Simulation of seasonal anomalies of atmospheric circulation using coupled atmosphere-ocean model

A coupled atmosphere-ocean model intended for the simulation of coupled circulation at time scales up to a season is developed. The semi-Lagrangian atmospheric general circulation model of the Hydrometeorological Centre of Russia, SLAV, is coupled with the sigma model of ocean general circulation developed at the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), INMOM. Using this coupled model, numerical experiments on ensemble modeling of the atmosphere and ocean circulation for up to 4 months are carried out using real initial data for all seasons of an annual cycle in 1989–2010. Results of these experiments are compared to the results of the SLAV model with the simple evolution of the sea surface temperature. A comparative analysis of seasonally averaged anomalies of atmospheric circulation shows prospects in applying the coupled model for forecasts. It is shown with the example of the El Niño phenomenon of 1997–1998 that the coupled model forecasts the seasonally averaged anomalies for the period of the nonstationary El Niño phase significantly better.     

Simulation of modern climate with the new version of the INM RAS climate model

The INMCM5.0 numerical model of the Earth’s climate system is presented, which is an evolution from the previous version, INMCM4.0. A higher vertical resolution for the stratosphere is applied in the atmospheric block. Also, we raised the upper boundary of the calculating area, added the aerosol block, modified parameterization of clouds and condensation, and increased the horizontal resolution in the ocean block. The program implementation of the model was also updated. We consider the simulation of the current climate using the new version of the model. Attention is focused on reducing systematic errors as compared to the previous version, reproducing phenomena that could not be simulated correctly in the previous version, and modeling the problems that remain unresolved.     

Simulation of snow cover characteristics with atmospheric general circulation models

A short review of snow cover parametrizations used in different atmospheric general circulation models is given. The results of comparison of 20-year mean integral characteristics of snow cover for North America and Eurasia obtained in three Russian models in the AMIP-2 experiments with observations and reanalysis data are analyzed. Results of the models of the Hydrometeorological Centre of Russia, the Institute of Numerical Mathematics of the Russian Academy of Sciences, and the Voeikov Main Geophysical Observatory are used. It is shown that all models better reproduce snow cover characteristics of Eurasia than those of North America, and snow area is reproduced with smaller errors than snow mass. It is also shown that the fall and winter snow cover formation is simulated more closely to the reference data than the spring snowmelt. It is also shown that 20-year mean snow cover changes in watersheds of the Siberian Ob, Yenisei, and Lena rivers are well reproduced in all models. In the fall and winter period of snow cover formation, the model results are close to one another. During a spring rapid snowmelt, the model of the Hydrometeorological Centre is closer to the reference data.     

Simulation of the Atlantic Ocean seasonal variability, using a quasi-isopycnic model

The paper discusses the data derived from a numerical experiment on the ocean’s response (between the equator and 64°N) to the seasonal variability of the atmospheric forcing (wind and heat flux through the ocean surface). A multilayer (7 layers) non-linear model is used incorporating the upper mixed layer interacting with the internal layers in the regimes of entraining and subduction. The restructuring of the layer composition, the currents and temperature variability, as well as the alternation of the entrainment and subduction regimes are analysed. Translated by Vladimir A. Puchkin.     

Atmosphere-ocean general circulation model with the carbon cycle

Results from numerical experiments with an atmosphere-ocean general circulation model coupled to the carbon evolution cycle are analyzed. The model is used to carry out an experiment on the simulation of the climate and carbon cycle change in 1861–2100 under a specified scenario of the carbon dioxide emission from fossil fuel and land use. The spatial distribution of vegetation, soil, and oceanic carbon in the 20th century is generally close to available estimates from observational data. The model adequately reproduces the observed growth of atmospheric CO₂ in the 20th century and the uptake of excess carbon by land ecosystems and by the ocean in the 1980s and 1990s. By 2100, the atmospheric CO₂ concentration is calculated to reach 742 ppmv under emission and land-use scenario A1B. The feedback between climate change and the carbon cycle in the model is positive, with a coefficient close to the mean of all the current models. The ocean and land uptakes of the CO₂ emission by 2100 in the model are 25 and 19%, which are also close to the mean over all models.     

Simulation of changes in global ozone and atmospheric dynamics in the 21st century with the chemistry-climate model SOCOL

The solar climate ozone links (SOCOL) three-dimensional chemistry-climate model is used to estimate changes in the ozone and atmospheric dynamics over the 21st century. With this model, four numerical time-slice experiments were conducted for 1980, 2000, 2050, and 2100 conditions. Boundary conditions for sea-surface temperatures, sea-ice parameters, and concentrations of greenhouse and ozone-depleting gases were set following the IPCC A1B scenario and the WMO A1 scenario. From the model results, a statistically significant cooling of the model stratosphere was obtained to be 4–5 K for 2000–2050 and 3–5 K for 2050–2100. The temperature of the lower atmosphere increases by 2–3 K over the 21st century. Tropospheric heating significantly enhances the activity of planetary-scale waves at the tropopause. As a result, the Eliassen-Palm flux divergence considerable increases in the middle and upper stratosphere. The intensity of zonal circulation decreases and the meridional residual circulation increases, especially in the winter-spring period of each hemisphere. These dynamic changes, along with a decrease in the concentrations of ozone-depleting gases, result in a faster growth of O₃ outside the tropics. For example, by 2050, the total ozone in the middle and high latitudes approaches its model level of 1980 and the ozone hole in Antarctica fills up. The superrecovery of the model ozone layer in the middle and high latitudes of both hemispheres occurs in 2100. The tropical ozone layer recovers far less slowly, reaching a 1980 level only by 2100.     

Exponential model of the seasonal thermocline

An exponential model of the seasonal thermocline is suggested within the framework of an integral hydrodynamic model of the upper ocean. The seasonal thermocline is discriminated as a boundary layer of finite thickness against the background of an asymptotic boundary layer described by an exponent. A self-similar distribution of the dimensionless temperature versus dimensionless depth is found. Its comparison with the dependence obtained previously (cubic parabola) provides a deviation of 10%. Thus, the exponential model of the seasonal thermodcline describes perfectly the temperature-depth distribution using field data.Translated by Mikhail M. Trufanov.     

Variations of the seasonal behavior of geostrophic circulation in the Black Sea

On the basis of the results of processing of the archival hydrological data, we analyze the seasonal behavior of geostrophic circulation in the Black Sea and its long-term variations. It is shown that the variations of currents on the decadal time scales with different manifestations in different seasons lead to changes in the characteristics of the seasonal course of geostrophic circulation in the second half of the last century. The intensification of winter circulation and weakening of summer circulation observed since the mid-1970s result in the increase in the amplitude of the annual course of current velocity on the sea surface. We also discuss possible causes of variations in the intensities of geostrophic currents in the Black Sea.     

On the formation of atmospheric seasonal precipitation in the Black Sea region

The climatic features of the formation of precipitation and their correlation with the baric situation in the Atlantic-European sector are studied on the basis of the data of the Sevastopol and Feodosiya coastal hydrometeorological stations. As the source data, we use the data arrays of daily precipitation at these stations in 1900–2005 and the data of reanalysis of the fields of atmospheric pressure in the Atlantic-European sector. The comparative statistical analysis of daily precipitation for the wet and dry summer and winter seasons and the estimates of extremely high levels of precipitation for the specified periods of repeatability are presented. The existence of the dependence of occurrence of wet and dry winter seasons in Sevastopol and Feodosiya on the large-scale baric fields in the Atlantic-European sector is confirmed. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 43–51, July–August, 2008.     

Simulation of climate changes in the 20th–22nd centuries with a coupled atmosphere-ocean general circulation model

The results of numerical experiments with a coupled atmosphere-ocean general circulation model on the reproduction of climate changes during the 20th century and on the simulation of possible climate changes during the 21st–22nd centuries according to three IPCC scenarios of variations in the concentrations of greenhouse and other gases, as well as the results of the experiments with the doubled and quadruple concentrations of CO₂, are considered. An increase in the near-surface air temperature during the 20th century and the features of the observed climate changes, such as warming in 1940–1950 and its slowing down in 1960–1970, are adequately reproduced in the model. According to the model, the air-temperature increase during the 22nd century (as compared to the end of the 20th century) varies from 2 K for the most moderate scenario to 5 K for the warmest scenario. This estimate is somewhat lower than the expected warming averaged over the data of all models presented in the third IPCC report. According to model data, in the 22nd century, under all scenarios, at the end of summer, a complete or almost complete sea-ice melting will occur in the Arctic. According to the model, by the year 2200, the sea level will vary by 20 to 45 cm as compared to the level at the end of the 20th century.     

Deep convection in the ocean general circulation model: Variability on the diurnal,seasonal, and interannual time scales

Features of geographical localization and of temporal variability of convective mixing were examined based on numerical experiments with the general ocean circulation model developed at the Hydrometeorological Research Center of the Russian Federation. The computations were performed using 6-h data on atmospheric forcing, which allows one to simulate the variability in a broad range of time scales—from diurnal to interannual. On the whole, the results of the numerical experiments are consistent with the available scarce observational data available on the deep convection in the North Atlantic. A pronounced regionalization of the deep convection in the open ocean is noted, as well as a significant spatial and temporal intermittence of convective events on time scales from a day to a few days. On the interannual time scale, a correlation is recognized with the variations of the atmospheric forcing and with the hydrophysical conditions in the ocean, in particular, with the cyclonic circulation within the baroclinic layer.     

Study of the low-frequency variability of the atmospheric general circulation with the use of time-dependent empirical orthogonal functions

The theory of both time-and space-dependent empirical orthogonal functions (EOFs) is outlined from a common point of view as a discrete version of the Karhunen-Loeve expansion. EOF techniques are used to process the results of a 1300-day-long numerical experiment in the mode of perpetual January with a daily step. As a result, the component determined by internal hydrothermodynamic processes was isolated from the general variability of the atmospheric circulation. To isolate intraseasonal variability (a winter season), the principal components of the 500-hPa height field were processed with a filter close to a π-shaped filter isolating the frequency band 0.1–0.01 day^?1. The spatial principal components were analyzed via the method of time-dependent EOFs. The spectral characteristics obtained can characterize the intraseasonal low-frequency variability and agree partially with empirical data.