Zhiyan Zuo

Seasonal-to-Interannual Prediction of the Asian Summer Monsoon in the NCEP Climate Forecast System Version 2

AbstractThe NCEP Climate Forecast System (CFS) is an important source of information for seasonal climate prediction in many Asian countries affected by monsoon climate. The authors provide a comprehensive analysis of the prediction of the Asian summer monsoon (ASM) by the new CFS version 2 (CFSv2) using the hindcast for 1983–2010, focusing on seasonal-to-interannual time scales. Many ASM features are well predicted by the CFSv2, including heavy monsoon rainfall centers, large-scale monsoon circulation patterns, and monsoon onset and retreat features. Several commonly used dynamical monsoon indices and their associated precipitation and circulation patterns can be predicted several months in advance. The CFSv2 has better skill in predicting the Southeast Asian monsoon than predicting the South Asian monsoon. Compared to CFS version 1 (CFSv1), the CFSv2 has increased skill in predicting large-scale monsoon circulation and precipitation features but decreased skill for the South Asian monsoon, although some...

Impact of Spring Soil Moisture on Surface Energy Balance and Summer Monsoon Circulation over East Asia and Precipitation in East China

Numerous studies have been conducted on the impact of soil moisture on the climate, but few studies have attempted to diagnose the linkage between soil moisture and climate variability using observational data. Here, using both observed and reanalysis data, the spring (April‐May) soil moisture is found to have a significant impact on the summer (June‐August) monsoon circulation over East Asia and precipitation in east China by changing surface thermal conditions. In particular, the spring soil moisture over a vast region from the lower and middle reaches of the Yangtze River valley to north China (the YRNC region) is significantly correlated to the summer precipitation in east China. When the YRNC region has a wetter soil in spring, northeast China and the lower and middle reaches of the Yangtze River valley would have abnormally higher precipitation in summer, while the region south of the Yangtze River valley would have abnormally lower precipitation. An analysis of the physical processes linking the spring soil moisture to the summer precipitation indicates that the soil moisture anomaly across the YRNC region has a major impact on the surface energy balance. Abnormally wet soil would increase surface evaporation and hence decrease surface air temperature (Ta). The reduced Ta in late spring would narrow the land‐sea temperature difference, resulting in the weakened East Asian monsoon in an abnormally strengthened western Pacific subtropical high that is also located farther south than its normal position. This would then enhance precipitation in the Yangtze River valley. Conversely, the abnormally weakened East Asian summer monsoon allows the western Pacific subtropical high to wander to south of the Yangtze River Valley, resulting in an abnormally reduced precipitation in the southern part of the country in east China.

Role of Thermal Condition over Asia in the Weakening Asian Summer Monsoon under Global Warming Background

AbstractThe large-scale Asian summer monsoon circulation has experienced a weakening tendency in recent decades. Using observed data and output from model experiments with the atmospheric component of the NCEP Climate Forecast System, the authors show that a relatively smaller warming in Asia compared to the surrounding regions may be a plausible reason for this change in the monsoon. Although the surface temperature over Asia has increased, the landmass has become a relative “heat sink” because of the larger warming in other regions of the world. Indeed, over Asia, the vertically integrated tropospheric temperature in the most recent decades is colder than that in the earlier decades, a feature different from the characteristics outside Asia.

Inter-decadal variations of springtime rainfall over southern China mainland for 1979–2004 and its relationship with Eurasian snow

This study analyzes the inter-decadal variations of rainfall over southern China in spring (March–April–May) using the observed precipitation data for 1979–2004. The result shows that the variations of spring rainfall over southeastern China are opposite to those over and southwestern China in both inter-annual and inter-decadal time scales. The precipitation over southern China exhibits an apparent inter-decadal shift in the late 1980s. The accumulated spring rainfall has reduced 30% over southeastern China after the late 1980s, whereas it has increased twice as much over southwestern China. The atmospheric circulations related to this shift show that an abnormal high at lower and middle troposphere appears over Asian middle and high latitudes, accompanied by stronger-than-normal northerly wind over eastern China. Consequently, the wet air flows from tropical oceans are weakened over southern China, resulting in less rainfall over southeastern China and more rainfall over southwestern China. Furthermore, the anomalous atmospheric circulation over Asian middle and high latitudes is closely related to the inter-decadal downward shift of Eurasian spring snow in the late 1980s, indicating that the inter-decadal shift of Eurasian spring snow in the late 1980s is probably an important factor in the decadal shift of spring rainfall over southern China.

Effects on Summer Monsoon and Rainfall Change Over China Due to Eurasian Snow Cover and Ocean Thermal Conditions

© 2013 Zhang et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Effects on Summer Monsoon and Rainfall Change Over China Due to Eurasian Snow Cover and Ocean Thermal Conditions

Long-Term Variations of Broad-Scale Asian Summer Monsoon Circulation and Possible Causes

AbstractThe widely applied Webster–Yang index (WYI), which measures the broad-scale dynamical features of the Asian summer monsoon (ASM), has experienced robust interannual and interdecadal variations and a decreasing tendency, with apparent shifts in 1972. The WYI exhibits moderate variability and frequent positive phases before 1972, intensive interannual variability during 1972–98, and an obvious decreasing tendency and mainly negative phase afterward. The vertical shear easterly anomalies over the tropics/subtropics and the anomalous vertical shear anticyclonic circulation over Eurasia (Eu) are the background for the decreasing WYI, associated with reduced summer precipitation around the Bay of Bengal and Sumatra. On interdecadal time scales, the negative (positive) Atlantic multidecadal oscillation (AMO) is characterized by cooling (warming) in Eurasian tropospheric temperature (TT) via the North Atlantic Oscillation. Global warming manipulates the increasing tendency and the interannual variability ...

Relationship between anomalies of Eurasian snow and southern China rainfall in winter

Characteristics of the snow water equivalent (SWE) over high-latitude Eurasia and its relation with precipitation in China during January, February and March (JFM) are investigated. The JFM Eurasian SWE exhibited a decadal downward shift in the late 1990s, marked by a frequently positive phase in 1979–98 and a negative phase afterward. The decadal shift corresponds to anomalous northeasterly flow over southeastern China. Consequently, warm and moist airflow from tropical oceans is weakened, accompanied by reduced rainfall over southeastern China. The US National Centers for the Environmental Prediction Climate Forecast System (CFS) capture both the interannual variation and the decreasing trend of JFM Eurasian SWE reasonably well for several months in advance. The relationship between Eurasian SWE and southeastern China rainfall is also captured by the CFS in the prediction.