This project is dealing with the estimation of present-day Earth’s mass transport and its redistribution by using observations from Gravity Recovery and Climate Experiment (GRACE) satellite mission. GRACE measures the gravity fluctuations which are primarily related to redistribution of water around the globe. GRACE data has yield profound new insights into melting rates of ice sheets and mountain glaciers, land hydrology, ocean circulation, and sea level rise.
In this project, first, the ice melting rate in the Greenlandic ice sheet is studied. This is done by analyzing the time series of monthly GRACE release 04 gravity field solutions from three different data sets, CSR (Center for Space Research), GFZ (Geoforschungszentrum), and JPL (Jet Propulsion Laboratory) with respect to their long-term temporal changes. The data are de-striped by applying a non-isotropic filter. Also, a method for reducing the leakage effects is developed. As an example, the ice mass balance is estimated of -163 ± 20 Gt/yr based on the CSR release 04 and smoothing by a parameter of a =1013 during April 2002 to February 2010. The results also show that the spatial distribution of the ice mass loss is changing with time and the ice mass loss is accelerating. For example, its acceleration is a rate of -32±6 Gt/yr2 during 2002 to 2011.
The second part of this project is concern with the determination of water mass changes in the Nordic Seas. It is determined by analyzing the time series of monthly GRACE level 2 release 04 data from GFZ during October 2002 to October 2010. The striping errors are reduced by using a non-isotropic filter and the data are smoothed by a parameter of a =1014 according to Gaussian smoothing radius of 530 km. The time series of water mass changes are used to study the steric sea height variations over the Nordic Seas during the same period of study. This is done by analyzing the time series of monthly sea level anomaly from ENVISAT (Environmental Satellite) altimetry data, cycles 10 to 93, among the time series of water mass changes. The results show that the interdisciplinary nature of the GRACE measurements have opened up the unique opportunity to enhance our knowledge on the interaction between Earth system components and their response to climate variability.
In the last part of this project, variations of the continental total water storage, total groundwater storage, and anthropogenic contributions across the Middle East are studied. By using a mascon analysis method and GRACE level 2 release 05 data from CSR during February 2003 to December 2012, the time series of total water storage, total ground water storage and anthropogenic contributions are estimated over this region. The region is subdivided to seven mascons including Iran, Iraq, Syria, eastern Turkey (east of 35º longitude), northern and southern Saudi Arabia (north and south of 25º latitude), and the region immediately west of Caspian Sea. The total groundwater storage, and anthropogenic contributions are separated from the total water storage by using the CLM4.5 (version 4.5 of the Community Land Model) hydrological model. The results show that Iran with a rate of 25±6 Gt/yr has the most groundwater loss rate during February 2003 to December 2012 in this region. The Iran’s rate of groundwater loss from the GRACE data is supported by an analysis of in situ well data from across Iran. The results also show that the GRACE mission is able to monitor monthly water storage changes within river basins and aquifers that are 200,000 km2 or larger in area, and, can contribute to water management at regional and national scales, and to international policy discussions as well.