The Anatomy of a Series of Cloud Bursts that Eclipsed the US Rainfall Record

2021 ◽  
Keyword(s):  
Deep Convection ◽  
Vertical Motion ◽  
Precipitable Water ◽  
Radar Data ◽  
Data Sets ◽  
Streamwise Vorticity ◽  
Convective Storms ◽  
Low Level ◽  
The Us ◽  
The Right

Abstract A series of extreme cloudbursts occurred on 14 April 2018 over the northern slopes of the island of Kaua‘i. The storm inundated some areas with 1262 mm (∼50”) of rainfall in a 24-hr period, eclipsing the previous 24-hr US rainfall record of 1100 mm (42”) set in Texas in 1979. Three periods of intense rainfall are diagnosed through detailed analysis of National Weather Service operational and special data sets. On the synoptic scale, a slowly southeastward propagating trough aloft over a deep layer of low level moisture (>40 mm of total precipitable water) produced prolonged instability over Kaua‘i. Enhanced NE to E low level flow impacted Kaua‘i’s complex terrain, which includes steep north and eastward facing slopes and cirques. The resulting orographic lift initiated deep convection. The wind profile exhibited significant shear in the troposphere and streamwise vorticity within the convective storm inflow. Evidence suggests that large directional shear in the boundary layer, paired with enhanced orographic vertical motion, produced rotating updrafts within the convective storms. Mesoscale rotation is manifest in the radar data during the latter two periods and reflectivity cores are observed to propagate both to the left and to the right of the mean shear, which is characteristic of supercells. The observations suggest that the terrain configuration in combination with the windshear separates the area of updrafts from the downdraft section of the storm, resulting in almost continuous heavy rainfall over Waipā Garden.

scholarly journals Numerical Simulation of Tornadogenesis in an Outer-Rainband Minisupercell of Typhoon Shanshan on 17 September 2006

2009 ◽  
Vol 137 (12) ◽  
pp. 4238-4260 ◽  
Author(s):  
Wataru Mashiko ◽  
Hiroshi Niino ◽  
Teruyuki Kato
Keyword(s):  
Momentum Equation ◽  
Precipitation Pattern ◽  
Streamwise Vorticity ◽  
Convective Storms ◽  
Low Level ◽  
Budget Analysis ◽  
Rapid Amplification ◽  
The Right ◽  
Left Front ◽  
Gust Front

Abstract On 17 September 2006, three tornadoes occurred along the east coast of Kyusyu Island in western Japan during the passage of an outer rainband in the right-front quadrant of Typhoon Shanshan. To clarify the structure of the tornado-producing storms and the mechanism of tornadogenesis, quadruply nested numerical simulations were performed using a nonhydrostatic model with an innermost horizontal grid spacing of 50 m. Several simulated convective storms in the outermost rainband exhibited characteristics of a minisupercell. One storm had a strong rotating updraft of more than 30 m s−1 and a large vertical vorticity exceeding 0.06 s−1. This storm spawned a tornado when the low-level mesocyclone intensified. The tornado was generated on the rear-flank gust front near the mesocyclone center when a secondary rear-flank downdraft (RFD) surge advanced cyclonically around the low-level mesocyclone and overtook the rear-flank gust front at its left-front edge. Backward trajectories and vorticity budget analysis along the trajectories indicate that the secondary RFD surge played a key role in tornadogenesis by barotropically transporting the large streamwise vorticity associated with the environmental low-level veering shear toward the surface. When the secondary RFD outflow surge boundary reached the rear-flank gust front, the horizontal convergence was enhanced, contributing to the rapid amplification of the vertically tilted streamwise vorticity. The diagnostics of the vertical momentum equation and several sensitivity experiments demonstrated that precipitation loading in the area of a hook-shaped precipitation pattern was crucial to the behavior of the RFD and the subsequent tornadogenesis.

scholarly journals Synoptic-Scale Dual Structure of Precipitable Water along the Eastern Pacific ITCZ

2014 ◽  
Vol 27 (16) ◽  
pp. 6288-6304 ◽  
Author(s):  
Guanghua Chen ◽  
Yukari N. Takayabu ◽  
Chie Yokoyama
Keyword(s):  
Vertical Structure ◽  
Deep Convection ◽  
Vertical Motion ◽  
Precipitable Water ◽  
Meridional Wind ◽  
Eastern Pacific ◽  
Boreal Summer ◽  
Synoptic Scale ◽  
The West ◽  
Dual Structure

Abstract Using 10-yr high-resolution satellite and reanalysis data, the synoptic-scale dual structure of precipitable water (PW), in which the southern and northern bands straddled at the ITCZ produce zonally propagating meridional dipoles, is observed over the eastern Pacific (EP) during boreal summer and fall. Composites indicate that the PW dipole, concurrent with the dipole-like filtered divergence, has a shift to the west of the anomalously cyclonic circulation. The vertical structure of filtered meridional wind is characterized by a wavenumber-1 baroclinic mode, and the vertical motion has two peaks situated at 850 and 300 hPa, respectively. To the east of the PW dipole, the shallow convection is embedded within the deep convection, forming a multilevel structure of meridional wind on the ITCZ equatorward side. To the west of the PW dipole, the deep convection tends to be suppressed because of the invasion of midlevel dry air advected by northerly flows. The generation and propagation of the dual PW band can be attributed to the divergence and advection terms related to specific humidity and three-dimensional wind. By comparison, the PW anomalies over the western North Pacific, only exhibiting a single band, coincide with the centers of synoptic disturbances with a barotropic vertical structure. Because of the weakening of lower-level divergence, the vertical motion, and the horizontal gradient of PW, the synoptic-scale PW signal is reduced significantly. The typical cases and statistics confirm that the strong meridional dipoles and westward-propagating disturbances are closely associated with the distortion and breakdown of ITCZ over the EP.

scholarly journals A High-Resolution Simulation of Asymmetries in Severe Southern Hemisphere Tropical Cyclone Larry (2006)

2009 ◽  
Vol 137 (12) ◽  
pp. 4171-4187 ◽  
Author(s):  
Hamish A. Ramsay ◽  
Lance M. Leslie ◽  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Southern Hemisphere ◽  
Inner Core ◽  
Mesoscale Model ◽  
Deep Convection ◽  
Vertical Motion ◽  
Vertical Shear ◽  
Low Level ◽  
Frictional Convergence

Abstract Advances in observations, theory, and modeling have revealed that inner-core asymmetries are a common feature of tropical cyclones (TCs). In this study, the inner-core asymmetries of a severe Southern Hemisphere tropical cyclone, TC Larry (2006), are investigated using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and the Kepert–Wang boundary layer model. The MM5-simulated TC exhibited significant asymmetries in the inner-core region, including rainfall distribution, surface convergence, and low-level vertical motion. The near-core environment was characterized by very low environmental vertical shear and consequently the TC vortex had almost no vertical tilt. It was found that, prior to landfall, the rainfall asymmetry was very pronounced with precipitation maxima consistently to the right of the westward direction of motion. Persistent maxima in low-level convergence and vertical motion formed ahead of the translating TC, resulting in deep convection and associated hydrometeor maxima at about 500 hPa. The asymmetry in frictional convergence was mainly due to the storm motion at the eyewall, but was dominated by the proximity to land at larger radii. The displacement of about 30°–120° of azimuth between the surface and midlevel hydrometeor maxima is explained by the rapid cyclonic advection of hydrometeors by the tangential winds in the TC core. These results for TC Larry support earlier studies that show that frictional convergence in the boundary layer can play a significant role in determining the asymmetrical structures, particularly when the environmental vertical shear is weak or absent.

scholarly journals The Role of Observed Environmental Conditions and Precipitation Evolution in the Rapid Intensification of Hurricane Earl (2010)

2015 ◽  
Vol 143 (6) ◽  
pp. 2207-2223 ◽  
Author(s):  
Gabriel Susca-Lopata ◽  
Jonathan Zawislak ◽  
Edward J. Zipser ◽  
Robert F. Rogers
Keyword(s):  
Structural Changes ◽  
Doppler Radar ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Radar Data ◽  
Rapid Intensification ◽  
Low Level ◽  
Upper Level ◽  
Wind Retrievals

Abstract An investigation into the possible causes of the rapid intensification (RI) of Hurricane Earl (2010) is carried out using a combination of global analyses, aircraft Doppler radar data, and observations from passive microwave satellites and a long-range lightning network. Results point to an important series of events leading to, and just after, the onset of RI, all of which occur despite moderate (7–12 m s−1) vertical wind shear present. Beginning with an initially vertically misaligned vortex, observations indicate that asymmetric deep convection, initially left of shear but not distinctly up- or downshear, rotates into more decisively upshear regions. Following this convective rotation, the vortex becomes aligned and precipitation symmetry increases. The potential contributions to intensification from each of these structural changes are discussed. The radial distribution of intense convection relative to the radius of maximum wind (RMW; determined from Doppler wind retrievals) is estimated from microwave and lightning data. Results indicate that intense convection is preferentially located within the upper-level (8 km) RMW during RI, lending further support to the notion that intense convection within the RMW promotes tropical cyclone intensification. The distribution relative to the low-level RMW is more ambiguous, with intense convection preferentially located just outside of the low-level RMW at times when the upper-level RMW is much greater than the low-level RMW.

Storm-Relative Helicity Revealed from Polarimetric Radar Measurements

2009 ◽  
Vol 66 (3) ◽  
pp. 667-685 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Alexander V. Ryzhkov
Keyword(s):  
Strong Positive Correlation ◽  
Convective Storms ◽  
Low Level ◽  
Initial Drop ◽  
Size Sorting ◽  
Radar Measurements ◽  
Microphysical Processes ◽  
Differential Sedimentation ◽  
The Right ◽  
Differential Reflectivity

Abstract The dual-polarization radar variables are especially sensitive to the microphysical processes of melting and size sorting of precipitation particles. In deep convective storms, polarimetric measurements of such processes can provide information about the airflow in and around the storm that may be used to elucidate storm behavior and evolution. Size sorting mechanisms include differential sedimentation, vertical transport, strong rotation, and wind shear. In particular, winds that veer with increasing height typical of supercell environments cause size sorting that is manifested as an enhancement of differential reflectivity (ZDR) along the right or inflow edge of the forward-flank downdraft precipitation echo, which has been called the ZDR arc signature. In some cases, this shear profile can be augmented by the storm inflow. It is argued that the magnitude of this enhancement is related to the low-level storm-relative environmental helicity (SRH) in the storm inflow. To test this hypothesis, a simple numerical model is constructed that calculates trajectories for raindrops based on their individual sizes, which allows size sorting to occur. The modeling results indicate a strong positive correlation between the maximum ZDR in the arc signature and the low-level SRH, regardless of the initial drop size distribution aloft. Additional observational evidence in support of the conceptual model is presented. Potential changes in the ZDR arc signature as the supercell evolves and the low-level mesocyclone occludes are described.

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 DYAMOND: the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Bjorn Stevens ◽  
Masaki Satoh ◽  
Ludovic Auger ◽  
Joachim Biercamp ◽  
Christopher S. Bretherton ◽  
...  
Keyword(s):  
General Circulation ◽  
Deep Convection ◽  
Precipitable Water ◽  
Energy Budgets ◽  
High Resolution Data ◽  
Convective Storms ◽  
Tropical Deep Convection ◽  
Basic Characteristics ◽  
Tropical Weather ◽  
The Tropics

Abstract A review of the experimental protocol and motivation for DYAMOND, the first intercomparison project of global storm-resolving models, is presented. Nine models submitted simulation output for a 40-day (1 August–10 September 2016) intercomparison period. Eight of these employed a tiling of the sphere that was uniformly less than 5 km. By resolving the transient dynamics of convective storms in the tropics, global storm-resolving models remove the need to parameterize tropical deep convection, providing a fundamentally more sound representation of the climate system and a more natural link to commensurately high-resolution data from satellite-borne sensors. The models and some basic characteristics of their output are described in more detail, as is the availability and planned use of this output for future scientific study. Tropically and zonally averaged energy budgets, precipitable water distributions, and precipitation from the model ensemble are evaluated, as is their representation of tropical cyclones and the predictability of column water vapor, the latter being important for tropical weather.

Sensitivities of Simulated Convective Storms to Environmental CAPE

2011 ◽  
Vol 139 (11) ◽  
pp. 3514-3532 ◽  
Author(s):  
Cody Kirkpatrick ◽  
Eugene W. McCaul ◽  
Charles Cohen
Keyword(s):  
Free Convection ◽  
Three Dimensional ◽  
Environmental Parameters ◽  
Precipitable Water ◽  
Relative Strength ◽  
Convective Storms ◽  
Low Level ◽  
Reduced Height ◽  
Character Feature ◽  
Lapse Rates

Abstract A set of 225 idealized three-dimensional cloud-resolving simulations is used to explore convective storm behavior in environments with various values of CAPE (450, 800, 2000, and 3200 J kg−1). The simulations show that when CAPE = 2000 J kg−1 or greater, numerous combinations of other environmental parameters can support updrafts of at least 10 m s−1 throughout an entire 2-h simulation. At CAPE = 450 J kg−1, it is very difficult to obtain strong storms, although one case featuring a supercell is found. For CAPE = 800 J kg−1, mature storm updraft speeds correlate positively with strong low-level lapse rates and reduced precipitable water. In some cases, updrafts at this CAPE value can reach speeds that rival predictions of parcel theory, but such efficient conversion of CAPE to kinetic energy does not extend to all storms at CAPE = 800 J kg−1, nor to any storms in simulations at lower or higher CAPE. In simulations with CAPE = 2000 or 3200 J kg−1, the strongest time-averaged mature updrafts, while supercellular in character, feature generally less than 60% of the speeds expected from parcel theory, and even the strongest updraft found at CAPE = 450 J kg−1 fails to reach that relative strength. When CAPE = 2000 J kg−1 or more, updrafts benefit from enhanced shear, higher levels of free convection, and reduced precipitable water. Strong low-level shear and a reduced height of the level of free convection correlate closely with low-level storm vertical vorticity when CAPE is at least 2000 J kg−1, consistent with previous findings. However, at CAPE = 800 J kg−1, low-level vorticity shares the same correlations with the environment as updraft strength. With respect to storm precipitation, in simulations initiated with only 30 mm of precipitable water (PW), all of the storms that last for an entire 2-h simulation tend to produce liquid precipitation at roughly similar rates, regardless of their CAPE. In environments where PW is increased to 60 mm, storms tend to produce the most rainfall at CAPE = 2000 J kg−1, with somewhat lesser rainfall rates at lower and higher CAPE. Nevertheless, over the simulation domain, the ground area that receives at least 10 mm of rainfall tends to increase as CAPE increases, owing to a greater number and size of precipitating updrafts in the domain.

Initiation of Convective Storms at Low-Level Mesoscale Boundaries in Southwestern Ontario

2018 ◽  
Vol 33 (2) ◽  
pp. 583-598 ◽  
Author(s):  
Lisa S. Alexander ◽  
David M. L. Sills ◽  
Peter A. Taylor
Keyword(s):  
Radar Data ◽  
Moving Boundaries ◽  
Lake Breeze ◽  
Convective Storm ◽  
Convective Storms ◽  
Low Level ◽  
New Findings ◽  
Gust Fronts ◽  
Storm Cells ◽  
The Relationship

Abstract The relationship between low-level mesoscale boundaries and convective storm initiation was investigated in southwestern Ontario, Canada. The influence of lake-breeze fronts, a type of boundary that frequently affects this region of the Great Lakes watershed in summer, presented a particular interest. Radar data were processed using thunderstorm cell identification and tracking algorithms. The distances between the locations of storm cells reaching an intensity of 40 dBZ and the closest low-level mesoscale boundary were measured. Considering only days not influenced by a warm front, more than 75% of cells developed within 30 km of a low-level mesoscale boundary. Further examination by boundary type showed that cell initiations associated with moving boundaries and storm gust fronts occurred most often 0–5 km behind the boundaries. However, cell initiations associated with lake-breeze fronts most often occurred 0–5 km ahead of the boundaries. The analysis also suggested that lake-breeze fronts would often initiate the first storms of the day, which in turn generated gust fronts that could initiate subsequent storms. Overall, the results were similar to a previous study investigating storm initiation in the vicinity of low-level mesoscale boundaries in eastern Colorado and include some new findings in relation to lake-breeze fronts. The findings can be used by forecasters as well as automated nowcasting algorithms in order to improve predictions of storm initiation.

scholarly journals Tornadogenesis and Early Tornado Evolution in the El Reno, Oklahoma, Supercell on 31 May 2013

2019 ◽  
Vol 147 (6) ◽  
pp. 2045-2066 ◽  
Author(s):  
Howard B. Bluestein ◽  
Kyle J. Thiem ◽  
Jeffrey C. Snyder ◽  
Jana B. Houser
Keyword(s):  
Doppler Radar ◽  
Leading Edge ◽  
Radar Data ◽  
Vertical Column ◽  
Low Level ◽  
X Band ◽  
Main Circulation ◽  
Coherent Vortex ◽  
The Right

Abstract This study documents the formation and part of the early evolution of a large, violent tornado near El Reno, Oklahoma, based on data from a mobile, polarimetric, rapid scan, X-band, Doppler radar. The main circulation associated with the tornado formed near the ground initially, ~90 s prior to the development of the vertically coherent vortex, which built upward through a vertical column of at least 3.5 km in less than 20 s, the update time of the Doppler radar data. Strong but broad rotation from 500 m to 1.5 km AGL also preceded the formation of the tornado at the surface by several minutes. A precipitation-loaded downdraft was observed in the right-forward flank of the storm, which could have enhanced evaporative cooling and allowed for a faster rate of baroclinic generation of low-level horizontal vorticity, while descending reflectivity cores in the right-rear quadrant might have enhanced low-level convergence to the rear of or along the leading edge of the rear-flank gust front. The intensification of the tornado occurred in spurts, not steadily, perhaps owing to surges in momentum at the surface associated with the precipitation-laden downdrafts. The tornado was highly tilted even when it was intensifying, calling into question the importance of a vertical juxtaposition of the mesocyclone aloft and the tornado at the surface. In this case study, while the development of a weak-echo hole was evidence of rotation, the absence of one did not mean that there was not a strong vortex, owing to the lofting of debris.

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