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Evidence of long term global decline in the Earth's thermospheric densities apparently related to anthropogenic effects
Author(s) -
Keating G. M.,
Tolson R. H.,
Bradford M. S.
Publication year - 2000
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2000gl003771
Subject(s) - atmospheric sciences , atmosphere (unit) , thermosphere , altitude (triangle) , environmental science , climatology , atmospheric temperature , atmosphere of earth , ionosphere , physics , geology , meteorology , geophysics , geometry , mathematics
A study was performed of the long‐term orbital decay of five Earth satellites with perigee altitudes averaging near 350km. To decouple long‐term trend measurements from the effects of solar variability, measurements were evaluated during the years of solar minimum (1976, 1986 and 1996). Atmospheric densities derived from these essentially global measurements showed substantial evidence of a decline averaging 9.8 ± 2.5% in thermospheric density over 20 years pointing toward a long‐term cooling of the upper atmosphere. Increases in greenhouse gases induced by human activity are hypothesized to warm the Earth's surface and lower atmosphere, but strongly cool the upper atmosphere. Assuming that the 10% increase in CO 2 over these 20 years caused cooling resulting in the 10% decline in density, a doubling of CO 2 could cause the thermospheric densities measured near 350km to decrease by a factor of 3. This decrease may shrink the altitude of a constant density surface by 40km before the end of the 21 st century.