Abstracts for the 5th International GAME Conf.
3-5 October 2001
Aichi Trade Center
Nagoya Japan
Interannual Variability in the Summertime Water Balance of Three Major River Basins over Northern Eurasia: Evaluation in the NCEP/DOE AMIP-II Reanalysis
Yoshiki Fukutomi (1), Hiromichi Igarashi (2), Kooiti Masuda (3), Tetsuzo Yasunari (4)
(1) Frontier Research System for Global Change (FRSGC)
(2) Institute of Geoscience, University of Tsukuba
(3) FRSGC
(4) Institute of Geoscience, University of Tsukuba and FRSGC
An accurate estimation of water balance over the broad Eurasian continental area is one of the important missions for the GAME (GEWEX Asian Monsoon Experiment) -Siberia project, which is planned for understanding the interactive processes between atmosphere and land surface, and their relation to the climate signals. In particular, the nature of the large-scale water balance at seasonal through interannual timescales over northern Eurasia has been required to determine in order to understand their influences on not only the regional climate variability but also that outside the region.
This study investigates the water balance in the three major river (Lena, Yenisey, and Ob) basins based on the currently released NCEP/DOE AMIP-II reanalysis (Reanalysis2F@R2) in combination with the CPC merged analysis of precipitation (CMAP) data and the Russian river flow data obtained from the NCAR. Computation of the atmospheric water budget of individual river basin is performed for the 17-year period from 1979 through 1995. The vertically integrated moisture flux, its divergence, and precipitable water content are computed from the R2. The surface evaporation is also estimated as a residual of the budget equation. The runoff is defined as a river discharge at the mouth of a river. The characteristics of each quantities of the budget equation in their annual cycle and interannual variability are examined. Primary focus is placed on the annual cycle and summertime interannual variability of precipitation, moisture convergence, and runoff in individual basin, and their connection to the large-scale moisture transport fields over Eurasia.
As a result, the feature of the area averaged climatological annual cycle in water budget terms for the Lena basin is similar to that for the yenisey. The annual cycle of the moisture convergence for these basins has two maxima, that is, one occurs in May and another does in September (in October for the Yeisey). The precipitation is maximally increased whereas the moisture convergence is much decreased in July that indicates the surface evaporation is a main contributor to the regional water supply for precipitation during the summer season. On the other hand, the moisture convergence for the Ob becomes negative (divergent condition), and the evaporation largely exceeds the precipitation throughout June to August, which suggests this basin works as an apparent moisture source region during this season. The runoff peak is observed in June that is probably due to the snowmelt effect starting from the spring season, and leads one month to the precipitation maximum (in July) for all basins.
Some interesting signatures are shown in the summertime (JJA) interannual variability of hydrological elements. Over the Lena and Ob basin, temporal signatures of both precipitation and moisture convergence indicate the 7 to 8 year cycle. Biennial or ENSO-like (4 to 5 year) timescale signals are comparatively weak. The runoff variation is significantly correlated with these two elements. In addition, the timeseries of each element for Lena shows out of phase with that for Ob. This feature is supported by the 95% significant cross-correlation. The timeseries of precipitation indicates that the wet (dry) phases for Lena (Ob) occurs in 1981-83 and 1987-89. On the other hand, the dry (wet) phase for Lena (Ob) appears in 1984-86 and 1991-93. The regression analysis results based on the precipitation index shows that the spatial patterns of precipitation and moisture transport anomalies over the east Siberia is opposite to the west Siberia. The relationships between these interannual changes and the hemispheric or global circulations will also be discussed.
Submittal Information
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Frontier Research System for Global Change, JAMSTEC Yokohama Institute for Earth Sciences | |
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3173-25 Showa-machi Kanazawa-ku Yokohama-city Kanagawa 236-0001 | |
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