Title: Moisture circulation anomalies over East Asia and their association with the El Niño-southern oscillation
Authors: Li, Xiuzhen (李秀珍)
Abstract: In this study, abnormal moisture circulation over East Asia and its association with the El Niño-Southern Oscillation (ENSO) are investigated.
Over East China, abnormal moisture circulation played a key role in the two rainfall shifts in the past few decades, with the first shift caused by weakened southerly transport over East China and the second shift related to the convergence of the outflows of two abnormal anticyclonic moisture circulations over the western North Pacific (WNP) and Mongolia. It is abnormal meridional rather than zonal water vapor flux, wind rather than moisture disturbance, dominates the abnormal moisture supply.
Over South China, great west-to-east discrepancies appear in the moisture circulation. Meridional moisture transport dominates Southeast China, while the zonal one dominates Southwest China. In the decaying spring, ENSO imposes opposite impact on moisture convergence over Southeast and Southwest China. El Niño, by stimulating the Philippine Sea Anticyclone (PSAC) and weakening the East Asian winter monsoon (EAWM), favors moisture convergence over Southeast China; while La Niña, by strengthening the EAWM, benefits moisture convergence over Southwest China.
Summer moisture circulation over East Asia is dominated by two modes: one with an anomalous anticyclonic moisture circulation over the tropical-subtropical WNP and the other shows a sandwich-like pattern. They couple well with ENSO in a quasi-4-yr cycle, with the PSAC serving as a "bridge." The eastward migration of PSAC in the decaying phase of a sustained El Niño causes +EOF1, and the easterly wind anomaly to its south favors the transition to a La Niña. While the northeastward migration of PSAC to the subtropical WNP in the decaying phases of a newly established El Niño, plays a crucial role in stimulating the +EOF2, and the westerly south to the southern cyclone over the tropical Pacific benefits the sustained development of El Niño.
Great discrepancies appear in the impacts of CP (Central Pacific) and EP (Eastern Pacific) ENSO on moisture circulation over China. The influence of CP ENSO is strong in the developing summer and fall, and weak in the mature winter and decaying spring and summer; while the impact of EP ENSO is weak in the developing summer, and strong from fall to the
decaying summer. Distinctive WPSH, PSAC, WNP cyclone response modulated by locations of maximum SSTAs and teleconnection with the SSTAs over Indian Ocean are possible physical mechanisms causing different impacts on moisture circulation over China during EP and CP ENSO.
Notes: CityU Call Number: QC915 .L5 2013; xx, 198 p. : ill. (some col.) 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2013.; Includes bibliographical references (p. 176-194)
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