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.