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Venus nighttime hydrogen bulge
Author(s) -
Brinton H. C.,
Taylor H. A.,
Niemann H. B.,
Mayr H. G.,
Nagy A. F.,
Cravens T. E.,
Strobel D. F.
Publication year - 1980
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/gl007i011p00865
Subject(s) - thermosphere , venus , exosphere , atmosphere of venus , atmospheric sciences , orbiter , altitude (triangle) , hydrogen , ionosphere , solar wind , atmospheric escape , saturn , local time , physics , plasma , astrophysics , ion , astrobiology , geophysics , planet , astronomy , geometry , mathematics , quantum mechanics , statistics
The concentration of atomic hydrogen in the Venus thermosphere near 165km altitude and ∼18° north latitude has been derived from Pioneer Venus in situ measurements of n(H + ), n(O + ), n(O), and n(CO 2 ), under the assumption of chemical equilibrium. Altitude profiles of derived n(H) suggest that chemical equilibrium prevails to an altitude of at least 200km on the dayside and to 165 km on the nightside. Measurements below these limits were made by the ion and neutral mass spectrometers on the orbiter spacecraft between December 1978 and July 1979, while periapsis traversed a complete diurnal cycle. The hydrogen concentration is found to rise sharply at both terminators from a dayside value of ∼5 × 10 4 cm −3 , and to exhibit an asymmetric nightside distribution with a peak density in the predawn sector approximately 400 times greater than the dayside value. Analysis suggests that wind‐induced diffusion, combined with exospheric return flow, can account for the observed hydrogen behavior. The large day‐night temperature contrast enhances advective transport, which produces the large n(H) diurnal variation; the shift of the n(H) nighttime maximum toward dawn is caused by atmospheric superrotation.