Description: The annual cycle of the components of the water and heat balances in the Lake Ladoga watershed is analyzed using outputs of 14 atmospheric general circulation models run in the framework of the international Atmospheric Model Intercomparison Project (AMIP). The model results are compared with observational data. The surface air temperature, short- and long-wave surface radiation balances, total cloud cover, precipitation, and water balance (precipitation minus evaporation) are considered for the lake and its watershed. The rms errors in the annual cycles of the water-balance components and their seasonal and interannual variability are estimated for each model. The simulated and observed data, accumulated throughout 1980-1988, agree within 20-30%.

Description: An analysis of intraseasonal probability distribution functions (PDFs) of temperature is performed using the results of various numerical experiments based on the global three-dimensional climate model developed at the Institute of Atmospheric Physics, Russian Academy of Sciences. It is noted that the main contribution to the intraseasonal variability of-surface air temperature in different regions, in particular, in Eurasia, is made by meridional (longitudinal) periodic structures in the field of temperature that arise due to the spatial resonance between synoptic waves and a wave associated with inhomogeneous properties of the underlying surface (land and ocean alternation along latitudinal belts). A comparison between empirical and model PDFs in different seasons shows that the model PDFS are, on the whole, insufficiently good agreement with the empirical PDFs (except in the winter season). An analysis of the tendencies of change in both the properties of temperature disturbances generated in the model and the intraseasonal PDFs for different regions with a doubled content of atmospheric carbon dioxide-shows that significant changes in the PDFS are characteristic for transition seasons. Specifically, the tendency of enhanced-PDF maxima corresponding to rather large-temperature deviations is noticed.

Description: The problem of the world greatest lake, the Caspian Sea, level changes attracts the increased attention due to its environmental consequences and unique natural characteristics. Despite the huge number of studies aimed to explain the reasons of the sea level variations the underlying mechanism has not yet been clarified. The important question is to what extent the CSL variability is linked to changes in the global climate system and to what extent it can be explained by internal natural variations in the Caspian regional hydrological system. In this study an evidence of a link between the El Nino/Southern Oscillation phenomenon and changes of the Caspian Sea level is presented. This link was also found to be dominating in numerical experiments with the ECHAM4 atmospheric general circulation model on the 20th century climate.

Description: Numerical results of global climate models are used to infer possible changes in regional hydrologic cycle characteristics, including precipitation and river runoff, in the 21st century. Both coupled atmosphere-ocean general circulation models and a climatic model of intermediate complexity, forced by scenarios of an anthropogenic increase in the atmospheric greenhouse cyas content, are used. The model results show that the precipitation amounts considerably increase in the high latitudes, in particular, over Eurasia, under anthropogenic warming in the 21st century. This is associated primarily with a large increase in the winter precipitation intensity, especially over northeastern Eurasia. The changes in summer precipitation differ widely, with a large neoative trend occurring in the midlatitudes. This trend is associated with corresponding changes in the probability of wet days. Despite a decline in summer precipitation over a large Eurasian region, the precipitation intensity increases. The relative contribution of intense precipitation to the total precipitation amount increases as well. Model estimates are presented for possible changes occurring in the 21st century in precipitation and river runoff over various regions, including the basins of the Volga, the Caspian Sea, the Neva, Lake Ladoga, the Ob, Yenisei, and Lena rivers. On the whole, the precipitation and runoff in these basins, as well as their variability, are found to generally increase in the 21st century against the background of considerable interannual and interdecadal variability. The average runoffs of the Volga, Ob, Yenisei, and Neva rivers somewhat decline in the first half of the 21st century in the general circulation climate models, whereas no such decline is found for the Lena runoff.

Description: The sensitivity of the hydrological cycle to changes in orbital forcing and atmospheric greenhouse gas (GHG) concentrations is assessed using a fully coupled atmosphere-ocean-sea ice general circulation model (Kiel Climate Model). An orbitally-induced intensification of the summer monsoon circulation during the Holocene and Eemian drives enhanced water vapor advection into the Northern Hemisphere, thereby enhancing the rate of water vapor changes by about 30% relative to the rate given by the Clausius-Clapeyron Equation, assuming constant relative humidity. Orbitally-induced changes in hemispheric-mean precipitation are fully attributed to inter-hemispheric water vapor exchange in contrast to a GHG forced warming, where enhanced precipitation is caused by increased both the moisture advection and evaporation. When considering the future climate on millennial time scales, both forcings combined are expected to exert a strong effect.

Description: Numerical experiments with the ECHAM5 atmospheric general circulation model have been performed in order to simulate the influence of changes in the ocean surface temperature (OST) and sea ice concentration (SIC) on climate characteristics in regions of Eurasia. The sensitivity of winter and summer climates to OST and SIC variations in 1998-2006 has been investigated and compared to those in 1968-1976. These two intervals correspond to the maximum and minimum of the Atlantic Long-Period Oscillation (ALO) index. Apart from the experiments on changes in the OST and SIC global fields, the experiments on OST anomalies only in the North Atlantic and SIC anomalies in the Arctic for the specified periods have been analyzed. It is established that temperature variations in Western Europe are explained by OST and SIC variations fairly well, whereas the warmings in Eastern Europe and Western Siberia, according to model experiments, are substantially (by a factor of 2-3) smaller than according to observational data. Winter changes in the temperature regime in continental regions are controlled mainly by atmospheric circulation anomalies. The model, on the whole, reproduces the empirical structure of changes in the winter field of surface pressure, in particular, the pressure decrease in the Caspian region; however, it substantially (approximately by three times) underestimates the range of changes. Summer temperature variations in the model are characterized by a higher statistical significance than winter ones. The analysis of the sensitivity of the climate in Western Europe to SIC variations alone in the Arctic is an important result of the experiments performed. It is established that the SIC decrease and a strong warming over the Barents Sea in the winter period leads to a cooling over vast regions of the northern part of Eurasia and increases the probability of anomalously cold January months by two times and more (for regions in Western Siberia). This effect is caused by the formation of the increased-pressure region with a center over the southern boundary of the Barents Sea during the SIC decrease and an anomalous advection of cold air masses from the northeast. This result indicates that, to estimate the ALO actions (as well as other long-scale climatic variability modes) on the climate of Eurasia, it is basically important to take into account (or correctly reproduce) Arctic sea ice changes in experiments with climatic models.