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Rainfall variations induced by the lunar gravitational atmospheric tide and their implications for the relationship between tropical rainfall and humidity
Author(s) -
Kohyama Tsubasa,
Wallace John M.
Publication year - 2016
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 - 10.1002/2015gl067342
Subject(s) - relative humidity , atmospheric sciences , humidity , lapse rate , environmental science , adiabatic process , precipitation , saturation (graph theory) , climatology , physics , geology , meteorology , thermodynamics , mathematics , combinatorics
Classical tidal theory predicts that the lunar gravitational semidiurnal tide ( L 2) should induce perturbations in relative humidity (RH). Adiabatic expansion in divergent flow in advance of the L 2 pressure minimum cools the air and reduces its saturation vapor pressure, thereby increasing the rate of condensation in saturated air parcels and causing the relative humidity (RH) of unsaturated parcels to rise. Here we detect a statistically significant L 2 signature in precipitation rate ( P ) in a 15 year, eight times daily, global precipitation data set acquired in the Tropical Rainfall Measuring Mission. Consistent with tidal theory and with the notion that L 2 modulates P mainly by perturbing RH, P varies out of phase with pressure, and it increases at a rate of about 10% per 1% increase in RH. These measurements thus provide a measure of the sensitivity of P to planetary‐scale changes in RH. Analysis of solar semidiurnal ( S 2) tidal statistics yields similar results.