ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-4-685-2004

Aspect sensitivity of VHF echoes from field aligned irregularities in meteor trails and thin ionization layers

Zhou

Q. H.

¹ Morton

Y. T.

¹ Mathews

J. D.

² Janches

² ³

Electrical and Computer Engineering Department, Miami University, Oxford, OH, USA

CSSL, Pennsylvania State University, University Park, PA, USA

Arecibo Observatory, Arecibo, Puerto Rico

07 05 2004

4 3 685 692

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The aspect sensitivity of VHF echoes from field aligned irregularities (FAI) within meteor trails and thin ionization layers is studied using numerical models. Although the maximum power is obtained when a radar is pointed perpendicular to the field line (<IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-685-img1.gif" ALT="$bot$">B), substantial power can be obtained off the <IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-685-img1.gif" ALT="$bot$">B direction if the ionization trail/layer is thin. When the FAI length along B is 20 m, the power observed 6° off <IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-685-img1.gif" ALT="$bot$">B is about 10 db below that perpendicular to the B direction. Meteoric FAI echoes can potentially be used to determine the diffusion rate in the mesopause region. Based on the aspect sensitivity analysis, we conclude that the range spread trail echoes far off <IMG WIDTH="15" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" src="acp-4-685-img1.gif" ALT="$bot$">B observed by powerful VHF radars are likely due to overdense meteors. Our simulation also shows that ionospheric FAI echoes can have an altitude smearing effect of about 4 km if the vertical extension of a FAI-layer is around 100 m, which has often been observed at Arecibo. The altitude smearing effect can account for the fact that the Es-layers observed by the Arecibo incoherent scatter radar are typically much narrower than FAI-layers and the occurrence of double spectral peaks around the Es-layer altitude in FAI echoes.