Abstract
Polar mesospheric summer echoes (PMSE) often show different layers. Artificial electron heating experiments are an important diagnostic tool to investigate the parameters in the PMSE regions. The response of PMSE to high frequency heating in the lower (80–85 km) and upper (85–90 km) PMSE layers is studied by analyzing PMSE observations carried out by the EISCAT VHF radar in July 2007. Different characteristics of modulated PMSE (e.g., PMSE intensity reduction, recovery, overshoot, ratios during the heating-on and heating-off times) are analyzed and compared at different situations such as only in one layer (lower or upper) and in both layers simultaneously without high-energy particle precipitation. Based on statistical results, it is found that in the lower layer all characteristics of modulated PMSE except PMSE recovery are greater than that in the upper layer. Electron temperature enhancement and PMSE modulation index due to ionospheric heating were calculated to show the enhanced electron temperature effect on PMSE. It is found that in both layers usually higher electron temperature enhancement corresponds to higher PMSE modulation index. However, the comparison of statistical results shows that in the lower layer electron temperature enhancement and PMSE modulation index are greater than that in the upper layer. Based on the relation of electron temperature enhancement to the PMSE modulation index, it is concluded that the variability of electron temperature enhancement may be responsible for the variations in different modulated PMSE characteristics between the lower and upper layers.
Highlights
At polar latitudes of earth’s mesosphere, there is an intriguing observational radar phenomenon caused by the electron density irregularities due to electron charging on dust, called polar mesospheric summer echoes (PMSE) (Ecklund and Balsley 1981)
Significant information can be obtained on the PMSE dusty plasma state by analyzing the shape of overshoot characteristic curve (OCC) during an overshoot heating cycle
For the rest of time, the PMSE intensity gradually recovers to the equilibrium state
Summary
At polar latitudes of earth’s mesosphere, there is an intriguing observational radar phenomenon caused by the electron density irregularities due to electron charging on dust, called polar mesospheric summer echoes (PMSE) (Ecklund and Balsley 1981). PMSE has been observed by different radars having operating frequencies in the range of 50-MHz to 1.3-GHz. The growth of water ice condensation on nuclei mostly meteoric particles produces noctilucent clouds (NLC). Many investigations show the dust layers (Berger and Von Zahn 2002) and their relation with PMSE (Eremenko et al 2005). Different dust particle sizes make the difference in the visibility of NLC and PMSE (Eremenko et al 2005).
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