Numerical simulation study of the Madden Julian Oscillation influences on spring precipitation in China

The influences of the two propagating phases of the Madden-Julian Oscillation (MJO) on spring precipitation in eastern China are studied through ensemble numerical simulations with the multi initial fields by using the IAP AGCM （Institute of Atmospheric Physics Atmospheric General Circulation Model）. When anomalous diabatic heating (strong MJO convection) is respectively introduced in an area over the equatorial eastern Indian Ocean and equatorial western Pacific, the anomalous patterns of spring precipitation in eastern China are reproduced very well as shown in the model’s results. And the numerical simulation results are similar to our previous data diagnoses, that is, corresponding to the 2-3 (6-7) phases, there is more precipitation in the middle and lower reaches of the Yangtze River (less precipitation in the most parts of eastern China). The analyses of the simulated geopotential height, wind, divergence, vorticity and water vapors transport showed that the genesis of anomalous spring rainfalls in eastern China is closely related to anomalous pattern of the atmospheric circulation over the western North Pacific/East Asia caused by anomalous diabatic heating (strong MJO convection activity). Through analyzing daily response fields, the physical process and mechanism for spring precipitation anomalies in eastern China due to the MJO activity are discussed. It is shown that atmosphere responses excited by anomalous diabatic heating over the equator are not only the Rossby and Kelvin wave patterns in the equatorial atmosphere, but also the Rossby wave-train pattern in the atmosphere from the tropics to middle-high latitudes. If the location of anomalous diabatic heating is different, the response pattern in the atmosphere will be different and its influence on weather and climate is also different. When there is anomalous convection heating over the equatorial eastern Indian Ocean (corresponding to the 2-3 phases of the MJO), the atmospheric Rossby wave train response will lead to an anomalous large scale circulation over the western North Pacific / East Asia, which is favourable to causing more precipitation in the middle and lower reaches of the Yangtze River. When there is anomalous convection heating over the equatorial western Pacific (corresponding to the 6-7 phases of the MJO), the atmospheric Rossby wave-train response will lead to an anomalous large-scale circulation over the western North Pacific/East Asia, which is unfavourable to causing spring precipitation in the most parts of eastern China.