Effect of vertical wind shear on the growth of convective clouds

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.

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

Journal of Climate ◽

10.1175/jcli-d-12-00183.1 ◽

2013 ◽

Vol 26 (21) ◽

pp. 8513-8528 ◽

Cited By ~ 8

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.

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Stratified Flow over Extended Obstacles and Its Application to Topographical Effect on Vertical Wind Shear

Journal of the Atmospheric Sciences ◽

10.1175/1520-0469(1970)027<0884:sfoeoa>2.0.co;2 ◽

1970 ◽

Vol 27 (6) ◽

pp. 884-889 ◽

Cited By ~ 10

Author(s):

K. K. Wong ◽

Timothy W. Kao

Keyword(s):

Wind Shear ◽

Vertical Wind Shear ◽

Stratified Flow ◽

Vertical Wind ◽

Topographical Effect

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

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0126.1 ◽

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.

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