentina (54.7°S, 68.1°W) are compared to a simultaneous GPS/MET temperature profile. The balloon observations of temperature and horizontal wind are interpreted by a large amplitude mountain wave propagating to the upper stratosphere. Wave characteristics and atmospheric background conditions are investigated in detail for this mountain wave observation. Finally, the GPS/MET experiment indicates enhanced sporadic E in the lower ionosphere over Southern Andes. We assume that these plasma irregularities are generated by enhanced, upward wave flux due to the possible orographic effect of Andes.
Highlights
Atmospheric Dynamics: Stratosphere/troposphere interactions; 3384 Meteorology and Atmospheric Dynamics: Waves and tides; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; 2427 Ionosphere: Ionosphere/atmsophere interactions (0335); 2439 Ionosphere: Ionospheric irregularities; KEYWORDS: stratospheric gravity waves, sporadic E, GPS radio occultation, orographic waves, mountain wave propagation, Andes
We have looked at the water vapor distribution (GPS/MET and ECMWF water vapor pressure at around h = 5 km) at midlatitudes during February 1997 and October 1995
[40] The global distributions of stratospheric gravity waves (GWs) fluctuations and lower ionospheric irregularities at midlatitudes have been analyzed by means of GPS radio occultation
Summary
[2] Temperature fluctuations of high resolution profiles are analyzed and discussed for investigation of global and regional distributions of stratospheric gravity waves (GWs) at midlatitudes. Further dynamic processes are wave-wave interaction, wave ducting by background wind, wave generation by shear flow, and wave absorption by critical wind levels All these processes have influence on the distribution of gravity waves while propagating from the troposphere to the stratosphere [Fetzer and Gille, 1994; Alexander and Vincent, 2000]. Neutral wind shears of upward propagating waves from the stratosphere generate thin ionization layers in the lower ionosphere due to an electrodynamical effect of neutral-ion collisions under influence of the geomagnetic field [Hines, 1960; Whitehead, 1960; Mathews, 1998] These ionization layers are regarded as qualitative tracers of neutral wave activity in the mesosphere/lower thermosphere (MLT region) and are detected by GPS radio occultation. GPS radio occultation allows correlative studies on fluctuations in the stratosphere and lower ionosphere, leading to improved knowledge on coupling of stratosphere, MLT region, and lower ionosphere by upward energy and momentum flux of atmospheric waves
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