Polar mesospheric clouds all tend to form at an extreme altitude range and are consequently not classified into height-related families.

# Polar mesospheric summer echoes ( PMSE ) have been studied, probing the mesosphere using the IRI as a powerful radar, and with a 28 MHz radar, and two VHF radars at 49 MHz and 139 MHz.

# REDIRECT Polar mesospheric clouds

Polar mesospheric clouds illuminated by the rising Sun.

Polar mesospheric clouds ( PMCs ) are a diffuse scattering layer of water ice crystals near the summer polar mesopause.

Polar mesospheric clouds generally increase in brightness and occurrence frequency with increasing

Polar mesospheric cloud observations have

Polar mesospheric summer echoes ( PMSE ) is the phenomenon of anomalous radar echoes found between 80-90 km in altitude from May through early August in the Arctic, and from November through to February in the Antarctic.

This means that noctilucent clouds form predominantly during summer when, counterintuitively, the mesosphere is coldest, therefore they can't be observed ( even if they are present ) inside the Polar circles because the Sun is never low enough under the horizon at this season at these latitudes.

* Polar stratospheric clouds

Polar stratospheric clouds or PSCs, also known as nacreous clouds (, from nacre, or mother of pearl, due to its iridescence ), are clouds in the winter polar stratosphere at altitudes of.

File: Polar Stratospheric Cloud veil type I. jpg | A veil of type I PSC, easily confused with cirrostratus clouds or tropospheric haze

File: Polar Stratospheric Cloud type I above Cirrus. jpg | A type I PSC ( white cloud above the orange tropospheric clouds ), showing fine horizontal structures in the veil.

Much of the biology in the area occurs along the major fronts of the current, the Subtropical, SubAntarctic, and the Antarctic Polar fronts, these are areas associated with well defined temperature changes.

There are six categories within the SSC scheme: Dry Polar ( similar to continental polar ), Dry Moderate ( similar to maritime superior ), Dry Tropical ( similar to continental tropical ), Moist Polar ( similar to maritime polar ), Moist Moderate ( a hybrid between maritime polar and maritime tropical ), and Moist Tropical ( similar to maritime tropical, maritime monsoon, or maritime equatorial ).

Polar unit vectors at two times t and t + dt for a particle with trajectory r ( t ); on the left the unit vectors u < sub > ρ </ sub > and u < sub > θ </ sub > at the two times are moved so their tails all meet, and are shown to trace an arc of a unit radius circle.

Polar bear and reindeer hunting in Greenland still occur but are regulated to avoid endangering the populations.

Such very rare events are known as Polar Cap Absorption ( or PCA ) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region.

Polar bears are genetically distinguishable in this region of the Arctic from those living elsewhere.

It should support modularity and hierarchies of classes ( Polar bears are bears, which are animals ).

Among the band's awards are an American Music Award in 2005, and the Polar Music Prize in 2006.

* Polar maps of the Arctic or Antarctic regions are conventionally centred on the pole ; the direction North would be towards or away from the centre of the map, respectively.

Distribution area from Polar overlaps with Coca-Cola of Northern New England in Massachusetts ; for example, Shaw's Supermarkets and Stop & Shop are generally supplied by Polar while Market Basket uses CCNNE.

1-liter bottles from CCNNE are short and squat while Polar are taller and skinnier.

Polar bears are believed rarely to travel beyond about 82 ° North owing to the scarcity of food, though tracks have been seen in the vicinity of the North Pole, and a 2006 expedition reported sighting a polar bear just from the Pole.

All four Circle_of_latitude # Major_circles_of_latitude | major circles of latitude that are defined by the Earth's tilt ( both Circle_of_latitude # Tropical_Circles | Tropical Circles and both Circle_of_latitude # Polar_Circles | Polar Circles ) will shift correspondingly.

Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene.

Purified phospholipids are commercially produced by companies like Lipoid, VAV Life Sciences, Avanti Polar etc.

Other public offices with presence on Svalbard are the Norwegian Directorate of Mining, the Norwegian Polar Institute, the Norwegian Tax Administration and the Church of Norway.

Polar bears are the iconic symbol of Svalbard, and one of the main tourist attractions.

The population of polar bears are locally recovering from the major culls of the 1960s and 1970s that came about due to the availability of snow scooters ; however, the Polar bear remains threatened at a global level, due to unsustainable levels of killing by humans and due to marine water pollution.

The mountains of the Polar Ural have exposed rock with sharp ridges though flattened or rounded tops are also found.

Both Polar and Nether-Polar Urals are typically Alpine ; they bear traces of Pleistocene glaciation, along with permafrost and extensive modern glaciation, that includes 143 extant glaciers.

The Nether-Polar Ural is wider, up to and higher than the Polar Ural, with the highest peaks of the Mount Narodnaya, the Mount Karpinsky ( Urals )) and the Manaraga ).

* 2008-" HiFlyer Polar Ice Expedition "-reaching the Gunnbjørn Fjeld summit, the highest peak in Greenland ( 3694 m ), with Leszek Cichy, Tomasz Walkiewicz, Mirosław Polowiec, Ryszard Rusinek.

* 1999 – NASA loses radio contact with the Mars Polar Lander moments before the spacecraft enters the Martian atmosphere.

However the mission failed with the loss of its mother ship, Mars Polar Lander after communication was lost after entry into Mars atmosphere on 3 December 1999.

The second letter describes the thermal characteristic of its source region: T for Tropical, P for Polar, A for arctic or Antarctic, M for monsoon, E for Equatorial, and S for superior air ( dry air formed by significant downward motion in the atmosphere ).

The Mars Climate Orbiter ( formerly the Mars Surveyor ' 98 Orbiter ) was a 338 kilogram ( 750 lb ) robotic space probe launched by NASA on December 11, 1998 to study the Martian climate, atmosphere, surface changes and to act as the communications relay in the Mars Surveyor ' 98 program, for Mars Polar Lander.

Because of vast amounts of water added to or removed from the oceans and atmosphere, the polar ice packs experience a significant impact from global changes in climate ; see " Polar ice packs " for details.

Scientists of the Research Unit Potsdam of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association have decrypted a mechanism in which a shrinking summertime sea ice cover changes the air pressure zones in the Arctic atmosphere and impacts on European winter weather.

This is in part because it is intermediary between the Hadley and Polar cells, with neither a strong heat source nor a strong cold sink to drive convection and, in part, because of the effects on the upper atmosphere of surface eddies, which act as destabilizing influences.

Intended to be the first spacecraft to penetrate below the surface of another planet, after entering the Mars atmosphere DS2 was to detach from the Mars Polar Lander mother ship and plummet to the surface using only an aeroshell impactor, with no parachute.

Polar region receive less intensive solar radiation because the sun's energy arrives at an oblique angle, spreading over a larger area, and also travels a longer distance through the Earth's atmosphere in which it may be absorbed, scattered or reflected, which is the same thing that causes winters to be colder than the rest of the year in temperate areas.

Polar twilight occurs in areas that are located at the inner border of the polar circles, where the sun will be on or below the horizon all day on the winter solstice, although there may still be enough light for normal outdoor activities during civil twilight because of light scattering by the upper atmosphere and refraction.