The comparative effects of frictional convergence and vertical wind shear on the interior asymmetries of a tropical cyclone

2014 ◽  
Vol 74 (3) ◽  
pp. 1517-1537
Author(s):  
Xingyou Huang ◽  
Xiaoping Tu ◽  
Hongyan Zhu
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Frictional Convergence

scholarly journals Rainfall Mechanisms for One of the Wettest Tropical Cyclones on Record in Australia—Oswald (2013)

2020 ◽  
Vol 148 (6) ◽  
pp. 2503-2525
Author(s):  
Difei Deng ◽  
Elizabeth A. Ritchie
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Heavy Rainfall ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Monsoon Trough ◽  
Vertical Wind ◽  
Lower Latitude ◽  
Cape York ◽  
Frictional Convergence

Abstract Tropical Cyclone Oswald (2013) is considered to be one of the highest-impact storms to make landfall in northern Australia even though it only reached a maximum category 1 intensity on the Australian category scale. After making landfall on the west coast of Cape York Peninsula, Oswald turned southward, and persisted for more than 7 days moving parallel to the coastline as far south as 30°S. As one of the wettest tropical cyclones (TCs) in Australian history, the favorable configurations of a lower-latitude active monsoon trough and two consecutive midlatitude trough–jet systems generally contributed to the maintenance of the Oswald circulation over land and prolonged rainfall. As a result, Oswald produced widespread heavy rainfall along the east coast with three maximum centers near Weipa, Townsville, and Rockhampton, respectively. Using high-resolution WRF simulations, the mechanisms associated with TC Oswald’s rainfall are analyzed. The results show that the rainfall involved different rainfall mechanisms at each stage. The land–sea surface friction contrast, the vertical wind shear, and monsoon trough were mostly responsible for the intensity and location for the first heavy rainfall center on the Cape York Peninsula. The second torrential rainfall near Townsville was primarily a result of the local topography and land–sea frictional convergence in a conditionally unstable monsoonal environment with frictional convergence due to TC motion modulating some offshore rainfall. The third rainfall area was largely dominated by persistent high vertical wind shear forcing, favorable large-scale quasigeostrophic dynamic lifting from two midlatitude trough–jet systems, and mesoscale frontogenesis lifting.

scholarly journals The Influence of Uniform Flow on Tropical Cyclone Intensity Change

2005 ◽  
Vol 62 (9) ◽  
pp. 3193-3212 ◽  
Author(s):  
Joey H. Y. Kwok ◽  
Johnny C. L. Chan
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Mesoscale Model ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Uniform Flow ◽  
Vertical Wind ◽  
Intensity Change ◽  
Westerly Flow

Abstract The influence of a uniform flow on the structural changes of a tropical cyclone (TC) is investigated using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). Idealized experiments are performed on either an f plane or a β plane. A strong uniform flow on an f plane results in a weaker vortex due to the development of a vertical wind shear induced by the asymmetric vertical motion and a rotation of upper-level anticyclone. The asymmetric vertical motion also reduces the secondary circulation of the vortex. On a β plane with no flow, a broad anticyclonic flow is found to the southeast of the vortex, which expands with time. Similar to the f-plane case, asymmetric vertical motion and vertical wind shear are also found. This beta-induced shear weakens the no-flow case significantly relative to that on an f plane. When a uniform flow is imposed on a β plane, an easterly flow produces a stronger asymmetry whereas a westerly flow reduces it. In addition, an easterly uniform flow tends to strengthen the beta-induced shear whereas a westerly flow appears to reduce it by altering the magnitude and direction of the shear vector. As a result, a westerly flow enhances TC development while an easterly flow reduces it. The vortex tilt and midlevel warming found in this study agree with the previous investigations of vertical wind shear. A strong uniform flow with a constant f results in a tilted and deformed potential vorticity at the upper levels. For a variable f, such tilting is more pronounced for a vortex in an easterly flow, while a westerly flow reduces the tilt. In addition, the vortex tilt appears to be related to the midlevel warming such that the warm core in the lower troposphere cannot extent upward, which leads to the subsequent weakening of the TC.

Effect of TC–Trough Interaction on the Intensity Change of Two Typhoons

2005 ◽  
Vol 20 (2) ◽  
pp. 199-211 ◽  
Author(s):  
Hui Yu ◽  
H. Joe Kwon
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Intensity Change ◽  
Eddy Flux ◽  
Upper Troposphere ◽  
Shallow Layer ◽  
Upper Level

Abstract Using large-scale analyses, the effect of tropical cyclone–trough interaction on tropical cyclone (TC) intensity change is readdressed by studying the evolution of upper-level eddy flux convergence (EFC) of angular momentum and vertical wind shear for two TCs in the western North Pacific [Typhoons Prapiroon (2000) and Olga (1999)]. Major findings include the following: 1) In spite of decreasing SST, the cyclonic inflow associated with a midlatitude trough should have played an important role in Prapiroon’s intensification to its maximum intensity and the maintenance after recurvature through an increase in EFC. The accompanied large vertical wind shear is concentrated in a shallow layer in the upper troposphere. 2) Although Olga also recurved downstream of a midlatitude trough, its development and maintenance were not strongly influenced by the trough. A TC could maintain itself in an environment with or without upper-level eddy momentum forcing. 3) Both TCs started to decay over cold SST in a large EFC and vertical wind shear environment imposed by the trough. 4) Uncertainty of input adds difficulties in quantitative TC intensity forecasting.

A Balanced Tropical Cyclone Test Case for AGCMs with Background Vertical Wind Shear

2015 ◽  
Vol 143 (5) ◽  
pp. 1762-1781 ◽  
Author(s):  
Fei He ◽  
Derek J. Posselt ◽  
Colin M. Zarzycki ◽  
Christiane Jablonowski
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
General Circulation ◽  
Vertical Wind Shear ◽  
Circulation Model ◽  
Background Field ◽  
Vertical Wind ◽  
Intensity Change ◽  
Test Case ◽  
The Impact

Abstract This paper presents a balanced tropical cyclone (TC) test case designed to improve current understanding of how atmospheric general circulation model (AGCM) configurations affect simulated TC development and behavior. It consists of an analytic initial condition comprising two independently balanced components. The first provides a vortical TC seed, while the second adds a planetary-scale zonal flow with height-dependent velocity and imposes background vertical wind shear (VWS) on the TC seed. The environmental flow satisfies the steady-state hydrostatic primitive equations in spherical coordinates and is in balance with other background field variables (e.g., temperature, surface geopotential). The evolution of idealized TCs in the test case framework is illustrated in 10-day simulations performed with the Community Atmosphere Model, version 5.1.1 (CAM 5.1.1). Environmental wind profiles with different magnitudes, directions, and vertical inflection points are applied to ensure that the technique is robust to changes in the VWS characteristics. The well-known shear-induced intensity change and structural asymmetry in tropical cyclones are well captured. Sensitivity of TC evolution to small perturbations in the initial vortex is also quantitatively addressed to validate the numerical robustness of the technique. It is concluded that the enhanced TC test case can be used to evaluate the impact of model choice (e.g., resolution, physical parameterizations) on the simulation and representation of TC-like vortices in AGCMs.

Computing Deep-Tropospheric Vertical Wind Shear Analyses for Tropical Cyclone Applications: Does the Methodology Matter?

2014 ◽  
Vol 29 (5) ◽  
pp. 1169-1180 ◽  
Author(s):  
Christopher S. Velden ◽  
John Sears
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Environmental Influence ◽  
Traditional Approach ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Intensity Change ◽  
Wind Fields ◽  
Wind Structure ◽  
Vector Difference

Abstract Vertical wind shear is well known in the tropical cyclone (TC) forecasting community as an important environmental influence on storm structure and intensity change. The traditional way to define deep-tropospheric vertical wind shear in most prior research studies, and in operational forecast applications, is to simply use the vector difference of the 200- and 850-hPa wind fields based on global model analyses. However, is this rather basic approach to approximate vertical wind shear adequate for most TC applications? In this study, the traditional approach is compared to a different methodology for generating fields of vertical wind shear as produced by the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (CIMSS). The CIMSS fields are derived with heavy analysis weight given to available high-density satellite-derived winds. The resultant isobaric analyses are then used to create two mass-weighted layer-mean wind fields, one upper and one lower tropospheric, which are then differenced to produce the deep-tropospheric vertical wind shear field. The principal novelty of this approach is that it does not rely simply on the analyzed winds at two discrete levels, but instead attempts to account for some of the variable vertical wind structure in the calculation. It will be shown how the resultant vertical wind shear fields derived by the two approaches can diverge significantly in certain situations; the results also suggest that in many cases it is superior in depicting the wind structure's impact on TCs than the simple two-level differential that serves as the common contemporary vertical wind shear approximation.

scholarly journals Factors Controlling Tropical Cyclone Intensification Over the Marginal Seas of China

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaomeng Li ◽  
Ruifen Zhan ◽  
Yuqing Wang ◽  
Jing Xu
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Inner Core ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Precipitation Rate ◽  
Forecast Errors ◽  
Key Factors ◽  
China Meteorological Administration ◽  
Marginal Seas

Tropical cyclone (TC) intensification over marginal seas, especially rapid intensification (RI), often poses great threat to lives and properties in coastal regions and is subject to large forecast errors. It is thus important to understand the characteristics of TC intensification and the involved key factors affecting TC intensification over marginal seas. In this study, the 6-hourly TC best-track data from Shanghai Typhoon Institute of China Meteorological Administration, ERA-Interim reanalysis data, and TRMM satellite rainfall products are used to analyze and compare the climatological characteristics and key factors of different intensification stratifications over the marginal seas of China (MSC) and the western North Pacific (WNP) during 1980–2018. The statistical results show that TC intensification over the MSC is more likely to occur when TCs experience relatively large intensities, weak vertical wind shear, small translation perpendicular to the coastline, relatively high fullness, strong upper-level divergence, low-level relative vorticity, and high inner-core precipitation rate. The box difference index method is used to quantify the relative contributions of these factors to TC RI. Results show that the initial (relative) intensity contributes the most to TC RI over both the MSC and the WNP. The inner-core precipitation rate and translation perpendicular to the coastline are of second importance to TC RI over the MSC, while both vertical wind shear and TC fullness are crucial to TC RI over the WNP. These findings may help understand TC activity over the MSC and provide a basis for improving intensity prediction of TCs in the MSC.

How does the relationship between ambient deep-tropospheric vertical wind shear and tropical cyclone tornadoes change between coastal and inland environments?

2021 ◽  
Author(s):  
Benjamin A. Schenkel ◽  
Michael Coniglio ◽  
Roger Edwards
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Radiosonde Data ◽  
Synoptic Scale ◽  
Near Surface ◽  
Tangential Wind ◽  
Convective Scale ◽  
The Relationship

AbstractThis work investigates how the relationship between tropical cyclone (TC) tornadoes and ambient (i.e., synoptic-scale) deep-tropospheric (i.e., 850–200-hPa) vertical wind shear (VWS) varies between coastal and inland environments. Observed U.S. TC tornado track data are used to study tornado frequency and location, while dropsonde and radiosonde data are used to analyze convective-scale environments. To study the variability in the TC tornado-VWS relationship, these data are categorized by both: 1) their distance from the coast and 2) reanalysis-derived VWS magnitude. The analysis shows that TCs produce coastal tornadoes regardless of VWS magnitude primarily in their downshear sector, with tornadoes most frequently occurring in strongly sheared cases. Inland tornadoes, including the most damaging cases, primarily occur in strongly sheared TCs within the outer radii of the downshear right quadrant. Consistent with these patterns, drop-sondes and coastal radiosondes show that the downshear right quadrant of strongly sheared TCs has the most favorable combination of enhanced lower-tropospheric near-surface speed shear and veering, and reduced lower-tropospheric thermodynamic stability for tornadic supercells. Despite the weaker intensity further inland, these kinematic conditions are even more favorable in inland environments within the downshear right quadrant of strongly sheared TCs, due to the strengthened veering of the ambient winds and the lack of changes in the TC outer tangential wind strength. The constructive superposition of the ambient and TC winds may be particularly important to inland tornado occurrence. Together, these results will allow forecasters to anticipate how the frequency and location of tornadoes and, more broadly, convection may change as TCs move inland.

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