Chongyin Li

Interdecadal Modulation of the Influence of La Nina Events on Mei-yu Rainfall over the Yangtze River Valley

The aim of this study was to investigate changes in the relationship between mei-yu rainfall over East China and La Niña events in the late 1970s, a period concurrent with the Pacific climate shift, using meiyu rainfall data and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. This relationship was modulated by the climate shift: Before the 1977/1978 climate shift and after the 1992/1993 climate shift, mei-yu rainfall levels were above normal in most La Niña years, whereas during the period 1979–1991, mei-yu rainfall was usually below normal levels in La Niña years.Both composite analyses and results from an atmospheric general circulation model show remarkable detail in terms of La Niña’s impacts on mei-yu rainfall in the late 1970s due to the change in the mean climatic state over the tropical Pacific. After the late 1970s, the tropical Pacific SSTs were warmer, and the mean state of low-level anticyclone circulation over the western North Pacific (WNP) weakened. Superimposed on La Niña-related cyclonic anomaly over the WNP, anticyclonic circulation weakened. Prior to the late 1970s, the mean state of low-level anticyclone circulation over the WNP was stronger and was less affected by La Niña-related anomalous cyclones. Anticyclone circulation may have brought moisture to the Yangtze River valley, leading to above-normal rainfall.

Effects of the East Asian summer monsoon on tropical cyclone genesis over the South China Sea on an interdecadal time scale

Tropical cyclone (TC) genesis over the South China Sea (SCS) during 1965–2004 was analyzed. The locations of TC genesis display evident seasonal changes, with the mean position of formation situated north of 15°N in summer (June-July-August) and south of 15°N in autumn (September-October-November). The TC genesis in summer underwent dramatic interdecadal variations, with more and less TC frequency during 1965–1974/1995–2004 and 1979–1993, respectively. In contrast, a significant interannual variation of TC genesis with a period of ∼4 years was observed in autumn.This study investigated the relationship of SCS TC genesis to the East Asian jet stream (EAJS) and the western North Pacific subtropical high (WNPSH) on an interdecadal time scale. Analysis and comparison of the impacts of the EAJS and the WNPSH on vertical wind shear changes indicate that changes in the WNPSH and EAJS intensity rather than EAJS meridional location are responsible for changes in TC genesis on an interdecadal time scale. Corresponding to a weaker EAJS, anomalous Rossby wave energy at upper levels displays equatorward propagation at midlatitudes and poleward propagation in the subtropics. This induces anomalous convergence and divergence of wave activity fluxes in East Asia around 30°N and the SCS, respectively. The anomalous divergence of wave activity fluxes reduces easterlies at upper levels over the SCS, which is favorable to TC genesis.

Water Vapor Transport and Moisture Budget over Eastern China: Remote Forcing from the Two Types of El Niño

AbstractThe water vapor transport and moisture budget over eastern China remotely forced by the cold-tongue (CT) and warm-pool (WP) El Nino show striking differences throughout their lifetime. The water vapor transport response is weak in the developing summer but strong in the remaining phases of CT El Nino, whereas the opposite occurs during WP El Nino. WP El Nino causes a moisture deficit over the Yangtze River valley (YZ) in the developing summer and over southeastern China (SE) in the developing fall, whereas CT El Nino induces a moisture surplus first over SE during the developing fall with the influential area expanding in the decaying spring and shifting northward in the decaying summer. It is the divergence of meridional water vapor transport that dominates the total water vapor divergence anomaly, with the divergence of zonal transport showing an opposite pattern with smaller magnitude.Investigation of the vertical profile of moisture budget shows a great baroclinicity, with the strongest abnorm...

Comparison of the Annual Cycles of Moisture Supply over Southwest and Southeast China

AbstractThe variation in regional precipitation over southeast and southwest China depends strongly on externally imported moisture rather than local evaporation. Associated with the different climate over the two regions, great discrepancies appear in the annual cycles of the moisture supply. Stationary moisture transport dominates externally imported moisture to a large extent, with transient transport being much weaker. The stationary moisture sink over southeast China is strong during spring and summer due to strong moisture input via the southern boundary and weak during fall and winter due to the offset between the output via the southern boundary and the net zonal boundary atmospheric flux. Zonal stationary moisture transport dominates the variation in moisture supply over southwest China. Negative net zonal boundary atmospheric flux countervails (collaborates) with positive meridional transport during the dry (wet) season.Stationary moisture circulations dominate regional atmospheric moisture conv...

Decadal Anomalies of Winter Precipitation over Southern China in Association with El Niño and La Niña

Using multiple datasets, this paper analyzes the characteristics of winter precipitation over southern China and its association with warm and cold phases of El Niño-Southern Oscillation during 1948–2011. The study proves that El Niño is an important external forcing factor resulting in above-normal winter precipitation in southern China. The study also reveals that the impact of La Niña on the winter precipitation in southern China has a decadal variability.During the winter of La Niña before 1980, the East Asian winter monsoon is stronger than normal with a deeper trough over East Asia, and the western Pacific subtropical high weakens with its high ridge retreating more eastward. Therefore, anomalous northerly winds dominate over southern China, leading to a cold and dry winter. During La Niña winter after 1980, however, the East Asian trough is weaker than normal, unfavorable for the southward invasion of the winter monsoon. The India-Burma trough is intensified, and the anomalous low-level cyclone excited by La Niña is located to the west of the Philippines. Therefore, anomalous easterly winds prevail over southern China, which increases moisture flux from the tropical oceans to southern China. Meanwhile, La Niña after 1980 may lead to an enhanced and more northward subtropical westerly jet over East Asia in winter. Since southern China is rightly located on the right side of the jet entrance region, anomalous ascending motion dominates there through the secondary vertical circulation, favoring more winter precipitation in southern China. Therefore, a cold and wet winter, sometimes with snowy and icy weathers, would occur in southern China during La Niña winter after 1980. Further analyses indicate that the change in the spatial distribution of sea surface temperature anomaly during the La Niña mature phase, as well as the decadal variation of the Northern Hemisphere atmospheric circulation, would be the important reasons for the decadal variability of the La Niña impact on the atmospheric circulation in East Asia and winter precipitation over southern China after 1980.

Evolution of the Madden–Julian Oscillation in Two Types of El Niño

AbstractEvolution characteristics of the Madden–Julian oscillation (MJO) during the eastern Pacific (EP) and central Pacific (CP) types of El Nino have been investigated. MJO activities are strengthened over the western Pacific during the predeveloping and developing phases of EP El Nino, but suppressed during the mature and decaying phases. In contrast, MJO activities do not show a clear relationship with CP El Nino before their occurrence over the western Pacific, but they increase over the central Pacific during the mature and decaying phases of CP El Nino. Lag correlation analyses further confirm that MJO activities over the western Pacific in boreal spring and early summer are closely related to EP El Nino up to 2–11 months later, but not for CP El Nino. EP El Nino tends to weaken the MJO and lead to a much shorter range of its eastward propagation. Anomalous descending motions over the Maritime Continent and western Pacific related to El Nino can suppress convection and moisture flux convergence the...

Recent Advances in Monsoon Studies in China

This review provides a synopsis of the major progress that has been made in monsoon studies in China and to further bridge the gap between the Chinese and international meteorological community. It consists of seven major sections. After the introduction, the second section begins with the global monsoon systems and their seasonal variation, based on some new methods proposed in recent years. Besides, some major intraseasonal features of East Asian monsoon, including the onset of South China Sea summer monsoon are discussed. In the third section, we review the interactions between ENSO and the East Asian monsoon, focusing in particular on the results of Chinese meteorologists that indicate the influence of ENSO on the East Asian summer monsoon (EASM) is obviously different from that on the tropical monsoon. Besides the tropical Pacific, other ocean basins, such as the Indian Ocean and the Atlantic Ocean, are also important to the East Asian monsoon, and this topic is discussed in the fourth section. In the fifth section, we address the role of land surface processes in East Asian monsoon. For example, we describe work that has shown more snow cover in spring on the Tibetan Plateau is followed by a weakened EASM and more summer rainfall in the Yangtze River valleys. The sixth section focuses on the influence of atmospheric circulation in the Southern Hemisphere (SH) on EASM, demonstrating how the signal from the SH is likely to provide new clues for the seasonal forecasting of summer rainfall in China. Finally, in the seventh section, we concentrate on the interdecadal variations of EASM. In particular, we look at a significant interdecadal variation that occurred at the end of the 1970s, and how our understanding of this feature could affect forecasting ability.

The Relationship between Contiguous El Niño and La Niña Revealed by Self-Organizing Maps

AbstractThis study introduces a new methodology for identifying El Nino and La Nina events. Sea surface temperature (SST) anomaly patterns for El Nino and La Nina onset, peak, and end phases are classified by self-organizing maps (SOM) analysis. Both onset and end phases for El Nino and La Nina exhibit eastern Pacific (EP) and central Pacific (CP) types. The SST anomaly patterns in peak phase can be classified into EP, EP-like, and CP types for El Nino, and EP, mixed (MIX), and CP types for La Nina.The general type of each El Nino or La Nina event is then defined according to the SST type for each of the three phases. There is no robust connection between the general types of the contiguous El Nino and La Nina except that the MIX La Nina rarely induces a subsequent CP El Nino. However, there are strong relationships between the end-phase type of El Nino and the onset-phase type of the subsequent La Nina. The EP-end-type El Nino favors transition to the CP-onset-type La Nina, while the CP-end-type El Nino ...

Research Progress in China on the Tropical Atmospheric Intraseasonal Oscillation

Tropical intraseasonal oscillation (including the Madden-Julian oscillation) is an important element of the atmospheric circulation system. The activities and anomalies of tropical intraseasonal oscillations affect weather and climate both inside and outside the tropical region. The study of these phenomena therefore represents one of the frontiers of atmospheric sciences. This review aims to synthesize and summarize studies of intraseasonal oscillation (ISO) by Chinese scientists within the last 5–10 years. We focus particularly on ISO’s mechanisms, its numerical simulations (especially the impacts of diabatic heating profiles), relationships and interactions with ENSO (especially over the western Pacific), impacts on tropical cyclone genesis and tracks over the northwestern Pacific, and influences on the onset and activity of the South and East Asian monsoons (especially rainfall over China). Among these, focuses of ongoing research and unresolved issues related to ISO are also discussed.

Seasonal evolution of dominant modes in south pacific SST and relationship with ENSO

A season-reliant empirical orthogonal function (S-EOF) analysis was applied to the seasonal mean SST anomalies (SSTAs) based on the HadISST1 dataset with linear trend removed at every grid point in the South Pacific (60.5°-19.5°S, 139.5°E-60.5°W) during the period 1979–2009. The spatiotemporal characteristics of the dominant modes and their relationships with ENSO were analyzed. The results show that there are two seasonally evolving dominant modes of SSTAs in the South Pacific with interannual and interdecadal variations; they account for nearly 40% of the total variance. Although the seasonal evolution of spatial patterns of the first S-EOF mode (S-EOF1) did not show remarkable propagation, it decays with season remarkably. The second S-EOF mode (S-EOF2) showed significant seasonal evolution and intensified with season, with distinct characteristics of eastward propagation of the negative SSTAs in southern New Zealand and positive SSTAs southeast of Australia. Both of these two modes have significant relationships with ENSO. These two modes correspond to the post-ENSO and ENSO turnabout years, respectively. The SEOF1 mode associated with the decay of the eastern Pacific (EP) and the central Pacific (CP) types of ENSO exhibited a more significant relationship with the EP/CP type of El Niño than that with the EP/CP type of La Niña. The S-EOF2 mode contacted with the EP type of El Niño changing into the EP/CP type of La Niña showed a more significant connection with the EP/CP type of La Niña.