East Asian Precipitation Pattern: Competition Between Monsoon and Transient Eddies

Abstract

This paper aims at investigating climate integrated column moisture transport (MT in brief hereafter) over the troposphere for 1971~2000 and the relationship between the MT divergence and seasonal precipitation in East Asia. The result made from ERA‐40 shows that the spatial pattern of the precipitation is approximately coincided with large‐scale MT divergence. A further decomposition manifests that the monthly‐wind moisture transport (MMT) is the dominant role for seasonal divergence patterns. The MMT convergence areas approximately fit the big precipitation areas, while its divergence almost covers the arid and semi‐arid zones in Northwest China and Mongolia. The transient eddy moisture transport (EMT) is about ten times smaller than MMT's in magnitude and plays a key role in the MT northward during the non‐monsoon period. Usually, the EMT divergence is of inverse phase to MMT's, suppressing the MMT impact on precipitation in summer monsoon zones, and it is the major one that supplies water vapor to the precipitation in arid and semi‐arid zones. However, their divergences are compatible and overlapped in phase around the phase transition belt of the MT divergence. It turns out that large‐scale precipitation characteristics greatly rely on the competition of the MMT and EMT, being the physical cause that leads to a specific pattern of the large‐scale precipitation. Besides, the mechanism of regional climate formation also implies possible mechanism of regional precipitation change. A case study shows that the severe floods in both the Yangtze River basin and Songhuajiang‐Nenjiang River basin in 1998 were resulted from anomalous MMT convergence with the monsoon MT, while both the MMT and EMT divergences led to anomalous dry climate in the north and the northwest of China. In addition, it is the strong EMT divergence resulting in significant rainfall reduction in south part of North China and the southeast coast of China. One could also make a further investigation on the causes that lead to the anomalies of the MMT or the EMT, or both. This is a new way for exploring the mechanism of regional climate change.

Thermodynamic characteristics and responses to ENSO of dominant intraseasonal modes in the East Asian summer monsoon

“…The anomalous transient eddy term in summer is smaller than winter because transient wave activity weakens rapidly from spring to summer (Nakamura 1992). In all four modes, the anomalous transient eddies have the opposite phase by supplying or blocking moisture over the boundary region of the mean flow and their role is smaller than the moisture flux convergence (Zhang et al 2011). In other words, the transient eddy divergence (convergence) is observed to influence a decrease (an increase) in rainfall (Zhang et al 2011).…”

“…The moisture budget studies have been widely known over the recent decade. For example, Zhang et al (2011) tried to show the moisture divergence by dividing into the monthly-wind moisture transport (MMT) and transient eddy moisture transport (EMT) divergence. They revealed that the MMT represents strong moisture convergence in the EASM region, while the EMT divergence has the opposite effect on the MMT.…”

Spatial patterns of sample entropy based on daily precipitation time series in China and their implications for land surface hydrological interactions

“…Lower SE regions are distributed in areas near the boundaries, such as the South China Sea and western Pacific Ocean in the South, Siberia and the Mongolian Plateau in the North and Southwest, and the Tibetan Plateau in the west. In relation to the monsoons in China, a southward marine monsoon in summer and a northward continental monsoon in winter dominate the WVS (Sheng, ; Zhang, ). Marine WV primarily originates from the western Pacific and the South China Sea in the South and from the Bay of Bengal in the Southwest.…”

“…Marine WV primarily originates from the western Pacific and the South China Sea in the South and from the Bay of Bengal in the Southwest. The continental sources are primarily Siberia in the North and the Caspian Sea and Southwest Tibetan Plateau in the west (Zhang, ). By comparing the entropy distribution and WVS regions, each major WVS region corresponds to a lower SE region (Table ).…”

“…Climatically, Eastern and Southern China are mainly dominated by the East Asia monsoon, and southwestern China is more affected by the Southwest Monsoon (Zhang, ; Tian et al ., ; Zhou and Yu, ; Frenken, ). In winter, the mainland is generally under the influence of dry cold air masses from Siberia (Zhang, ; Frenken, ). The Tibetan Plateau and Qinling Mountains prevent the monsoon from penetrating deeply into the Northwest of the continent, resulting in low precipitation and the Gobi‐desert there (Shi, ), as shown in Figure .…”