Two Types of Diurnal Variations in Heavy Rainfall during July over Korea

AbstractThis study examined the characteristics of the diurnal variations of heavy rainfall (⩾110 mm in 12 hours) in Korea and the related atmospheric circulation for July from 1980–2020. During the analysis period, two dominant pattens of diurnal variation of the heavy rainfall emerged: all-day heavy rainfall (AD) and morning only heavy rainfall (MO) types. For the AD-type, the heavy rainfall is caused by abundant moisture content in conjunction with active convection in the morning (0000–1200, LST; LST = UTC + 9) and the afternoon hours (1200–2400 LST). These systems are related to the enhanced moisture inflow and upward motion induced by the strengthening of the western North Pacific subtropical high and upper-tropospheric jet. For the MO-type, heavy rainfall occurs mostly in the morning hours; the associated atmospheric patterns are similar to the climatology. We find that the atmospheric pattern related to severe heavy rainfalls in 2020 corresponds to a typical AD-type and resembles the 1991 heavy-rainfall system in its overall synoptic/mesoscale circulations. The present results imply that extremely heavy rainfall episodes in Korea during the 2020 summer may occur again in the future associated with the recurring atmospheric phenomenon related to the heavy rainfall.

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Change in Tropical Cyclone Activity during the Break of the Western North Pacific Summer Monsoon in Early August

Journal of Climate ◽

10.1175/jcli-d-15-0587.1 ◽

2016 ◽

Vol 29 (7) ◽

pp. 2457-2469 ◽

Cited By ~ 3

Author(s):

Ke Xu ◽

Riyu Lu

Keyword(s):

Tropical Cyclone ◽

Summer Monsoon ◽

North Pacific ◽

Western North Pacific ◽

Cyclonic Circulation ◽

Tropical Cyclone Activity ◽

Upward Motion ◽

Mariana Islands ◽

Cyclone Activity

Abstract The modulation of tropical cyclone (TC) activity by the western North Pacific (WNP) monsoon break is investigated by analyzing the subseasonal evolution of TCs and corresponding circulations, based on 65 years of data from 1950 to 2014. The monsoon break has been identified as occurring over the WNP in early August. The present results show that TC occurrence decreases (increases) remarkably to the east of the Mariana Islands (southeast of Japan) during the monsoon break, which is closely related to local anomalous midtropospheric downward (upward) motion and lower-tropospheric anticyclonic (cyclonic) circulation, in comparison with the previous and subsequent convective periods in late July and mid-August. These changes of TC activity and the corresponding circulation during the monsoon break are more significant in typical monsoon break years when the monsoon break phenomenon is predominant. The reverse changes of TC activity to the east of the Mariana Islands and to the southeast of Japan during the monsoon break are closely associated with the out-of-phase subseasonal evolutions over these two regions from late July to mid-August, which are both contributed to greatly by 10–25-day oscillations. Finally, the roles of midlatitude and tropical disturbances on 10–25-day oscillations are also discussed.

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Spatio-Temporal Dynamics of East Asia Atmospheric Rivers and their Atmospheric Steering and Climatic Regulation

10.5194/egusphere-egu2020-257 ◽

2020 ◽

Author(s):

Mengxin Pan ◽

Mengqian Lu ◽

Upmanu Lall ◽

Qizhen Dong

Keyword(s):

East Asia ◽

North Pacific ◽

Western North Pacific ◽

Heavy Rainfall ◽

Asian Monsoon ◽

Monsoon Season ◽

Asia Pacific ◽

Annual Rainfall ◽

Atmospheric Rivers ◽

Persistent Heavy Rainfall

<p>The identification, climatic modulation and hydrological impact of Atmospheric Rivers (ARs) is an emergent scientific topic in recent years. ARs are important and yet understudied for East Asia (EA). We use our new AR identification algorithm (Pan & Lu, 2019), to build up a comprehensive AR catalog for this region for the first time. &#160;Interesting patterns are found: (1) there is a dominant AR route, originating from the Arabian Sea, crossing over the Bay of Bengal and Indochina, South China Sea (SCS) and Southeast China (SEC), and terminating in the western North Pacific; and (2) a nine-stage annual pattern in the climatological frequency is revealed. &#160;Stage 1: mid-Mar to mid-May, the formation of Western North Pacific Subtropical Height (WNPSH) near the SCS steers and confines AR in its northwest flank over SEC. &#160;Stages 2-5: during the monsoon season from mid-May to late-Aug, the evolution of AR follow the intra-seasonal progression of Asia-Pacific monsoon (including South Asian monsoon, East Asian monsoon and western North Pacific monsoon. Stages 6-9: late-Aug to mid-Mar, ARs leave EA and only occur over the North Pacific. Over all stages, we find the contribution of AR grows significantly with more extreme rainfall (i.e., from the annual rainfall, heavy rainfall, persistent heavy rainfall to large spatial extent persistent heavy rainfall), especially in spring and early-monsoon season. This emphasizes ARs&#8217; significant role in extreme or catastrophic rainfall events. Intriguingly, divergence of AR trajectories (also in their characteristics) occurs along the extratropical direction, and such divergent features have spatially heterogenous dependence on the leading modes of a collection of steering atmospheric and regulating climatic signals. Large divergence indicates high sensitivity of AR to transient steering; while small divergence promises high predictability of ARs, thus their associated hydrological impacts.</p>

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Seasonal and Diurnal Variations in Cloud-Top Phase over the Western North Pacific during 2017–2019

Remote Sensing ◽

10.3390/rs13091687 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1687

Author(s):

Xiaoyong Zhuge ◽

Xiaolei Zou ◽

Xin Li ◽

Fei Tang ◽

Bin Yao ◽

...

Keyword(s):

North Pacific ◽

Sichuan Basin ◽

Western North Pacific ◽

Lower Troposphere ◽

Surface Air Temperature ◽

Diurnal Variations ◽

Boreal Winter ◽

Near Surface ◽

Seasonal And Diurnal Variations ◽

The Sichuan Basin

The cloud-top-phase climatology over the western North Pacific (WNP) has received little attention. Using 3 years (2017–2019) of cloud-top-phase products from the Advanced Himawari Imager onboard the Japanese Himawari-8 satellite, this study examines the seasonal and diurnal variations in the cloud-top phase over the WNP. Results show that over the low- and mid-latitude maritime regions, ice (water) clouds occur more (less) frequently during boreal winter than summer. Water clouds are more likely to be related to moisture conditions in the lower troposphere than to the underlying sea surface temperature. Owing to the combined effects of moist air mass transport and ocean currents (topography), the WNP region east of Hokkaido (the Sichuan Basin) has a high frequency of water clouds in summer (winter). Furthermore, supercooled water cloud populations have a clear seasonal cycle. The fraction of water clouds that are supercooled appears to be modulated by the near-surface air temperature. A diurnal cycle is seen in ice-cloud populations, which are highest in the late afternoon over both ocean and land except for the Sichuan Basin where summer nocturnal precipitation is typical. The occurrences of continental water clouds peak at noon in summer but early morning (around sunrise) in winter. An increase in the frequency of continental summer water clouds around noon is found to be associated with variations in both the cloud-top elevation of already-existing water clouds and new formations of boundary-layer clouds.

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Quasi-Periodic Behavior of the Pacific–Japan Pattern Affecting Propagation Routes of Summertime Wave Patterns and the Associated Tropical Cyclone Tracks over the Western North Pacific

Monthly Weather Review ◽

10.1175/mwr-d-15-0080.1 ◽

2016 ◽

Vol 144 (1) ◽

pp. 393-408 ◽

Cited By ~ 6

Author(s):

Ken-Chung Ko ◽

Jyun-Hong Liu

Keyword(s):

North Pacific ◽

Western North Pacific ◽

Heavy Rainfall ◽

Large Scale ◽

Asian Summer Monsoon ◽

Northern South China Sea ◽

Wave Pattern ◽

Pressure System ◽

Wave Patterns ◽

Periodic Fluctuations

Abstract This study introduces a modified Pacific–Japan (PJ) index that exhibits a substantial periodicity of 5–16 days in the East Asian summer monsoon region. The quasi-periodic fluctuations of the PJ index can indicate changes in the large-scale circulation systems. In the PJ high phase, the wave pattern propagates northwestward from the western North Pacific tropics to an area near northern Luzon and is then forced to move westward because of a stationary, anomalous high pressure system over southern Japan. The tropical cyclones (TCs) associated with the anomalous low pressure systems tend to follow a straight-moving propagation route through the northern South China Sea. The anomalous cyclonic flow causes heavy rainfall in eastern Taiwan. However, in the PJ low phase, the wave pattern and TCs follow a recurving propagation route toward higher latitudes. The circulation pattern typically brings heavy rainfall to northern Taiwan in the PJ low phase. Therefore, wave patterns under the influence of the quasi-periodic fluctuations of the PJ pattern affect rainfall because of the changing propagation routes of the wave patterns, as well as the TC tracks.

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