Relationship between the Modes of Winter Tropical Pacific SST Anomalies and the Intraseasonal Variations of the Following Summer Rainfall Anomalies in China

In present study,EOF analysis and extended singular value decomposition (ESVD) analysis are performed to explore the relationship between the winter tropical sea surface temperature anomalies (SSTAs) in the Pacific and the following summer rainfall anomalies in China.The two leading modes of winter tropical SSTAs in the Pacific are the SSTAs pattern characterized by "positive anomalies in the East and negative anomalies in the West" like the typical eastern Pacific El Nio and negative anomalies in the West and the central Pacific warming pattern characterized by "positive anomalies in the central region but negative anomalies in the East and West".The intraseasonal variations of the rainfall anomalies during the following summer in China that are associated with the eastern Pacific warming mode are characterized by positive anomalies south of the Yangtze River and negative anomalies in the Yangtze-Huai River Valley in June,and negative anomalies in South China and positive anomalies in the Yangtze River Valley and North China in July and August.In contrast,after the central Pacific warming mode,the corresponding intraseasonal variations of China’s summer rainfall are characterized by a nearly consistent pattern during the three summer months,which is positive in the South China coast and North China and negative in the Yangtze River Valley except for the positive anomalies in the Yangtze-Huai River Valley in July.These results may provide a reference for the seasonal prediction of the summer drought and flood distributions in China.

Current observation and analysis based on mooring systems in the Andaman Sea

The basic structure and intraseasonal evolution of currents in the southeastern Andaman Sea was analyzed based on data collected in 2017 from two subsurface moorings(C1 and C5).Periodic variation in the upper ocean currents of the Andaman Sea was investigated by combining observational and satellite data.Mooring observations show that rapid changes of current speed and direction occurred in May and June,with a significant increase in current velocity at the C1 mooring.In the second half of the year,southward flow dominated at the C1 mooring,and alternating northward and southward flows were evident at the C5 mooring during the same period but the northward flow prevailed in boreal winter.In addition,analysis of the power spectra of the upper currents revealed that the tidal period at both moorings is primarily semidiurnal with weaker energy than that of the low-frequency currents.The upper ocean currents at the C1 and C5 moorings exhibited intraseasonal variation of 30-60 d and 120 d,while the zonal current at the C1 mooring exhibited a notable period of approximately 180 d.Further analysis indicated that the variability of currents in the Andaman Sea is influenced primarily by equatorial Kelvin waves and Rossby wave packets.Moreover,our results suggest that equatorial Kelvin waves from the eastern Indian Ocean entered the Andaman Sea in the form of Wyrtki Jets and propagated primarily along two distinct pathways during the observation period.In addition to coastal boundary Kelvin waves,it was found that a branch of the Wyrtki Jet that directly enters the Andaman Sea and flows northward along the slope of the continental shelf,and reflected Rossby wave packets by topography.

The Variations of Dominant Convection Modes over Asia, Indian Ocean, and Western Pacific Ocean during the Summers of 1997-2004

The NOAA daily outgoing longwave radiation （OLR） and the Global Precipitation Climatology Project （GPCP）daily precipitation data are used to study the variation of dominant convection modes and their relationships over Asia, the Indian Ocean, and the western Pacific Ocean during the summers from 1997 to 2004. Major findings are as follows： （1） Regression analysis with the OLR indicates the convective variations over Asian monsoon region are more closely associated with the convective activities over the western subtropical Pacific （WSP） than with those over the northern tropical Indian Ocean （NTIO）. （2） The EOF analysis of OLR indicates the first mode （EOF1） exhibits the out-of-phase variations between eastern China and India, and between eastern China and the WSP. The OLR EOF1 primarily exhibits seasonal and even longer-term variations. （3） The OLR EOF2 mostly displays in-phase convective variations over India, the Bay of Bengal, and southeastern China. A wavelet analysis reveals intraseasonal variation （ISV） features in 2000, 2001, 2002, and 2004. However, the effective ISV does not take place in every year and it seems to occur only when the centers of an east-west oriented dipole reach enough intensity over the tropical Indian and western Pacific Oceans. （4） The spatial patterns of OLR EOF3 are more complicated than those of EOF1 and EOF2, and an effective ISV is noted from 1999 to 2004. The OLR EOF3 implies there is added complexity of the OLR pattern when the effective ISV occurs. （5） The correlation analysis suggests the precipitation over India is more closely associated with the ISV, seasonal variations, and even longer-term variations than precipitation occurring over eastern China.

夏季对流和环流10-25天季内变化与西太平洋暖池热力状况的关系(英文)

This study focuses on the characteristics of 10-25-day oscillation associated with the interannual variability of the thermal state in the western Pacific warm pool. The time series of 10-25-day oscillation shows a distinct feature between warm (WARM case) and cold (COLD case) summers over the western Pacific warm pool. The significant negative relationship between the time series of 10-25-day convection anomalies in Warm and Cold cases appears over most of Asian-Pacific region manifesting the interactions between the convection on interannual and 10-25-day intraseasonal time scales. At the peak and trough stages of 10-25-day convection oscillation, a Gill-type low-level atmospheric circulation anomaly, cyclonic or anticyclonic. appears northwest of the convection anomaly. This relationship between the convection and circulation exists both in Warm case and in Cold case. However, at other stages rather than the peak and trough stages, there is no Gill-type circulation response, and the circulation anomaly shows a distinct feature between the Warm and Cold cases, although the convection oscillation exhibits a roughly similar feature.