scholarly journals Potential Vorticity Mixing and Rapid Intensification in the Numerically Simulated Supertyphoon Haiyan (2013)

2020 ◽  
Vol 77 (6) ◽  
pp. 2067-2090
Author(s):  
Satoki Tsujino ◽  
Hung-Chi Kuo
Keyword(s):  
Potential Vorticity ◽  
Inner Core ◽  
Model Simulation ◽  
Pressure Change ◽  
Central Pressure ◽  
Rapid Intensification ◽  
Budget Analysis ◽  
Tangential Wind ◽  
Balanced Dynamics ◽  
Omega Equation

Abstract The inner-core dynamics of Supertyphoon Haiyan (2013) undergoing rapid intensification (RI) are studied with a 2-km-resolution cloud-resolving model simulation. The potential vorticity (PV) field in the simulated storm reveals an elliptical and polygonal-shaped eyewall at the low and middle levels during RI onset. The PV budget analysis confirms the importance of PV mixing at this stage, that is, the asymmetric transport of diabatically generated PV to the storm center from the eyewall and the ejection of PV filaments outside the eyewall. We employ a piecewise PV inversion (PPVI) and an omega equation to interpret the model results in balanced dynamics. The omega equation diagnosis suggests eye dynamical warming is associated with the PV mixing. The PPVI indicates that PV mixing accounts for about 50% of the central pressure fall during RI onset. The decrease of central pressure enhances the boundary layer (BL) inflow. The BL inflow leads to contraction of the radius of the maximum tangential wind (RMW) and the formation of a symmetric convective PV tower inside the RMW. The eye in the later stage of the RI is warmed by the subsidence associated with the convective PV towers. The results suggest that the pressure change associated with PV mixing, the increase of the symmetric BL radial inflow, and the development of a symmetric convective PV tower are the essential collaborating dynamics for RI. An experiment with 500-m resolution shows that the convergence of BL inflow can lead to an updraft magnitude of 20 m s−1 and to a convective PV tower with a peak value of 200 PVU (1 PVU = 10−6 K kg−1 m2 s−1).

scholarly journals Vertical Vortex Development in Hurricane Michael (2018) during Rapid Intensification

2021 ◽  
Author(s):  
Alexander J. DesRosiers ◽  
Michael M. Bell ◽  
Ting-Yu Cha
Keyword(s):  
Inner Core ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Vertical Gradient ◽  
Machine Learning Techniques ◽  
Rapid Intensification ◽  
Wind Retrieval ◽  
Retrieval Technique ◽  
Budget Analysis ◽  
Tangential Wind

AbstractThe landfall of Hurricane Michael (2018) at category 5 intensity occurred after rapid intensification (RI) spanning much of the storm’s lifetime. Four Hurricane Hunter aircraft missions observed the RI period with tail Doppler radar (TDR). Data from each of the 14 aircraft passes through the storm were quality controlled via a combination of interactive and machine learning techniques. TDR data from each pass were synthesized using the SAMURAI variational wind retrieval technique to yield three-dimensional kinematic fields of the storm to examine inner core processes during RI. Vorticity and angular momentum increased and concentrated in the eyewall region. A vorticity budget analysis indicates the tendencies became more axisymmetric over time. In this study we focus in particular on how the eyewall vorticity tower builds vertically into the upper levels. Horizontal vorticity associated with the vertical gradient of tangential wind was tilted into the vertical by the eyewall updraft to yield a positive vertical vorticity tendency inward atop the existing vorticity tower, that is further developed locally upward and outward along the sloped eyewall through advection and stretching. Observed maintenance of thermal wind balance from a thermodynamic retrieval shows evidence of a strengthening warm core, which aided in lowering surface pressure and further contributed to the efficient intensification in the latter stages of this RI event.

A Numerical Study on Rapid Intensification of Typhoon Vicente (2012) in the South China Sea. Part I: Verification of Simulation, Storm-Scale Evolution, and Environmental Contribution

2017 ◽  
Vol 145 (3) ◽  
pp. 877-898 ◽  
Author(s):  
Xiaomin Chen ◽  
Yuqing Wang ◽  
Kun Zhao ◽  
Dan Wu
Keyword(s):  
South China Sea ◽  
South China ◽  
Inner Core ◽  
Model Simulation ◽  
Numerical Study ◽  
Northern South China Sea ◽  
Monsoon Circulation ◽  
Rapid Intensification ◽  
China Sea ◽  
Tangential Wind

Typhoon Vicente (2012) underwent an extreme rapid intensification (RI) over the northern South China Sea just before its landfall in south China. The extreme RI, the sudden track deflection, and the inner- and outer-core structures of Vicente were reasonably reproduced in an Advanced Research version of the Weather Research and Forecasting (WRF-ARW) Model simulation. The evolutions of the axisymmetric inner-core radar reflectivity and the primary circulation of the simulated Vicente before its landfall were verified against the Doppler radar observations. Two intensification stages were identified: 1) the asymmetric intensification stage (i.e., RI onset), represented by a relatively slow intensification rate accompanied by a distinct eyewall contraction; and 2) the axisymmetric RI stage with very slow eyewall contraction. Results from a storm-scale tangential wind tendency budget indicated that the primary spinup mechanism during the first stage was the radial eddy momentum transport, which was beneficial to accelerate primary circulation inside the radius of maximum wind (RMW) and thus conducive to eyewall contraction. In contrast, the principal spinup mechanism during the second stage was mainly ascribed to the forced secondary circulation in response to diabatic heating in the eyewall and boundary layer friction, which efficiently transported the absolute angular momentum radially inward and vertically upward to increase the primary circulation in the eyewall region throughout the troposphere. Further analysis revealed that the interaction between the monsoon circulation and storm-scale vorticity anomalies played an important role in erecting the tilted vortex and spinning up the midtropospheric TC circulation during the first stage.

scholarly journals Reply to “Comments on ‘Revisiting the Balanced and Unbalanced Aspects of Tropical Cyclone Intensification’”

2018 ◽  
Vol 75 (7) ◽  
pp. 2497-2505 ◽  
Author(s):  
Junyao Heng ◽  
Yuqing Wang ◽  
Weican Zhou
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Model Simulation ◽  
Surface Friction ◽  
Fast Response ◽  
Tangential Wind ◽  
Physics Model ◽  
Balanced Dynamics ◽  
Balanced Solution

Abstract In their comment, Montgomery and Smith critique the recent study of Heng et al. that revisited the balanced and unbalanced aspects of tropical cyclone (TC) intensification based on diagnostics of a full-physics model simulation using the Sawyer–Eliassen equation. Heng et al. showed that the balanced dynamics reproduced to a large extent the secondary circulation in the full-physics model simulation and concluded that balanced dynamics can well explain TC intensification in their full-physics model simulation. Montgomery and Smith suspect the balanced solution in Heng et al. because the basic-state vortex is not exactly in thermal wind balance in the boundary layer and possibly a too-large diffusivity in the numerical model was used. In this reply, we first indicate that the boundary layer spinup mechanism proposed by Smith et al. is a fast response of the TC boundary layer to surface friction and should not be a major mechanism of TC intensification. We then evaluate the possible effect of imbalance in the basic state in the boundary layer on the balanced solution. The results show that although the removal of the imbalance in the boundary layer leads to about a one-third reduction in the maximum inflow near the surface in the inner-core region, the overall effect on the tangential wind budget is marginal because of other compensations. We also show that both the horizontal and vertical diffusivities in the model used in Heng et al. are reasonable based on previous observational studies. Therefore, we conclude that all results in Heng et al. are valid. Some related issues are also discussed.

scholarly journals Secondary Eyewall Formation in an Idealized Tropical Cyclone Simulation: Balanced and Unbalanced Dynamics

2016 ◽  
Vol 73 (10) ◽  
pp. 3911-3930 ◽  
Author(s):  
Hui Wang ◽  
Chun-Chieh Wu ◽  
Yuqing Wang
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Model Simulation ◽  
Surface Friction ◽  
Secondary Eyewall Formation ◽  
Budget Analysis ◽  
Tangential Wind ◽  
Spiral Rainbands ◽  
Physics Model ◽  
Balanced Dynamics

Abstract The secondary eyewall formation (SEF) in an idealized simulation of a tropical cyclone (TC) is examined from the perspective of both the balanced and unbalanced dynamics and through the tangential wind (Vt) budget analysis. It is found that the expansion of the azimuthal-mean Vt above the boundary layer occurs prior to the development of radial moisture convergence in the boundary layer. The Vt expansion results primarily from the inward angular momentum transport by the mid- to lower-tropospheric inflow induced by both convective and stratiform heating in the spiral rainbands. In response to the Vt broadening is the development of radial inflow convergence and the supergradient flow near the top of the inflow boundary layer. Results from the Vt budget analysis show that the combined effect of the mean advection and the surface friction is to spin down Vt in the boundary layer, while the eddy processes (eddy radial and vertical advection) contribute positively to the spinup of Vt in the SEF region in the boundary layer. Therefore, eddies play an important role in the spinup of Vt in the boundary layer during SEF. The balanced Sawyer–Eliassen solution can well capture the secondary circulation in the full-physics model simulation. The radial inflow diagnosed from the Sawyer–Eliassen equation is shown to spin up Vt and maintain the vortex above the boundary layer. However, the axisymmetric balanced dynamics cannot explain the spinup of Vt in the boundary layer, which results mainly from the eddy processes.

Fluctuations in inner-core structure during the rapid intensification of Super Typhoon Nepartak (2016)

2020 ◽  
Author(s):  
Sam Hardy ◽  
Juliane Schwendike ◽  
Roger K. Smith ◽  
Chris J. Short ◽  
Michael J. Reeder ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Structural Changes ◽  
Inner Core ◽  
Single Case ◽  
Three Dimensional ◽  
Core Structure ◽  
Rapid Intensification ◽  
Budget Analysis ◽  
Tangential Wind ◽  
The Mean

AbstractThe key physical processes responsible for inner-core structural changes and associated fluctuations in the intensification rate for a recent, high-impact western North Pacific tropical cyclone that underwent rapid intensification (Nepartak, 2016) are investigated using a set of convection-permitting ensemble simulations. Fluctuations in the inner-core structure between ring-like and monopole states develop in 60% of simulations. A tangential momentum budget analysis of a single fluctuation reveals that during the ring-like phase, the tangential wind generally intensifies, whereas during the monopole phase, the tangential wind remains mostly constant. In both phases, the mean advection terms spin up the tangential wind in the boundary layer, whereas the eddy advection terms deepen the storm’s cyclonic circulation by spinning up the tangential wind between 1.5 and 4 km. Further calculations of the azimuthally-averaged, radially-integrated vertical mass flux suggest that periods of near-constant tangential wind tendency are accompanied by a weaker eyewall updraft, which is unable to evacuate all the mass converging in the boundary layer. Composite analyses calculated from 18 simulations produce qualitatively similar results to those from the single case, a finding that is also in agreement with some previous observational and modelling studies. Above the boundary layer, the integrated contribution of the eddy term to the tangential wind tendency is over 80% of the contribution from the mean term, irrespective of inner-core structure. Our results strongly indicate that to fully understand the storm’s three-dimensional evolution, the contribution of the eddies must be quantified.

scholarly journals Revisiting the Balanced and Unbalanced Aspects of Tropical Cyclone Intensification

2017 ◽  
Vol 74 (8) ◽  
pp. 2575-2591 ◽  
Author(s):  
Junyao Heng ◽  
Yuqing Wang ◽  
Weican Zhou
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Model Simulation ◽  
Surface Friction ◽  
Core Region ◽  
Physics Model ◽  
The One ◽  
Balanced Dynamics ◽  
Balanced Solution

Abstract The balanced and unbalanced aspects of tropical cyclone (TC) intensification are revisited with the balanced contribution diagnosed with the outputs from a full-physics model simulation of a TC using the Sawyer–Eliassen (SE) equation. The results show that the balanced dynamics can well capture the secondary circulation in the full-physics model simulation even in the inner-core region in the boundary layer. The balanced dynamics can largely explain the intensification of the simulated TC. The unbalanced dynamics mainly acts to prevent the boundary layer agradient flow in the inner-core region from further intensification. Although surface friction can enhance the boundary layer inflow and make the inflow penetrate more inward into the eye region, contributing to the eyewall contraction, the net dynamical effect of surface friction on TC intensification is negative. The sensitivity of the balanced solution to the procedure used to ensure the ellipticity condition for the SE equation is also examined. The results show that the boundary layer inflow in the balanced response is very sensitive to the adjustment to inertial stability in the upper troposphere and the calculation of radial wind at the surface with relatively coarse vertical resolution in the balanced solution. Both the use of the so-called global regularization and the one-sided finite-differencing scheme used to calculate the surface radial wind in the balanced solution as utilized in some previous studies can significantly underestimate the boundary layer inflow. This explains why the boundary layer inflow in the balanced response is too weak in some previous studies.

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.

Inner-core dynamics during the rapid intensification of Hurricane Wilma (2005) with a steady radius of the maximum wind

2020 ◽  
Author(s):  
Nannan Qin ◽  
Da-Lin Zhang ◽  
William Miller ◽  
Chanh Kieu
Keyword(s):  
Inner Core ◽  
Vertical Motion ◽  
Rapid Intensification ◽  
Flux Divergence ◽  
Hurricane Wilma ◽  
Maximum Wind ◽  
Budget Analysis ◽  
Core Dynamics ◽  
Major Process ◽  
Frictional Dissipation

<p>Recent studies show that some hurricanes may undergo rapid intensification (RI) without contracting the radius of maximum wind (RMW). A cloud-resolving WRF-prediction of Hurricane Wilma (2005) is used herein to examine what controls the RMW contraction and how a hurricane could undergo RI without contraction. Results show that the processes controlling the RMW contraction are different within and above the planetary boundary layer (PBL). In the PBL, radial inflows contribute to contraction, with frictional dissipation acting as an inhibiting factor. Above the PBL, radial outflows and vertical motion govern the RMW contraction, with the former inhibiting it. A budget analysis of absolute angular momentum (AAM) shows that the radial AAM flux convergence is the major process accounting for the spinup of the maximum rotation, while the vertical flux divergence of AAM and the frictional sink in the PBL oppose the spinup. During the RI stage with no RMW contraction, the local AAM tendencies in the eyewall are smaller in magnitude and narrower in width than those during the contracting RI stage. In addition, the AAM following the time-dependent RMW decreases with time in the PBL and remains nearly constant aloft during the contracting stage, whereas it increases during the non-contracting stage. These results reveal different constraints for the RMW contraction and RI, and help explain why a hurricane vortex can still intensify after the RMW ceases contraction</p>

Numerical Study on the Extremely Rapid Intensification of an Intense Tropical Cyclone: Typhoon Ida (1958)

2015 ◽  
Vol 72 (11) ◽  
pp. 4194-4217 ◽  
Author(s):  
Sachie Kanada ◽  
Akiyoshi Wada
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Numerical Study ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Central Pressure ◽  
Rapid Intensification ◽  
Near Surface ◽  
Warm Core ◽  
Upper Level

Abstract Extremely rapid intensification (ERI) of Typhoon Ida (1958) was examined with a 2-km-mesh nonhydrostatic model initiated at three different times. Ida was an extremely intense tropical cyclone with a minimum central pressure of 877 hPa. The maximum central pressure drop in 24 h exceeded 90 hPa. ERI was successfully simulated in two of the three experiments. A factor crucial to simulating ERI was a combination of shallow-to-moderate convection and tall, upright convective bursts (CBs). Under a strong environmental vertical wind shear (>10 m s−1), shallow-to-moderate convection on the downshear side that occurred around the intense near-surface inflow moistened the inner-core area. Meanwhile, dry subsiding flows on the upshear side helped intensification of midlevel (8 km) inertial stability. First, a midlevel warm core appeared below 10 km in the shallow-to-moderate convection areas, being followed by the development of the upper-level warm core associated with tall convection. When tall, upright, rotating CBs formed from the leading edge of the intense near-surface inflow, ERI was triggered at the area in which the air became warm and humid. CBs penetrated into the upper troposphere, aligning the areas with high vertical vorticity at low to midlevels. The upper-level warm core developed rapidly in combination with the midlevel warm core. Under the preconditioned environment, the formation of the upright CBs inside the radius of maximum wind speeds led to an upright axis of the secondary circulation within high inertial stability, resulting in a very rapid central pressure deepening.

Double warm-core structure and potential vorticity diagnosis during the rapid intensification of Supertyphoon Lekima (2019)

2021 ◽  
Author(s):  
Donglei Shi ◽  
Guanghua Chen
Keyword(s):  
Potential Vorticity ◽  
Diabatic Heating ◽  
Inner Core ◽  
Deep Layer ◽  
Rapid Intensification ◽  
Latent Heat Release ◽  
Wind Fields ◽  
Warm Core ◽  
Upper Level ◽  
Pv Generation

AbstractThe rapid intensification (RI) of supertyphoon Lekima (2019) is investigated from the perspective of balanced potential vorticity (PV) dynamics using a high-resolution numerical simulation. The PV budget shows that the inner-core PV anomalies (PVAs) formed during the RI mainly comprise an eyewall PV tower generated by diabatic heating, a high-PV bridge extending into the eye resulting from the PV mixing, and an upper-tropospheric high-PV core induced by the PV intrusion from stratosphere. The inversion of the total PVA at the end of the RI captures about 90% of changes in pressure and wind fields, indicating that the storm is quasi-balanced. The piecewise PV inversion further demonstrates that the eyewall and mixed PVAs induce the upper-level and midlevel warm cores in the eye region, respectively. The two warm cores cause nearly all the balanced central pressure decrease and thus dominate the RI, with the contribution of the upper warm core being twice that of the midlevel one. In contrast, the upper-tropospheric PV core induces significant warming near the tropopause and deep-layer cooling beneath, reinforcing the upper-level warm core but causing little surface pressure drop.By comparing the diabatic PV generation due to the convective burst (CB) and non-CB precipitation, we found that the non-CB precipitation accounts for a larger portion for the eyewall PVA and thus the associated upper-level warming, distinct from previous studies that primarily attributed the upper-level warm-core formation to the CB. Nevertheless, CBs act to be more efficient PV generators due to their vigorous latent heat release and are thus favorable for RI.

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