SPATIAL-TEMPORAL STRUCTURES OF TREND AND OSCILLATORY VARIABILITIES OFPRECIPITATION OVER NORTHERN EURASIA

Combinations of statistical analyses including principal component ana lysis, and uni-and multivariate singular spectrum analyses, were carri ed out to characterize the spatial-temporal structures of trend and in terannual oscillatory variabilities of precipitation over the major no rth-flowing river basins in the former Soviet Union. The series of mon thly precipitation were corrected for the biases of precipitation meas urement due to the gauge-type change and changes in observing procedur es. An upward trend was found in the monthly precipitation series for the last half century. This upward trend was stronger in the North Dvi na and Pechora River basins, and in the Ob-Irtysh River basins, but mu ch weaker (still upward, though) in the Yenisey-Lena River basins. The notable increases of precipitation over the southwestern part-the Vol ga and Ural River basins-were found to be due at least in part to the upward phase of some quasi-century periodicity. Generally speaking, th e precipitation increases appeared to be more apparent during the cold seasons in the western half of the sector, while in the eastern part, it appeared to be equally or more notable during summer. On the inter annual timescales, signals of 4-5-yr and quasi-biennial oscillations w ere found in the space-time-dependent precipitation series. The 4-5-yr oscillation was quite apparent over the entire Northern Eurasian sect or, being stronger over the southeastern and western parts. This oscil lation appeared to propagate eastward. The quasi-biennial oscillation was generally weaker; it was very weak during the 1955-65 period. This oscillation was relatively stronger in the western half of the sector and weaker over the eastern half.