Diurnal Circulations and Rainfall in Taiwan during SoWMEX/TiMREX (2008)

2013 ◽  
Vol 141 (11) ◽  
pp. 3851-3872 ◽  
Author(s):  
James H. Ruppert ◽  
Richard H. Johnson ◽  
Angela K. Rowe
Keyword(s):  
Deep Convection ◽  
Heavy Rain ◽  
Early Morning ◽  
Southwest Monsoon ◽  
Land Breeze ◽  
Mountain Range ◽  
Local Circulation ◽  
Low Level ◽  
Budget Analysis ◽  
Using Data

Abstract The diurnal cycle of the local circulation, rainfall, and heat and moisture budgets is investigated in Taiwan's heavy rain (mei-yu) season using data from the 2008 Southwest Monsoon Experiment/Terrain-influenced Monsoon Rainfall Experiment (SoWMEX/TiMREX). Comparisons are made between an undisturbed (UNDIST; 22–29 May) and disturbed period (DIST; 31 May–4 June). Many aspects of the diurnal evolution in surface flows and rainfall were similar during both periods. At night and during early morning hours, the low-level southwesterly flow was deflected around Taiwan's main topographic barrier, the Central Mountain Range (CMR), with rainfall focused near areas of enhanced offshore confluence created by downslope and land-breeze flows. During the day, the flow switched to onshore and upslope, rainfall shifted inland, and deep convection developed along the coastal plains and windward slopes. Atmospheric budget analysis indicates a day-to-evening transition of convective structure from shallow to deep to stratiform. Evaporation associated with the evening/nighttime stratiform precipitation likely assisted the nocturnal katabatic flow. Though the flow impinging on Taiwan was blocked during both periods, a very moist troposphere and strengthened low-level oncoming flow during DIST resulted in more widespread and intense rainfall that was shifted to higher elevations, which resembled a more weakly blocked regime. Correspondingly, storm cores were tilted upslope during DIST, in contrast to the more erect storms characteristic of UNDIST. There were much more lofted precipitation-sized ice hydrometeors within storms during DIST, the upslope advection of which led to extensive stratiform rain regions overlying the CMR peaks, and the observed upslope shift in rainfall.

Formation of Nocturnal Offshore Rainfall near the West Coast of Sumatra: Land Breeze or Gravity Wave?

2021 ◽  
Vol 149 (3) ◽  
pp. 715-731
Author(s):  
Hedanqiu Bai ◽  
Gumilang Deranadyan ◽  
Courtney Schumacher ◽  
Aaron Funk ◽  
Craig Epifanio ◽  
...  
Keyword(s):  
West Coast ◽  
Large Scale ◽  
Deep Convection ◽  
Propagation Speed ◽  
Early Morning ◽  
Land Breeze ◽  
Maritime Continent ◽  
The West ◽  
Rainfall Events ◽  
Low Level

AbstractAfternoon deep convection over the Maritime Continent islands propagates offshore in the evening to early morning hours, leading to a nocturnal rainfall maximum over the nearby ocean. This work investigates the formation of the seaward precipitation migration off western Sumatra and its intraseasonal and seasonal characteristics using BMKG C-band radar observations from Padang and ERA5 reanalysis. A total of 117 nocturnal offshore rainfall events were identified in 2018, with an average propagation speed of 4.5 m s−1 within 180 km of Sumatra. Most offshore propagation events occur when the Madden–Julian oscillation (MJO) is either weak (real-time multivariate MJO index < 1) or active over the Indian Ocean (phases 1–3), whereas very few occur when the MJO is active over the Maritime Continent and western Pacific Ocean (phases 4–6). The occurrence of offshore rainfall events also varies on the basis of the seasonal evolution of the large-scale circulation associated with the Asian–Australian monsoons, with fewer events during the monsoon seasons of December–February and June–August and more during the transition seasons of March–May and September–November. Low-level convergence, resulting from the interaction of the land breeze and background low-level westerlies, is found to be the primary driver for producing offshore convective rain propagation from the west coast of Sumatra. Stratiform rain propagation speeds are further increased by upper-level easterlies, which explains the faster migration speed of high reflective clouds observed by satellite. However, temperature anomalies associated with daytime convective latent heating over Sumatra indicate that gravity waves may also modulate the offshore environment to be conducive to seaward convection migration.

scholarly journals Dynamical Modulation of Wintertime Synoptic-Scale Cyclone Activity over the Japan Sea due to Changbai Mountain in the Korean Peninsula

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Hiroyuki Shimizu ◽  
Ryuichi Kawamura ◽  
Tetsuya Kawano ◽  
Satoshi Iizuka
Keyword(s):  
Korean Peninsula ◽  
Japan Sea ◽  
Changbai Mountain ◽  
Mountain Range ◽  
Synoptic Scale ◽  
Cyclone Activity ◽  
Low Level ◽  
Budget Analysis ◽  
Eddy Heat Flux ◽  
The Japan Sea

The dynamical impact of the Changbai Mountain Range in the Korean Peninsula on the extratropical cyclone activity over the Japan Sea in early winter is examined using the Weather Research Forecasting model. We have conducted two independent long-term integrations over 15 winter months (December only) from 2000 to 2014 with and without modified topography. The results show that the Changbai Mountain Range plays a vital role in increasing cyclone track frequency, low-level poleward eddy heat flux, and the local deepening rate over the Japan Sea through enhancement of the lower-tropospheric baroclinic zone (LTBZ). This mountain range gives rise to activation of the synoptic-scale cyclone activity over that region. From our case study on three typical cyclones, it is found that mesoscale structures in the vicinity of a cyclone’s center are dynamically modulated when it passes through the LTBZ and that cyclogenesis is triggered around that zone. A vorticity budget analysis shows that the stretching term relevant to enhanced low-level convergence plays a dominant role in intensifying cyclonic vorticities. We confirmed that the composite features of the three typical cases are consistent with the statistical ones of the dynamical modulation of the Changbai Mountain on synoptic-scale cyclone activity.

scholarly journals Characteristic Features of Warm-Type Rain Producing Heavy Rainfall over the Korean Peninsula Inferred from TRMM Measurements

2013 ◽  
Vol 141 (11) ◽  
pp. 3873-3888 ◽  
Author(s):  
B. J. Sohn ◽  
Geun-Hyeok Ryu ◽  
Hwan-Jin Song ◽  
Mi-Lim Ou
Keyword(s):  
Water Vapor ◽  
Liquid Water ◽  
Korean Peninsula ◽  
Heavy Rainfall ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Heavy Rain ◽  
Low Level ◽  
The North ◽  
Characteristic Features

Abstract In contrast to the view that deep convection causes heavy rainfall, Tropical Rainfall Measuring Mission (TRMM) measurements demonstrate that heavy rainfall (ranging from moderate to extreme rain rate) over the Korean peninsula is associated more with low-level clouds (referred to as warm-type clouds in this study) than with conventional deep convective clouds (cold-type clouds). Moreover, it is noted that the low-level warm-type clouds producing heavy rainfall over Korea appear to be closely linked to the atmospheric river, which can form a channel that transports water vapor across the Korean peninsula along the northwestern periphery of the North Pacific high. Much water vapor is transported through the channel and converges on the Korean peninsula when warm-type heavy rain occurs there. It may be possible to produce abundant liquid water owing to the excess of water vapor; this could increase the rate and extent of raindrop growth, primarily below the melting layer, causing heavy rain when these drops fall to the surface. The occurrence of heavy rainfall (also exhibited as medium-depth convection in radar observations over Okinawa, Japan) due to such liquid-water-rich lower warm clouds should induce difficulties in retrieving rainfall from space owing to the lack of scattering-inducing ice crystals over land and the warmer cloud tops. An understanding of the microphysical processes involved in the production of warm-type rain appears to be a prerequisite for better rain retrieval from space and rain forecasting in this wet region.

Stratiform Precipitation Processes in Cyclones Passing over a Coastal Mountain Range

2018 ◽  
Vol 75 (3) ◽  
pp. 983-1004 ◽  
Author(s):  
Joseph P. Zagrodnik ◽  
Lynn A. McMurdie ◽  
Robert A. Houze
Keyword(s):  
Drop Size ◽  
Heavy Rain ◽  
Windward Side ◽  
Mountain Range ◽  
Case Study Analysis ◽  
Low Level ◽  
Olympic Mountains ◽  
Drop Size Distributions ◽  
Lower Slope

Abstract The Olympic Mountains Experiment (OLYMPEX) documented precipitation and drop size distributions (DSDs) in landfalling midlatitude cyclones with gauges and disdrometers located at various distances from the coast and at different elevations on the windward side of the mountain range. Statistics of the drop size and gauge data for the season and case study analysis of a high-rainfall-producing storm of the atmospheric river type show that DSDs during stratiform raining periods exhibit considerable variability in regions of complex terrain. Seasonal statistics show that different relative proportions of drop sizes are present, depending on synoptic and mesoscale conditions, which vary within a single storm. The most frequent DSD regime contains modest concentrations of both small and large drops with synoptic factors near their climatological norms and moderate precipitation enhancement on the lower windward slopes. The heaviest rains are the most strongly enhanced on the lower slope and have DSDs marked by large concentrations of small to medium drops and varying concentrations of large drops. During the heavy-rain period of the case examined here, the low-level flow was onshore and entirely up terrain, the melting level was ~2.5 km, and stability moist neutral so that large amounts of small raindrops were produced. At the same time, melting ice particles produced at upper levels contributed varying amounts of large drops to the DSD, depending on the subsynoptic variability of the storm structure. When the low-level flow is directed downslope and offshore, small-drop production at low altitudes is reduced or eliminated.

scholarly journals Pannonian Basin Nocturnal Boundary Layer and Fog Formation: Role of Topography

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 712
Author(s):  
Joan Cuxart ◽  
Maja Telisman Prtenjak ◽  
Blazenka Matjacic
Keyword(s):  
Boundary Layer ◽  
Pannonian Basin ◽  
Temperature Inversion ◽  
Early Morning ◽  
Mountain Range ◽  
Mountain Ranges ◽  
Mesoscale Structures ◽  
Downslope Flows ◽  
Using Data ◽  
Ecmwf Model

Under high-pressure systems, the nocturnal atmospheric boundary layer in the Pannonian Basin is influenced by gravity flows generated at the mountain ranges and along the valleys, determining the variability of wind and temperature at a local scale and the presence of fog. The mechanisms at the mountain foothills are explored at Zagreb Airport using data from a sodar and high-resolution WRF-ARW numerical simulations, allowing identification of how the downslope flows from the nearby Medvednica mountain range condition the temperature inversion and the visibility at night and early morning. These flows may progress tens of kilometres away from the mountain ranges, merging with valley flows and converging in the central areas of the basin. The ECMWF model outputs allow us to explore the mesoscale structures generated in form of low-level jets, how they interact when they meet, and what is the effect of the synoptic pressure field over eastern Europe, to illustrate the formation of a basin-wide cold air pool and the generation of fog in winter.

Statistical Relationships Between Two Types of Heavy Rainfall and Low-Level Jets in South China

2021 ◽  
pp. 1-53
Author(s):  
Xiaoqing Li ◽  
Yu Du
Keyword(s):  
South China ◽  
Heavy Rainfall ◽  
Northern South China Sea ◽  
Early Morning ◽  
Land Breeze ◽  
Beibu Gulf ◽  
Low Level ◽  
Warm Sector ◽  
Low Level Jets ◽  
Statistical Relationships

AbstractTwo types of heavy rainfall, namely warm-sector and frontal heavy rainfall, coexist in South China during the pre-summer rainy season and manifest as varying mechanisms and features. They both exhibit close relationships with two types of low-level jets (LLJs): the boundary layer jet (BLJ) and synoptic-system-related low-level jet (SLLJ), but in different ways. The motivation of the present study is to elucidate the statistical relations between two types of heavy rainfall and LLJs over South China using TRMM rainfall data and ERA5 reanalysis. Generally, warm-sector heavy rainfall mainly occurs over coastal areas and during the early morning, which is primarily caused by the interaction between the nocturnal BLJ and land breeze. In contrast, frontal heavy rainfall is mostly concentrated in inland regions and modulated by distinct diurnal forcings at different locations. Statistical analysis indicates that 76% (62%) of the warm-sector (frontal) heavy rainfall events are associated with LLJs. In the presence of heavy rainfall, low-level winds are often strengthened over Beibu Gulf, northern South China Sea, and the south side of fronts, corresponding to two branches of southerly BLJs at ~950 hPa over the ocean and the southwesterly SLLJs at ~850–700 hPa on land, respectively. Furthermore, BLJs are shown to be linked to both types of heavy rainfall and with the most frequent occurrences of rainfall in their exit region, whereas SLLJs are more closely associated with frontal heavy rainfall. The left side (entrance) of the SLLJ axis is favorable for frontal (warm-sector) heavy rainfall production. The regional rainfall distributions are affected by the structures and locations of LLJs.

scholarly journals Climatological and synoptic aspect of hailstorm and squall over Guwahati Airport during pre-monsoon season

MAUSAM ◽  
2021 ◽  
Vol 61 (3) ◽  
pp. 383-390
Author(s):  
G. K. DAS ◽  
H. R. BISWAS ◽  
R. P. SAMUI ◽  
P. A. KORE ◽  
L. A. SIDDIQUE ◽  
...  
Keyword(s):  
Sea Level ◽  
Monsoon Season ◽  
Uttar Pradesh ◽  
Heavy Rain ◽  
Early Morning ◽  
Thunderstorm Activity ◽  
Low Level ◽  
North East India ◽  
North East ◽  
Late Evening

Premonsoon season in north-east India is known for thunderstorm activity with moderate to heavy rain, gusty wind, squall and sometimes with the occurrences of hail fall. In this paper an attempt has been made to find out the climatological and synoptical aspects of hailstorms as well as squall over Guwahati Airport (26.18° N, 91.75° E) during Premonsoon season. 20 years data from 1987 to 2006 have been analyzed. The frequency of hail and squall during premonsoon season is observed to be 1.35 and 3.65 respectively. The most favourable time of occurrence of hail is during afternoon to late evening and that for the occurrence of squall is during evening to early morning over Guwahati Airport. The significant synoptic situations associated with occurrence of hail are Sea level trough from East Uttar Pradesh/Bihar to North-East India and low level cycir over Bihar and neighbourhood.  

Quasi-idealized numerical simulations of processes involved in orogenic convection initiation over the Sierras de Córdoba mountains

2021 ◽  
Author(s):  
Christopher A. Davis
Keyword(s):  
Numerical Simulations ◽  
Mountain Range ◽  
Moist Convection ◽  
Low Level ◽  
Physical Mechanisms ◽  
Convergence Line ◽  
Synoptic Conditions ◽  
Deep Moist Convection ◽  
Outflow Boundary ◽  
Convection Initiation

Abstract The Sierras de Córdoba (SDC) mountain range in Argentina is a hotspot of deep moist convection initiation (CI). Radar climatology indicates that 44% of daytime CI events that occur near the SDC in spring and summer seasons and that are not associated with the passage of a cold front or an outflow boundary involve a northerly LLJ, and these events tend to preferentially occur over the southeast quadrant of the main ridge of the SDC. To investigate the physical mechanisms acting to cause CI, idealized convection-permitting numerical simulations with a horizontal grid spacing of 1 km were conducted using CM1. The sounding used for initializing the model featured a strong northerly LLJ, with synoptic conditions resembling those in a previously postulated conceptual model of CI over the region, making it a canonical case study. Differential heating of the mountain caused by solar insolation in conjunction with the low-level northerly flow sets up a convergence line on the eastern slopes of the SDC. The southern portion of this line experiences significant reduction in convective inhibition, and CI occurs over the SDC southeast quadrant. Thesimulated storm soon acquires supercellular characteristics, as observed. Additional simulations with varying LLJ strength also show CI over the southeast quadrant. A simulation without background flow generated convergence over the ridgeline, with widespread CI across the entire ridgeline. A simulation with mid- and upper-tropospheric westerlies removed indicates that CI is minimally influenced by gravity waves. We conclude that the low-level jet is sufficient to focus convection initiation over the southeast quadrant of the ridge.

scholarly journals Sensitivity Study of WRF Numerical Modeling for Forecasting Heavy Rainfall in Sri Lanka

Atmosphere ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 378 ◽  
Author(s):  
Channa Rodrigo ◽  
Sangil Kim ◽  
Il Jung
Keyword(s):  
Sri Lanka ◽  
Heavy Rainfall ◽  
Weather Prediction ◽  
Wrf Model ◽  
Heavy Rain ◽  
Heavy Precipitation ◽  
Sensitivity Study ◽  
Southwest Monsoon ◽  
Northeast Monsoon ◽  
Pressure System

This study aimed to determine the predictability of the Weather Research and Forecasting (WRF) model with different model physics options to identify the best set of physics parameters for predicting heavy rainfall events during the southwest and northeast monsoon seasons. Two case studies were used for the evaluation: heavy precipitation during the southwest monsoon associated with the simultaneous onset of the monsoon, and a low pressure system over the southwest Bay of Bengal that produced heavy rain over most of the country, with heavy precipitation associated with the northeast monsoon associated with monsoon flow and easterly disturbances. The modeling results showed large variation in the rainfall estimated by the model using the various model physics schemes, but several corresponding rainfall simulations were produced with spatial distribution aligned with rainfall station data, although the amount was not estimated accurately. Moreover, the WRF model was able to capture the rainfall patterns of these events in Sri Lanka, suggesting that the model has potential for operational use in numerical weather prediction in Sri Lanka.

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