GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.3 - POSTER GNGTS 2023 the contrary, when not compensated, the single load element violates mass conservation (Bevis et al., 2016). REAR is optimized for the challenging task of computing deformations to a very high harmonic degree: indeed, the computationally intensive portions of REAR are multi-threaded with OpenMP to efficiently take advantage of modern multi-core systems. This feature is essential for the accurate evaluation of geodetic variables in response to surface mass variations of small spatial wavelength. Such approach is especially suitable for investigating the effects of present-day retreat of small glaciers and lakes evaporation due to climate change, as well as the impact of human infrastructures like dams. REAR computes the response to surface loads in two steps: 1. For a given SNREI model, REAR evaluates the solution for a finite size disk load of unit thickness that constitutes a discrete realization of the elastic Green’s function (Farrell, 1972). To this aim, the user shall configure the radius of the disk load, the range of load-observer distances, and shall provide an external set of deformation coefficients. 2. The Green’s functions are combined with a specific surface load model to obtain predictions of geodetic variables a set of user-supplied coordinates. If uncertainties on the surface load model are known, these are mapped into uncertainties on the modeled geodetic variables. REAR is released along with an User Guide that contains a brief introduction about the theory of the surface loading problem, and a detailed worked example in which is computed the present-day displacement of Greenland in response to recent ice mass loss (see Fig. 1). Here, to demonstrate the capabilities of REAR, we model the present-day elastic rebound in Greenland. Together with the Antarctic ice sheet, the Greenland ice sheet (GRIS) represents one of the only two ice sheets remained on the Earth after the last glacial maximum, reached between 26.5 and 19.0 kyrs ago (Clark, 2009). The GRIS, with its 7,2 m of sea level equivalent (Aschwanden et al., 2019), plays a fundamental role in the regulation of the Earth climate: its presence influences the ocean water temperature, salinity and currents (Driesschaert et al., 2007; Weijer et al., 2012), and its status regulates numerous climatological feedback (Box et al., 2012; Chu, 2014); hence, many research projects are currently monitoring its evolution. Among these, satellite missions like GRACE, ICESat1 and ICESat2 have contributed significantly, during last decades, to establish a complete and accurate picture of the mass balance of the Greenland ice sheet. We assumed as input surface load the mass balance M3 (Sørensen et al., 2011) obtained from data collected during ICESat1 mission, referring to the time period from October 2003 to March 2008, and shown in Fig.1. The file describing this mass balance, greeM3R.dat, is available in REAR folder DATA/. As we can see from Fig. 1, the highest rates are reached especially around the peripherical Glaciers (Kangerdlugssuaq Glacier [KG], Jakobshavn Isbræ [JI], the Helheim Glacier [HG] and the Southeast Glaciers [SG]) and are of the order of >2 m/yr; on the contrary, in the interior, it is possible to notice a slight accumulation, probably due to the increasing precipitation caused by a warmer climate (Velicogna and Wahr, 2006).