Radio Science

Multifrequency observations of Polar Mesosphere Summer Echoes using Alaskan radar facilities: Comparisons and scattering calculations

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Abstract

[1] We present polar mesospheric radar observations at three frequency bands (MF/HF/VHF) and eight radar frequencies: 2.43, 3.3, 4.53, 4.9, 7.6, 28, 50, and 139 MHz, in order to better understand the well known but still not fully understood Polar Mesosphere Summer Echoes (PMSE). The echo morphology at the different frequencies is described by means of case studies where PMSE events were observed concurrently using at least two radar systems deployed over the Alaskan central region. The identity of MF and HF radar echoes as PMSE is resolved for the first time by means of simultaneous measurements made with VHF radars, the reference sensors employed traditionally for PMSE studies. On the basis of echo duration and radar reflectivity estimates, we suggest that low-power HF radars would be more appropriate for PMSE monitoring. This is confirmed by a radar target analysis of turbulent scattering mechanisms in the polar summer mesosphere. MF radars show highly organized PMSE layers quite often but are more susceptible to ionospheric absorption and higher-altitude returns associated with geomagnetic activity. Both phenomena produce a blanking effect in MF PMSE, which at times can persist for hours. HF and VHF radars are less affected by absorption events, but the PMSE echoes become weaker as the radar frequency increases.

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