Integrated firn elevation change model for glaciers and ice caps Björn Saß*, Tobias Sauter, Matthias Braun FriedrichAlexanderUniversität ErlangenNürnberg (FAU), Germany *[email protected]
1 BACKGROUND 2 MODEL a 4 The test site The model is implemented in What is the change in height by Vestfonna Ice Cap (VIC) (~2340 km²) on Python 2.7 and is based on a the densification of firn on Nordaustlandet, north east of Svalbard. surface energy and snowpack Vertical spanning: 0 630 m asl glaciers and ice caps? [5] model (COSIMA ). Mean elevation: 386 m asl Geodetic elevation change [4,7] measurements are a promising tool [6] Mean ELA: 380 m asl (S N) [2] Forcing: subdaily reanalysis to derive high resolution mass (MAR[1]) data (fig. a): The VIC is a polythermal ice cap with a dome balances of glaciers and ice caps. air temperature [K] like shape and gentle slopes. Most outlet Up to now, geodetic mass incoming shortwave radiation [W m2] glaciers calve into surrounding seas. balances inherit an uncertainty relative humidity [%] Melting can occur up to summit in summer which occurs when converting air pressure [hPa] season and mass balance year starts in geodetic volume change into wind speed [m s1] September, with ablation period from June to glacier mass balance. The allphase precipitation [m] August. [2] inaccuracy results from an cloud cover fraction. inadequate conversion factor The VIC showed almost balanced conditions (density) which neglects altitude Model concept: in the last two decades, while the outlets were dependent firn density variations, steady retreating, with the exception of the re firn layer thickness and not advance of the largest outlet glacier towards homogenous density variations NW (surge). [2,10,11] with varying climate conditions.
To improve the accuracy of glacier [7] 3 hourly firn elevation change [m] of modelpoints (fig. a) Firn thickness was 1996 10 m at summit , mass balances measured in recent studies suggest it to be 15 20 m thick geodetic manner we develop a MAR 1 [4]. Melt water percolation and refreezing play transferable firn elevation change 535 m asl a major role on the ice cap.
model to minimize this systematic (RES)[8] error. The main scope of the firn MAR 2 27 km 386 model are short term GMBs (35 m asl
yr) due to a high variability in the [m] 5 CONCLUSION [13] Firn compaction [m]: dρ MAR 3 possible conversion factor . 15 km 230 m asl For calibration and validation we have to run sensitivity tests against insitu 3 RESULTS dM/dt = (dh/dt dρ/dt) * S * ρice MAR 4 7 km [2] 456 measuerments (stakes (SMB) , snow pits Exemplary model run: m asl d (density & depth)[3], RES (stratigraphy)[8], We selected four MAR modelpoints (fig. a) for a 9 year test phase, with firn cores (aging)[4])(fig. c) to tune the 20 m depth, 0.5 m layer thickness, an idealized bottom temperature of b e parametrization. 3.7°C[7] and one year spin up. Fig. b gives a brief overview about firn c elevation change in meter. The firn evolution fits to the homogeneous Insitu data archive (IPY KINNVIKA) The elevation gain in the interior of VIC snowpack pattern over the ice cap reported by Möller et al. (2011)[3]. approve the observed accumulation Acknowledgements: increase in Northeastern Svalbard and a TanDEMX data provided under DLR AO [11,14] XTI_GLAC0264 and corresponding elevation increase uphill . Geodetic measurements: XTI_GLAC6770. Glacier outlines are taken out of the Global Land Ice The second project part comprises an extensive analysis of the geodetic Measurements from Space (GLIMS) Glacier Database mass balance of the test site. Fig. d & e give a first impression on how (http://www.glims.org/). TDM DEMs for Dec 2010 and April 2012 are ICESat elevation tracks are published by NASA National the elevation of two TanDEMX DEMs compared to one ICESat track Snow and Ice Data Center ready, but they show no significant elevation (NSIDC) Distributed Active Archive Center (DAAC). (spring 2004) has changed between 2004 and 2012. The firn compaction CryoSat2 data are change (signal is in error bar)! TDM DEM postprocessed by V. Helm (AWI Bremerhaven). Detailed signal is not yet removed, nevertheless, mind the thickening on the Info about IPY Kinnvika on for 2015 is in process. http://www.kinnvika.net. We give thanks to Mariusz northwestern face of the ice cap (fig. e). Grabiec and Marco Möller for insitu data provision.
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