Abstract
This study investigated water balance components in the three major river basins of Siberia (the Lena, Yenisey, and Ob) based on the National Centers for Environmental Prediction (NCEP)–Department of Energy (DOE) Atmospheric Model Intercomparison Project II (AMIP-II) reanalysis. The primary focus is the nature of the interannual signatures of summer precipitation, moisture convergence, and runoff in individual basins, and their linkage to the large-scale water transport and circulation fields over northern Eurasia from 1979 to 1995. The temporal characteristics of the hydrological cycle and the associated large-scale circulation structure are discussed.
Some interesting features are found in the interannual variability of basin-scale hydrometeorological elements. In the Lena and Ob basins, the temporal signatures of both precipitation and moisture convergence indicate a cycle of approximately 6 to 8 yr. The mid- and late-summer runoff variation is significantly correlated with these two elements. Moreover, the time series of each element for the Lena is almost exactly out of phase with that for the Ob. The basin-averaged precipitation time series show that the relatively wet phases for the Lena occurred in the early and late 1980s, during relatively dry phases for the Ob. Similarly, the dry phases for the Lena and wet phases for the Ob occurred in the mid-1980s and early 1990s.
The structures of the large-scale moisture transport and circulation anomalies responsible for the precipitation variability for each basin are examined using regression analysis. The space–time fields of precipitation, moisture flux, and geopotential height anomalies are related to the basin-averaged precipitation index. Out-of-phase patterns of precipitation and circulation anomalies between eastern and western Siberia are evident in the regression maps. When the Lena basin is unusually wet, an anomalous cyclonic circulation accompanied by high positive precipitation anomalies is established over the basin, while an anomalous anticyclonic circulation with negative precipitation anomalies is produced over the Ob; the reverse situation is equally evident at other times. Thus, an east–west dipole structure of circulation and precipitation anomalies is formed over northern Eurasia. The “seesawlike” interchange of dry and wet regimes associated with this dipole pattern occurs between eastern and western Siberia on a timescale of about 6 to 8 yr. Regression patterns of geopotential height anomalies show good agreement with their summer leading mode derived from a rotated empirical orthogonal function analysis. These results imply that a large-scale mode of atmospheric teleconnective variability modulates the summer hydrological cycle in the northern Eurasian domain.
Corresponding author address: Dr. Yoshiki Fukutomi, JAMSTEC Yokohama Institute for Earth Sciences, 3173-25 Showamachi Kanazawa-ku, Yokohama City, Kanagawa 236-0001 Japan. Email: fukutomi@jamstec.go.jp
