Variation Characteristics Of The Tropical Indian Ocean-Western Pacific Atmospheric Water Cycle And Its Impact On Summer Precipitation In Eastern China

Using the monthly reanalysis datasets of NCEP/NCAR for 1958-2015,and the observed monthly mean precipitation and air temperature of 160 stations in China provided by the National Climate Center of the China Meteorological Administration,the characteristics of the atmospheric water cycle in the tropical Indian Ocean-western Pacific(60°-140°E,10°S-30°N)and its impact on summer precipitation to eastern China were analyzed from the aspects of water vapor transport and water vapor source and sink in this paper.Firstly,we use a multivariate empirical orthogonal function identifying the two major modes of anomalous water vapor transport over the tropical Indian Ocean-western Pacific from the significant global warming since the 1980s.The first mode(EOF1)shows anomalous water vapor transport along the anticyclone from the tropical Western Pacific to eastern China over the South China Sea and the bay of Bengal respectively.Anomalous water vapor converge over the middle and lower reaches of Yangtze River valley with significant upward movement.These anomalies were more contributed to the precipitation over the middle and lower reaches of Yangtze River valley.The second mode(EOF2)shows the anomalies of an anti-cyclonic water vapor transport from the tropical India ocean along Arabia sea,India Peninsula,Indo-China Peninsula,and the anomalies of a cyclonic water vapor transport appeared over Southern China,corresponding with the anomalous water vapor convergence and ascending motion over Southern China,which is more conducive to precipitation there.Secondly,the difference between the two major modes of anomalous water vapor transport before and after significant global warming is further compared.The results show that two major modes of anomalous water vapor transport over the tropical Indian Ocean-western Pacific(60°-140°E,10°S-30°N)experienced a significant interdecadal change in the mid-1980s.The first mode(EOF1)shows that the anti-cyclonic water vapor transport over the northwestern Pacific moves significantly southward after the mid-1980s.Before the mid-1980s,the anomalous water vapor originates from the subtropical western Pacific and moves through the South China Sea and the Bay of Bengal to eastern China.However,the anomalous water vapor mainly originates from the tropical western Pacific and moves through the South China Sea to eastern China after the mid-1980s.The second mode(EOF2)reflects the enhanced effect of the anomalous water vapor transport over the tropical Indian Ocean on East Asia after the mid-1980s.Before the mid-1980s,the distribution of the water vapor anomalies is uneven over the tropical Indian Ocean and the magnitude of water vapor is relatively small,so it has a weak effect on rainfall over East Asia.After the mid-1980s,anomalous anti-cyclonic water vapor transport originates from the tropical Indian Ocean and moves along the Arabia Sea,Indian Peninsula and Indo-China Peninsula and then forms an anomalous cyclonic water vapor transport over South China,these processes contribute to rainfall anomalies over South China.Furthermore,the possible causes of the interdecadal transition are investigated for the two major modes.The significant interdecadal transition in anomalous water vapor transport is associated with the enhanced effect of the sea surface temperature(SST).Before the mid-1980s,the relationships between the two major modes and the SST of the tropical oceans are relatively weak.After the mid-1980s,the EOF1 becomes significantly regulated by the El Nino-Southen Oscillation(ENSO)in the previous winter,and the positive(negative)phase of the principal component of the first mode(PCI)corresponds to significantly positive(negative)SST anomalies over the tropical northern Indian Ocean and Maritime Continent during the same period.For EOF2,the anomalous water vapor transport over the tropical Indian Ocean is related to the enhanced interannual variability of tropical Indian Ocean dipole(TIOD)after the mid-1980s.On this basis,we have also explored the factor of the main modes of the anomalous water vapor source and sink over the tropical Indian Ocean-Western Pacific during summer.We found that the main mode of the anomalous water vapor source and sinks over the tropical Indian Ocean-western Pacific mainly include three key regions:Bay of Bengal,Marine Continent,and the Northwestern Pacific.The Bay of Bengal and Marine Continent are anomalous water vapor sources,and the northwestern Pacific is an anomalous water vapor sink.Water vapor source and sink anomalies over the Bay of Bengal are mainly affected by TIOD over the same period.The water vapor source and sink of northwestern Pacific is mainly regulated by the development phase of ENSO.Anomalous water vapor source and sink over the Maritime Continent are jointly affected by the two factors.