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Radar scattering from the summer polar mesosphere: theory and observations
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Radar scattering from the summer polar mesosphere: theory and observations

Author: John Yungdo Nagamichi Cho
Publisher: 1993.
Edition/Format: Thesis/dissertation : Manuscript : English
Summary:
The anomalously large radar reflectivities observed in the summer polar mesosphere have eluded satisfactory explanation until now. We propose that the following chain of causality is responsible for the so-called polar mesosphere summer echoes (PMSE): The uniquely low temperatures in the summer mesopause produce ice aerosols.

Because the aerosols exist in a plasma, they become electrically charged. The ambient

We support the above concept by developing a quantitative theory of ambipolar diffusion in the mesosphere. We then apply the results to isotropic turbulence and Fresnel radar scatter to show that the observed radar reflectivities can be explained by the theory. We show that the presence of realistic charged aerosols are sufficient to explain PMSE.

We also show that dressed aerosol radar scatter, proposed by others as a generation mechanism for PMSE, can only apply to echoes detected by UHF radars. We present data taken with the Sondrestrom 1.29-GHz radar, which we believe to be the first PMSE event observed above the gigahertz, and attribute it to dressed aerosol scatter.

In the summer of 1991, we used the Cornell University portable radar interferometer (CUPRI) to observe the mesosphere while rockets carrying in situ sensors were flown through two PMSE occurrences and a noctilucent cloud/PMSE event. We present a selection of first results from this campaign (NLC-91).

The first simultaneous height comparison between noctilucent clouds and PMSE show that the radar scatteriang region was near or slightly above the visible cloud layer. We also infer from aspect sensitivity measurements and Doppler spectrograms that there were two distinct types of PMSE: enhanced turbulent scatter and partial (Fresnel) reflection from steep edges in the electron density. Both mechanisms require and anomalously low electron diffusion coefficient.  Read more...

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Details

Material Type: Thesis/dissertation, Manuscript
Document Type: Book, Archival Material
All Authors / Contributors: John Yungdo Nagamichi Cho
OCLC Number: 63531172
Description: vix, 204 leaves : ill. ; 29 cm.
Responsibility: by John Yungdo Nagamichi Cho.

Abstract:

The anomalously large radar reflectivities observed in the summer polar mesosphere have eluded satisfactory explanation until now. We propose that the following chain of causality is responsible for the so-called polar mesosphere summer echoes (PMSE): The uniquely low temperatures in the summer mesopause produce ice aerosols.

Because the aerosols exist in a plasma, they become electrically charged. The ambient electrons become coupled to the aerosols through electric fields and their effective diffusivity is retarded due to the large size of the aerosols. The reduction in diffusivity allows electron density inhomogeneities to be maintained at the radar Bragg scales. The radar waves are then scattered by the inhomogeneities.

We support the above concept by developing a quantitative theory of ambipolar diffusion in the mesosphere. We then apply the results to isotropic turbulence and Fresnel radar scatter to show that the observed radar reflectivities can be explained by the theory. We show that the presence of realistic charged aerosols are sufficient to explain PMSE.

We also show that dressed aerosol radar scatter, proposed by others as a generation mechanism for PMSE, can only apply to echoes detected by UHF radars. We present data taken with the Sondrestrom 1.29-GHz radar, which we believe to be the first PMSE event observed above the gigahertz, and attribute it to dressed aerosol scatter.

In the summer of 1991, we used the Cornell University portable radar interferometer (CUPRI) to observe the mesosphere while rockets carrying in situ sensors were flown through two PMSE occurrences and a noctilucent cloud/PMSE event. We present a selection of first results from this campaign (NLC-91).

The first simultaneous height comparison between noctilucent clouds and PMSE show that the radar scatteriang region was near or slightly above the visible cloud layer. We also infer from aspect sensitivity measurements and Doppler spectrograms that there were two distinct types of PMSE: enhanced turbulent scatter and partial (Fresnel) reflection from steep edges in the electron density. Both mechanisms require and anomalously low electron diffusion coefficient.

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