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

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.  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.  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.  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’ 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>

scholarly journals Upper-Tropospheric Forcing on Late July Monsoon Transition in East Asia and the Western North Pacific

2012 ◽  
Vol 25 (11) ◽  
pp. 3929-3941 ◽  
Author(s):  
Chi-Hua Wu ◽  
Ming-Dah Chou
Keyword(s):  
East Asia ◽  
South Asian ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Asian Monsoon ◽  
Monsoon Circulation ◽  
South Asian Monsoon ◽  
The South ◽  
The North

By investigating the large-scale circulation in the upper troposphere, it is demonstrated that the rapid late July summer monsoon transition in the East Asia and western North Pacific (EA-WNP) is associated with a weakened westerly at the exit of the East Asian jet stream (EAJS). Even in a normally stable atmosphere under the influence of the North Pacific (NP) high in late July, convection rapidly develops over the midoceanic region of the western NP (15°–25°N, 150°–170°E). Prior to the rapid transition, the EAJS weakens and shifts northward, which induces a series of changes in downstream regions; the northeastern stretch of the Asian high weakens, upper-tropospheric divergence in the region southwest of the mid-NP trough increases, and convection is enhanced. At the monsoon transition, upper-level high potential vorticity intrudes southward and westward, convection expand from the mid NP westward to cover the entire subtropical western NP, the lower-tropospheric monsoon trough deepens, surface southwesterly flow strengthens, and the western stretch of the NP high shifts northward ~10° latitude to the south of Japan. This series of changes indicates that the EA-WNP late July monsoon transition is initiated from changes in the upper-tropospheric circulation via the weakening of the EAJS south of ~45°N. The weakening of the EAJS south of ~45°N is related to a reduced gradient of the geopotential height on the northern flank of the Asian high, which is related to the massive inland heating and weakening of the South Asian monsoon circulation. The exact timing of the monsoon onset might be tied to the hypothesized “Silk Road pattern” and/or a strong weakening of the South Asian monsoon circulation.

scholarly journals Intraseasonal Variability of the East Asia-Pacific Teleconnection and Its Impacts on Multiple Tropical Cyclone Genesis Over the Western North Pacific

2021 ◽  
Vol 8 ◽  
Author(s):  
Xin Lin ◽  
Lan Wang ◽  
Jianyun Gao ◽  
Xiaoxiao Chen ◽  
Wei Zhang
Keyword(s):  
East Asia ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Intraseasonal Variability ◽  
Asia Pacific ◽  
Boreal Summer ◽  
Relative Role ◽  
The Impact

A daily East Asia–Pacific teleconnection (EAP) index was constructed to investigate the impact of the intraseasonal variability (ISV) of this index on the genesis of multiple tropical cyclones (MTC) in boreal summer over the western North Pacific (WNP). The result indicates that the EAP index has dominant intraseasonal periods of 10–20 days, 20–40 days and 50–70 days, respectively. The ISV of the EAP during 1979–2019 can be classified into three types, a single-period-domination type (37%), a multiple period coexistence type (24%) and a transition type (39%). It is found that during El Niño (La Niña) summers, the ISV of the EAP is dominated by a higher-frequency (lower-frequency) oscillation with a period of around 20–30 (50–70) days. The distinctive ISV characteristics during the different ENSO years were accompanied with different dynamic and thermodynamic background conditions over the WNP and the South China Sea, which modulated the frequency and location of MTC genesis. By examining the relative contributions of individual environmental variables of the Genesis Potential Index, we found that the low-level absolute vorticity and mid-level relative humidity are two important environmental factors modulating MTC genesis. However, the relative role of these variables tends to change with the EAP ISV phase. The environmental condition over the SCS appears less influenced by ENSO. A more southern location of MTC genesis during El Niño is attributed to the change of the environmental humidity.

scholarly journals Spatiotemporal patterns of synchronous heavy rainfall events in East Asia during the Baiu season

2021 ◽  
Author(s):  
Frederik Wolf ◽  
Ugur Ozturk ◽  
Kevin Cheung ◽  
Reik V. Donner
Keyword(s):  
System Dynamics ◽  
East Asia ◽  
Heavy Rainfall ◽  
Spatial Organization ◽  
Monsoon Season ◽  
Spatiotemporal Patterns ◽  
Extreme Weather Events ◽  
Earth System ◽  
Rainfall Events ◽  
Heavy Rainfall Events

<p>Investigating the synchrony and interdependency of heavy rainfall occurrences is crucial to understand the underlying physical mechanisms and reduce physical and economic damages by improved forecasting strategies. In this context, studies utilizing functional network representations have recently contributed to significant advances in the understanding and prediction of extreme weather events.</p><p>To thoroughly expand on previous works employing the latter framework to the East Asian Summer Monsoon (EASM) system, we focus here on changes in the spatial organization of synchronous heavy precipitation events across the monsoon season (April to August) by studying the temporal evolution of corresponding network characteristics in terms of a sliding window approach. Specifically, we utilize functional climate networks together with event coincidence analysis for identifying and characterizing synchronous activity from daily rainfall estimates with <span>a spatial resolution of 0.25° </span>between 1998 and 2018. Our results demonstrate that the formation of the Baiu front as a main feature of the EASM is reflected by a double-band structure of synchronous heavy rainfall with two centers north and south of the front. Although the two separated bands are strongly related to either low- or high-level winds which are commonly assumed to be independent, we provide evidence that it is rather their mutual interconnectivity that changes during the different phases of the EASM season in a characteristic way.</p><p>Our findings shed some new light on the interplay between tropical and extratropical factors controlling the EASM intraseasonal evolution, which could potentially help improving future forecasts of the Baiu onset in different regions of East Asia.</p><p> </p><p>Further details: F. Wolf, U. Ozturk, K. Cheung, R.V. Donner: Spatiotemporal patterns of synchronous heavy rainfall events in East Asia during the Baiu season. Earth System Dynamics (in review). Discussion Paper: Earth System Dynamics Discussions, (2020)</p>

scholarly journals Coupling Modes of Climatological Intraseasonal Oscillation in the East Asian Summer Monsoon

2016 ◽  
Vol 29 (17) ◽  
pp. 6363-6382 ◽  
Author(s):  
Zehao Song ◽  
Congwen Zhu ◽  
Jingzhi Su ◽  
Boqi Liu
Keyword(s):  
East Asia ◽  
North Pacific ◽  
East Asian Summer Monsoon ◽  
Western North Pacific ◽  
Diabatic Heating ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Intraseasonal Oscillation ◽  
Rainfall Anomaly ◽  
Asian Summer

Abstract The present study used harmonic and multivariate empirical orthogonal function (MV-EOF) analyses to identify the existence of climatological intraseasonal oscillation (CISO) in the diabatic heating, precipitation, and circulation of the East Asian summer monsoon (EASM). The strongest CISO signals are found in the north of the western North Pacific, possibly because of the horizontal gradient of diabatic heating induced by the seasonal land–sea thermal contrast. Further, the phase relationship between the diabatic heating components maintains the EASM CISO. The first two coupling modes of EASM CISO in the circulation are robust during May through August, with a period of 40–80 days, and exhibit phase locking to the stepwise establishment of the EASM, which reveals the coaction of the Mongolian cyclone (MC) around Lake Baikal at 850 hPa, the western North Pacific subtropical high (WNPSH) at 500 hPa, and the South Asian high (SAH) over the Tibetan Plateau (TP) at 200 hPa. The first mode shows that the jointly enhanced MC, WNPSH, and SAH correspond to a tripole rainfall anomaly with strong mei-yu and baiu fronts over East Asia. The second mode, however, indicates the eastward and northwestward propagation of MC and WNPSH, respectively, with suppressed SAH, as well as a dipole rainfall anomaly over East Asia. Both the observations and numerical simulation verify the importance of daily diabatic heating and SST in maintaining the CISO modes over the WNP, where the condensation heating related to atmospheric forcing determines the local intraseasonal air–sea interaction.

scholarly journals Future Change in Tropical Cyclone Activity over the Western North Pacific in CORDEX-East Asia Multi-RCMs Forced by HadGEM2-AO

2019 ◽  
Vol 32 (16) ◽  
pp. 5053-5067 ◽  
Author(s):  
Hyeonjae Lee ◽  
Chun-Sil Jin ◽  
Dong-Hyun Cha ◽  
Minkyu Lee ◽  
Dong-Kyou Lee ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
East Asia ◽  
North Pacific ◽  
Western North Pacific ◽  
Climate Models ◽  
Regional Climate ◽  
Vertical Wind Shear ◽  
Coastal Regions ◽  
The Future ◽  
Cordex East Asia

AbstractFuture changes in tropical cyclone (TC) activity over the western North Pacific (WNP) are analyzed using four regional climate models (RCMs) within the Coordinated Regional Climate Downscaling Experiment (CORDEX) for East Asia. All RCMs are forced by the HadGEM2-AO under the historical and representative concentration pathway (RCP) 8.5 scenarios, and are performed at about 50-km resolution over the CORDEX-East Asia domain. In the historical simulations (1980–2005), multi-RCM ensembles yield realistic climatology for TC tracks and genesis frequency during the TC season (June–November), although they show somewhat systematic biases in simulating TC activity. The future (2024–49) projections indicate an insignificant increase in the total number of TC genesis (+5%), but a significant increase in track density over East Asia coastal regions (+17%). The enhanced TC activity over the East Asia coastal regions is mainly related to vertical wind shear weakened by reduced meridional temperature gradient and increased sea surface temperature (SST) at midlatitudes. The future accumulated cyclone energy (ACE) of total TCs increases significantly (+19%) because individual TCs have a longer lifetime (+6.6%) and stronger maximum wind speed (+4.1%) compared to those in the historical run. In particular, the ACE of TCs passing through 25°N increases by 45.9% in the future climate, indicating that the destructiveness of TCs can be significantly enhanced in the midlatitudes despite the total number of TCs not changing greatly.

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