Polar mesospheric summer echoes
- Polar mesospheric summer echoes
Polar mesospheric summer echoes (PMSE) is the phenomenon of anomalous radar echoes found in the polar latitudes from May through early August between 80-90 km in altitude. The usual instrument for observing PMSE is the a VHF Mesosphere-Stratosphere-Troposphere (MST) radar, although lidars and sounding rockets have also been used.
Generally PMSE exhibits dramatic variations in height and intensity as well as large variations in Doppler shift. PMSE occur in both the Arctic and Antarctic regions. PMSE is sometimes accompanied by noctilucent clouds.
PMSE is believed to be caused by structural irregularities in the ionospheric electron density at lower altitudes. The exact cause of PMSE is not yet known, although theorists have proposed steep electron density gradients, heavy positive ions, dressed aerosols, gravity waves and turbulence as possible explanations.
See also
* [http://www.copernicus.org/EGU/acp/acp/4/2601/acp-4-2601.pdf Polar mesosphere summer echoes (PMSE): review of observations and current understanding]
* [http://www.eiscat.se/raw/pmse.html PMSE at EISCAT] 224 MHz observations
* [http://www.aad.gov.au/default.asp?casid=14831 First observations of Polar Mesosphere Summer Echoes (PMSE) above Davis] Antarctic PMSE
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