scholarly journals Structure and Evolution of Deeply Developed Convective Cells in a Long-Lived Cumulonimbus Cloud under a Weak Vertical Wind-Shear Condition

2005 ◽  
Vol 83 (3) ◽  
pp. 351-371 ◽  
Author(s):  
Yukari SHUSSE ◽  
Kazuhisa TSUBOKI ◽  
Biao GENG ◽  
Haruya MINDA ◽  
Takao TAKEDA
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Convective Cells ◽  
Shear Condition ◽  
Cumulonimbus Cloud

Extreme Helicity and Intense Convective Towers in Hurricane Bonnie

2008 ◽  
Vol 136 (11) ◽  
pp. 4355-4372 ◽  
Author(s):  
John Molinari ◽  
David Vollaro
Keyword(s):  
Wind Shear ◽  
Extreme Values ◽  
Negative Impact ◽  
Spatial Scales ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Vortical Hot Towers ◽  
Hurricane Bonnie ◽  
Convective Cells

Abstract Helicity was calculated in Hurricane Bonnie (1998) using tropospheric-deep dropsonde soundings from the NASA Convection and Moisture Experiment. Large helicity existed downshear of the storm center with respect to the ambient vertical wind shear. It was associated with veering, semicircular hodographs created by strong, vortex-scale, radial-vertical flow induced by the shear. The most extreme values of helicity, among the largest ever reported in the literature, occurred in the vicinity of deep convective cells in the downshear-left quadrant. These cells reached as high as 17.5 km and displayed the temporal and spatial scales of supercells. Convective available potential energy (CAPE) averaged 861 J kg−1 downshear, but only about one-third as large upshear. The soundings nearest the deep cells were evaluated using two empirical supercell parameters that make use of CAPE, helicity, and/or shear. These parameters supported the possible existence of supercells as a consequence of the exceptional helicity combined with moderate but sufficient CAPE. Ambient vertical wind shear exceeded 12 m s−1 for 30 h, yet the hurricane maintained 50 m s−1 maximum winds. It is hypothesized that the long-lived convective cells enabled the storm to resist the negative impact of the shear. Supercells in large-helicity, curved-hodograph environments appear to provide a useful conceptual model for intense convection in the hurricane core. Helicity calculations might also give some insight into the behavior of vortical hot towers, which share some characteristics with supercells.

A Squall-Line-Like Principal Rainband in Typhoon Hagupit (2008) Observed by Airborne Doppler Radar

2014 ◽  
Vol 71 (7) ◽  
pp. 2733-2746 ◽  
Author(s):  
Xiaowen Tang ◽  
Wen-Chau Lee ◽  
Michael Bell
Keyword(s):  
Wind Shear ◽  
Doppler Radar ◽  
Structural Characteristics ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Squall Line ◽  
Cold Pool ◽  
Low Level ◽  
Squall Lines ◽  
Convective Cells

Abstract This study examines the structure and dynamics of Typhoon Hagupit’s (2008) principal rainband using airborne radar and dropsonde observations. The convection in Hagupit’s principal rainband was organized into a well-defined line with trailing stratiform precipitation on the inner side. Individual convective cells had intense updrafts and downdrafts and were aligned in a wavelike pattern along the line. The line-averaged vertical cross section possessed a slightly inward-tilting convective core and two branches of low-level inflow feeding the convection. The result of a thermodynamic retrieval showed a pronounced cold pool behind the convective line. The horizontal and vertical structures of this principal rainband show characteristics that are different than the existing conceptual model and are more similar to squall lines and outer rainbands. The unique convective structure of Hagupit’s principal rainband was associated with veering low-level vertical wind shear and large convective instability in the environment. A quantitative assessment of the cold pool strength showed that it was quasi balanced with that of the low-level vertical wind shear. The balanced state and the structural characteristics of convection in Hagupit’s principal rainband were dynamically consistent with the theory of cold pool dynamics widely applied to strong and long-lived squall lines. The analyses suggest that cold pool dynamics played a role in determining the principal rainband structure in addition to storm-scale vortex dynamics.

scholarly journals An Observational Study of Mesoscale Convective Systems with Heavy Rainfall over the Korean Peninsula

2006 ◽  
Vol 21 (2) ◽  
pp. 125-148 ◽  
Author(s):  
Hyung Woo Kim ◽  
Dong Kyou Lee
Keyword(s):  
Observational Study ◽  
Korean Peninsula ◽  
Wind Shear ◽  
Heavy Rainfall ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Mesoscale Convective Systems ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract A heavy rainfall event induced by mesoscale convective systems (MCSs) occurred over the middle Korean Peninsula from 25 to 27 July 1996. This heavy rainfall caused a large loss of life and property damage as a result of flash floods and landslides. An observational study was conducted using Weather Surveillance Radar-1988 Doppler (WSR-88D) data from 0930 UTC 26 July to 0303 UTC 27 July 1996. Dominant synoptic features in this case had many similarities to those in previous studies, such as the presence of a quasi-stationary frontal system, a weak upper-level trough, sufficient moisture transportation by a low-level jet from a tropical storm landfall, strong potential and convective instability, and strong vertical wind shear. The thermodynamic characteristics and wind shear presented favorable conditions for a heavy rainfall occurrence. The early convective cells in the MCSs initiated over the coastal area, facilitated by the mesoscale boundaries of the land–sea contrast, rain–no rain regions, saturated–unsaturated soils, and steep horizontal pressure and thermal gradients. Two MCSs passed through the heavy rainfall regions during the investigation period. The first MCS initiated at 1000 UTC 26 July and had the characteristics of a supercell storm with small amounts of precipitation, the appearance of a mesocyclone with tilting storm, a rear-inflow jet at the midlevel of the storm, and fast forward propagation. The second MCS initiated over the upstream area of the first MCS at 1800 UTC 26 July and had the characteristics of a multicell storm, such as a broken areal-type squall line, slow or quasi-stationary backward propagation, heavy rainfall in a concentrated area due to the merging of the convective storms, and a stagnated cluster system. These systems merged and stagnated because their movement was blocked by the Taebaek Mountain Range, and they continued to develop because of the vertical wind shear resulting from a low-level easterly inflow.

scholarly journals Atlantic Hurricanes and Climate Change. Part II: Role of Thermodynamic Changes in Decreased Hurricane Frequency

2013 ◽  
Vol 26 (21) ◽  
pp. 8513-8528 ◽  
Author(s):  
Megan S. Mallard ◽  
Gary M. Lackmann ◽  
Anantha Aiyyer
Keyword(s):  
Case Studies ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Effect Of Temperature ◽  
Physical Processes ◽  
Thermodynamic Conditions ◽  
Atlantic Hurricanes ◽  
Reduced Activity

Abstract A method of downscaling that isolates the effect of temperature and moisture changes on tropical cyclone (TC) activity was presented in Part I of this study. By applying thermodynamic modifications to analyzed initial and boundary conditions from past TC seasons, initial disturbances and the strength of synoptic-scale vertical wind shear are preserved in future simulations. This experimental design allows comparison of TC genesis events in the same synoptic setting, but in current and future thermodynamic environments. Simulations of both an active (September 2005) and inactive (September 2009) portion of past hurricane seasons are presented. An ensemble of high-resolution simulations projects reductions in ensemble-average TC counts between 18% and 24%, consistent with previous studies. Robust decreases in TC and hurricane counts are simulated with 18- and 6-km grid lengths, for both active and inactive periods. Physical processes responsible for reduced activity are examined through comparison of monthly and spatially averaged genesis-relevant parameters, as well as case studies of development of corresponding initial disturbances in current and future thermodynamic conditions. These case studies show that reductions in TC counts are due to the presence of incipient disturbances in marginal moisture environments, where increases in the moist entropy saturation deficits in future conditions preclude genesis for some disturbances. Increased convective inhibition and reduced vertical velocity are also found in the future environment. It is concluded that a robust decrease in TC frequency can result from thermodynamic changes alone, without modification of vertical wind shear or the number of incipient disturbances.

The Intensity- and Size-Dependent Response of Tropical Cyclones to Increasing Vertical Wind Shear

2021 ◽  
Author(s):  
Peter M. Finocchio ◽  
Rosimar Rios-Berrios
Keyword(s):  
Wind Field ◽  
Wind Shear ◽  
Diabatic Heating ◽  
Inner Core ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Vertical Coupling ◽  
Tangential Wind

AbstractThis study describes a set of idealized simulations in which westerly vertical wind shear increases from 3 to 15 m s−1 at different stages in the lifecycle of an intensifying tropical cyclone (TC). The TC response to increasing shear depends on the intensity and size of the TC’s tangential wind field when shear starts to increase. For a weak tropical storm, increasing shear decouples the vortex and prevents intensification. For Category 1 and stronger storms, increasing shear causes a period of weakening during which vortex tilt increases by 10–30 km before the TCs reach a near-steady Category 1–3 intensity at the end of the simulations. TCs exposed to increasing shear during or just after rapid intensification tend to weaken the most. Backward trajectories reveal a lateral ventilation pathway between 8–11 km altitude that is capable of reducing equivalent potential temperature in the inner core of these TCs by nearly 2°C. In addition, these TCs exhibit large reductions in diabatic heating inside the radius of maximum winds (RMW) and lower-entropy air parcels entering downshear updrafts from the boundary layer, which further contributes to their substantial weakening. The TCs exposed to increasing shear after rapid intensification and an expansion of the outer wind field reach the strongest near-steady intensity long after the shear increases because of strong vertical coupling that prevents the development of large vortex tilt, resistance to lateral ventilation through a deep layer of the middle troposphere, and robust diabatic heating within the RMW.

Assessing the influence of complex terrain on severe convective environments in northeastern Alabama

2021 ◽  
Author(s):  
Branden Katona ◽  
Paul Markowski
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Spatial Distributions ◽  
Convective Storm ◽  
Self Organizing Maps ◽  
Low Level ◽  
Wind Regimes

AbstractStorms crossing complex terrain can potentially encounter rapidly changing convective environments. However, our understanding of terrain-induced variability in convective stormenvironments remains limited. HRRR data are used to create climatologies of popular convective storm forecasting parameters for different wind regimes. Self-organizing maps (SOMs) are used to generate six different low-level wind regimes, characterized by different wind directions, for which popular instability and vertical wind shear parameters are averaged. The climatologies show that both instability and vertical wind shear are highly variable in regions of complex terrain, and that the spatial distributions of perturbations relative to the terrain are dependent on the low-level wind direction. Idealized simulations are used to investigate the origins of some of the perturbations seen in the SOM climatologies. The idealized simulations replicate many of the features in the SOM climatologies, which facilitates analysis of their dynamical origins. Terrain influences are greatest when winds are approximately perpendicular to the terrain. In such cases, a standing wave can develop in the lee, leading to an increase in low-level wind speed and a reduction in vertical wind shear with the valley lee of the plateau. Additionally, CAPE tends to be decreased and LCL heights are increased in the lee of the terrain where relative humidity within the boundary layer is locally decreased.

scholarly journals The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part I: Overview and Observations

2018 ◽  
Vol 146 (11) ◽  
pp. 3773-3800 ◽  
Author(s):  
David R. Ryglicki ◽  
Joshua H. Cossuth ◽  
Daniel Hodyss ◽  
James D. Doyle
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Convective Cloud ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Brightness Temperatures ◽  
Idealized Modeling ◽  
Hurricane Prediction ◽  
Upper Level

Abstract A satellite-based investigation is performed of a class of tropical cyclones (TCs) that unexpectedly undergo rapid intensification (RI) in moderate vertical wind shear between 5 and 10 m s−1 calculated as 200–850-hPa shear. This study makes use of both infrared (IR; 11 μm) and water vapor (WV; 6.5 μm) geostationary satellite data, the Statistical Hurricane Prediction Intensity System (SHIPS), and model reanalyses to highlight commonalities of the six TCs. The commonalities serve as predictive guides for forecasters and common features that can be used to constrain and verify idealized modeling studies. Each of the TCs exhibits a convective cloud structure that is identified as a tilt-modulated convective asymmetry (TCA). These TCAs share similar shapes, upshear-relative positions, and IR cloud-top temperatures (below −70°C). They pulse over the core of the TC with a periodicity of between 4 and 8 h. Using WV satellite imagery, two additional features identified are asymmetric warming/drying upshear of the TC relative to downshear, as well as radially thin arc-shaped clouds on the upshear side. The WV brightness temperatures of these arcs are between −40° and −60°C. All of the TCs are sheared by upper-level anticyclones, which limits the strongest environmental winds to near the tropopause.

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