General features and synoptic-scale environments of mesoscale convective systems over South China during the 2013–2017 pre-summer rainy seasons

2021 ◽  
pp. 105954
Author(s):  
Yangruixue Chen ◽  
Yali Luo ◽  
Bo Liu
Keyword(s):  
South China ◽  
Mesoscale Convective Systems ◽  
Synoptic Scale ◽  
Convective Systems ◽  
Mesoscale Convective

scholarly journals Different Representation of Mesoscale Convective Systems in Convection-Permitting and Convection-Parameterizing NWP Models and Its Implications for Large-Scale Forecast Evolution

Atmosphere ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 503 ◽  
Author(s):  
Karsten Peters ◽  
Cathy Hohenegger ◽  
Daniel Klocke
Keyword(s):  
Large Scale ◽  
Weather Prediction ◽  
Mesoscale Convective Systems ◽  
Limited Area ◽  
Synoptic Scale ◽  
Mean Flow ◽  
Convective Systems ◽  
Western Africa ◽  
Mesoscale Convective ◽  
The Difference

Representing mesoscale convective systems (MCSs) and their multi-scale interaction with the large-scale atmospheric dynamics is still a major challenge in state-of-the-art global numerical weather prediction (NWP) models. This results in potentially defective forecasts of synoptic-scale dynamics in regions of high MCS activity. Here, we quantify this error by comparing simulations performed with a very large-domain, convection-permitting NWP model to two operational global NWP models relying on parameterized convection. We use one month’s worth of daily forecasts over Western Africa and focus on land regions only. The convection-permitting model matches remarkably well the statistics of westward-propagating MCSs compared to observations, while the convection-parameterizing NWP models misrepresent them. The difference in the representation of MCSs in the different models leads to measurably different synoptic-scale forecast evolution as visible in the wind fields at both 850 and 650 hPa, resulting in forecast differences compared to the operational global NWP models. This is quantified by computing the correlation between the differences and the number of MCSs: the larger the number of MCSs, the larger the difference. This fits the expectation from theory on MCS–mean flow interaction. Here, we show that this effect is strong enough to affect daily limited-area forecasts on very large domains.

scholarly journals Extreme Rainstorms that Caused Devastating Flooding across the East Coast of Peninsular Malaysia during November and December 2014

2017 ◽  
Vol 32 (3) ◽  
pp. 849-872 ◽  
Author(s):  
Ooi See Hai ◽  
Azizan Abu Samah ◽  
Sheeba Nettukandy Chenoli ◽  
Kumarenthiran Subramaniam ◽  
Muhammad Yunus Ahmad Mazuki
Keyword(s):  
South China Sea ◽  
South China ◽  
East Coast ◽  
Extreme Rainfall ◽  
Peninsular Malaysia ◽  
The South China Sea ◽  
Mesoscale Convective Systems ◽  
Cold Air ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract During the early boreal winter (northeast) monsoon (November–December), cold air frequently bursts out from intense Siberian highs toward the Chinese coast in response to the development and movement of a 500-hPa trough. The resultant strong low-level northwesterlies turn into northeasterlies across the South China Sea as “cold surges.” On interacting with the near-equatorial trough, mesoscale convective systems form north of the trough, normally giving rise to heavy downpours and severe flooding, mainly along the coastal stretch in the east coast states of Peninsular Malaysia. In November 2014, a 1-week-long episode of heavy downpours, producing more than 800 mm of rain, occurred along the coastal stretch of northeastern Peninsular Malaysia. However, during December 2014, two episodes of extreme rainfall occurred mostly over inland and mountainous areas of the east coast of Peninsular Malaysia, in particular across its northern sector. These two unusual events, which lasted a total of 11 days and delivered more than 1100 mm of precipitation, resulted in extreme and widespread flooding, as well as extensive damage, in many inland areas. Analysis shows that the stronger wind surges from the South China Sea due to very intense cold-air outbreaks of the Siberian high developed under ENSO-neutral conditions. In addition, the mesoscale convective systems that developed across the northeastern Indian Ocean (near northern Sumatra) in response to the propagation of a 500-hPa short-wave trough across the Indian subcontinent toward China were the combined factors for these unusual extreme rainfall and flooding events along the east coast of Peninsular Malaysia.

scholarly journals Models for Multiscale Interactions. Part II: Madden–Julian Oscillation, Moisture, and Convective Momentum Transport

2016 ◽  
Vol 56 ◽  
pp. 10.1-10.5 ◽  
Author(s):  
Andrew J. Majda ◽  
Samuel N. Stechmann
Keyword(s):  
Tropical Cyclones ◽  
Momentum Transport ◽  
Mesoscale Convective Systems ◽  
Equatorial Waves ◽  
Madden Julian Oscillation ◽  
Synoptic Scale ◽  
Convective Systems ◽  
Convectively Coupled Equatorial Waves ◽  
Mesoscale Convective ◽  
Convective Momentum Transport

Abstract It is well known that the envelope of the Madden–Julian oscillation (MJO) consists of smaller-scale convective systems, including mesoscale convective systems (MCS), tropical cyclones, and synoptic-scale waves called “convectively coupled equatorial waves” (CCW). In fact, recent results suggest that the fundamental mechanisms of the MJO involve interactions between the synoptic-scale CCW and their larger-scale environment (Majda and Stechmann). In light of this, this chapter reviews recent and past work on two-way interactions between convective systems—both MCSs and CCW—and their larger-scale environment, with a particular focus given to recent work on MJO–CCW interactions.

Effect of Stratiform Heating on the Planetary-Scale Organization of Tropical Convection

2015 ◽  
Vol 73 (1) ◽  
pp. 371-392 ◽  
Author(s):  
Qiang Deng ◽  
Boualem Khouider ◽  
Andrew J. Majda ◽  
R. S. Ajayamohan
Keyword(s):  
Deep Convection ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Warm Pool ◽  
Mesoscale Convective Systems ◽  
Model Parameters ◽  
Synoptic Scale ◽  
Convective Systems ◽  
Planetary Scale ◽  
Mesoscale Convective

Abstract It is widely recognized that stratiform heating contributes significantly to tropical rainfall and to the dynamics of tropical convective systems by inducing a front-to-rear tilt in the heating profile. Precipitating stratiform anvils that form from deep convection play a central role in the dynamics of tropical mesoscale convective systems. The wide spreading of downdrafts that are induced by the evaporation of stratiform rain and originate from in the lower troposphere strengthens the recirculation of subsiding air in the neighborhood of the convection center and triggers cold pools and gravity currents in the boundary layer, leading to further lifting. Here, aquaplanet simulations with a warm pool–like surface forcing, based on a coarse-resolution GCM of approximately 170-km grid mesh, coupled with a stochastic multicloud parameterization, are used to demonstrate the importance of stratiform heating for the organization of convection on planetary and intraseasonal scales. When the model parameters, which control the heating fraction and decay time scale of the stratiform clouds, are set to produce higher stratiform heating, the model produces low-frequency and planetary-scale MJO-like wave disturbances, while parameters associated with lower-to-moderate stratiform heating yield mainly synoptic-scale convectively coupled Kelvin-like waves. Furthermore, it is shown that, when the effect of stratiform downdrafts is reduced in the model, the MJO-scale organization is weakened, and a transition to synoptic-scale organization appears despite the use of larger stratiform heating parameters. Rooted in the stratiform instability, it is conjectured here that the strength and extent of stratiform downdrafts are key contributors to the scale selection of convective organizations, perhaps with mechanisms that are, in essence, similar to those of mesoscale convective systems.

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