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A model-based reconstruction of recent Siberian climate - focusing on snow cover
Eine modellbasierte Rekonstruktion des rezenten Klimas in Sibirien mit Fokus auf die Schneebedeckung
Dokument 1.pdf (5.588 KB)
Freie Schlagwörter (Englisch):
Regional climate model , COSMO-CLM , hindcast, Siberia , snow cover
Storch, Hans von (Prof. Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
Snow cover is an important feature of the terrestrial landscape in Siberia. Variability and changes of snow cover have profound implications for surface energy and water balance, first due to its high short-wave albedo, high thermal emissivity and low heat conductivity, and second due to the control of evaporation, water storage, soil moisture, river discharge and freshwater transport. The snow properties affect moreover the soil temperature and thus the thermal state of permafrost and the biogeochemical cycle.
Monitoring of Siberian climate parameters, including those for snow cover, is complicated by the lack of in situ measurements, especially in the arctic regions. The sparse station density and limited length of data records makes it difficult to obtain a detailed regional overview of past and ongoing changes. The need of long-term climate information with less spatial and temporal gaps has motivated the effort to generate a model-based reconstruction of recent Siberian climate using the regional model COSMO-CLM (CCLM).
Although CCLM has been used for several areas, no simulations have been conducted for Siberia before. Therefore, different sensitivity experiments have been performed to identify important regional-specific processes and related adjustments that can be used for a specific model configuration for Siberia. These adjustments are an increased soil column depth down to 92m, the application of the multi-layer snow model and the reduction of the minimal heat diffusion that has implications on the turbulence parameterization to better account for the stable conditions during the winter high pressure system.
One hindcast simulation has been conducted from 1948-2010 at about 50 km grid spacing using NCEP-R1 as driving global reanalysis to obtain a reconstruction of 63 years and to investigate long-term regional changes of climate parameters focusing on snow cover. A second climate reconstruction has been performed for comparison using ERA-40 reanalysis as forcing that range from 1958-2001.
In terms of snow cover, snow water equivalent (SWE) is one important parameter to consider. CCLM-NCEP1 is able to provide more realistic SWE information from 1987-2010 relative to the global driving data NCEP-R1 and thus show a clear added value when compared with the satellite-derived SWE product of ESA GlobSnow as reference. The temporal consistency of CCLM is higher than that presented by ERA-Interim and NCEPR2.
In general, changes and interannual variations of mean SWE are characterized by strong spatial and seasonal variability. According to CCLM-NCEP1, regional averages for the period of 1981-2010 show only minor changes of SWE during fall, whereas during winter and spring stronger changes occur with varying patterns throughout the region. Both hindcasts show stronger interannual variations of snow cover extent during the transition seasons spring and fall than in winter. During spring a negative tendency is evident since the early 1980s, which has ceased in recent years.