scholarly journals On the Initial Development of Asymmetric Vertical Motion and Horizontal Relative Flow in a Mature Tropical Cyclone Embedded in Environmental Vertical Shear

2013 ◽  
Vol 70 (11) ◽  
pp. 3471-3491 ◽  
Author(s):  
Yamei Xu ◽  
Yuqing Wang
Keyword(s):  
Tropical Cyclone ◽  
Dominant Role ◽  
Vertical Motion ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Asymmetric Flow ◽  
Initial Development ◽  
Budget Analysis ◽  
Tangential Wind ◽  
Relative Flow

Abstract In this paper, the authors focus on the initial development of asymmetric vertical motion and horizontal relative flow in a mature tropical cyclone (TC) embedded in an environmental vertical shear. The fully compressible, nonhydrostatic TC model was used to perform a series of numerical experiments with a mature TC with different intensities embedded in shear with different magnitudes and different vertical profiles. Results show that the development of both the wavenumber-1 asymmetric vertical motion and horizontal relative flow for a TC embedded in vertical shear is quite sensitive to both the magnitude and the vertical profile of wind shear, as well as the intensity of the TC itself. Diagnostic analysis based on the quasi-balanced potential vorticity inversion indicates that the balanced dynamics can only explain a small portion of the asymmetric vertical motion and relative flow. The unbalanced processes contribute predominantly to the development of the asymmetric flow in the simulations. It is shown that the eyewall of a mature TC plays a role somewhat like a material cylinder embedded in an environmental flow with vertical shear. The interaction between the environmental shear and the eyewall produces vertical gradient of convergence/divergence of horizontal wind around the lateral edge of the eyewall. This forces much stronger asymmetric vertical motion than the balanced processes do and drives significant horizontal relative divergent flow over the storm core, which opposes vertical shear and reduces the vertical tilt of the storm axis. In addition, the budget analysis for the axisymmetric tangential wind demonstrates that the asymmetric flow plays a dominant role in weakening the storm top down.

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.

The Role of Shearwise and Transverse Quasigeostrophic Vertical Motions in the Midlatitude Cyclone Life Cycle

2006 ◽  
Vol 134 (4) ◽  
pp. 1174-1193 ◽  
Author(s):  
Jonathan E. Martin
Keyword(s):  
Life Cycle ◽  
Vertical Motion ◽  
Development Stage ◽  
Life Cycles ◽  
Vertical Shear ◽  
Mature Stage ◽  
Motion Field ◽  
Initial Development ◽  
Frontal Zones ◽  
Oriented Parallel

Abstract The total quasigeostrophic (QG) vertical motion field is partitioned into transverse and shearwise couplets oriented parallel to, and along, the geostrophic vertical shear, respectively. The physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle is then illustrated by examination of the life cycles of two recently observed cyclones. The analysis suggests that the origin and subsequent intensification of the lower-tropospheric cyclone responds predominantly to column stretching associated with the updraft portion of the shearwise QG vertical motion, which displays a single, dominant, middle-tropospheric couplet at all stages of the cyclone life cycle. The transverse QG omega, associated with the cyclones’ frontal zones, appears only after those frontal zones have been established. The absence of transverse ascent maxima and associated column stretching in the vicinity of the surface cyclone center suggests that the transverse ω plays little role in the initial development stage of the storms examined here. Near the end of the mature stage of the life cycle, however, in what appears to be a characteristic distribution, a transverse ascent maximum along the western edge of the warm frontal zone becomes superimposed with the shearwise ascent maximum that fuels continued cyclogenesis. It is suggested that use of the shearwise/transverse diagnostic approach may provide new and/or supporting insight regarding a number of synoptic processes including the development of upper-level jet/front systems and the nature of the physical distinction between type A and type B cyclogenesis events.

scholarly journals Tropical Cyclone Motion in Response to Land Surface Friction

2006 ◽  
Vol 63 (4) ◽  
pp. 1324-1337 ◽  
Author(s):  
Martin L. M. Wong ◽  
Johnny C. L. Chan
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Vertical Motion ◽  
Moisture Flux ◽  
Internal Boundary ◽  
Asymmetric Flow ◽  
Horizontal Advection ◽  
Surface Moisture ◽  
Tangential Wind ◽  
The Asymmetry

Abstract Numerical experiments are performed with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) to study the effects of surface-moisture flux and friction over land on the movement of tropical cyclones (TCs). On an f plane, the TCs are initially placed 150 km due east of a north–south-oriented coastline in an atmosphere at rest. It is found that a TC could drift toward land when the roughness length is 0.5 m over land, with an average drift speed of ∼1 m s−1. Friction, but not surface-moisture flux over land, is apparently essential for the movement toward land. The friction-induced asymmetry in the large-scale flow is the primary mechanism responsible for causing the TC drift. The mechanism responsible for the development of the large-scale asymmetric flow over the lower to midtroposphere (∼900–600 hPa) appears to be the creation of asymmetric vorticity by the divergence term in the vorticity equation. Horizontal advection then rotates the asymmetric vorticity to give a northeasterly flow in the TC periphery (∼500–1000 km from the TC center). The flow near the TC center has a more northerly component because of the stronger rotation by the tangential wind of the TC at inner radii. However, the TC does not move with the large-scale asymmetric flow. Potential vorticity budget calculations indicate that while the horizontal advection term is basically due to the effect of advection by the large-scale asymmetric flow, the diabatic heating and vertical advection terms have to be considered in determining the vortex landward drift, because of the strong asymmetry in vertical motion. Two mechanisms could induce the asymmetry in vertical motion and cause a deviation of the TC track from the horizontal asymmetric flow. First, the large-scale asymmetric flow in the upper troposphere differs from that in the lower troposphere, both in magnitude and direction, which results in a vertical shear that could force the asymmetry. A vertical tilt of the vortex axis is also found that is consistent with the direction of shear and also the asymmetry in rainfall and vertical motion. Second, asymmetric boundary layer convergence that results from the internal boundary layer could also force an asymmetry in vertical motion.

The Role of Tropical Waves in Tropical Cyclogenesis

2006 ◽  
Vol 134 (9) ◽  
pp. 2397-2417 ◽  
Author(s):  
William M. Frank ◽  
Paul E. Roundy
Keyword(s):  
Tropical Cyclone ◽  
Phase Relationship ◽  
Vertical Motion ◽  
Longwave Radiation ◽  
Wave Activity ◽  
Vertical Shear ◽  
Tropical Cyclogenesis ◽  
Strong Impact ◽  
Tropical Wave ◽  
The Waves

Abstract This paper analyzes relationships between tropical wave activity and tropical cyclogenesis in all of the earth’s major tropical cyclone basins. Twenty-nine years of outgoing longwave radiation data and global reanalysis winds are filtered and analyzed to determine statistical relationships between wave activity in each basin and the corresponding cyclogenesis. Composite analyses relative to the storm genesis locations show the structures of the waves and their preferred phase relationships with genesis. Five wave types are examined in this study, including mixed Rossby–gravity waves, tropical-depression-type or easterly waves, equatorial Rossby waves, Kelvin waves, and the Madden–Julian oscillation. The latter is not one of the classical tropical wave types, but is a wavelike phenomenon known to have a strong impact on tropical cyclogenesis. Tropical cyclone formation is strongly related to enhanced activity in all of the wave filter bands except for the Kelvin band. In each basin the structure of each composite wave and the phase relationship between the wave and cyclogenesis are similar, suggesting consistent forcing mechanisms. The waves appear to enhance the local circulations by increasing the forced upward vertical motion, increasing the low-level vorticity at the genesis location, and by modulating the vertical shear. Convective anomalies of waves associated with genesis are detectable in the analyses as long as 1 month prior to genesis. This opens up the possibility of developing statistically based genesis forecasts.

scholarly journals Reexamining the Near-Core Radial Structure of the Tropical Cyclone Primary Circulation: Implications for Vortex Resiliency

2005 ◽  
Vol 62 (2) ◽  
pp. 408-425 ◽  
Author(s):  
Kevin J. Mallen ◽  
Michael T. Montgomery ◽  
Bin Wang
Keyword(s):  
Tropical Cyclone ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Core Region ◽  
Vertical Shear ◽  
Theoretical Studies ◽  
True Nature ◽  
Radial Profiles ◽  
Tangential Wind ◽  
Radial Structure

Abstract Recent theoretical studies, based on vortex Rossby wave (VRW) dynamics, have established the importance of the radial structure of the primary circulation in the response of tropical cyclone (TC)–like vortices to ambient vertical wind shear. Linear VRW theory suggests, in particular, that the degree of broadness of the primary circulation in the near-core region beyond the radius of maximum wind strongly influences whether a tilted TC vortex will realign and resist vertical shear or tilt over and shear apart. Fully nonlinear numerical simulations have verified that the vortex resiliency is indeed sensitive to the initial radial structure of the idealized vortex. This raises the question of how well the “true” nature of a TC’s primary circulation is represented by idealized vortices that are commonly used in some theoretical studies. In this paper the swirling wind structure of TCs is reexamined by utilizing flight-level observations collected from Atlantic and eastern Pacific storms during 1977–2001. Hundreds of radial profiles of azimuthal-mean tangential wind and relative vorticity are constructed from over 5000 radial flight leg segments and compared with some standard idealized vortex profiles. This analysis reaffirms that real TC structure in the near-core region is characterized by relatively slow tangential wind decay in conjunction with a skirt of significant cyclonic relative vorticity possessing a negative radial gradient. This broadness of the primary circulation is conspicuously absent in some idealized vortices used in theoretical studies of TC evolution in vertical shear. The relationship of the current findings to the problem of TC resiliency is discussed.

scholarly journals Quadrant-Dependent Evolution of Low-Level Tangential Wind of a Tropical Cyclone in the Shear Flow

2016 ◽  
Vol 73 (3) ◽  
pp. 1159-1177 ◽  
Author(s):  
Jian-Feng Gu ◽  
Zhe-Min Tan ◽  
Xin Qiu
Keyword(s):  
Tropical Cyclone ◽  
Shear Flow ◽  
Vertical Wind Shear ◽  
Intensity Change ◽  
Low Level ◽  
Budget Analysis ◽  
Steady Stage ◽  
Tangential Wind ◽  
Low Level Jet ◽  
The Right

Abstract This study investigates the quadrant-by-quadrant evolution of the low-level tangential wind near the eyewall of an idealized simulated mature tropical cyclone embedded in a unidirectional shear flow. It is found that the quadrant-averaged tangential wind in the right-of-shear quadrants weakens continuously, while that in the left-of-shear quadrants experiences a two-stage evolution: a quasi-steady stage followed by a weakening stage after the imposing of vertical wind shear. This leads to a larger weakening rate in the right-of-shear and a stronger jet in the left-of-shear quadrants. The budget analysis shows that the quadrant-dependent evolution of tangential wind is controlled through the balance between the generalized Coriolis force (GCF; i.e., the radial advection of absolute angular momentum) and the advection terms. The steady decreasing of the GCF is primarily responsible for the continuous weakening of jet strength in the right-of-shear quadrants. For the left-of-shear quadrants, the quasi-steady stage is due to the opposite contributions by the enhanced GCF and negative tendency of advections cancelling out each other. The later weakening stage is the result of both the decreased GCF and the negative tangential advection. The combination of storm-relative flows at vortex scale and the convection strength both within and outside the eyewall determines the evolution of boundary layer inflow asymmetries, which in turn results in the change of GCF, leading to the quadrant-dependent evolution of low-level jet strength and thus the overall storm intensity change.

Development and Rapid Intensification of Tropical Cyclone OCKHI (2017) over the North Indian Ocean

2020 ◽  
Vol 3 (3) ◽  
Author(s):  
Geetha B ◽  
Balachandran S
Keyword(s):  
Tropical Cyclone ◽  
Indian Ocean ◽  
North Indian Ocean ◽  
Vertical Shear ◽  
Rapid Intensification ◽  
Initial Development ◽  
Structural Mechanism ◽  
The North ◽  
Mature Phase ◽  
South Indian

Tropical Cyclone OCKHI over the North Indian Ocean during 2017 underwent dramatic development and rapid intensification very close to the land - Sri Lanka, extreme South Indian coast and Lakshadweep area during its initial developmental stage and caused extensive damages over these areas. On examining the physical and structural mechanism involved in such development, it is observed that the initial development was associated with axi-symmetrisation of the vortex that could be associated with Vortex Rossby waves near the eyewall. Associated with the expulsion of high vorticity from the centre during asymmetry mixing, there was outward propagation of eddy angular momentum flux in the lower levels that strengthened a low level anticyclone to the northeast of the TC centre which in turn enhanced the cyclonic inflow near the TC centre. The rapid intensification phase was associated with vertical non-uniform heating with upper and lower tropospheric warming associated with latent heat release in convection.  During the mature phase, the system sustained ‘very severe’ intensity even under increasing vertical shear and lower ocean heat flux under the influence of a break in the sub tropical ridge to the north of the system centre that enhanced the poleward outflow in the upper troposphere.

scholarly journals Mechanisms of Convection Initiation in the Southwestern Xinjiang, Northwest China: A Case Study

Atmosphere ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1335
Author(s):  
Abuduwaili Abulikemu ◽  
Jie Ming ◽  
Xin Xu ◽  
Xiaoyong Zhuge ◽  
Yuan Wang ◽  
...  
Keyword(s):  
Wrf Model ◽  
Northwest China ◽  
Radiative Heating ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Convective System ◽  
Mountainous Area ◽  
Vertical Acceleration ◽  
Budget Analysis ◽  
Convection Initiation

The mechanism of convection initiation (CI) occurring in the Southwest Xinjiang, Northwest China is investigated using quantitative budget analysis of vertical momentum for the first time. The Weather Research and Forecasting (WRF) model is used to reproduce and analyze the CI events. The observations showed that many CIs occurred continuously, with an intense mesoscale convective system eventually forming. The overall features of the CIs were well captured by the simulation. Lagrangian vertical momentum budgets, in which the vertical acceleration was decomposed into dynamic and buoyant components, were performed along the backward trajectories of air parcels within two convective cells. The results showed that the buoyant acceleration is the major contributor in both the slow and rapid lifting period of the CI, while the dynamic acceleration also showed a considerably positive effect only during the rapid lifting period. The buoyant acceleration during the slow lifting period was due to the warm advection generated by the radiative heating near the mountainous area on the south side of Tarim Basin in the afternoon. The buoyant acceleration during the rapid lifting period was from the latent heat release within the convective cell. Further decomposition of the dynamic acceleration showed that the vertical twisting related to the vertical shear of horizontal wind almost completely dominated the dynamic acceleration, while the horizontal curvature and extension showed very weak contribution. These findings provide some new insights into the roles of buoyant and dynamic forcing in the mechanism of CI in Southwest Xinjiang.

Modeling Interaction of a Tropical Cyclone with Its Cold Wake

2017 ◽  
Vol 74 (12) ◽  
pp. 3981-4001 ◽  
Author(s):  
Sue Chen ◽  
Russell L. Elsberry ◽  
Patrick A. Harr
Keyword(s):  
Tropical Cyclone ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Intensity Decrease ◽  
Budget Analysis ◽  
Momentum Budget ◽  
Thermodynamic Effect ◽  
Tangential Wind ◽  
Time Invariant ◽  
Fully Coupled

Abstract This study first examines the tropical cyclone (TC) intensity response to its cold wake with time-invariant, stationary cold wakes and an uncoupled version of COAMPS-TC, and second with simulated cold wakes from the fully coupled version. The objective of the uncoupled simulations with the time-invariant cold wake is to fix the thermodynamic response and to isolate the dynamic response of the TC to the cold wake. While the stationary TC over a cold wake has an immediate intensity decrease, the intensity decrease with a long trailing wake from the moving TC was delayed. This time delay is attributed to a “wake jet” that leads to an enhanced inward transport of moist air that tends to offset the effect of decreasing enthalpy flux from the ocean. In the fully coupled version, the TC translating at 2 m s−1 generated a long trailing cold wake, and again the intensity decrease was delayed. Lagrangian trajectories released behind the TC center at four times illustrate the inward deflection and ascent and descent as the air parcels cross the trailing cold wake. The momentum budget analysis indicates large radial and tangential wind tendencies primarily due to imbalances among the pressure gradient force, the Coriolis, and the horizontal advection as the parcels pass over the cold wake. Nevertheless, a steadily increasing radial inflow (wake jet) is simulated in the region of a positive moisture anomaly that tends to offset the thermodynamic effect of decreasing enthalpy flux.

scholarly journals Long-term mean vertical velocity measured by MST radar at Gadanki (13.5° N, 79.2° E)

2009 ◽  
Vol 27 (2) ◽  
pp. 451-459 ◽  
Author(s):  
P. V. Rao ◽  
P. Vinay Kumar ◽  
M. C. Ajay Kumar ◽  
G. Dutta
Keyword(s):  
Vertical Velocity ◽  
Vertical Motion ◽  
Vertical Wind ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Direct Measurements ◽  
Semidiurnal Variation ◽  
Vertical Beam ◽  
Tropical Station

Abstract. MST radars are capable of measuring vertical motion along a vertically directed beam. We present 8 years (1995–2003) averaged profile of vertical velocity in the troposphere and the lower stratosphere over Gadanki (13.5° N, 79.2° E), a tropical station. A downward mid-tropospheric w is observed with a reversal of sign around 10 km and a further reversal can also be seen at ~17 km. A significant diurnal and semidiurnal variation in vertical wind is observed for all heights with subsidence during the evening hours. Seasonal variability of vertical wind is also found to be quite appreciable. Vertical velocities have been derived using symmetric pairs of off-vertical beams and a comparison has been made with direct vertical beam measurements. Vertical components estimated from E-W and N-S radial velocities do not match and are also found to have discrepancy with direct measurements. Plausible causes of the discrepancy have been investigated with the help of some case studies. Vertical shear in horizontal wind, gradients in horizontal velocities and echo power imbalance may be some of the factors responsible for the observed discrepancy.

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