scholarly journals Rapid Mesoscale Environmental Changes Accompanying Genesis of an Unusual Tornado

2016 ◽  
Vol 31 (3) ◽  
pp. 763-786 ◽  
Author(s):  
Steven E. Koch ◽  
Randolph Ware ◽  
Hongli Jiang ◽  
Yuanfu Xie
Keyword(s):  
Environmental Changes ◽  
Rapid Development ◽  
Microwave Radiometer ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Low Level ◽  
Short Period ◽  
Stretching Deformation ◽  
Upper Level Jet

Abstract This study documents a very rapid increase in convective instability, vertical wind shear, and mesoscale forcing for ascent leading to the formation of a highly unusual tornado as detected by a ground-based microwave radiometer and wind profiler, and in 1-km resolution mesoanalyses. Mesoscale forcing for the rapid development of severe convection began with the arrival of a strong upper-level jet streak with pronounced divergence in its left exit region and associated intensification of the low-level flow to the south of a pronounced warm front. The resultant increase in stretching deformation along the front occurred in association with warming immediately to its south as low-level clouds dissipated. This created a narrow ribbon of intense frontogenesis and a rapid increase in convective available potential energy (CAPE) within 75 min of tornadogenesis. The Windsor, Colorado, storm formed at the juncture of this warm frontogenesis zone and a developing dryline. Storm-relative helicity suddenly increased to large values during this pretornadic period as a midtropospheric layer of strong southeasterly winds descended to low levels. The following events also occurred simultaneously within this short period of time: a pronounced decrease in midtropospheric equivalent potential temperature θe accompanying the descending jet, an increase in low-level θe associated with the surface sensible heating, and elimination of the capping inversion and convective inhibition. The simultaneous nature of these rapid changes over such a short period of time, not fully captured in Storm Prediction Center mesoanalyses, was likely critical in generating this unusual tornadic event.

scholarly journals A 7-Year Climatology of Warm-Sector Heavy Rainfall over South China during the Pre-Summer Months

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 914
Author(s):  
Tao Chen ◽  
Da-Lin Zhang
Keyword(s):  
South China ◽  
Heavy Rainfall ◽  
Large Scale ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Precipitable Water ◽  
Atmospheric Parameter ◽  
Low Level ◽  
Warm Sector

In view of the limited predictability of heavy rainfall (HR) events and the limited understanding of the physical mechanisms governing the initiation and organization of the associated mesoscale convective systems (MCSs), a composite analysis of 58 HR events over the warm sector (i.e., far ahead of the surface cold front), referred to as WSHR events, over South China during the months of April to June 2008~2014 is performed in terms of precipitation, large-scale circulations, pre-storm environmental conditions, and MCS types. Results show that the large-scale circulations of the WSHR events can be categorized into pre-frontal, southwesterly warm and moist ascending airflow, and low-level vortex types, with higher frequency occurrences of the former two types. Their pre-storm environments are characterized by a deep moist layer with >50 mm column-integrated precipitable water, high convective available potential energy with the equivalent potential temperature of ≥340 K at 850 hPa, weak vertical wind shear below 400 hPa, and a low-level jet near 925 hPa with weak warm advection, based on atmospheric parameter composite. Three classes of the corresponding MCSs, exhibiting peak convective activity in the afternoon and the early morning hours, can be identified as linear-shaped, a leading convective line adjoined with trailing stratiform rainfall, and comma-shaped, respectively. It is found that many linear-shaped MCSs in coastal regions are triggered by local topography, enhanced by sea breezes, whereas the latter two classes of MCSs experience isentropic lifting in the southwesterly warm and moist flows. They all develop in large-scale environments with favorable quasi-geostrophic forcing, albeit weak. Conceptual models are finally developed to facilitate our understanding and prediction of the WSHR events over South China.

Observations of a Squall Line and Its Near Environment Using High-Frequency Rawinsonde Launches during VORTEX2

2010 ◽  
Vol 138 (11) ◽  
pp. 4076-4097 ◽  
Author(s):  
George H. Bryan ◽  
Matthew D. Parker
Keyword(s):  
Wind Shear ◽  
Deep Layer ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Squall Line ◽  
Cold Pool ◽  
Low Level ◽  
Stratiform Region ◽  
Gust Front

Abstract Rawinsonde data were collected before and during passage of a squall line in Oklahoma on 15 May 2009 during the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). Nine soundings were released within 3 h, allowing for unprecedented analysis of the squall line’s internal structure and nearby environment. Four soundings were released in the prestorm environment and they document the following features: low-level cooling associated with the reduction of solar isolation by a cirrus anvil; abrupt warming (1.5 K in 30 min) above the boundary layer, which is probably attributable to a gravity wave; increases in both low-level and deep-layer vertical wind shear within 100 km of the squall line; and evidence of ascent extending at least 75 km ahead of the squall line. The next sounding was released ∼5 km ahead of the squall line’s gust front; it documented a moist absolutely unstable layer within a 2-km-deep layer of ascent, with vertical air velocity of approximately 6 m s−1. Another sounding was released after the gust front passed but before precipitation began; this sounding showed the cold pool to be ∼4 km deep, with a cold pool intensity C ≈ 35 m s−1, even though this sounding was located only 8 km behind the surface gust front. The final three soundings were released in the trailing stratiform region of the squall line, and they showed typical features such as: “onion”-shaped soundings, nearly uniform equivalent potential temperature over a deep layer, and an elevated rear inflow jet. The cold pool was 4.7 km deep in the trailing stratiform region, and extended ∼1 km above the melting level, suggesting that sublimation was a contributor to cold pool development. A mesoscale analysis of the sounding data shows an upshear tilt to the squall line, which is consistent with the cold pool intensity C being much larger than a measure of environmental vertical wind shear ΔU. This dataset should be useful for evaluating cloud-scale numerical model simulations and analytic theory, but the authors argue that additional observations of this type should be collected in future field projects.

scholarly journals Environment and Early Evolution of the 8 May 2009 Derecho-Producing Convective System

2011 ◽  
Vol 139 (4) ◽  
pp. 1083-1102 ◽  
Author(s):  
Michael C. Coniglio ◽  
Stephen F. Corfidi ◽  
John S. Kain
Keyword(s):  
United States ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Early Evolution ◽  
Convective System ◽  
Similar Time ◽  
Low Level ◽  
Central United States ◽  
Lapse Rates

This study documents the complex environment and early evolution of the remarkable derecho that traversed portions of the central United States on 8 May 2009. Central to this study is the comparison of the 8 May 2009 derecho environment to that of other mesoscale convective systems (MCSs) that occurred in the central United States during a similar time of year. Synoptic-scale forcing was weak and thermodynamic instability was limited during the development of the initial convection, but several mesoscale features of the environment appeared to contribute to initiation and upscale growth, including a mountain wave, a midlevel jet streak, a weak midlevel vorticity maximum, a “Denver cyclone,” and a region of upper-tropospheric inertial instability. The subsequent MCS developed in an environment with an unusually strong and deep low-level jet (LLJ), which transported exceptionally high amounts of low-level moisture northward very rapidly, destabilized the lower troposphere, and enhanced frontogenetical circulations that appeared to aid convective development. The thermodynamic environment ahead of the developing MCS contained unusually high precipitable water (PW) and very large midtropospheric lapse rates, compared to other central plains MCSs. Values of downdraft convective available potential energy (DCAPE), mean winds, and 0–6-km vertical wind shear were not as anomalously large as the PW, lapse rates, and LLJ. In fact, the DCAPE values were lower than the mean values in the comparison dataset. These results suggest that the factors contributing to updraft strength over a relatively confined area played a significant role in generating the strong outflow winds at the surface, by providing a large volume of hydrometeors to drive the downdrafts.

Convective-storm environments in subtropical South America from high-frequency soundings during RELAMPAGO-CACTI

2021 ◽  
Author(s):  
Russ S. Schumacher ◽  
Deanna A. Hence ◽  
Stephen W. Nesbitt ◽  
Robert J. Trapp ◽  
Karen A. Kosiba ◽  
...  
Keyword(s):  
South America ◽  
High Frequency ◽  
Wind Shear ◽  
Field Experiments ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Mobile Platforms ◽  
Convective Storms ◽  
Low Level

AbstractDuring the RELAMPAGO-CACTI field experiments in 2018-19, an unprecedented number of balloon-borne soundings were collected in Argentina. Radiosondes were launched from both fixed and mobile platforms, yielding 2712 soundings during the period 15 October 2018-30 April 2019. Approximately 20% of these soundings were collected by highly mobile platforms, strategically positioned for each intensive observing period, and launching approximately once per hour. The combination of fixed and mobile soundings capture both the overall conditions characterizing the RELAMPAGO-CACTI campaign, as well as the detailed evolution of environments supporting the initiation and upscale growth of deep convective storms, including some that produced hazardous hail and heavy rainfall. Episodes of frequent convection were characterized by sufficient quantities of moisture and instability for deep convection, along with deep-layer vertical wind shear supportive of organized or rotating storms. Eleven soundings showed most-unstable convective available potential energy (MUCAPE) exceeding 6000 J kg−1, comparable to the extreme instability observed in other parts of the world with intense deep convection. Parameters used to diagnose severe-storm potential showed that conditions were often favorable for supercells and severe hail, but not for tornadoes, primarily owing to insufficient low-level wind shear. High-frequency soundings also revealed the structure and evolution of the boundary layer leading up to convection initiation, convectively generated cold pools, the South American Low-Level Jet (SALLJ), and elevated nocturnal convection. This sounding dataset will enable improved understanding and prediction of convective storms and their surroundings in subtropical South America, as well as comparisons with other heavily studied regions such as the central United States that have not previously been possible.

scholarly journals A Transition Mechanism for the Spontaneous Axisymmetric Intensification of Tropical Cyclones

2013 ◽  
Vol 70 (1) ◽  
pp. 112-129 ◽  
Author(s):  
Yoshiaki Miyamoto ◽  
Tetsuya Takemi
Keyword(s):  
Tropical Cyclones ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Three Dimensional ◽  
Horizontal Wind ◽  
Low Level ◽  
Transition Mechanism ◽  
Budget Analysis ◽  
Axisymmetric Structure ◽  
Physics Model

Abstract A mechanism for the transition of tropical cyclones (TCs) to the spontaneous rapid intensification (RI) phase is proposed based on numerical results of a three-dimensional full-physics model. The intensification phase of the simulated TC is divided into three subphases according to the rate of intensification: 1) a slowly intensifying phase, 2) an RI phase, and 3) an adjustment phase toward the quasi-steady state. The evolution of a TC vortex is diagnosed by the energy budget analysis and the degree of axisymmetric structure of the TC vortex, and the simulated TC is determined to be axisymmetrized 12 h before the onset of RI. It is found that equivalent potential temperature θe in the lowest layer suddenly increases inside the radius of maximum azimuthally averaged horizontal wind rma after the TC becomes nearly axisymmetric. Forward trajectory analyses revealed that the enhanced convective instability in the TC core region where the eyewall subsequently forms results from the increased inertial stability of the TC core after the axisymmetrization. Since fluid parcels remain longer inside rma, owing to the increased inertial stability, the parcels obtain more enthalpy from the underlying ocean. As a result, low-level θe and hence convective available potential energy (CAPE) increase. Under the condition with increased CAPE, the eyewall is intensified and the secondary circulation is enhanced, leading to the increased convergence of low-level inflow; this process is considered to be the trigger of RI. Once the eyewall forms, the simulated TC starts its RI.

scholarly journals The Development of Severe Vortices within Simulated High-Shear, Low-CAPE Convection

2019 ◽  
Vol 147 (6) ◽  
pp. 2189-2216 ◽  
Author(s):  
Keith D. Sherburn ◽  
Matthew D. Parker
Keyword(s):  
Wind Shear ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Convective System ◽  
High Shear ◽  
Low Level ◽  
Factor Ii ◽  
Strong Surface ◽  
Perturbation Pressure ◽  
Lapse Rates

Abstract Environments characterized by large values of vertical wind shear and modest convective available potential energy (CAPE) are colloquially referred to as high-shear, low-CAPE (HSLC) environments. Convection within these environments represents a considerable operational forecasting challenge. Generally, it has been determined that large low-level wind shear and steep low-level lapse rates—along with synoptic-scale forcing for ascent—are common ingredients supporting severe HSLC convection. This work studies the specific processes that lead to the development of strong surface vortices in HSLC convection, particularly associated with supercells embedded within a quasi-linear convective system (QLCS), and how these processes are affected by varying low-level shear vector magnitudes and lapse rates. Analysis of a control simulation, conducted with a base state similar to a typical HSLC severe environment, reveals that the key factors in the development of a strong surface vortex in HSLC embedded supercells are (i) a strong low- to midlevel mesocyclone, and (ii) a subsequent strong low-level updraft that results from the intense, upward-pointing dynamic perturbation pressure gradient acceleration. Through a matrix of high-resolution, idealized simulations, it is determined that sufficient low-level shear vector magnitudes are necessary for the development of low- to midlevel vertical vorticity [factor (i)], while steeper low-level lapse rates provide stronger initial low-level updrafts [factor (ii)]. This work shows why increased low-level lapse rates and low-level shear vector magnitudes are important to HSLC convection on the storm scale, while also revealing similarities between surface vortexgenesis in HSLC embedded supercells and higher-CAPE supercells.

scholarly journals A Composite Perspective on Bore Passages during the PECAN Campaign

2019 ◽  
Vol 147 (4) ◽  
pp. 1395-1413 ◽  
Author(s):  
David M. Loveless ◽  
Timothy J. Wagner ◽  
David D. Turner ◽  
Steven A. Ackerman ◽  
Wayne F. Feltz
Keyword(s):  
Water Vapor ◽  
Observational Studies ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Future Research ◽  
High Temporal Resolution ◽  
Convective Initiation ◽  
Low Level ◽  
Capping Inversion ◽  
The Impact

Abstract Atmospheric bores have been shown to have a role in the initiation and maintenance of elevated convection. Previous observational studies of bores have been case studies of more notable events. However, this creates a selection bias toward extraordinary cases, while discussions of the differences between bores that favor convective initiation and maintenance and bores that do not are lacking from the literature. This study attempts to fill that gap by analyzing a high-temporal-resolution thermodynamic profile composite of eight bores observed by multiple platforms during the Plains Elevated Convection at Night (PECAN) campaign in order to assess the impact of bores on the environment. The time–height cross section of the potential temperature composite displays quasi-permanent parcel displacements up to 900 m with the bore passage. Low-level lifting is shown to weaken the capping inversion and reduce convective inhibition (CIN) and the level of free convection (LFC). Additionally, low-level water vapor increases by about 1 g kg−1 in the composite mean. By assessing variability across the eight cases, it is shown that increases in low-level water vapor result in increases to convective available potential energy (CAPE), while drying results in decreased CAPE. Most cases resulted in decreased CIN and LFC height with the bore passage, but only some cases resulted in increased CAPE. This suggests that bores will increase the potential for convective initiation, but future research should be directed toward better understanding cases that result in increased CAPE as those are the types of bores that will increase severity of convection.

scholarly journals Observations of a Nondeveloping Tropical Disturbance in the Western North Pacific during TCS-08 (2008)

2015 ◽  
Vol 143 (7) ◽  
pp. 2459-2484 ◽  
Author(s):  
Andrew B. Penny ◽  
Patrick A. Harr ◽  
Michael M. Bell
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Low Level ◽  
The North ◽  
Cloud Clusters ◽  
Potential Formation ◽  
Shearing Deformation ◽  
Upper Level

Abstract Large uncertainty still remains in determining whether a tropical cloud cluster will develop into a tropical cyclone. During The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC)/Tropical Cyclone Structure-2008 (TCS-08) field experiment, over 50 tropical cloud clusters were monitored for development, but only 4 developed into a tropical cyclone. One nondeveloping tropical disturbance (TCS025) was closely observed for potential formation during five aircraft research missions, which provided an unprecedented set of observations pertaining to the large-scale and convective environments of a nondeveloping system. The TCS025 disturbance was comprised of episodic convection that occurred in relation to the diurnal cycle along the eastern extent of a broad low-level trough. The upper-level environment was dominated by two cyclonic cells in the tropical upper-tropospheric trough (TUTT) north of the low-level trough in which the TCS025 circulation was embedded. An in-depth examination of in situ observations revealed that the nondeveloping circulation was asymmetric and vertically misaligned, which led to larger system-relative flow on the mesoscale. Persistent environmental vertical wind shear and horizontal shearing deformation near the circulation kept the system from becoming better organized and appears to have allowed low equivalent potential temperature () air originating from one of the TUTT cells to the north (upshear) to impact the thermodynamic environment of TCS025. This in turn weakened subsequent convection that might otherwise have improved alignment and contributed to the transition of TCS025 to a tropical cyclone.

scholarly journals Mesocyclone Evolution Associated with Varying Shear Profiles during the 24 June 2003 Tornado Outbreak

2011 ◽  
Vol 26 (6) ◽  
pp. 808-827 ◽  
Author(s):  
Philip N. Schumacher ◽  
Joshua M. Boustead
Keyword(s):  
Large Scale ◽  
Wind Profile ◽  
Convective Available Potential Energy ◽  
Geographical Area ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Moist Convection ◽  
Low Level ◽  
Low Level Jet ◽  
Tornado Outbreak

Abstract The morphology of mesocyclones associated with the regional tornado outbreak on 24 June 2003 is examined to illustrate the effects of changing vertical wind profiles. The large-scale environment supported deep moist convection, with forcing for ascent and convective instability. Postevent analysis indicated there were changes in the shear in space and time across a small geographical area. The event was separated into sectors based on both the synoptic setting and the differing shear profiles. Near the surface warm front, the vertical wind profile and mesocyclone evolution exhibited a classic appearance and produced significant tornadoes. In the warm sector, where no discernible surface boundaries were evident, classic supercells initially were favored but only produced short-lived tornadoes rated as F0 on the Fujita scale. The vertical wind profile changed as a low-level jet intensified after 0000 UTC 25 June. The majority of the vertical wind shear became located below 3 km. Meanwhile, mesocyclone elevation lowered and rotational velocity increased. As the dynamically induced low-level jet and an area of mixed-layer (ML) convective available potential energy (CAPE) became juxtaposed where the boundary layer was uncapped, strong low-level mesocyclones and 32 tornadoes developed in an area with no discernible surface boundaries. The event illustrates the need for warning meteorologists to monitor not only the amount of shear present, but also its distribution in the hodograph owing to its strong correspondence with mesocyclone morphology.

scholarly journals Doppler Radar Analysis of a Tornadic Miniature Supercell during the Landfall of Typhoon Mujigae (2015) in South China

2017 ◽  
Vol 98 (9) ◽  
pp. 1821-1831 ◽  
Author(s):  
Kun Zhao ◽  
Mingjun Wang ◽  
Ming Xue ◽  
Peiling Fu ◽  
Zhonglin Yang ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Vertical Direction ◽  
Ground Level ◽  
Large Cell ◽  
Small Surface ◽  
Low Level ◽  
Wind Analysis ◽  
Lifting Condensation Level

Abstract On 4 October 2015, a miniature supercell embedded in an outer rainband of Typhoon Mujigae produced a major tornado in Guangdong province of China, leading to 4 deaths and up to 80 injuries. This study documents the structure and evolution of the tornadic miniature supercell using coastal Doppler radars, a sounding, videos, and a damage survey. This tornado is rated at least EF3 on the enhanced Fujita scale. It is by far the strongest typhoon rainband tornado yet documented in China, and possessed double funnels near its peak intensity. Radar analysis indicates that this tornadic miniature supercell exhibited characteristics similar to those found in United States landfalling hurricanes, including a hook echo, low-level inf low notches, an echo top below 10 km, a small and shallow mesocyclone, and a long lifespan (3 h). The environmental conditions—which consisted of moderate convective available potential energy (CAPE), a low lifting condensation level, a small surface dewpoint depression, a large veering low-level vertical wind shear, and a large cell-relative helicity—are favorable for producing miniature supercells. The mesocyclone, with its maximum intensity at 2 km above ground level (AGL), formed an hour before tornadogenesis. A tornado vortex signature (TVS) was identified between 1 and 3 km AGL, when the parent mesocyclone reached its peak radar-indicated intensity of 30 m s−1. The TVS was located between the updraft and forward-flank downdraft, near the center of the mesocyclone. Dual-Doppler wind analysis reveals that tilting of the low-level vorticity into the vertical direction and subsequent stretching by a strong updraft were the main contributors to the mesocyclone intensification.

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