Observational Analysis of Heavy Rainfall Mechanisms Associated with Severe Tropical Storm Bilis (2006) after Its Landfall

2009 ◽  
Vol 137 (6) ◽  
pp. 1881-1897 ◽  
Author(s):  
Shuanzhu Gao ◽  
Zhiyong Meng ◽  
Fuqing Zhang ◽  
Lance F. Bosart
Keyword(s):  
Heavy Rainfall ◽  
Inner Core ◽  
Southern China ◽  
North Pacific Ocean ◽  
Mainland China ◽  
Vertical Wind Shear ◽  
Tropical Storm ◽  
Moist Convection ◽  
Second Stage ◽  
Deep Moist Convection

Abstract This observational study attempts to determine factors responsible for the distribution of precipitation over large areas of southern China induced by Bilis, a western North Pacific Ocean severe tropical storm that made landfall on the southeastern coast of mainland China on 14 July 2006 with a remnant circulation that persisted over land until after 17 July 2006. The heavy rainfalls associated with Bilis during and after its landfall can be divided into three stages. The first stage of the rainfall, which occurred in Fujian and Zhejiang Provinces, could be directly induced by the inner-core storm circulation during its landfall. The third stage of rainfall, which occurred along the coastal areas of Guangdong and Fujian Provinces, likely resulted from the interaction between Bilis and the South China Sea monsoon enhanced by topographical lifting along the coast. The second stage of the rainfall, which appeared inland around the border regions between Jiangxi, Hunan, and Guangdong Provinces, caused the most catastrophic flooding and is the primary focus of the current study. It is found that during the second stage of the rainfall all three ingredients of deep moist convection (moisture, instability, and lifting) are in place. Several mechanisms, including vertical wind shear, warm-air advection, frontogenesis, and topography, may have contributed simultaneously to the lifting necessary for the generation of the heavy rainfall at this stage.

Lagrangian Description of Air Masses Associated with Latent Heat Release in Tropical Storm Karl (2016) during Extratropical Transition

2019 ◽  
Vol 147 (7) ◽  
pp. 2657-2676 ◽  
Author(s):  
Christian Euler ◽  
Michael Riemer ◽  
Tobias Kremer ◽  
Elmar Schömer
Keyword(s):  
Inner Core ◽  
Vertical Wind Shear ◽  
Conveyor Belt ◽  
Tropical Storm ◽  
Vertical Shear ◽  
Lagrangian Description ◽  
Environment Impact ◽  
Extratropical Transition ◽  
Air Masses ◽  
Core Convection

Abstract Extratropical transition (ET) of tropical cyclones involves distinct changes of the cyclone’s structure that are not yet well understood. This study presents for the first time a comprehensive Lagrangian description of structure change near the inner core. A large sample of trajectories is computed from a convection-permitting numerical simulation of the ET of Tropical Storm Karl (2016). Three main airstreams are considered: those associated with the inner-core convection, inner-core descent, and the developing warm conveyor belt. Analysis of these airstreams is performed both in thermodynamic and physical space. Prior to ET, Karl is embedded in weak vertical wind shear and its intensity is impeded by excessive detrainment from the inner-core convection. At the start of ET, vertical shear increases and Karl intensifies, which is attributable to reduced detrainment and thus to the formation of a well-defined outflow layer. During ET, the thermodynamic changes of the environment impact Karl’s inner-core convection predominantly by a decrease of θe values in the inflow layer. Notably, notwithstanding Karl’s weak intensity, its inner core acts as a “containment vessel” that transports high-θe air into the increasingly hostile environment. Inner-core descent has two origins: (i) mostly from upshear-left above 4-km height in the environment and (ii) boundary layer air that ascends in the inner core first and then descends, performing rollercoaster-like trajectories. At the end of the tropical phase of ET, the developing warm conveyor belt comprises air masses from several different source regions, and only partly from the cyclone’s developing warm sector, as expected for extratropical cyclones.

scholarly journals A Subtropical Oceanic Mesoscale Convective Vortex Observed during SoWMEX/TiMREX

2011 ◽  
Vol 139 (8) ◽  
pp. 2367-2385 ◽  
Author(s):  
Hsiao-Wei Lai ◽  
Christopher A. Davis ◽  
Ben Jong-Dao Jou
Keyword(s):  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Southwest Monsoon ◽  
Convective System ◽  
Vortex Center ◽  
Moist Convection ◽  
Low Level ◽  
Mesoscale Convective ◽  
Deep Moist Convection ◽  
Mesoscale Convective Vortex

AbstractThis study examines a subtropical oceanic mesoscale convective vortex (MCV) that occurred from 1800 UTC 4 June to 1200 UTC 6 June 2008 during intensive observing period (IOP) 6 of the Southwest Monsoon Experiment (SoWMEX) and the Terrain-influenced Monsoon Rainfall Experiment (TiMREX). A dissipating mesoscale convective system reorganized within a nearly barotropic vorticity strip, which formed as a southwesterly low-level jet developed to the south of subsiding easterly flow over the southern Taiwan Strait. A cyclonic circulation was revealed on the northern edge of the mesoscale rainband with a horizontal scale of 200 km. An inner subvortex, on a scale of 25–30 km with maximum shear vorticity of 3 × 10−3 s−1, was embedded in the stronger convection. The vortex-relative southerly flow helped create local potential instability favorable for downshear convection enhancement. Strong low-level convergence suggests that stretching occurred within the MCV. Higher θe air, associated with significant potential and conditional instability, and high reflectivity signatures near the vortex center suggest that deep moist convection was responsible for the vortex stretching. Dry rear inflow penetrated into the MCV and suppressed convection in the upshear direction. A mesolow was also roughly observed within the larger vortex. The presence of intense vertical wind shear in the higher troposphere limited the vortex vertical extent to about 6 km.

Genesis of Pre–Hurricane Felix (2007). Part II: Warm Core Formation, Precipitation Evolution, and Predictability

2010 ◽  
Vol 67 (6) ◽  
pp. 1730-1744 ◽  
Author(s):  
Zhuo Wang ◽  
M. T. Montgomery ◽  
T. J. Dunkerton
Keyword(s):  
Initial Conditions ◽  
Numerical Technique ◽  
Transformation Process ◽  
Tropical Storm ◽  
Convective Precipitation ◽  
Moist Convection ◽  
Near Surface ◽  
Warm Core ◽  
Stratiform Precipitation ◽  
Deep Moist Convection

Abstract This is the second of a two-part study examining the simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework. Here several open issues are addressed concerning the formation of the storm’s warm core, the evolution and respective contribution of stratiform versus convective precipitation within the parent wave’s pouch, and the sensitivity of the development pathway reported in Part I to different model physics options and initial conditions. All but one of the experiments include ice microphysics as represented by one of several parameterizations, and the partition of convective versus stratiform precipitation is accomplished using a standard numerical technique based on the high-resolution control experiment. The transition to a warm-core tropical cyclone from an initially cold-core, lower tropospheric wave disturbance is analyzed first. As part of this transformation process, it is shown that deep moist convection is sustained near the pouch center. Both convective and stratiform precipitation rates increase with time. While stratiform precipitation occupies a larger area even at the tropical storm stage, deep moist convection makes a comparable contribution to the total rain rate at the pregenesis stage, and a larger contribution than stratiform processes at the storm stage. The convergence profile averaged near the pouch center is found to become dominantly convective with increasing deep moist convective activity there. Low-level convergence forced by interior diabatic heating plays a key role in forming and intensifying the near-surface closed circulation, while the midlevel convergence associated with stratiform precipitation helps to increase the midlevel circulation and thereby contributes to the formation and upward extension of a tropospheric-deep cyclonic vortex. Sensitivity tests with different model physics options and initial conditions demonstrate a similar pregenesis evolution. These tests suggest that the genesis location of a tropical storm is largely controlled by the parent wave’s critical layer, whereas the genesis time and intensity of the protovortex depend on the details of the mesoscale organization, which is less predictable. Some implications of the findings are discussed.

Practical Predictability of the 20 May 2013 Tornadic Thunderstorm Event in Oklahoma: Sensitivity to Synoptic Timing and Topographical Influence

2015 ◽  
Vol 143 (8) ◽  
pp. 2973-2997 ◽  
Author(s):  
Yunji Zhang ◽  
Fuqing Zhang ◽  
David J. Stensrud ◽  
Zhiyong Meng
Keyword(s):  
Boundary Layer ◽  
Vertical Mixing ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Moist Convection ◽  
Atmospheric Conditions ◽  
Low Level ◽  
Deep Moist Convection ◽  
Simulation Time

Abstract The practical predictability of severe convective thunderstorms during the 20 May 2013 severe weather event that produced the catastrophic enhanced Fujita scale 5 (EF-5) tornado in Moore, Oklahoma, was explored using ensembles of convective-permitting model simulations. The sensitivity of initiation and the subsequent organization and intensity of the thunderstorms to small yet realistic uncertainties in boundary layer and topographical influence within a few hours preceding the thunderstorm event was examined. It was found that small shifts in either simulation time or terrain configuration led to considerable differences in the atmospheric conditions within the boundary layer. Small shifts in simulation time led to changes in low-level moisture and instability, primarily through the vertical distribution of moisture within the boundary layer due to vertical mixing during the diurnal cycle as well as advection by low-level jets, thereby influencing convection initiation. Small shifts in terrain led to changes in the wind field, low-level vertical wind shear, and storm-relative environmental helicity, altering locally enhanced convergence that may trigger convection. After initiation, an upscale growth of errors resulting from deep moist convection led to large forecast uncertainties in the timing, intensity, structure, and organization of the developing mesoscale convective system and its embedded supercells.

Impacts of Coastal Terrain on Warm-Sector Heavy-Rain-Producing MCSs in Southern China

2021 ◽  
Keyword(s):  
Heavy Rainfall ◽  
Southern China ◽  
Coastal Region ◽  
Vertical Wind Shear ◽  
Heavy Rain ◽  
Early Morning ◽  
Cold Pool ◽  
Near Surface ◽  
Warm Sector ◽  
Shear Component

Abstract Warm-sector heavy rainfall in southern China refers to the heavy rainfall that occurs within a weakly-forced synoptic environment under the influence of monsoonal airflows. It is usually located near the southern coast, and is characterized by poor predictability and a close relationship with coastal terrain. This study investigates the impacts of coastal terrain on the initiation, organization and heavy-rainfall potential of MCSs in warm-sector heavy rainfall over southern China using quasi-idealized WRF simulations and terrain-modification experiments. Typical warm-sector heavy rainfall events were selected to produce composite environments that forced the simulations. MCSs in these events all initiated in the early morning and developed into quasi-linear convective systems along the coast with a prominent backbuilding process. When the small coastal terrain is removed, the maximum 12-h rainfall accumulation decreases by ~46%. The convection initiation is advanced ~2 h with the help of orographic lifting associated with flow interaction with the coastal hills in the control experiment. Moreover, the coastal terrain weakens near-surface winds and thus decreases the deep-layer vertical wind shear component perpendicular to the coast and increases the component parallel to the coast; the coastal terrain also concentrates the moisture and instability over the coastal region by weakening the boundary layer jet. These modifications lead to faster upscale growth of convection and eventually a well-organized MCS. The coastal terrain is beneficial for backbuilding convection and thus persistent rainfall by providing orographic lifting for new cells on the western end of the MCS, and by facilitating a stronger and more stagnant cold pool, which stimulates new cells near its rear edge.

scholarly journals Diurnal Cycle of a Heavy Rainfall Corridor over East Asia

2017 ◽  
Vol 145 (8) ◽  
pp. 3365-3389 ◽  
Author(s):  
Guixing Chen ◽  
Weiming Sha ◽  
Toshiki Iwasaki ◽  
Zhiping Wen
Keyword(s):  
East Asia ◽  
Heavy Rainfall ◽  
Southern China ◽  
Central China ◽  
Moist Convection ◽  
Low Level ◽  
Effective Discharge ◽  
Upward Transport ◽  
Convection Initiation ◽  
The Impact

Moist convection occurred repeatedly in the midnight-to-morning hours of 11–16 June 1998 and yielded excessive rainfall in a narrow latitudinal corridor over East Asia, causing severe flood. Numerical experiments and composite analyses of a 5-day period are performed to examine the mechanisms governing nocturnal convection. Both simulations and observations show that a train of MCSs concurrently developed along a quasi-stationary mei-yu front and coincided with the impact of a monsoon surge on a frontogenetic zone at night. This process was regulated primarily by a nocturnal low-level jet (NLLJ) in the southwesterly monsoon that formed over southern China and extended to central China. In particular, the NLLJ acted as a mechanism of moisture transport over the plains. At its northern terminus, the NLLJ led to a zonal band of elevated conditionally unstable air where strong low-level ascent overcame small convective inhibition, triggering new convection in three preferred plains. An analysis of convective instability shows that the low-tropospheric intrusion of moist monsoon air generated CAPE of ~1000 J kg−1 prior to convection initiation, whereas free-atmospheric forcing was much weaker. The NLLJ-related horizontal advection accounted for most of the instability precondition at 100–175 J kg−1 h−1. At the convective stage, instability generation by the upward transport of moisture increased to ~100 J kg−1 h−1, suggesting that ascending inflow caused feedback in convection growth. The convection dissipated in late morning with decaying NLLJ and moisture at elevated layers. It is concluded that the diurnally varying summer monsoon acted as an effective discharge of available moist energy from southern to central China, generating the morning-peak heavy rainfall corridor.

Influence of Equatorial Waves on the Genesis of Super Typhoon Haiyan (2013)

2015 ◽  
Vol 72 (12) ◽  
pp. 4591-4613 ◽  
Author(s):  
Shoujuan Shu ◽  
Fuqing Zhang
Keyword(s):  
Environmental Conditions ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Sensitivity Analyses ◽  
Tropical Region ◽  
Moist Convection ◽  
Super Typhoon ◽  
Equatorial Wave ◽  
Deep Moist Convection ◽  
Cyclonic Disturbance

Abstract The influence of equatorial wave disturbances on the genesis of Super Typhoon Haiyan (2013) is investigated through spectral, composite, and ensemble sensitivity analysis of various observational datasets in combination with predictions from an operational ensemble. Under the favorable large-scale environmental conditions of the Asian monsoon combined with the Madden–Julian oscillation (MJO), the incipient Haiyan develops from a cyclonic disturbance that originates from a train of westward-propagating mixed Rossby–gravity (MRG) waves. Haiyan eventually develops in the monsoon trough region at the leading edge of the moist MJO phase that has strong low-level convergence, high moisture content, and weak shear, along with high sea surface temperature. These favorable environmental conditions promote the intensification of deep moist convection that facilitates the development of the cyclonic disturbance from an MRG wave into a tropical depression, which later intensifies rapidly into Super Typhoon Haiyan, one of the world’s strongest and most destructive tropical storms ever recorded. Results from ensemble sensitivity analyses are consistent with this finding and further show that the uncertainties in tropical waves and their interactions can impact the large-scale environment surrounding Haiyan’s precursor and therefore limit the predictability of tropical cyclone formation and intensity. The better-performing members tend to have a stronger initial MRG wave disturbance, which provides a stronger initial seed for the later development of the storm, as well as a stronger moist MJO wave in the tropical region, which not only promotes deep convection near the precursor location, but also reduces the environmental vertical wind shear by strengthening the tropical westerlies.

Mechanisms for Quasi-Stationary Behavior in Simulated Heavy-Rain-Producing Convective Systems

2009 ◽  
Vol 66 (6) ◽  
pp. 1543-1568 ◽  
Author(s):  
Russ S. Schumacher
Keyword(s):  
Deep Convection ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Cold Pool ◽  
Convective System ◽  
Moist Convection ◽  
Initial State ◽  
Low Level ◽  
Convective Systems ◽  
Deep Moist Convection

Abstract In this study, idealized numerical simulations are used to identify the processes responsible for initiating, organizing, and maintaining quasi-stationary convective systems that produce locally extreme rainfall amounts. Of particular interest are those convective systems that have been observed to occur near mesoscale convective vortices (MCVs) and other midlevel circulations. To simulate the lifting associated with such circulations, a low-level momentum forcing is applied to an initial state that is representative of observed extreme rain events. The initial vertical wind profile includes a sharp reversal of the vertical wind shear with height, indicative of observed low-level jets. Deep moist convection initiates within the region of mesoscale lifting, and the resulting convective system replicates many of the features of observed systems. The low-level thermodynamic environment is nearly saturated, which is not conducive to the production of a strong surface cold pool; yet the convection quickly organizes into a back-building line. It is shown that a nearly stationary convectively generated low-level gravity wave is responsible for the linear organization, which continues for several hours. New convective cells repeatedly form on the southwest end of the line and move to the northeast, resulting in large local rainfall amounts. In the later stages of the simulated convective system, a cold pool does develop, but its interaction with the strong reverse shear at low levels is not optimized for the maintenance of deep convection along its edge. A series of sensitivity experiments shows some of the effects of hydrometeor evaporation and melting, planetary rotation, and the imposed mesoscale forcing.

How Does Hurricane Edouard (2014) Evolve toward Symmetry before Rapid Intensification? A High-Resolution Ensemble Study

2020 ◽  
Vol 77 (4) ◽  
pp. 1329-1351 ◽  
Author(s):  
George R. Alvey ◽  
Ed Zipser ◽  
Jonathan Zawislak
Keyword(s):  
High Resolution ◽  
Inner Core ◽  
Initial Conditions ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Tropical Storm ◽  
Sea Surface ◽  
Rapid Intensification ◽  
Upper Troposphere ◽  
Stratiform Precipitation

Abstract A 14-member high-resolution ensemble of Edouard (2014), a moderately sheared tropical storm that underwent rapid intensification (RI), is used to determine causes of vortex alignment and precipitation symmetry prior to RI. Half the members intensify similarly to the NHC’s best track, while the other seven ensemble members fail to reproduce intensification. Analyses of initial conditions (vertical wind shear, sea surface temperatures, relative humidity, vortex structure) reveal that lower humidity and weaker, more tilted vortices in nonintensifying members likely increase their susceptibility to boundary layer flushing episodes. As the simulations progress, vortex tilt, inner-core humidity, and azimuthal variations in the structure of precipitation best differentiate the two ensemble subsets. Although all members initially are slowly intensifying asymmetric storms, the RI members are unique in that they have more persistent deep convection downshear, which favors vortex alignment via the stretching term and/or precession. As deep convection transitions to stratiform precipitation and anvil clouds in the upshear quadrants, evaporation and sublimation of condensate advected from the downshear quadrants moisten the middle to upper troposphere. This is hypothesized to promote an increase in precipitation symmetrization, a necessary precursor for RI.

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