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Abstract Atmospheric river (AR) and its impact on monsoon rainfall in East Asia are investigated by considering their month‐to‐month variations during the East Asian summer monsoon (EASM). The AR in the EASM, defined as an anomalously enhanced plume‐like water vapor transport, frequently forms over eastern China, Korea and western Japan. However, its characteristics vary from the early (June‐July) to the late (August‐September) period of the EASM. In the early EASM, AR is typically characterized by a quasi‐stationary monsoon southwesterly along the northern boundary of the western North Pacific subtropical high (WNPSH), which is further intensified by a migrating extratropical cyclone in the north. In contrast, the late‐EASM AR, which is less frequent than the early EASM AR, is primarily organized by a migrating extratropical cyclone. The quasi‐stationary monsoon southwesterly is less influential as the northern boundary of the WNPSH shifts northward, being decoupled from the subtropical ocean. Both the early‐ and late‐EASM ARs contribute substantially to monsoon rainfall, especially to heavy rainfall events. In the early EASM, 35%–70% of total rainfall amount and 60%–80% of heavy rainfall events in eastern China, Korea and western Japan are associated with AR. Although weakened, AR‐related rainfall is still significant in the late EASM in Korea and western Japan. These results indicate that AR is a key ingredient of EASM precipitation and its subseasonal variations should be taken into account to better understand and predict AR‐related extreme precipitation in East Asia.
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Object-oriented Composite Analysis of Warm Sector Rainfall in North China
Warm sector rainfall (WSR) occurs, by definition, in a warm air region that is isolated from any forcing related to synoptic frontal boundaries at the surface. This study explores the use of an object-oriented technique to objectively and automatically identify various WSR events over North China from June to September in 2012-2017. A total of 768 substantive events are identified over the 6 years. They have a mean maximum rainfall accumulation of 35 mm/hr. Most such events occur over the plains; with two frequency maxima, one to the south of the Yanshan Mountain Ranges, and the other near the junction of Henan, Shandong and Jiangsu provinces. WSR-related rainstorms can form in all warm-season months but are most commonly seen between mid-July and mid-August (40% of all events occurred then). Geographically, the region at greatest risk moves gradually northward from mid-June to mid-August, consistent with the progression of the East Asian summer monsoon. There are two diurnal peaks in WSR activity, one from late afternoon to early evening and the other from late evening to early morning. Three classes of upper-level synoptic pattern seem to be conducive to WSR: i) a “Mongolia front pattern”, ii) “northern China front pattern”, iii) a “southern front pattern”. All of these patterns are accompanied by warm and moist southwesterly flow at low levels. Prior to WSR events, there is usually an upper level trough. According to other studies, such a feature is not usually seen for WSR events in South China.
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- Award ID(s):
- 1712290
- PAR ID:
- 10158499
- Date Published:
- Journal Name:
- Monthly Weather Review
- ISSN:
- 0027-0644
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1175/MWR-D-19-0038.1
