Vyacheslav Khon

Wave heights in the 21st century Arctic Ocean simulated with a regional climate model

While wave heights globally have been growing over recent decades, observations of their regional trends vary. Simulations of future wave climate can be achieved by coupling wave and climate models. At present, wave heights and their future trends in the Arctic Ocean remain unknown. We use the third-generation wave forecast model WAVEWATCH-III forced by winds and sea ice concentration produced within the regional model HIRHAM, under the anthropogenic scenario SRES-A1B. We find that significant wave height and its extremes will increase over different inner Arctic areas due to reduction of sea ice cover and regional wind intensification in the 21st century. The opposite tendency, with a slight reduction in wave height appears for the Atlantic sector and the Barents Sea. Our results demonstrate the complex wave response in the Arctic Ocean to a combined effect of wind and sea ice forcings in a climate-change scenario during the 21st

Response of the hydrological cycle to orbital and greenhouse gas forcing

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.

Climate Changes in Siberia

This chapter provides observational evidence of climatic variations in Siberia for three time scales: during the past 10,000 years, during the past millennium prior to instrumental observations, and for the past 130 years during the period of large-scale meteorological observations. The observational evidence is appended with the global climate model projections for the twenty-first century based on the most probable scenarios of the future dynamics of the major anthropogenic and natural factors responsible for contemporary climatic changes. Historically, climate of Siberia varied broadly. It was both warmer and colder than the present. However, during the past century, it became much warmer; the cold season precipitation north of 55°N increased, but no rainfall increase over most of Siberia has occurred. This led to drier summer conditions and to increased possibility of droughts and fire weather. Projections of the future climate indicate the further temperature increases, more in the cold season and less in the warm season, significant changes in the hydrological cycle in Central and southern Siberia (summer dryness), ecosystems’ shifts, and changes in the permafrost distribution and stability. Observed and projected frequencies of various extreme events have increased recently and are projected to further increase. While in the north of Siberia, contemporary models predict warmer winters at the end of the twenty-first century and paleoreconstructions hint to warmer summers compared to the present warming observed during the period of instrumental observations. These three groups of estimates are broadly consistent with each other.

Tropical circulation and hydrological cycle response to orbital forcing

The intensity of the two major atmospheric tropical circulations, the Hadley and Walker circulation, has been analyzed in simulations with the Kiel Climate Model (KCM) of the early Eemian and the early Holocene, both warmer climate epochs compared to the late Holocene, or pre-industrial era. The KCM was forced by changes in orbital parameters corresponding to the early and late Holocene (9.5kyr BP and pre-industrial) and the early Eemian (126kyr BP). An intensification of the Southern Hemisphere (SH) winter Hadley cell and a northward extension of its rising branch, the Intertropical Convergence Zone, relative to pre-industrial are simulated for both warm periods. The Walker circulations rising branch is shifted westward towards the Indian Ocean due to an increased zonal tropical sea surface temperature (SST) gradient across the Indo-Pacific Ocean, which drives enhanced easterlies over this region. The simulated vertically-integrated water vapor transport across the Equator shows the strongest response for the SH winter (boreal summer) Hadley cell over the Pacific Ocean due to an enhanced cross-equatorial SST gradient in the tropical Pacific during the early Holocene and the early Eemian. The orbitally-induced increase of the cross-equatorial insolation gradient in the tropical Pacific leads to a strengthening (weakening) of the wind speed and enhanced (reduced) evaporative cooling over the southern (northern) tropical Pacific, which reinforces the initial radiatively-forced meridional SST gradient change. The increased cross-equatorial insolation gradient in combination with the strong wind-evaporation-SST feedback and changing humidity are important mechanisms to enhance the SH winter Hadley circulation response to orbital forcing. nKey Points: nIntensification of the SH winter Hadley cell for the early Holocene and Eemian. nWalker circulations rising branch is shifted westward towards the Indian Ocean. nWES feedback plays key role in intensification of the Hadley circulation.

Variations in the Ice Cover of the Arctic Basin in the 21st Century Based on Model Simulations: Estimates of the Perspectives of the Northern Sea Route

Trends in variations of the ice cover of the ArcticBasin were analyzed based on the daily data of simula-tions for the 21st century to estimate possible perspec-tives of the Northern Sea Route. Numerical simulationsusing the coupled atmosphere–ocean general circula-tion model (AOGCM) ECHAM5/MPI-OM were usedin the analysis [1, 2] under a sufficiently aggressiveSRES-A2 scenario [3] of anthropogenic emission ofgreenhouse gases into the atmosphere.Variation in the sea ice area in the Arctic Ocean isone of the key factors and indicators of climaticchanges in the Arctic. The processes of ice formationand melting are related to a number of physical factors.Ice formation depends not only on the meteorologicalfactors that influence cooling of the ocean, but also onthe characteristics of the upper ocean layer, in particu-lar its temperature, salinity, and thickness. A transitionfrom the ice-free regime to the ice regime is related tothe reconstruction of the vertical structure of the oce-anic layer with the formation of a halocline, which lim-its significantly the vertical exchange [4].According to the satellite data (see, for example,http://nsidc.org), since the end of the 1970s, the mini-mal area of sea ice in the Arctic basin in Septemberdecreased annually by 60000 km