Convective Contribution to the Genesis of Hurricane Ophelia (2005)

2009 ◽  
Vol 137 (9) ◽  
pp. 2778-2800 ◽  
Author(s):  
Robert A. Houze ◽  
Wen-Chau Lee ◽  
Michael M. Bell
Keyword(s):  
Latent Heat ◽  
Doppler Radar ◽  
Potential Temperature ◽  
Convective Cell ◽  
Cyclonic Vorticity ◽  
Stratiform Region ◽  
Unstable Layer ◽  
Tropical Depressions ◽  
Convective Cells ◽  
Gust Front

Abstract The convection occurring in the tropical depression that became Hurricane Ophelia (2005) was investigated just prior to tropical storm formation. Doppler radar showed a deep, wide, intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail. The updraft of the cell was 10 km wide, 17 km deep, had updrafts of 10–20 m s−1 throughout its mid- to upper levels, and contained a cyclonic vorticity maximum. The massive convective updraft was maintained by strong positive buoyancy, which was maximum at about the 10-km level, probably aided by latent heat of freezing. Evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft. The convective updraft was fed by a layer of strong inflow that was several kilometers deep. Wind-induced turbulence, just above the ocean surface, enriched the equivalent potential temperature of the boundary layer of the inflow air, thus creating an unstable layer with little convective inhibition. This air was raised to its level of free convection when it encountered the denser air in the rainy core of the convection. The updraft motion and latent heat release in the intense cell generated potential vorticity throughout the low to midlevels, and contained a cyclonic vortex at the midlevels. Vorticity generated throughout the depth of the low to midtroposphere within convective updraft cells was subsequently incorporated into a stratiform region attached to the region of active convective cells. The vorticity perturbations at the low to midlevels in convective cells and their attached stratiform regions were available to be axisymmetrized into the larger-scale intensifying depression vortex.

Dynamics of the Stratiform Sector of a Tropical Cyclone Rainband

2013 ◽  
Vol 70 (7) ◽  
pp. 1891-1911 ◽  
Author(s):  
Anthony C. Didlake ◽  
Robert A. Houze
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Upward Transport ◽  
Radial Outflow ◽  
Convective Cells ◽  
Low Entropy

Abstract Airborne Doppler radar documented the stratiform sector of a rainband within the stationary rainband complex of Hurricane Rita. The stratiform rainband sector is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells. Upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow. Beneath, downward transport is organized into descending radial inflow in response to two regions of latent cooling. In the outer, upper regions of the rainband, sublimational cooling introduces horizontal buoyancy gradients, which produce horizontal vorticity and descending inflow similar to that of the trailing-stratiform region of a mesoscale convective system. Within the zone of heavier stratiform precipitation, melting cooling along the outer rainband edge creates a midlevel horizontal buoyancy gradient across the rainband that drives air farther inward beneath the brightband. The organization of this transport initially is robust but fades downwind as the convection dissipates. The stratiform-induced secondary circulation results in convergence of angular momentum above the boundary layer and broadening of the storm's rotational wind field. At the radial location where inflow suddenly converges, a midlevel tangential jet develops and extends into the downwind end of the rainband complex. This circulation may contribute to ventilation of the eyewall as inflow of low-entropy air continues past the rainband in both the boundary layer and midlevels. Given the expanse of the stratiform rainband region, its thermodynamic and kinematic impacts likely help to modify the structure and intensity of the total vortex.

scholarly journals Coarse, intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm

2010 ◽  
Vol 10 (22) ◽  
pp. 10803-10827 ◽  
Author(s):  
M. T. Montgomery ◽  
Z. Wang ◽  
T. J. Dunkerton
Keyword(s):  
High Resolution ◽  
Deep Convection ◽  
Potential Temperature ◽  
Wrf Model ◽  
Tropical Storm ◽  
Critical Layer ◽  
Tropical Cyclogenesis ◽  
Cyclonic Vorticity ◽  
Easterly Wave ◽  
Tropical Depressions

Abstract. Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together. Implications of these findings are discussed in relation to an upcoming field experiment for the most active period of the Atlantic hurricane season in 2010 that is to be conducted collaboratively between the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), and the National Aeronautics and Space Adminstration (NASA).

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 Observational Analysis of the 27 May 1997 Central Texas Tornadic Event. Part II: Tornadoes

2007 ◽  
Vol 135 (3) ◽  
pp. 727-735 ◽  
Author(s):  
Adam L. Houston ◽  
Robert B. Wilhelmson
Keyword(s):  
Boundary Layer ◽  
Observational Study ◽  
Cold Front ◽  
Convective Cell ◽  
Horizontal Shear ◽  
Low Level ◽  
Central Texas ◽  
Low Levels ◽  
Convective Cells ◽  
Gust Front

Abstract The 27 May 1997 central Texas tornadic event has been investigated in a two-part observational study. As demonstrated in Part I, the 1D environment associated with this event was unfavorable for significant (≥F2) tornadoes. Yet, the storm complex produced at least six significant tornadoes, including one rated F5 (the Jarrell, Texas, tornado). The purpose of this article is to examine the spatiotemporal interrelationships between tornadoes, preexisting boundaries, antecedent low-level mesocyclones, convective cells, and midlevel mesocyclones. It is shown that each of the six observed tornadoes that produced greater than F0 damage formed along the storm-generated gust front, not along preexisting boundaries. Half of these tornadoes formed on the distorted gust front, the portion of the storm-generated gust front whose orientation was deformed largely by the horizontal shear across the cold front. The remaining three tornadoes developed at the gust front cusp (the persistent gust front inflection located at the northeast end of the gust front distortion). Unlike the tornadoes south of the gust front cusp, these tornadoes are found to be associated with antecedent mesocyclones located in the low levels above the boundary layer. Furthermore, these mesocyclonic tornadoes are found to be larger and more destructive than the three nonmesocyclonic tornadoes. The formation of the Jarrell tornado is found to occur as a nearly stationary convective cell became collocated with a south-southwestward-moving low-level mesocyclone near the gust front cusp—a behavior that resembles the formation of nonsupercell tornadoes. It is argued that the back-building propagation/maintenance of the storm complex enabled this juxtaposition of convective cells with vorticity along the distorted gust front and may have therefore enabled tornado formation. Each of the convective cells without midlevel mesocyclones was found to remain farther from the boundaries than the mesocyclonic cells. Since the cells nearest to the boundaries were longer lived than the remaining cells, it is argued that cells near the boundaries were mesocyclonic because the boundaries yielded cells that were more likely to support temporally coherent midlevel rotation.

scholarly journals Seven-Doppler Radar and In Situ Analysis of the 25–26 June 2015 Kansas MCS during PECAN

2019 ◽  
Vol 148 (1) ◽  
pp. 211-240 ◽  
Author(s):  
Rachel L. Miller ◽  
Conrad L. Ziegler ◽  
Michael I. Biggerstaff
Keyword(s):  
Doppler Radar ◽  
Mesoscale Convective System ◽  
Cold Pool ◽  
Convective System ◽  
Stable Layer ◽  
Kinematic Evolution ◽  
Stratiform Region ◽  
Stationary Front ◽  
Mesoscale Convective ◽  
Convective Cells

Abstract This case study analyzes a nocturnal mesoscale convective system (MCS) that was observed on 25–26 June 2015 in northeastern Kansas during the Plains Elevated Convection At Night (PECAN) project. Over the course of the observational period, a broken line of elevated nocturnal convective cells initiated around 0230 UTC on the cool side of a stationary front and subsequently merged to form a quasi-linear MCS that later developed strong, surface-based outflow and a trailing stratiform region. This study combines radar observations with mobile and fixed mesonet and sounding data taken during PECAN to analyze the kinematics and thermodynamics of the MCS from 0300 to 0630 UTC. This study is unique in that 38 consecutive multi-Doppler wind analyses are examined over the 3.5 h observation period, facilitating a long-duration analysis of the kinematic evolution of the nocturnal MCS. Radar analyses reveal that the initial convective cells and linear MCS are elevated and sustained by an elevated residual layer formed via weak ascent over the stationary front. During upscale growth, individual convective cells develop storm-scale cold pools due to pockets of descending rear-to-front flow that are measured by mobile mesonets. By 0500 UTC, kinematic analysis and mesonet observations show that the MCS has a surface-based cold pool and that convective line updrafts are ingesting parcels from below the stable layer. In this environment, the elevated system has become surface based since the cold pool lifting is sufficient for surface-based parcels to overcome the CIN associated with the frontal stable layer.

The Multiple-Vortex Structure of the El Reno, Oklahoma, Tornado on 31 May 2013

2018 ◽  
Vol 146 (8) ◽  
pp. 2483-2502 ◽  
Author(s):  
Howard B. Bluestein ◽  
Kyle J. Thiem ◽  
Jeffrey C. Snyder ◽  
Jana B. Houser
Keyword(s):  
Doppler Radar ◽  
Radar Data ◽  
Rapid Scan ◽  
X Band ◽  
Close Range ◽  
Formation And Evolution ◽  
Using Data ◽  
Secondary Vortices ◽  
The Right ◽  
Gust Front

Abstract This study documents the formation and evolution of secondary vortices associated within a large, violent tornado in Oklahoma based on data from a close-range, mobile, polarimetric, rapid-scan, X-band Doppler radar. Secondary vortices were tracked relative to the parent circulation using data collected every 2 s. It was found that most long-lived vortices (those that could be tracked for ≥15 s) formed within the radius of maximum wind (RMW), mainly in the left-rear quadrant (with respect to parent tornado motion), passing around the center of the parent tornado and dissipating closer to the center in the right-forward and left-forward quadrants. Some secondary vortices persisted for at least 1 min. When a Burgers–Rott vortex is fit to the Doppler radar data, and the vortex is assumed to be axisymmetric, the secondary vortices propagated slowly against the mean azimuthal flow; if the vortex is not assumed to be axisymmetric as a result of a strong rear-flank gust front on one side of it, then the secondary vortices moved along approximately with the wind.

High-Temporal Resolution Polarimetric X-Band Doppler Radar Observations of the 20 May 2013 Moore, Oklahoma, Tornado

2015 ◽  
Vol 143 (7) ◽  
pp. 2711-2735 ◽  
Author(s):  
James M. Kurdzo ◽  
David J. Bodine ◽  
Boon Leng Cheong ◽  
Robert D. Palmer
Keyword(s):  
Temporal Resolution ◽  
Doppler Radar ◽  
Medical Center ◽  
Small Scale ◽  
High Temporal Resolution ◽  
Radar Observations ◽  
University Of Oklahoma ◽  
X Band ◽  
Damage Indicators ◽  
Gust Front

Abstract On 20 May 2013, the cities of Newcastle, Oklahoma City, and Moore, Oklahoma, were impacted by a long-track violent tornado that was rated as an EF5 on the enhanced Fujita scale by the National Weather Service. Despite a relatively sustained long track, damage surveys revealed a number of small-scale damage indicators that hinted at storm-scale processes that occurred over short time periods. The University of Oklahoma (OU) Advanced Radar Research Center’s PX-1000 transportable, polarimetric, X-band weather radar was operating in a single-elevation PPI scanning strategy at the OU Westheimer airport throughout the duration of the tornado, collecting high spatial and temporal resolution polarimetric data every 20 s at ranges as close as 10 km and heights below 500 m AGL. This dataset contains the only known polarimetric radar observations of the Moore tornado at such high temporal resolution, providing the opportunity to analyze and study finescale phenomena occurring on rapid time scales. Analysis is presented of a series of debris ejections and rear-flank gust front surges that both preceded and followed a loop of the tornado as it weakened over the Moore Medical Center before rapidly accelerating and restrengthening to the east. The gust front structure, debris characteristics, and differential reflectivity arc breakdown are explored as evidence for a “failed occlusion” hypothesis. Observations are supported by rigorous hand analysis of critical storm attributes, including tornado track relative to the damage survey, sudden track shifts, and a directional debris ejection analysis. A conceptual description and illustration of the suspected failed occlusion process is provided, and its implications are discussed.

scholarly journals Planetary boundary layer evolution over the Amazon rain forest in episodes of deep moist convection at ATTO

2019 ◽  
Author(s):  
Maurício I. Oliveira ◽  
Otávio C. Acevedo ◽  
Matthias Sörgel ◽  
Ernani L. Nascimento ◽  
Antonio O. Manzi ◽  
...  
Keyword(s):  
Heat Flux ◽  
Potential Temperature ◽  
Sensible Heat Flux ◽  
Moist Convection ◽  
Early Afternoon ◽  
Virtual Potential Temperature ◽  
Gust Fronts ◽  
Deep Moist Convection ◽  
Tall Tower ◽  
Gust Front

Abstract. In this study, high-frequency, multi-level measurements performed from late October to mid-November of 2015 at a 80-m tall tower of the Amazon Tall Tower Observatory (ATTO) project in central Amazonas State, Brazil, were used to diagnose the evolution of thermodynamic and kinematic variables as well as scalar fluxes during the passage of outflows generated by deep moist convection (DMC). Outflow associated with DMC activity over or near the tall tower was identified through the analysis of storm echoes in base reflectivity data from S-band weather radar at Manaus, combined with the detection of gust fronts and cold pools utilizing tower data. Four outflow events were selected, three of which took place during the early evening transition or nighttime hours and one during the early afternoon. Results show that the magnitude of the drop in virtual potential temperature and changes in wind velocity during outflow passages vary according to the type, organization, and life cycle of the convective storm. Overall, the nocturnal events highlighted the passage of well-defined gust fronts with moderate decrease in virtual potential temperature and increase in wind speed. The early afternoon event lacked a sharp gust front and only a gradual drop in virtual potential temperature was observed, probably because of weak or undeveloped outflow. Sensible heat flux (H) experienced an increase at the time of gust front arrival, which was possibly due to sinking of colder air. This was followed by a prolonged period of negative H, associated with enhanced nocturnal negative H in the storms' wake. In turn, increased latent heat flux (LE) was observed following the gust front, owing to drier air coming from the outflow; however, malfunctioning of the moisture sensors during rain precluded a better assessment of this variable. Substantial enhancements of Turbulent Kinetic Energy (TKE) were observed during and after gust front passage, with values comparable to those measured in grass fire experiments, evidencing the highly turbulent character of convective outflows. The early afternoon event displayed slight decreases in the aforementioned quantities in the passage of the outflow. Finally, a conceptual model of the time evolution of H in nocturnal convective outflows observed at the tower site is presented.

scholarly journals High-Resolution Simulation of the Electrification and Lightning of Hurricane Rita during the Period of Rapid Intensification

2011 ◽  
Vol 68 (3) ◽  
pp. 477-494 ◽  
Author(s):  
Alexandre O. Fierro ◽  
Jon M. Reisner
Keyword(s):  
High Resolution ◽  
Latent Heat ◽  
Functional Relationship ◽  
Doppler Radar ◽  
Propagation Speed ◽  
Radar Data ◽  
Lightning Activity ◽  
Rapid Intensification ◽  
Hurricane Rita ◽  
Resolution Simulation

Abstract In this paper, a high-resolution simulation establishing relationships between lightning and eyewall convection during the rapid intensification phase of Rita will be highlighted. The simulation is an attempt to relate simulated lightning activity within strong convective events (CEs) found within the eyewall and general storm properties for a case from which high-fidelity lightning observations are available. Specifically, the analysis focuses on two electrically active eyewall CEs that had properties similar to events observed by the Los Alamos Sferic Array. The numerically simulated CEs were characterized by updraft speeds exceeding 10 m s−1, a relatively more frequent flash rate confined in a layer between 10 and 14 km, and a propagation speed that was about 10 m s−1 less than of the local azimuthal flow in the eyewall. Within an hour of the first CE, the simulated minimum surface pressure dropped by approximately 5 mb. Concurrent with the pulse of vertical motions was a large uptake in lightning activity. This modeled relationship between enhanced vertical motions, a noticeable pressure drop, and heightened lightning activity suggests the utility of using lightning to remotely diagnose future changes in intensity of some tropical cyclones. Furthermore, given that the model can relate lightning activity to latent heat release, this functional relationship, once validated against a derived field produced by dual-Doppler radar data, could be used in the future to initialize eyewall convection via the introduction of latent heat and/or water vapor into a hurricane model.

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