Regional temporal gravity field variations from GRACE products with a special look on to Turkey
19/09/2016 | 16:30 | Session 1: Current and future satellite gravity missions
Author(s): Nevin Betul Avsar, Bihter Erol and Senol Hakan Kutoglu
Nevin Betul Avsar, Bihter Erol and Senol Hakan Kutoglu
Temporal variations in the Earth’s gravity field are the result of mass transport and redistribution within the dynamic Earth system. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has significantly contributed to improve the knowledge of dynamic processes of the Earth. In this study, temporal gravity field variations are analyzed in the region covering Turkey as well (having the latitudes of 30°N<ϕ<50°N and longitudes of 20°E<λ<60°E). In order to detect the gravity field parameters and water storage changes in the region, the Release 03 first version (RL03-v1) of the Centre National d’Etudes Spatiales/Groupe de Recherches de Géodésie Spatiale (CNES/GRGS) time-variable gravity field models are employed as well as comparing with the Jet Propulsion Laboratory (JPL) monthly Mascon grids (JPL-RL05.1M). The RL03-v1, based on GRACE and LAser GEOdynamics Satellite-1/2 (LAGEOS-1/2) data, consists of the monthly sets of spherical harmonic coefficients up to degree/order 80. These monthly solutions do not need the additional filtering. The Mass Concentration blocks (or “mascons”) provides an alternative to solving for gravity variations in terms of spherical harmonics as the native basis function. Unlike the RL05 unconstrained spherical harmonic solutions, the constrained mascon solutions typically do not need to be de-striped or smoothed. A better separation of land and ocean signals is advantage of mascon solution.
Beside the comparisons of the GRACE monthly solutions, the Total Water Storage (TWS) variations are validated using time-series based on WaterGAP Global Hydrology Model (WGHM) and Global Land Data Assimilation System (GLDAS-1) land surface models. The found results are interpreted under consideration of remote sensing meteorological data. The purpose of study is two-fold. As a performance validation of GRACE spherical harmonics and mascon approaches in comparison to the land surface models is aimed at first, in addition to a focused look to the critical basins specifically in terms of the increasing/decreasing TWS trend in the interested region specifically in Turkey is taken into account as another purpose in this contribution.
Variations at the considered gravity field parameters (gravity anomaly, geoid undulation) and TWS in the extended region based on GRACE coefficients are calculated using the International Center for Global Gravity Field Models (ICGEM) Calculation Service from August 2002 to June 2014 in varying spatial resolutions. Thus, 143 monthly time series of the variables are constituted, separately, containing 6 missing solutions.
The trend and seasonal periodicities in the time series are identified by a method based on the Least Squares Adjustment. The linear trend, phase and amplitude of the annual variations are then examined and compared. The results showing increasing/decreasing linear trend of the variations over the region for the 12-year period are indicated and specifically interpreted considering the meteorological and other Earth phenomena that may affect the basin showing the extreme variations.