Polar mesospheric summer echoes (PMSE) is the phenomenon of anomalous radar echoes found between 80 and 90 km in altitude from May through early August in the Arctic, and from November through to February in the Antarctic. These strong radar echoes are associated with the extremely cold temperatures that occur above continental Antarctica during the summer. Rocket and radar measurements indicate that a partial reflection from a multitude of ion layers and constructive interference causes at least some of the PMSE.
Generally PMSE exhibits dramatic variations in height and intensity as well as large variations in
Doppler shift. PMSE exhibit strong signal power enhancements of scattering cross section at VHF radar frequencies in the range 50 MHz to 250 MHz, at times even to over 1 GHz, that occur in summer at high latitudes. The peak PMSE height is slightly below the summer mesopause temperature minimum at 88 km, and above the noctilucent cloud (NLC) and/or
polar mesospheric cloud (PMC) layer at 83–84 km. The usual instrument for observing PMSE is a
VHF Mesosphere-
Stratosphere-
Troposphere
The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
(MST)
radar
Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...
, although
LIDARs and
sounding rockets have also been used.
PMSE is believed to be caused by structural irregularities in the
ionospheric
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays a ...
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
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
In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere ...
and turbulence as possible explanations.
PMSE occurs in both the Arctic and Antarctic regions, and is sometimes accompanied by
noctilucent clouds
Noctilucent clouds, or night shining clouds, are tenuous cloud-like phenomena in the upper atmosphere of Earth. When viewed from space, they are called polar mesospheric clouds (PMCs), detectable as a diffuse scattering layer of water ice crysta ...
.
See also
*
Ionogram
An ionosonde, or chirpsounder, is a special radar for the examination of the ionosphere. The basic ionosonde technology was invented in 1925 by Gregory Breit and Merle A. Tuve and further developed in the late 1920s by a number of prominent phys ...
References
External links
Polar mesosphere summer echoes (PMSE): review of observations and current understanding
224 MHz observations
First observations of Polar Mesosphere Summer Echoes (PMSE) above Davis
Antarctic PMSE
Radio frequency propagation
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