Vertical motion at TEHN (Iran) from Caspian Sea and other environmental loads. (December 2018) - Wang, Song-Yun
Highlights: We compare GPS heights and predicted load deformation at GPS station TEHN in Iran at both seasonal and long-term time scales. We combine GRACE, altimetry of Caspian Sea level change and numerical model prediction to quantify different loads at TEHN. We identify seasonal time scale differences in TEHN height time series and discuss possible causes. Abstract: We compare Global Positioning System (GPS) height time series at GPS station TEHN in Tehran, Iran, with predicted load deformation from various sources, including the Caspian Sea, the atmosphere, terrestrial water storage (TWS), the oceans, and glacial isostatic adjustment (GIA). The study covers the period October 2004 to December 2015, and uses data from the Gravity Recovery and Climate Experiment (GRACE), satellite altimetry, and data-assimilating climate models. Predicted load deformation agrees well with an average of 4 GPS height time series (JPL, SOPAC, MEaSUREs and NGL) at both seasonal and longer timer time scales. At seasonal time scales, changes in atmospheric pressure and TWS are dominant, while groundwater depletion and Caspian Sea level change account for about 85% of the ∼1 mm/yr average uplift rate. TWS loading derived from GRACE mascon solutions leads to better agreement with GPS results (in combination with other components) than that from GRACE spherical harmonics solutions, benefited from improved accuracy and spatial resolution of GRACE mascons. The four GPS height time series show good consistency at long-term time scales, but significantly large discrepancy at seasonal time scales for undocumented reasons. We discuss possible error sources for GPS observations and loading computation.