Aspect sensitivity of VHF echoes from field aligned irregularities in meteor trails and thin ionization layers
[摘要] The aspect sensitivity of VHF echoes from field aligned irregularities (FAI)within meteor trails and thin ionization layers is studied using numericalmodels. Although the maximum power is obtained when a radar is pointedperpendicular to the field line (
B), substantial power canbe obtained off the
B direction if the ionizationtrail/layer is thin. When the FAI length along
B is 20 m, the powerobserved 6° off
B is about 10 db below thatperpendicular to the
B direction. Meteoric FAI echoes canpotentially be used to determine the diffusion rate in the mesopause region.Based on the aspect sensitivity analysis, we conclude that the range spreadtrail echoes far off
B observed by powerful VHF radars arelikely due to overdense meteors. Our simulation also shows that ionosphericFAI echoes can have an altitude smearing effect of about 4 km if thevertical extension of a FAI-layer is around 100 m, which has often beenobserved at Arecibo. The altitude smearing effect can account for the factthat the Es-layers observed by the Arecibo incoherent scatter radar aretypically much narrower than FAI-layers and the occurrence of doublespectral peaks around the Es-layer altitude in FAI echoes.
