Abstract:

The monthly gravity anomalies calculated by the GRACE Mission (NASA/GFZ Gravity Recovery And Climate Experiment) and precipitation data achieved by TRMM (Tropical Rainfall Measuring Mission) are compared and analyzed. The study area is the Amazon Basin which is located within 20S-15N and 285W-315W. The gravity anomalies are calculated at 500km altitude by the monthly spherical harmonic coefficients provided by UTCSR (the University of Texas, Center for Space Research) GRACE L-2 product. The GGM02S (Grace Gravity Model), which is achieved using 363-day data by UTCSR between April 2004 and December 2005, is then subtracted. To remove the tidal effects, low-order zonal coefficients are not included in the calculation whereas harmonic coefficients are used up to the degree 13 at 500km altitude. The study periods are between October 2002 and December 2003, without December 2002 and January 2003 due to the lack of GRACE data. The TRMM satellite was launched by NASA and NASDA (National Space Development Agency, Japan) in November 1997 for the purpose of researching and monitoring tropical precipitation as well as force and energy of atmospheric circulation which determines climate and weather patterns. The average TRMM measured precipitation for the period corresponding to GGM02S (between April 2004 and December 2005) is subtracted. Then, the differentials between the monthly TRMM precipitation and the average precipitation are used to calculate the gravity anomalies by Gauss-Legendre quadrature integration in spherical Earth coordinates at 500km altitude. In calculating the gravity anomalies, the total precipitation is divided by two because half of the precipitation is assumed to be evaporated. In making comparisons between GRACE and TRMM gravity anomalies in the Amazon Basin, good correspondence is shown for February and March which enjoys the most precipitation in a year, but other months display some differences. This is attributed to the influx of precipitation into the river. For calculating the amount of water flowing into the river, inversion by using the differences of GRACE and TRMM anomalies are implemented. From the result of this study, the periodic observation and calculation of global scale water storage mass balances are achieved by using GRACE and TRMM satellites which through forward modeling provide a better understanding of the hydroclimatology of the Amazon River and Basin.