The Geminid meteor shower during the ECOMA sounding rocket campaign: specular and head echo radar observations

The ECOMA (Existence of Charge state Of meteoric smoke particles in the Middle Atmosphere) sounding rocket campaign was conducted during the Geminid meteor shower in December 2010 in order to explore whether there is a change of the properties of meteoric smoke particles due to the stream. In parallel to the rocket flights, three radars monitored the Geminid activity located at the launch site in Northern Norway and in Northern Germany to gain information about the meteor flux into the atmosphere. The results presented here are based on specular meteor radar observations measuring the radiant position, the velocity and the meteor flux into the atmosphere during the Geminids. Further, the MAARSY (Middle Atmosphere Alomar Radar System) radar was operated to conduct meteor head echo experiments. The interferometric capabilities of MAARSY permit measuring the meteor trajectories within the radar beam and to determine the source radiant and geocentric meteor velocity, as well as to compute the meteor orbit.

Distortion of meteor count rates due to cosmic radio noise and atmospheric particularities

The determination of the meteoroid flux is still a scientifically challenging task. This paper focusses on the impact of extraterrestrial noise sources as well as atmospheric phenomena on the observation of specular meteor echoes. The effect of cosmic radio noise on the meteor detection process is estimated by computing the relative difference between radio loud and radio quiet areas and comparing the monthly averaged meteor flux for fixed signal-to-noise ratios or fixed electron line density measurements. Related to the cosmic radio noise is the influence of D-layer absorption or interference with sporadic E-layers, which can lead to apparent day-to-day variation of the meteor flux of 15–20%.

Frequency Dependence of Radar Meteor Echo Rates

Meteor rates have been measured with a large HF Radar at a number of frequencies. At the top end of the HF band our results match those of Greenhow (1963). However at lower frequencies we find high echo rates which indicate that past observations measured only a few percent of the total meteor flux incident on the Earth’s atmosphere. This explains the ‘missing mass’ discrepancy observed when radar results are compared with satellite or visual data. Accounting for’this missing mass results in a four-fold increase in the calculated total meteoroid mass influx to the surface of the Earth from 4000 to 16,000 tonnes per year. Our results also imply that the majority of echoes originate from altitudes above 100 km.

METEOR RADAR STATISTICS. II

Mean daily values of meteor flux for three categories of meteor echoes are tabulated for the period 1958 to 1962. The variation of echo rate with echo duration is studied. The difficulty of using this relation to determine the mass distribution of meteoroids in interplanetary space is noted.