Low-frequency variations in the atmospheric branch of the global hydrological cycle

Abstract

According to the atmospheric water balance equation, the divergence of the water vapor flux is responsible for the exchange of water vapor between its source and sink regions. Because the water vapor flux divergence is primarily determined by the divergent circulation, time variations of the global hydrological cycle reflect the pronounced low-frequency modes of the global divergent circulation, that is, the annual and intraseasonal (30-60 day) modes. The annual variation of the hydrological cycle is illustrated. Two years (1979-80) of daily precipitation estimates from the Goddard Laboratory for Atmospheres and 14 years (1979-92) of upper-air data generated by the Global Data Assimilation System at the National Meteorological Center are used in making quantitative estimates of the annual and intraseasonal variations in the global hydrological cycle. -from Authors