Open AccessNoctilucent cloud observed in late April at South Pole Station: Temperature anomaly or meteoritic debris?
Author(s) -
Warren Stephen G.,
Thomas Gary E.,
Hernandez G.,
Smith Roger W.
Publication year - 1997
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/96jd02513
Subject(s) - mesopause , solstice , meteoroid , geology , debris , atmospheric sciences , airglow , mesosphere , ice nucleus , meteor (satellite) , environmental science , astrobiology , physics , meteorology , stratosphere , geodesy , latitude , oceanography , nucleation , thermodynamics
A sunlit cloud was observed near the horizon at South Pole Station (90°S), four months after summer solstice in 1992, at a solar depression angle of 14.6°. The angular location of the transition from sunlit to twilit cloud in the photograph establishes the cloud height at about 80 km. The cloud extended horizontally at least from 81° to 85°S and from 40°W to 20°E. The probable origin of this cloud by formation of water‐ice crystals near the mesopause suggests that mesospheric temperatures occasionally deviate by at least 70 K from their climatological means. An alternative explanation that the cloud was a debris cloud formed by disintegration of a reentering man‐made satellite is ruled out. A debris cloud from an entering meteoroid is a possible explanation but would be unprecedented. Hydroxyl airglow emissions at the south pole in May give a frequency of 1% for mesopause temperatures below 155 K, consistent with the rarity of out‐of‐season sightings of noctilucent clouds in Antarctica.