Long-term Changes in the Main Components of Lake Khanka Water Regime

Changes in annual total precipitation and annual pan evaporation for the Lake Khanka water area during the period of 1949–2015 are analyzed based on observational data of weather stations within the lake basin. The reliability of the calculated values of characteristics affecting evaporation changes was confirmed by their comparison with observations at the 20-m² evaporation pan installed at Astrakhanka lake station. It is shown that against a background of significant interannual fluctuations of annual precipitation during the whole period under study, its trends are almost absent. However, a rather stable increase in annual precipitation value caused by the summer precipitation rise has been noted since the early 2000s. The value of annual pan evaporation decreased from 1949 to 2015, and the rate of its decrease till 1980 was higher than in the next period. Moreover, some evaporation increase has been observed in the recent decade. The main contribution to the evaporation change is made by wind speed changes which cause about 50% of evaporation variance. Air humidity deficit is the second affecting factor that determines a little over 20% of annual evaporation variance. It is demonstrated that the increase in annual precipitation is possible by the middle of the 21st century, while the change in annual evaporation from the Lake Khanka water area would be minimal. Under such changes in the main components of the lake water regime, no reduction of its level due to natural climate processes should be expected.     

Evapotranspiration in the basins of the Northern Dvina and the Western Dvina rivers and its variability

Considered is a possibility of using the previously developed method for estimating the evapotranspiration from the river basin based on the observations at the network of water- and soil-evaporation stations and on the data on the land use dynamics for the Northern Dvina and Western Dvina river catchments. It is demonstrated that the method enables to obtain rather realistic and reliable estimates both of evapotranspiration over the basin and of the contribution of different landscapes to its value. The value of evapotranspiration and its interannual variability depend not only on the trends in the fluctuations of evaporation from the water surface and the land surface, but also on the changes in landscape characteristics. The present paper is a continuation of the papers dealing with the study of the basins of the Volga and Don rivers started under V.S. Golubev’s leadership and participation.     

Evapotranspiration in the Don River basin and its variability

Issues concerning the use of earlier developed technique of estimating evapotranspiration from the river basins using observational results from the network of water-and soil-evaporation stations are considered. Some parameters of the calculations and the technique itself are specified. The dynamics of basic elements of the underlying surface of the Don basin participating in the process of evaporation and runoff formation is estimated. It is shown that evapotranspiration and its interannual variability depend on tendencies towards changes in evaporation from the water and land surface, on the one hand, and changes in landscape characteristics, on the other hand. The work continues similar studies started under the leadership of V.S. Golubev in the Volga River basin.     

Investigation of the Energy Balance in the Water–Air Boundary Layer under the Conditions of Developing Wind Waves

We present the results of the analysis of the energy balance in a wind–water system under the conditions of developing waves. Our investigation is based on the use of the experimental data obtained in a water channel and taken from the literature. We propose an expression for the energy balance between the air flow and wavy water surface based on the data of simultaneous measurements of the vertical wind profiles and drift currents and the parameters of waves for various fetches and indifferent density stratification.     

On Wind Profiles over Developing Wind Wave in the Water-Air Interface

The results of studying the vertical profile of wind velocity and the vortex-formation mechanism in the atmospheric layer immediately adjacent to the water surface under the condition of developing wind wave are considered. Materials of field and laboratory experiments are used.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 295–300.Original Russian Text Copyright © 2005 by Anisimova, Pokazeev, Soboleva, A. Speranskaya, O. Speranskaya.     

Wind-wave generation and the wind velocity structure in the air above a wavy water surface

Research results are presented, under natural and laboratory conditions, concerning the process of wind-wave generation. The complementary problem, the effect of waves on the structure of the wind field above them, is also studied.     

Interaction between Streams and Lower Surfaces of Ice Cover

The structure of the boundary layer is studied at the lower ice surface in Lake Baikal and the Moskva River. The Rossby parameter is used to compare the roughness of the lower ice surfaces in these water bodies. An attempt is made to estimate the thickness of the boundary layers under study.     

Evaluation of the AMIP soil moisture simulations

The Atmospheric Model Intercomparison Project (AMIP) conducted simulations by 30 different atmospheric general circulation models forced by observed sea surface temperatures for the 10-year period, 1979–1988. These models include a variety of different soil moisture parameterizations which influence their simulations of the entire land surface hydrology, including evaporation, soil moisture, and runoff, and their simulations of the energy balance at the surface. Here we compare these parameterizations, and evaluate their simulations of soil moisture by comparing them with actual observations of soil moisture, literally ground truth. We compared model-generated ‘data sets' and simulations of soil moisture with observations from 150 stations in the former Soviet Union for 1979–1985 and Illinois for 1981–1988. The spatial patterns, mean annual cycles, and interannual variations were compared to plant-available soil moisture in the upper 1 m of soil. The model-generated ‘data sets' are quite different from the observations, and from each other in many regions, even though they use the same bucket model calculation method. The AMIP model simulations are also quite different from each other, especially in the tropics. Models with 15-cm field capacities do not capture the observed large high latitude values of soil moisture. In addition, none of the models properly simulate winter soil moisture variations in high latitudes, keeping soil moisture constant, while observations show that soil moisture varies in the winter as much as in other seasons. The observed interannual variations of soil moisture were not captured by any of the AMIP models. Several models have large soil moisture trends during the first year or two of the AMIP simulations, with potentially large impacts on global hydrological cycle trends and on other climate elements. This is because the simulations were begun without spinning up the soil moisture to the model climatology. The length of time it took for each to reach equilibrium depended on the particular parameterization. Although observed temporal autocorrelation time scales are a few months, some models had much longer time scales than that. In particular, the three parameterizations based on the Simple Biosphere model (SiB) had trends in some regions for virtually the entire AMIP simulation period.     

Redistribution of momentum fluxes on the water-air interface

We present the results of investigation of the transformation of a momentum flux coming from the atmosphere into a water reservoir and establish the relationship between the surface velocity of the drift current and the dynamic velocity of wind. For the initial stage of the development of wind waves, we propose a dependence that enables one to determine the momentum flux spent for an increase in the intensity of waves via the momentum flux coming into the water reservoir from the wind. The behavior of the ratio of the momentum flux spent for the increase in the intensity of waves to the total momentum flux coming from the atmosphere into the water is studied depending on the dimensionless fetch and age of waves. In our analysis, we used both our own experimental data and the data available from the scientific literature. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Potential and visible evaporation and its variations in European Russia over the recent 50 years by experimental data

Variations in pan evaporation in European Russia from 1951 to 2010 have been studied, and regions with specific variations of potential evaporation have been identified. It is shown that evaporation decseases all over the territory under consideration, and intensity of its decreasing up to the late 1970s was far in excess of that in the decades that followed. The decrease in the variations in evaporation may be regarded as an indicator of reduction of intensity of heat and moisture exchange between the underlying surface and the atmosphere. A new characteristic of the moisture regime of the territory, i.e., visible evaporation, was introduced to characterize, in this case, the amount of free moisture in the atmosphere that can be involved in the terrestrial water cycle. The humidity of the territory in the European Russia has shown to have increased since 1966. Regions where changes in the moisture regime show common patterns have been identified and the specific features of humidity distribution in different natural zones of European Russia have been assessed.