Sensitivity of Tropical Cyclone Inner-Core Size and Intensity to the Radial Distribution of Surface Entropy Flux

2010 ◽  
Vol 67 (6) ◽  
pp. 1831-1852 ◽  
Author(s):  
Jing Xu ◽  
Yuqing Wang
Keyword(s):  
Tropical Cyclone ◽  
Radial Distribution ◽  
Inner Core ◽  
Critical Role ◽  
Convective Available Potential Energy ◽  
Core Size ◽  
Surface Entropy ◽  
Storm Intensity ◽  
Entropy Flux ◽  
Spiral Rainbands

Abstract The surface energy (entropy) flux is critical to the development and maintenance of a tropical cyclone (TC). However, it is unclear how sensitive the inner-core size and intensity of a TC could be to the radial distribution of the surface entropy flux under the TC. Such a potential sensitivity is examined in this study using the multiply nested, fully compressible, nonhydrostatic TC model TCM4. By artificially eliminating the surface entropy fluxes in different radial extent in different experiments, the effect of the surface entropy flux in the different radial ranges on the inner-core size and intensity of a simulated TC is evaluated. Consistent with recent findings from axisymmetric models, the entropy flux in the eye region of a TC is found to contribute little to the storm intensity, but it plays a role in reducing the radius of maximum wind (RMW). Although surface entropy fluxes under the eyewall contribute greatly to the storm intensity, those outside the eyewall up to a radius of about 2–2.5 times the RMW are also important. Farther outward, the surface entropy fluxes are found to be crucial to the growth of the storm inner-core size but could reduce the storm intensity. The surface entropy flux outside the inner core plays a critical role in maintaining high convective available potential energy (CAPE) outside the eyewall and thus active spiral rainbands. The latent heat release in these rainbands is responsible for the increase in the inner-core size of the simulated TC. A positive feedback is identified to explain changes in the inner-core size of the simulated storms in different experiments. Implications of the results for both observations and numerical prediction of TC structure and intensity changes are briefly discussed.

scholarly journals The Role of Near-Core Convective and Stratiform Heating/Cooling in Tropical Cyclone Structure and Intensity

2018 ◽  
Vol 75 (1) ◽  
pp. 297-326 ◽  
Author(s):  
Guanghua Chen ◽  
Chun-Chieh Wu ◽  
Yi-Hsuan Huang
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Core Region ◽  
Intensity Change ◽  
Moderate Intensity ◽  
Convective Heating ◽  
Core Size ◽  
Heating And Cooling ◽  
Diabatic Processes ◽  
Spiral Rainbands

The effects of convective and stratiform diabatic processes in the near-core region on tropical cyclone (TC) structure and intensity change are examined by artificially modifying the convective and stratiform heating/cooling between 40- and 80-km radii. Sensitivity experiments show that the absence of convective heating in the annulus can weaken TC intensity and decrease the inner-core size. The increased convective heating generates a thick and polygonal eyewall, while the storm intensifies more gently than that in the control run. The removal of stratiform heating can slow down TC intensification with a moderate intensity, whereas the doubling of stratiform heating has little effect on the TC evolution compared to the control run. The halved stratiform cooling facilitates TC rapid intensification and a compact inner-core structure with the spiral rainbands largely suppressed. With the stratiform cooling doubled, the storm terminates intensification and eventually develops a double-eyewall-like structure accompanied by the significantly outward expansion of the inner-core size. The removal of both stratiform heating and cooling generates the strongest storm with the structure and intensity similar to those in the experiment with stratiform cooling halved. When both stratiform heating and cooling are doubled, the storm first decays rapidly, followed by the vertical connection of the updrafts at mid- to upper levels in the near-core region and at lower levels in the collapsed eyewall, which reinvigorates the eyewall convection but with a large outward slope.

scholarly journals Sensitivity of the Simulated Tropical Cyclone Inner-Core Size to the Initial Vortex Size*

2010 ◽  
Vol 138 (11) ◽  
pp. 4135-4157 ◽  
Author(s):  
Jing Xu ◽  
Yuqing Wang
Keyword(s):  
Angular Momentum ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Mature Stage ◽  
Core Size ◽  
Initial Size ◽  
Radial Extent ◽  
Tangential Wind ◽  
Vortex Size ◽  
Spiral Rainbands

Abstract The multiply nested, fully compressible, nonhydrostatic tropical cyclone model version 4 (TCM4) is used to examine and understand the sensitivity of the simulated tropical cyclone (TC) inner-core size to its initial vortex size. The results show that although the simulated TC intensity at the mature stage is weakly dependent on the initial vortex size for the general settings, the simulated TC inner-core size is largely determined by the initial vortex size. The initial vortex size is critical to both the energy input from the ocean and the effectiveness of the inward angular momentum transport by the transverse circulation driven by eyewall convection and diabatic heating in spiral rainbands. Strong outer winds in a storm with a large initial size lead to large entropy fluxes to a large radial extent outside the eyewall, favoring the development of active spiral rainbands. Latent heat released in spiral rainbands plays a key role in increasing the low-level radial inflow and accelerating tangential winds outside the eyewall, leading to outward expansion of tangential wind fields and thus increasing the inner-core size of the simulated storm. On the contrary, a storm with a small initial size has weaker outer winds and smaller surface entropy fluxes outside the eyewall and is accompanied by less active spiral rainbands and thus a much slower increase in the inner-core size. The effectiveness of the inward transport of absolute angular momentum to increase the tangential winds outside the eyewall is largely determined by the radial extent of the vertical absolute vorticity, which is shown to be higher in a large size vortex. The relative importance of the initial vortex size and the environmental relative humidity (RH) to the TC inner-core size is also evaluated. It is found that the inner-core size of the simulated storm at the mature stage depends more heavily on the initial vortex size than on the initial RH of the environment.

scholarly journals A Simple Derivation of Tropical Cyclone Ventilation Theory and Its Application to Capped Surface Entropy Fluxes

2017 ◽  
Vol 74 (9) ◽  
pp. 2989-2996 ◽  
Author(s):  
Daniel R. Chavas
Keyword(s):  
Phase Space ◽  
Wind Speed ◽  
Tropical Cyclone ◽  
Analytical Solutions ◽  
Heat Engine ◽  
Vertical Wind Shear ◽  
Intensity Change ◽  
Necessary Condition ◽  
Surface Entropy ◽  
Entropy Flux

Abstract In a recent study, a theory was presented for the dependence of tropical cyclone intensity on the ventilation of dry air by environmental vertical wind shear. This theory was found to successfully capture the statistics of intensity dynamics in the historical record. This theory is rederived here from a simple three-term power budget and extended to analytical solutions for the complete phase space, including the change in storm intensity itself. The derivation is then generalized to the case of a capped surface entropy flux wind speed, including analytical solutions defined relative to both the traditional potential intensity and the capped-flux potential intensity. The results demonstrate that a cap on the surface entropy flux wind speed reduces the potential intensity of the system and effectively amplifies the detrimental effect of ventilation on the tropical cyclone heat engine. However, such a cap does not alter the qualitative structure of the phase-space solution for intensity change phrased relative to the capped-flux potential intensity. Thus, the wind speed dependence of surface entropy fluxes is important for intensity change in real-world storms, though it is not a necessary condition for intensification in general. Indeed, a residual power surplus may remain available to intensify a storm even in the presence of a cap, though intensification may be fully suppressed for sufficiently strong ventilation. This work complements a recent numerical simulation study and provides further evidence that there is no disconnect between extant tropical cyclone theory and the finding in numerical simulations that a storm may intensify in the presence of capped surface entropy fluxes.

scholarly journals The Role of Inner-Core Moisture in Tropical Cyclone Predictability and Practical Forecast Skill

2017 ◽  
Vol 74 (7) ◽  
pp. 2315-2324 ◽  
Author(s):  
Kerry Emanuel ◽  
Fuqing Zhang
Keyword(s):  
Tropical Cyclone ◽  
Wind Field ◽  
Inner Core ◽  
Forecast Skill ◽  
Initial Condition ◽  
Tropical Cyclone Intensity ◽  
Cyclone Intensity ◽  
Storm Intensity ◽  
Tropical Cyclone Intensity Forecasts

Abstract Errors in tropical cyclone intensity forecasts are dominated by initial-condition errors out to at least a few days. Initialization errors are usually thought of in terms of position and intensity, but here it is shown that growth of intensity error is at least as sensitive to the specification of inner-core moisture as to that of the wind field. Implications of this finding for tropical cyclone observational strategies and for overall predictability of storm intensity are discussed.

scholarly journals Kinematic Structure of Mesovortices in the Eyewall of Hurricane Ike (2008) Derived from Ground-Based Dual-Doppler Analysis

2016 ◽  
Vol 144 (11) ◽  
pp. 4245-4263 ◽  
Author(s):  
Stephanie M. Wingo ◽  
Kevin R. Knupp
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Kinematic Structure ◽  
Hurricane Ike ◽  
Local Pressure ◽  
Vertical Vorticity ◽  
Storm Intensity ◽  
Vertical Extent ◽  
Perturbation Pressure ◽  
Doppler Analysis

Abstract Previous work has shown that vorticity mixing in the tropical cyclone (TC) inner core can promote mesovortex (MV) formation and impact storm intensity. Observations of MVs have largely been serendipitous but are necessary to improve understanding of these features and their role in TC dynamics. This study presents nearly 10 h of ground-based dual-Doppler analysis of MVs in the eyewall of Hurricane Ike (2008) near and during landfall. Derived 3D winds, vertical vorticity, horizontal divergence, and perturbation pressures are analyzed. Results indicate persistent kinematic field arrangements and evolving vertical structures. Perturbation pressure retrievals suggest local pressure minima associated with the MVs. Preferential updraft locations appear to transition cyclonically about the local vorticity maximum as the MVs progress around the eye. Based on published observational datasets, the dual-Doppler updraft magnitudes in Ike’s MVs are within the top 5%–10% of TC vertical velocities. The MVs are marked by peak vorticity in the lowest 2 km and contain vertically coherent vorticity structures extending to 8 km AGL. After prolonged land interaction, the MV structures deteriorate. First, the vertical extent of localized vorticity diminishes, followed by a deterioration in the prelandfall characteristic kinematic arrangements. This supports the notion that the replenishment of a high vorticity annulus contributes to MV production and maintenance, and when the elevated vorticity aloft is not maintained, MV kinematic patterns become less consistent. It is unclear whether the decay of the vertically coherent vorticity structures occurs in response to land interaction, TC inner core processes, or some combination of both.

scholarly journals Equilibrium Tropical Cyclone Size in an Idealized State of Axisymmetric Radiative–Convective Equilibrium*

2014 ◽  
Vol 71 (5) ◽  
pp. 1663-1680 ◽  
Author(s):  
Daniel R. Chavas ◽  
Kerry Emanuel
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Cloud Model ◽  
Critical Role ◽  
Tropical Meteorology ◽  
Length Scale ◽  
Coriolis Parameter ◽  
Nondimensional Parameter ◽  
Empirical Estimates ◽  
Radial Length

Abstract Tropical cyclone size remains an unsolved problem in tropical meteorology, yet size plays a significant role in modulating damage. This work employs the Bryan cloud model (CM1) to systematically explore the sensitivity of the structure of an axisymmetric tropical cyclone at statistical equilibrium to the set of relevant model, initial, and environmental external parameters. The analysis is performed in a highly idealized state of radiative–convective equilibrium (RCE) governed by only four thermodynamic parameters, which are shown to modulate the storm structure primarily via modulation of the potential intensity. Using dimensional analysis, the authors find that the equilibrium radial wind profile is primarily a function of a single nondimensional parameter given by the ratio of the storm radial length scale to the parameterized eddy radial length scale. The former is found to be the ratio of the potential intensity to the Coriolis parameter, matching the prediction for the “natural” storm length scale embedded within prevailing axisymmetric tropical cyclone theory; the Rossby deformation radius is shown not to be fundamental. Beyond this primary scaling, a second nondimensional parameter representing the nondimensional Ekman suction velocity is found to modulate the far outer wind field. Implications of the primary nondimensional parameter are discussed, including the critical role of effective turbulence in modulating inner-core structure and new insight into empirical estimates of the radial mixing length.

scholarly journals Balanced Contribution to the Intensification of a Tropical Cyclone Simulated in TCM4: Outer-Core Spinup Process*

2011 ◽  
Vol 68 (3) ◽  
pp. 430-449 ◽  
Author(s):  
Hironori Fudeyasu ◽  
Yuqing Wang
Keyword(s):  
Angular Momentum ◽  
Tropical Cyclone ◽  
Diabatic Heating ◽  
Inner Core ◽  
Three Dimensional ◽  
Outer Core ◽  
Middle Troposphere ◽  
Tangential Wind ◽  
Spiral Rainbands ◽  
Balance Dynamics

Abstract The balanced contribution to the intensification of a tropical cyclone simulated in the three-dimensional, nonhydrostatic, full-physics tropical cyclone model version 4 (TCM4), in particular the spinup of the outer-core circulation, is investigated by solving the Sawyer–Eliassen equation and by computing terms in the azimuthal-mean tangential wind tendency equation. Results demonstrate that the azimuthal-mean secondary circulation (radial and vertical circulation) and the spinup of the midtropospheric outer-core circulation in the simulated tropical cyclone are well captured by balance dynamics. The midtropospheric inflow develops in response to diabatic heating in mid–upper-tropospheric stratiform (anvil) clouds outside the eyewall in active spiral rainbands and transports absolute angular momentum inward to spin up the outer-core circulation. Although the azimuthal-mean diabatic heating rate in the eyewall is the largest, its contribution to radial winds and thus the spinup of outer-core circulation in the middle troposphere is rather weak. This is because the high inertial stability in the inner-core region resists the radial inflow in the middle troposphere, limiting the inward transport of absolute angular momentum. The result thus suggests that diabatic heating in spiral rainbands is the key to the continued growth of the storm-scale circulation.

scholarly journals How Do Outer Spiral Rainbands Affect Tropical Cyclone Structure and Intensity?*

2009 ◽  
Vol 66 (5) ◽  
pp. 1250-1273 ◽  
Author(s):  
Yuqing Wang
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Surface Pressure ◽  
Diabatic Heating ◽  
Inner Core ◽  
Phase Changes ◽  
Wave Radiation ◽  
Atmospheric Column ◽  
Tangential Wind ◽  
Spiral Rainbands

Abstract A long-standing issue on how outer spiral rainbands affect the structure and intensity of tropical cyclones is studied through a series of numerical experiments using the cloud-resolving tropical cyclone model TCM4. Because diabatic heating due to phase changes is the main driving force of outer spiral rainbands, their effect on the tropical cyclone structure and intensity is evaluated by artificially modifying the heating and cooling rate due to cloud microphysical processes in the model. The view proposed here is that the effect of diabatic heating in outer spiral rainbands on the storm structure and intensity results mainly from hydrostatic adjustment; that is, heating (cooling) of an atmospheric column decreases (increases) the surface pressure underneath the column. The change in surface pressure due to heating in the outer spiral rainbands is significant on the inward side of the rainbands where the inertial stability is generally high. Outside the rainbands in the far field, where the inertial stability is low and internal atmospheric heating is mostly lost to gravity wave radiation and little is left to warm the atmospheric column and lower the local surface pressure, the change in surface pressure is relatively small. This strong radially dependent response reduces the horizontal pressure gradient across the radius of maximum wind and thus the storm intensity in terms of the maximum low-level tangential wind while increasing the inner-core size of the storm. The numerical results show that cooling in the outer spiral rainbands maintains both the intensity of a tropical cyclone and the compactness of its inner core, whereas heating in the outer spiral rainbands decreases the intensity but increases the size of a tropical cyclone. Overall, the presence of strong outer spiral rainbands limits the intensity of a tropical cyclone. Because heating or cooling in the outer spiral rainbands depends strongly on the relative humidity in the near-core environment, the results have implications for the formation of the annular hurricane structure, the development of concentric eyewalls, and the size change in tropical cyclones.

scholarly journals Effects of Diabatic Heating and Cooling in the Rapid Filamentation Zone on Structure and Intensity of a Simulated Tropical Cyclone

2014 ◽  
Vol 71 (9) ◽  
pp. 3144-3163 ◽  
Author(s):  
Qingqing Li ◽  
Yuqing Wang ◽  
Yihong Duan
Keyword(s):  
Tropical Cyclone ◽  
Numerical Experiments ◽  
Diabatic Heating ◽  
Inner Core ◽  
Size Increase ◽  
Core Size ◽  
Heating And Cooling ◽  
Tc Model

Abstract The effects of diabatic heating and cooling in the rapid filamentation zone (RFZ), within which inner rainbands are often active, on tropical cyclone (TC) structure and intensity are investigated based on idealized numerical experiments using a cloud-resolving TC model (TCM4). The results show that removal of heating (cooling) in the RFZ would reduce (increase) the TC intensity. Diabatic heating in the RFZ plays an important role in increasing the inner-core size whereas diabatic cooling tends to limit the inner-core size increase or even reduce the inner-core size of a TC. Removal of both diabatic heating and cooling in the RFZ greatly suppresses the activity of inner rainbands but leads to the quasi-periodic development of a convective ring immediately outside of the inner core. A similar convective ring also develops in an experiment with the removal of diabatic heating only in the RFZ. With diabatic cooling removed only in the RFZ, an annular-hurricane-like structure arises with the outer rainbands largely suppressed.

scholarly journals Impacts of Evaporation of Rainwater on Tropical Cyclone Structure and Intensity—A Revisit

2015 ◽  
Vol 72 (4) ◽  
pp. 1323-1345 ◽  
Author(s):  
Qingqing Li ◽  
Yuqing Wang ◽  
Yihong Duan
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Potential Temperature ◽  
Outer Core ◽  
Cold Pool ◽  
Equivalent Potential Temperature ◽  
Core Size ◽  
Size Change ◽  
Equivalent Potential ◽  
The Impact

Abstract The impact of evaporation of rainwater on tropical cyclone (TC) intensity and structure is revisited in this study. Evaporative cooling can result in strong downdrafts and produce low–equivalent potential temperature air in the inflow boundary layer, particularly in the region outside the eyewall, significantly suppressing eyewall convection and reducing the final intensity of a TC. Different from earlier findings, results from this study show that outer rainbands still form but are short lived in the absence of evaporation. Evaporation of rainwater is shown to facilitate the formation of outer rainbands indirectly by reducing the cooling due to melting of ice particles outside the inner core, not by the cold-pool dynamics, as previously believed. Only exclusion of evaporation in the eyewall region or the rapid filamentation zone has a very weak effect on the inner-core size change of a TC, whereas how evaporation in the outer core affects the inner-core size depends on how active the inner rainbands are. More (less) active inner rainbands may lead to an increase (a decrease) in the inner-core size.

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