Solar control of meteor radar rates

Meteor radar observations carried out in August-September 1953-84 at theOnsala Space Observatory in Sweden show long-term, as well as short termvariations in meteor radar rates. These rate variations are associatedwith position in the solar cycle, and with variations in the solar windsector structure. An inverse correlation is found between meteor radarrates and the solar cycle. The magnitude of this effect is quite large;about twice as many radar echoes are observed at solar minimum as atsolar maximum. We propose that this long-term inverse correlation withthe sunspot number is caused by a solar cycle controlled variation ofthe atmospheric density gradient at meteor ablation heights (90-110 km).Day-to-day variations in meteor radar rates, which correlate withshort-term geomagnetic activity have also been detected. A superposedepoch analysis based on solar wind sector boundaries as key dates showsthat a minimum in meteor radar rates occurs about 3 days after theEarth's passage of a solar wind sector boundary. (Less)