Studies on the influence of magnetic cloud, stream interface and polar mesospheric summer echoes in the mesosphere and lower thermosphere (MLT) region using model calculations and observations.

Abstract

The response of Mesosphere and Lower Thermosphere (MLT) temperature to energetic particle precipitation over the Earth's polar regions is not uniform due to complex phenomena within the MLT environment. Nevertheless, the modification of MLT temperatures may require an event based study to be better observed. Three Geospace events examined in this study are: Magnetic Clouds (MC), solar wind Stream Interfaces (SI) and Polar Mesospheric Summer Echoes (PMSE). The MC is a transient ejection in the solar wind defined as the region between the preceding half of the z{ component of southward interplanetary magnetic field (IMF{Bz) and the trailing half, which contained strong northward peak or vice versa, with an accompanied large density enhancement that strongly compressed the magnetosphere. The varied instrumentation which is located not only in South African National Antarctic Expedition (SANAE) IV, but also at Halley, a same radial distance (L ~ 4) location in the Southern hemisphere, and at the vicinity of conjugate location in Northern hemisphere provide an opportunity to test the theories applied to high latitude heating rates on arrival of MC. The Halley riometer is used to monitor coincidences of absorption with arrival of a fortuitous MC that was observed on 8 November 2004. Using Monte Carlo Energy Transport Model (MCETM), the corresponding altitude of electron and proton energy distribution indicates the importance of MC triggered geomagnetic storms on mesospheric dynamics. At the arrival of SI near the Earth's bow nose, compressional streams propagate into the inner magnetosphere, where they fueled magnetospheric storms. A number of SI events were obtained close in time to the pass of temperature retrieval onboard the Thermosphere Ionosphere Mesosphere Energetic and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) over SANAE IV. The relationship between the ionospheric absorption measured by riometer and the layer of energetic particle precipitation from National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites (NOAA/POES) was examined during these events. Here, a superposed

epoch technique is described and implemented to obtain average temperature profiles during SI{triggered particle precipitation. Prior to SI onset, there is no signifIcant temperature decrease below 100 km, whereas at the onset of the SI{triggered precipitation, we observe an immediate superposed average temperature decrease of about 35 K around 95 km. Results indicate that, cooling effects due to the production of mesospheric odd hydrogen might be major contributors to temperature decrease under compressed solar wind stream. PMSE, as a one{type Geospace event, exists because the electrically charged{ice particles reduce the mobility of mesospheric free electrons. In this study, first long term observations of PMSE, with Super Dual Auroral Radar Network (SuperDARN) SANAE IV HF radar (hereafter in this thesis referred as SuperDARN{PMSE), is presented. An extraction algorithm is described and implemented to obtain SuperDARN{PMSE during the summer period of years from 1998 to 2007. We examined the SuperDARN{PMSE occurrence rate in relation to geomagnetic activity and ow of mesospheric winds. Furthermore, the temperature changes in relation to SuperDARN{PMSE has been studied. The SuperDARN{PMSE peaks coincide with lower summer mesopause temperature and higher geomagnetic activity. Analysis of neutral wind variations, in relation to SuperDARN{PMSE peaks, indicates the importance of pole to pole mesospheric transport circulations. In addition, the mid{latitudes thermospheric zonal winds variations from the year 2005 to 2008 and its relevance to magnetospheric activity are examined. These studies could be directed towards achieving a more self{consistent interpretation of how the MLT energy budget is affected by magnetospheric processes.