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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Development of late s pring–early summer rainstorms in southern East Asia from the e astward propagating m id‐tropospheric cyclones of South Asia
From mid‐May to late June, the eastward propagation of some mid‐tropospheric cyclones (MTCs) originating in the Bay of Bengal (BOB)‐Burma (BUM) region across northern Indochina and southwest China to East Asia are observed. From 1979 to 2016, 137 MTCs were identified for the BOB‐BUM region. Eighty‐eight MTCs were trapped over northern Indochina, but 49 were propagated by the southwesterly flow of the BOB mid‐tropospheric trough to reach East Asia. Thirty‐one moved across Taiwan, but 18 did not. Eventually, all these MTCs moved to Okinawa. The former group of rainstorms produced rainfall ≥100 mm·day−1over Taiwan, while 44 rainstorms generated rainfall ≥50 mm·day−1over Okinawa. The 49 eastward propagating through‐Indochina MTCs exhibited the following salient features: (a) initial formation mostly occurred in the mid‐troposphere ahead/within the BOB trough in the morning over the BOB, but in the afternoon‐evening over BUM. (b) The eastward propagating BOB‐BUM MTCs underwent two descending processes: descending one mandatory level 6 hr after formation, and descending again from 700 to 925 hPa over southeastern China to interact with a low‐level cyclonic shear flow. (c) Intensified (weakened) by dipole anomalous circulation cells, the confluent monsoon southwesterly flow west (east) of Taiwan facilitated the merger of the MTC with a local front. (d) Rainfall produced by rainstorms over Taiwan/Okinawa was maintained by the intensified convergence of water vapour flux toward Taiwan/Okinawa. This hydrological process was stronger toward Taiwan than Okinawa and generated more rainfall in the former region. The impact of the BOB‐BUM MTC on East Asian weather is confirmed by this study.
more » « less- NSF-PAR ID:
- 10401141
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal of Climatology
- Volume:
- 43
- Issue:
- 3
- ISSN:
- 0899-8418
- Format(s):
- Medium: X Size: p. 1293-1313
- Size(s):
- ["p. 1293-1313"]
- Sponsoring Org:
- National Science Foundation
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