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Title: Variability of 40-300keV electrons at geosynchronous orbit
Author: Szita, Sarah
ISNI:       0000 0001 3495 0344
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1998
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The energetic electron population at geosynchronous orbit is highly variable and affected by many different time-dependent processes. Substorm injections recur on time scales of hours, local time variations result from the geomagnetic field asymmetry, magnetic storms create periods of enhanced activity and quiet periods result in continual loss, seasonal variations are driven by changes in the Earth's magnetic field geometry around its orbit, and solar cycle variations occur on time scales of years. From 1988-1995, the SEM-2 (Space Environment Monitor) onboard the geostationary satellite Meteosat P2 detected 42.9-300keV electrons in five differential energy ranges. This energy range is ideal to investigate two important components of the geosynchronous environment: the trapped radiation belt population and the lower energy substorm injected electrons. The SEM-2's 30 look directions allow the determination of the symmetry axis of the particle distribution, and comparison with the Tsyganenko 89 magnetic field model shows that this provides a good indication of the magnetic field direction. The dependence of radiation belt intensity and substorm injection signatures on local time and geomagnetic activity is quantified in models based on flux probability distributions, and the effects of including a time lag behind Kp for the high energy data are explored. A longer term model is constructed to give the probable range of observed flux in terms of mission duration. Injection frequency is investigated using wavelet analysis and found to depend on solar wind speed. Wavelets are also used to investigate a 16-day periodicity which may relate to previous observations interpreted as planetary wave signatures. The solar cycle dependence of both populations is examined. The lower energy population peaks at solar maximum, but is also enhanced in the declining phase which has the dominant effect on the higher energy electrons.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Earth's magnetic field geometry; Solar cycle