HR: 1340h
AN: G33B-1247    [Abstracts]
TI: Detection of Characteristic Precipitation Anomaly Patterns of El Nino / La Nina in Time- variable Gravity Fields by GRACE
AU: * Heki, K
EM: heki@mail.sci.hokudai.ac.jp
AF: Dept. Natural History Sci., Hokkaido Univ., N10 W8, Kita-ku, Sapporo-city, 060-0810, Japan
AU: Morishita, Y
EM: s040105r@ec.hokudai.ac.jp
AF: Dept. Natural History Sci., Hokkaido Univ., N10 W8, Kita-ku, Sapporo-city, 060-0810, Japan
AB: GRACE (Gravity Recovery and Climate Experiment) satellites, launched in March 2002, have been mapping monthly gravity fields of the Earth, allowing us to infer changes in surface mass, e.g. water and ice. Past findings include the ice mass loss in southern Greenland (Luthcke et al., 2006) and its acceleration in 2004 (Velicogna and Wahr, 2006), crustal dilatation by the 2004 Sumatra Earthquake (Han et al., 2006) and the postseismic movement of water in mantle (Ogawa and Heki, 2007). ENSO (El Nino and Southern Oscillation) brings about global climate impacts, together with its opposite phenomenon, La Nina. Ropelewski and Halpert (1987) showed typical precipitation patterns in ENSO years; characteristic regional-scale precipitation anomalies occur in India, tropical and southern Africa and South America. Nearly opposite precipitation anomalies are shown to occur in La Nina years (Ropelewski and Halpert, 1988). Here we report the detection of such precipitation anomaly patterns in the GRACE monthly gravity data 2002 - 2007, which includes both La Nina (2005 fall - 2006 spring) and El Nino (2006 fall - 2007 spring) periods. We modeled the worldwide gravity time series with constant trends and seasonal changes, and extracted deviations of gravity values at two time epochs, i.e. February 2006 and 2007, and converted them into the changes in equivalent surface water mass. East Africa showed negative gravity deviation (-20.5 cm in water) in 2006 February (La Nina), which reversed to positive (18.7 cm) in 2007 February (El Nino). Northern and southern parts of South America also showed similar see-saw patterns. Such patterns closely resemble to those found meteorologically (Ropelewski and Halpert, 1987; 1988), suggesting the potential of GRACE as a sensor of inter-annual precipitation anomalies through changes in continental water storage. We performed numerical simulations of soil moisture changes at grid points in land area incorporating the CMAP precipitation data, NCEP/NCAR temperature data, and potential evapotranspiration calculated after Thornswaite (1942). We took out the soil moisture anomalies in 2006 February and 2007 February by modeling its time series in the same way as gravity, and confirmed that they are quantitatively consistent with GRACE gravity deviations. Out study demonstrates that satellite gravity data can detect not only of global warming signals in high latitude regions but also inter-annual climate changes in low and middle latitude continental regions.
DE: 1217 Time variable gravity (7223, 7230)
DE: 1223 Ocean/Earth/atmosphere/hydrosphere/cryosphere interactions (0762, 1218, 3319, 4550)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1866 Soil moisture
DE: 4522 ENSO (4922)
SC: Geodesy [G]
MN: 2007 Fall Meeting