Temporal And Spatial Distribution Of The Interannual Variability Of The Global Precipitation In The Tropical Region

Temporal and spatial distribution of the global precipitation in the tropical region and its possible leading factors were analyzed by using the method of Season-reliant Empirical Orthogonal Function and power spectrum analysis based on the National Center for Environmental Prediction/National Center of Atmospheric Research (NCEP/NCAR) reanalysis data and Climate Prediction Center Merged Analysis of Precipitation (CMAP) data (31.250S-31.250N,1.250-358.750E) from 1979~2006. According to the eigenvalues of the S-EOF modes in the tropical precipitation derived for the period of 1979-2006, we chose and discussed the first 2 modes in detail which are well distinguished from each other and from the rest modes at the 95% confidence level. And in further study, the influences of the anomalies of the sea surface tempreture and the atmosphere circumfluence on the spatial distribution of the global precipitation in the tropical region were also studied.In the present thesis, we used S-EOF analysis to extract the major modes of tropical precipitation. The first two modes account for, respectively, 23.7% and 12.2% of the total variance and we found that the two modes are well distinguished from each other and from the rest modes at the 95% confidence level. The two modes are considered statistically distinguishable and significant. We have confined our analysis to the two major modes. The characteristic of the spatial distribution for the first mode is that in the region of the tropical maritime continent, the equatorial America, and the equatorial Atlantic Ocean, there are the minus anomalies in all seasons, in the region of the central-west ern Pacific there is a positive anomaly, and in the eastern equatorial Pacific Ocean, especially in the austral eastern equatorial Pacific Ocean, there is the a little anomaly. The seasonal variabilities of the minus anomaly and the positive anomaly showed from the boreal summer, the intension of the anomalies start to increase, reach their maximum in the winter, then decrease, and in the next summer, they become most weak. The largest fractional variance of the first mode is in the region of the maritime continent, and the equatorial Pacific Ocean, and seasonal changes indicate in the spring and summer less than its in the fall and winter.The characteristic of the spatial distribution for the first mode is that in the region of the central-western Pacific and about 200S there are the narrow positive anomalies, in the region of the central-eastern Pacific in the austral hemisphere there is a narrow negative anomaly, and in the region of the southeast Pacific and the southern Atlantic there is a little anomaly. But the region of the maritime continent and the Indian Ocean depend on the evolution of seasons. The power spectrum analysis showed that the first principal component has a single spectral peak 4.5 year and the second principal component exhibits a single spectral peak centered at the six-year and nine-year.The major factor which leads to the first mode of the tropical precipitation is the seasonal evolution of the El Nino. Regression of the corresponding fields with reference to the first principal component shows that in the Pacific Ocean, the distribution characteristic of the SST is on low level, negative anomaly in the western Pacific Ocean, and positive anomaly in the central-easten Pacific Ocean. There is a positive anomaly high in the western Pacific Ocean, while a negative anomaly high in the eastern Pacific Ocean, then generate the abnormal westerly wind, which bring the moisture from the tropical central-western Pacific Ocean to the eastern. According to the conservation of mass, there must be the convergence in the western Pacific Ocean, which could strengthen here Hadley circulation. Meantime, there is a pair of non-symmetrical cyclonic anomalies leads the meridional wind converging in the western Pacific Ocean, and the diverging in the eastern Pacific Ocean. Because of the double influences, the first mode of the tropical precipitation only locate in the single narrow equatorial region, and with development of the El Nino and the westerly wind, this zone of the precipitation could cross all of the Pacific Ocean, reaching the coast of the America.In the high level, easterly wind appears in the eastern Pacific Ocean, and the positive high dominates all over the central-eastern Pacific Ocean. The divergence of the positive high anomaly intensify the ascending in the region. The vertical velocity also indicates all the eastern Pacific Ocean appears ascending, which in turn intensify the positive anomaly of the tropical precipitation.The major factor which leads the second mode of the tropical precipitation is the seasonal evolution of the El Nino Modoki. Regression of the corresponding fields with reference to the second principal component shows that in the Pacific Ocean, the distribution characteristic of the SST is positive anomaly in the central Pacific Ocean while positive anomaly in the western and easten Pacific Ocean. A negative strong anomaly low locates in the middle latitude of the austral Pacific Ocean, while the subtropical high in the southeast Pacific Ocean and the high in the Australia become stronger in the spring, which make the abnormal westerly wind appear in the western Pacific Ocean, and the the abnormal easterly wind appear in the western Pacific Ocean. The westerly and easterly anomaly converged in the central-western Pacific Ocean, which lead here positive anomaly of the precipitation. The westerly wind from the western Pacific Ocean divided into two branches near the 1800E, the northeastward in the boreal hemisphere, and the southeast in the austral hemiphere, which bring the moisture from the western Pacific Ocean to its middle. According to the wind anomaly, in the middle of the Pacific Ocean, there are two positive anomaly of the precipitation, one of which locates in the northern hemisphere representing the ITCZ and another of which locates in the southern hemisphere representing the SPCZ. On the high level, the divergence of the abnormal high near the dataline strengthen the ascending motion in the centre of the Pacific Ocean, and the vertical velocity also affirm that the centre of the Pacific Ocean is the ascending region and the western and eastern Pacific Ocean is the descending region, which lead to the wet anomaly in the central-west Pacific Ocean and dry anomaly in the western and eastern Pacific Ocean.