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 The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...

. 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 Noctilucent clouds (NLCs), 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 ...

(PMC) layer at 83–84 km. The usual instrument for observing PMSE is a VHF

Mesosphere The mesosphere (; ) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define limits: it be ...

Stratosphere The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher ...

Troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

(MST)

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

, although

LIDAR Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...

s and

sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are often ...

s 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 ...

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

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 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 the oc ...

and turbulence as possible explanations. PMSE occurs in both the Arctic and Antarctic regions, and is sometimes accompanied by

noctilucent clouds Noctilucent clouds (NLCs), 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 ...

. A much less frequent phenomena, related to PMSE, is known as Mesospheric Summer Echoes (MSE). MSE can be observed at middle latitudes, e.g., along the

Baltic coast The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

. Many years of MSE observations using VHF

radars Radar is a system that uses radio waves to determine the distance ('' ranging''), direction (azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircr ...

Northern Germany Northern Germany (, ) is a linguistic, geographic, socio-cultural and historic region in the northern part of Germany which includes the coastal states of Schleswig-Holstein, Mecklenburg-Vorpommern and Lower Saxony and the two city-states Hambur ...

show that MSE occurs less frequently because the formation mechanism requires the transport of very cold polar air by equatorward mesospheric winds.

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 {{science-stub

See also

References

External links