Radio meteors above the Arctic Circle radiants, orbits and estimated magnitudes

Sammanfattning: This thesis presents results based on data collected with the 930 MHz EISCAT UHF radar system and three SKiYMet specular meteor radars. It describes in detail a method for meteoroid orbit calculation.The EISCAT UHF system comprises three identical 32 m parabolic antennae: one high-power transmitter/receiver and two remote receivers. Precise meteoroid deceleration and radar cross section are determined from 410 meteor head echoes simultaneously observed with all three receivers between 2002 and 2005, during four 24h runs at the summer/winter solstice and the vernal/autumnal equinox. The observations are used to calculate meteoroid orbits and estimate meteor visual magnitudes. None of the observed meteors appear to be of extrasolar or asteroidal origin; comets, particularly short period (<200 years) ones, may be the dominant source for the particles observed. About 40% of the radiants are associated with the north apex sporadic meteor source and 58% of the orbits are retrograde. The geocentric velocity distribution is bimodal with a prograde population centred around 38 km/s and a retrograde population peaking at 59 km/s. The absolute visual magnitudes of meteors are estimated to be in the range of +9 to +5 using a single-object numerical ablation model. They are thus observable using intensified CCD cameras with telephoto lenses.The thesis also investigates diurnal meteor rate differences and sporadic meteor radiant distributions at different latitudes using specular meteor trail radar measurements from 68°N, from 55°N and from 8°S. The largest difference in amplitude of the diurnal flux variation is at equatorial latitudes, the lowest variation is found at high latitudes. The largest seasonal variation of the diurnal flux is observed with the high-latitude meteor radar. The investigations show a variation in the sources with both latitude and time of day.The EISCAT UHF system and the high-latitude meteor radar are located close to the Arctic Circle. Such a geographical position means that zenith points towards the North Ecliptic Pole (NEP) once every day all year round. This particular geometry allows the meteoroid influx from the north ecliptic hemisphere to be compared throughout the year as the ecliptic plane coincides with the local horizon. Considering only the hour when NEP is closest to zenith, the EISCAT UHF head echo rate is about a factor of three higher at summer solstice than during the other seasons, a finding which is consistent with the high-latitude meteor radar measurements.