Hot Towers Research Articles

Using Ground-Based Radar Observations to Evaluate Asymmetric Convection and Eyewall Dynamics during the Landfall of Hurricane Harvey (2017)

Abstract Asymmetric dynamics in tropical cyclones (TCs) are vital to understanding intensity change and convective distribution at landfall. The growth of barotropic–convective instability (e.g., mesovortices), vortical hot towers, and vortex Rossby waves (VRWs) have been considered through numerical modeling studies, often by mean–eddy partitioning of the tangential wind tendency. Unfortunately, few observational datasets exist that are sufficient for such study. A University of Oklahoma Shared Mobile Atmospheric Research and Teaching radar observed major Hurricane Harvey (2017) as it intensified just before landfall near Port Aransas, Texas. Combined with a coastal WSR-88D radar, dual-Doppler derived kinematic analyses were constructed every ∼6 min at 1-km spatial resolution during Hurricane Harvey’s landfall. In this study, observations of asymmetric mesovortices on the interior edge of Harvey’s eyewall are documented. The asymmetries promoted a dual exchange of vorticity in the TC eyewall and represent an example of an eddy mechanism of intensity change on various time scales. Considering the combined effects of resolvable asymmetries, we examine the change in the tangential wind as a function of mean–eddy kinematics before and after landfall. Before landfall, the low-level eddy contribution was positive to the low-level tangential wind tendency. Following landfall, the contribution from the low-level eddy became weakly positive to weakly negative. Finally, the evolution of some asymmetric features in Harvey’s eyewall are shown to manifest in a VRW-like response that initiates rainbands just outside of Harvey’s eyewall.

Turbulent vortex dynamo in the Earth’s atmosphere and the emerging opportunity to affect tropical cyclogenesis

The interpretation of tropical cyclogenesis as an extreme threshold event in the helical atmospheric turbulence allows us to discuss the idea on affecting the birth of a hurricane. A hypothetical way is based on the crucial role of the intense vortical cloud convection, known as Vortical Hot Towers, in the excitation and maintenance of large-scale helical-vortex instability. Some quantitative estimates are given, for which results of idealized cloud-resolving numerical simulation have been applied. The modern numerical modeling of atmospheric processes makes it possible to investigate and evaluate the possibilities of managing the instability, for example, on the basis of “Hurricane Nature Run.”

Characteristics and mechanism of vertical coupling in the genesis of tropical cyclone Durian (2001)

The vertical coupling (VC) process and mechanism during the genesis of a tropical cyclone (TC) implied by the weak vertical shear of horizontal wind, one of the key factors impacting TC genesis, constitute important but unanswered fundamental scientific problems. This paper carried out a targeted investigation of this problem through numerical simulation and theoretical analyses. The main conclusions are as follows. Even if TC genesis occurs in a barotropic environment, a VC process still occurs between the trough (vortex) at the middle level and that at the lower level in the TC embryo area. VC mainly occurs at the tropical disturbance (TDS) stage. Only after the VC is accomplished can the tropical depression (TD) organize further by itself and develop into the tropical storm (TS) stage or the stronger tropical typhoon (TY) stage through the WISHE (wind-induced surface heat exchange) mechanism. In the VC process, vortical hot towers (VHTs) play vertical connecting roles and are the actual practitioners of the VC. Through the VHTs’ vertical connections, the middle- and lower-troposphere trough axes move towards each other and realize the VC. VHTs can produce intensive cyclonic vorticity in the lower troposphere, which is mainly contributed by the stretching term. The tilting term can produce a single dipole or double dipole of vorticity, but the positive and negative vorticity pairs offset each other roughly. While the stretching term ensures that the cyclonic rotations of the wind field in the middle and lower levels tend to be consistent, the tilting term acts to uniformly distribute the horizontal wind in the vertical direction, and both terms facilitate the VC of the wind field. With the latent heat of condensation, VHTs heat the upper and middle troposphere so that the 352 K equivalent potential temperature contour penetrates vertically into the 925–300 hPa layer, realizing the VC of the temperature field. While forming cloud towers, VHTs make the ambient air become moist and nearly saturated so that the 95% relative humidity contour penetrates vertically into the 925–400 hPa layer, realizing the VC of the humidity field. Due to the collective contributions of the VHTs, the embryo area develops into a warm, nearly saturated core with strong cyclonic vorticity. The barotropic instability mechanism may also occur during TC genesis over the Northwest Pacific and provide rich large-scale environmental vorticity for TC genesis. The axisymmetric distribution of VHTs is an important sign of TC genesis. When a TC is about to form, there may be accompanying phenomena between the axisymmetric process of VHTs and vortex Rossby waves.

Impact of Background Dynamic and Thermodynamic States on Distinctive Annual Cycle of Near-Equatorial Tropical Cyclogenesis over the Western North Pacific

In a sharp contrast to tropical cyclone (TC) genesis over the main development region of the western North Pacific (WNP), near-equatorial (0°–5°N) TCs exhibit a distinctive annual cycle, peaking in boreal winter and being inactive in boreal summer. The relative roles of dynamic and thermodynamic background states on near-equatorial TCs formation were investigated based on the observational diagnosis of the genesis potential index (GPI) and high-resolution model simulations. It is found that the background vorticity makes a major contribution to the distinctive annual cycle, while mean temperature and specific humidity fields are not critical. Numerical simulations further indicate that seasonal mean cyclonic vorticity in boreal winter has three effects on TC genesis near the equator. First, the environmental cyclonic vorticity interacts with TC vortex to promote a mid-level outflow, which strengthens boundary layer friction induced ascending motion and thus condensational heating. Second, it produces an equivalent Coriolis effect (via enhanced absolute vorticity), which strengthens positive feedback between primary and secondary circulation. Third, it helps to merge small-scale vortical hot towers (VHTs) into a mesoscale core through vorticity segregation process. However, background vorticity in boreal summer has an opposite effect on TC development near the equator.

On the Creation and Evolution of Small-Scale Low-Level Vorticity Anomalies during Tropical Cyclogenesis

Abstract Recent numerical modeling and observational studies indicate the importance of vortical hot towers (VHTs) in the transformation of a tropical disturbance to a tropical depression. It has recently been recognized that convective-scale downdraft outflows that form within VHTs also preferentially develop positive vertical vorticity around their edges, which is considerably larger in magnitude than ambient values. During a numerical simulation of tropical cyclogenesis it is found that particularly strong low-level convectively induced vorticity anomalies (LCVAs) occasionally form as convection acts on the enhanced vorticity at the edges of cold pools. These features cycle about the larger-scale circulation and are associated with a coincident pressure depression and low-level wind intensification. The LCVAs studied are considerably deeper than the vorticity produced at the edges of VHT cold pool outflows, and their evolution is associated with persistent convection and vortex merger events that act to sustain them. Herein, we highlight the formation and evolution of two representative LCVAs and discuss the environmental parameters that eventually become favorable for one LCVA to reach the center of a larger-scale circulation as tropical cyclogenesis occurs.

“Convective Hot Tower” Signatures and Rapid Intensification of Severe Typhoon Vicente (1208)

ABSTRACT Severe typhoon vicente (1208) was the first tropical cyclone that necessitated the issuance of No. 10 Hurricane Signal in Hong Kong since Typhoon York back in 1999. Hurricane force winds were recorded over the southwestern part of Hong Kong during the passage of vicente. In the evening on 23 July 2012, “convective hot towers” appeared on the eyewall of Vicente and were captured on both radar imagery and lightning location map. The corresponding cloud top overshot 15 km up to the top of the troposphere, accompanied by cloud-to-ground lightning. Such observations signified that the associated updraft turned violent at the locations of convective hot towers. Shortly afterwards, Vicente intensified rapidly to a severe typhoon over the South China Sea to the south-southwest of Hong Kong around midnight, reaching its peak intensity with an estimated maximum sustained wind of 155 km/h near its centre. It is the first time in the century-long tropical cyclone history of Hong Kong that the signature of “con-vective hot towers” in a rapidly intensifying typhoon can be observed in details by multiple remote-sensing platforms. This paper serves to document such rare observational evidence and share the main results as a checklist for reference by operational forecasters when monitoring proximate typhoons for signs of rapid intensification.

The Study of Inland Eyewall Reformation of Typhoon Fanapi (2010) Using Numerical Experiments and Vorticity Budget Analysis

AbstractNumerical simulations of Typhoon Fanapi (2010) interacting with the terrain of Taiwan are conducted using the Advanced Research Weather Research and Forecasting model (ARW, version 3.3.1) on a triply nested grid (with the finest grid size of 1 km and 55 vertical levels). Fanapi made landfall on eastern Taiwan at 0000 UTC 19 September and left Taiwan at 1200 UTC 19 September 2010, producing heavy rainfall and severe floods. After landfall, the Fanapi eyewall weakened and broke down over the Central Mountain Range. Vortical hot towers (VHTs) occurred along the Fanapi rainband, and the VHTs in land have weaker maximum updrafts (7.0–8.0 m/s), narrower diameter (7.0–11.5 km), and shallower depth (6.5–9.0 km), compared with oceanic VHTs over the Taiwan Strait. The VHTs over the Taiwan Strait remained organized along the rainband and propagated toward the southeast quadrant of the Fanapi circulation over land by the tangential flow. These organized VHTs in the southeast quadrant help transport cyclonic vorticity from lower into middle levels and then cooperate with the rich vorticity within the rainband by horizontal vorticity advection to rebuild the Fanapi eyewall upward from the bottom. The vorticity balance within the entire Fanapi circulation is largely dominated by its southeast quadrant with organized VHTs over Taiwan Island. In the simulation with no latent heat release, the VHTs quickly decay and radiate outward from the eyewall as gravity‐wave perturbations.

Satellite Observations of Stratospheric Gravity Waves Associated With the Intensification of Tropical Cyclones

AbstractForecasting the intensity of tropical cyclones is a challenging problem. Rapid intensification is often preceded by the formation of “hot towers” near the eyewall. Driven by strong release of latent heat, hot towers are high‐reaching tropical cumulonimbus clouds that penetrate the tropopause. Hot towers are a potentially important source of stratospheric gravity waves. Using 13.5 years (2002–2016) of Atmospheric Infrared Sounder observations of stratospheric gravity waves and tropical cyclone data from the International Best Track Archive for Climate Stewardship, we found empirical evidence that stratospheric gravity wave activity is associated with the intensification of tropical cyclones. The Atmospheric Infrared Sounder and International Best Track Archive for Climate Stewardship data showed that strong gravity wave events occurred about twice as often for tropical cyclone intensification compared to storm weakening. Observations of stratospheric gravity waves, which are not affected by obscuring tropospheric clouds, may become an important future indicator of storm intensification.

On the Path from the Turbulent Vortex Dynamo Theory to Diagnosis of Tropical Cyclogenesis

An overview of researches is presented, which was focused on application of a theoretical hypothesis on the turbulent vortex dynamo to the study of tropical cyclogenesis. The dynamo effect is related to the special properties of small-scale helical turbulence with the broken mirror symmetry and was hypothesized to result in large-scale vortices generation in both hydrodynamic and atmospheric turbulence. To introduce this abstract theory into tropical cyclone research, a recent discovery of vortical moist convection in the tropics is emphasized. Based on this finding, we discuss and substantiate the crucial role of rotating cumulonimbus clouds, known as vortical hot towers (VHTs), as a necessary element to provide the dynamo effect. An analogy is traced between the role of interaction “moist convection—vertical wind shear” in creating the vortex dynamo in the atmosphere and the role of the mean electromotive force providing the MHD dynamo in electrically conducting medium. Throughout the review of novel results, a pivotal role of the Russian-American collaboration on examining a helical self-organization of moist convective atmospheric turbulence under tropical cyclone formation by use of cloud-resolving numerical simulation is accented. The efforts resulted in application of the vortex dynamo theory to diagnose a time when cyclogenesis commences in a favorable tropical environment. This may help elaborate a universally accepted definition of tropical cyclogenesis that currently does not exist and contribute to practical purposes of diagnosis and forecasting.

Is the State of the Air-Sea Interface a Factor in Rapid Intensification and Rapid Decline of Tropical Cyclones?

Tropical storm intensity prediction remains a challenge in tropical meteorology. Some tropical storms undergo dramatic rapid intensification and rapid decline. Hurricane researchers have considered particular ambient environmental conditions including the ocean thermal and salinity structure and internal vortex dynamics (e.g., eyewall replacement cycle, hot towers) as factors creating favorable conditions for rapid intensification. At this point, however, it is not exactly known to what extent the state of the sea surface controls tropical cyclone dynamics. Theoretical considerations, laboratory experiments, and numerical simulations suggest that the air-sea interface under tropical cyclones is subject to the Kelvin-Helmholtz type instability. Ejection of large quantities of spray particles due to this instability can produce a two-phase environment, which can attenuate gravity-capillary waves and alter the air-sea coupling. The unified parameterization of waveform and two-phase drag based on the physics of the air-sea interface shows the increase of the aerodynamic drag coefficient with wind speed up to hurricane force ( m s-1). Remarkably, there is a local minimum-"an aerodynamic drag well"-at around m s-1. The negative slope of the dependence on wind-speed between approximately 35 and 60 m s-1 favors rapid storm intensification. In contrast, the positive slope of wind-speed dependence above 60 m s-1 is favorable for a rapid storm decline of the most powerful storms. In fact, the storms that intensify to Category 5 usually rapidly weaken afterward.

Asymptotics for moist deep convection I: refined scalings and self-sustaining updrafts

Moist processes are among the most important drivers of atmospheric dynamics,and scale analysis and asymptotics are cornerstones of theoretical meteorology. Accounting for moist processes in systematic scale analyses therefore seems of considerable importance for the field. Klein & Majda (TCFD, 20, 525--552, (2006)) proposed a scaling regime for the incorporation of moist bulk microphysics closures in multiscale asymptotic analyses of tropical deep convection. This regime is refined here to allow for mixtures of ideal gases and to establish consistency with a more general multiple scales modelling framework for atmospheric flows. Deep narrow updrafts, so-called "hot towers", constitute principal building blocks of larger scale storm systems. They are analysed here in a sample application of the new scaling regime. A single quasi-onedimensional columnar cloud is considered on the vertical advective (or tower life cycle) time scale. The refined asymptotic scaling regime is essential for this example as it reveals a new mechanism for the self-sustainance of such updrafts. Even for strongly positive convectively available potential energy (CAPE), a vertical balance of buoyancy forces is found in the presence of precipitation. This balance induces a diagnostic equation for the vertical velocity and it is responsible for the generation of self-sustained balanced updrafts. The time dependent updraft structure is encoded in a Hamilton-Jacobi equation for the precipitation mixing ratio. Numerical solutions of this equation suggest that the self-sustained updrafts may strongly enhance hot tower life cycles.

Optimization of Distillation Separations Using Feed Splitting by a Homotopy Continuation Method

It is a common procedure to save energy in industrial distillation towers by preheating and precooling the feed with heat transfer from the bottom and top products. An example is oil sweetening by distillation. It is shown here using simulation that if, before entering the unit, the oil feed is split into two streams and only one of them is preheated, further savings of energy (up to 50%) can be achieved. The same results are achieved by splitting the feed to an ethane–ethylene distillation column and precooling only one part of it just before entering the tower. In this study, the effects of feed splitting into hot and cold towers were investigated in order to reduce the duties of the reboiler or condenser and the total annual cost (TAC). Also, consideration was given to obtaining a common design in order to achieve greater flexibility for the required operating schemes. The investigation was carried out as an optimization problem defined by effective parameters affecting the reboiler and condenser duty ...

Kinetic Energy Budget during the Genesis Period of Tropical Cyclone Durian (2001) in the South China Sea

Abstract A set of kinetic energy (KE) budget equations associated with four horizontal flow components was derived to study the KE characteristics during the genesis of Tropical Cyclone (TC) Durian (2001) in the South China Sea using numerical simulation data. The genesis process was divided into three stages: the monsoon trough stage (stage 1), the midlevel mesoscale convective vortex (MCV) stage (stage 2), and the establishment stage of the TC vortex (stage 3). Analysis showed that the KE of the symmetric rotational flow (SRF) was the largest and kept increasing, especially in stages 2 and 3, representing the symmetrization process during TC genesis. The KE of the SRF was mainly converted from the KE of the symmetric divergent flow (SDF), largely transformed from the available potential energy (APE). It was found that vortical hot towers (VHTs) emerged abundantly, aggregated, and merged within the MCV region in stages 1 and 2. From the energy budget perspective, massive moist-convection-produced latent heat was concentrated and accumulated within the MCV region, especially in stage 2, and further warmed the atmosphere, benefiting the accumulation of APE and the transformation from APE to KE. As a result, the midlevel circulation (or MCV) grew strong rapidly. In stage 3, the intensity and number of VHTs both decreased. However, affected by increasing lower-level inward radial wind, latent heat released by the organized convection, instead of disorganized VHTs in the first two stages, continuously contributed to the strengthening of the surface TC circulation as well as the warm core.

The Inland Eyewall Reintensification of Typhoon Fanapi (2010) Documented from an Observational Perspective Using Multiple-Doppler Radar and Surface Measurements

Abstract This study documents observational changes in the eyewall of Typhoon Fanapi (2010) after landfall in Taiwan. The observations indicate that Fanapi’s eye and eyewall disappeared on the eastern side of Taiwan’s Central Mountain Range (CMR) after landfall, but reemerged on the western side of CMR. The cyclonic circulation, increasing wind speed, a low-level low pressure and high temperature zone, the associated updrafts and downdrafts, and surface pressure and rainfall measurements all support the existence of a reintensified eyewall. The storm slowed down during the redeveloping stage, thus prolonging the rainfall duration over Taiwan. On the western side of CMR a northwest–southeast-oriented rainband formed at an earlier stage, possibly due to the large-scale interaction between Fanapi’s remnant flow and the environment. However, the subsequent reintensification might be attributed to the interaction between the circulation and topography. This is supported by the finding that adjacent to CMR, strong wind develops vertically from lower levels, indicating that the reintensification appears to be initiated through a bottom-up process. A vorticity budget analysis shows that at lower layers the stretching mechanism plays a leading role in increasing positive vorticity, followed by the contributions from tilting and horizontal advection. The horizontal advection plays a comparable role to the vertical advection in increasing low- to midlevel vorticity. The vertical advection aloft is responsible for transporting the vorticity upward. Finally, this research provides a relatively rare documentation of the vortical hot towers (VHTs) over terrain using ground-based radars, in contrast to most previous studies focusing on maritime VHTs using simulations or aircraft measurements.

Reassessing the Use of Inner-Core Hot Towers to Predict Tropical Cyclone Rapid Intensification*

Abstract The hot tower (HT) in the inner core plays an important role in tropical cyclone (TC) rapid intensification (RI). With the help of Tropical Rainfall Measurement Mission (TRMM) data and the Statistical Hurricane Intensity Prediction Scheme dataset, the potential of HTs in operational RI prediction is reassessed in this study. The stand-alone HT-based RI prediction scheme showed little skill in the northern Atlantic (NA) and eastern and central Pacific (ECP), but yielded skill scores of >0.3 in the southern Indian Ocean (SI) and western North Pacific (WNP) basins. The inaccurate predictions are due to four scenarios: 1) RI events may have already begun prior to the TRMM overpass. 2) RI events are driven by non-HT factors. 3) The HT has already dissipated or has not occurred at the TRMM overpass time. 4) Large false alarms result from the unfavorable environment. When the HT was used in conjunction with the TC’s previous 12-h intensity change, the potential intensity, the percentage area from 50 to 200 km of cloud-top brightness temperatures lower than −10°C, and the 850–200-hPa vertical shear magnitude with the vortex removed, the predictive skill score in the SI was 0.56. This score was comparable to that of the RI index scheme, which is considered the most advanced RI prediction method. When the HT information was combined with the aforementioned four environmental factors in the NA, ECP, South Pacific, and WNP, the skill scores were 0.23, 0.32, 0.42, and 0.42, respectively.

When will Cyclogenesis Commence Given a Favorable Tropical Environment?: To the 30th anniversary of the hypothesis on the turbulent vortex dynamo and dedicated to the memory of Soviet-Russian scientist, Professor Semen Samoilovich Moiseev

A numerical diagnosis of tropical cyclogenesis in a quiescent, rotating environment is presented to suggest an answer to the above question. Our research approach employs near-cloud-resolving numerical simulations to quantitatively analyze helical self-organization of moist-convective atmospheric turbulence. The simulations permit a diagnosis of cyclogenesis when the primary and secondary circulations in a forming hurricane vortex become linked by special convective coherent structures – Vortical Hot Towers (VHTs). The VHTs are argued to be intrinsic elements of the turbulent vortex dynamo in the tropical atmosphere of the Earth. It is discussed how the generated linkage makes the nascent vortex an integral helical system, supporting a positive feedback between the circulations. The feedback is sustained by only modest fluxes of latent heat from the underlying ocean, convective instability and vortical convection. The feedback indicates a release of potential energy that is converted into kinetic energy of developing large-scale helical vortex. Energy exchange between the primary and secondary circulation and their further mutual intensification is inferred from the numerical experiments.

Tropical cyclogenesis: a numerical diagnosis based on helical flow organization

A numerical diagnosis for tropical cyclogenesis is proposed based on nearcloud-resolving atmospheric simulation. Calculation and analyses of helical and energetic characteristics together with hydro- and thermodynamic flow fields allow the diagnosis of tropical cyclogenesis as an event when the primary and secondary circulations become linked on system scales thereby making the nascent large-scale vortex helical. A key process of vertical vorticity generation from horizontal components and its amplification by special convective coherent structures – Vortical Hot Towers (VHTs) – is highlighted. The process is found to be a pathway for generation of a velocity field with linked vortex lines of horizontal and vertical vorticity on local and system scales. The role of VHTs as connectors of the primary and secondary circulation is emphasized.

Numerical diagnosis of tropical cyclogenesis based on a hypothesis of helical self-organization of moist convective atmospheric turbulence

A novel diagnosis for tropical cyclogenesis is presented by examining helical self-organization of moist convective atmospheric turbulence in a rotating, non-homogeneous atmosphere. Our original research approach employed near-cloud-resolving numerical simulations, which allows quantitative diagnosis of cyclogenesis when the primary and secondary circulations in a forming hurricane vortex become linked by deep rotating cumulonimbus cores—Vortical Hot Towers (VHTs). It is shown here how the generated linkage makes the nascent vortex an integral helical system and allows a positive energetic feedback between the circulations that, with adequate moisture fluxes from the underlying sea surface to maintain convective instability, provides a self-sustaining amplification process on the system-scale circulation. The performed investigation suggests that diagnoses using helicity may not only provide an answer to the important question of when will cyclogenesis commence, given a favorable tropical environment, but will help develop a universally accepted definition of tropical cyclogenesis that does not yet exist.

A Spatial Filter Approach to Evaluating the Role of Convection on the Evolution of a Mesoscale Vortex

Abstract A new spatial filter is proposed that exploits a spectral gap in power between the convective scale and the system (“vortex”) scale during tropical cyclone (TC) genesis simulations. Using this spatial separation, this study analyzes idealized three-dimensional numerical simulations of deep moist convection in the presence of a symmetric midlevel vortex to quantify and understand the energy cascade between the objectively defined convective scale and system scale during the early stages of tropical cyclogenesis. The simulations neglect surface momentum, heat, and moisture fluxes to focus on generation and enhancement of vorticity within the interior to more completely close off the energy budget and to be consistent for comparison with prior benchmark studies of modeled TC genesis. The primary contribution to system-scale intensification comes from the convergence of convective-scale vorticity that is supplied by vortical hot towers (VHTs). They contribute more than the convergence of system-scale vorticity to the spinup of vorticity in these simulations by an order of magnitude. Analysis of the change of circulation with time shows an initial strengthening of the surface vortex, closely followed by a growth of the mid- to upper-level circulation. This evolution precludes any possibility of a stratiform precipitation–induced top-down mechanism as the primary contributor to system-scale spinup in this simulation. Instead, an upscale cascade of rotational kinetic energy during vortex mergers is responsible for spinup of the simulated mesoscale vortex. The spatial filter employed herein offers an alternative approach to the traditional symmetry–asymmetry paradigm, acknowledges the highly asymmetric evolution of the system-scale vortex itself, and may prove useful to future studies on TC genesis.

Global Distribution of Hot Towers in Tropical Cyclones Based on 11-Yr TRMM Data

Abstract Global distribution of hot towers in tropical cyclones (TCs) is statistically quantified using an 11-yr Tropical Rainfall Measuring Mission (TRMM) Tropical Cyclone Precipitation Feature (TCPF) database. From 6003 individual TRMM overpasses of 869 TCs, about 1.6% of TC convective systems are found to penetrate 14 km and about 0.1% of them even reach the 380-K potential temperature level. Among six TC-prone basins, the highest population of TC convective systems and those with hot towers are found over the northwest Pacific (NWP) basin. However, the greatest percentage of TCPFs that are hot towers [overshooting TCPFs (OTCPFs)] is found over the North Indian Ocean basin. Larger overshooting distance and ice mass are also found in this basin. The monthly variation of OTCPFs resembles that of TC activities in each basin. The percentage of OTCPFs is much higher in the inner core (IC) region (10%) than that in the inner rainband (IB; 2%) and outer rainband (OB; 1%) regions. OTCPFs in the IC region have much larger overshooting distance, area, volume, and ice mass than those in the IB and OB regions. The percentage of OTCPFs in the IC region increases as both TC intensity and intensification rate increase. About 17% of IC features in rapidly intensifying storms penetrate over 14 km, while the percentage is down to 11% for slowly intensifying, 9% for neutral, and 8% for weakening storms. A very good linear relationship is found between TC intensification rate and the percentage of TCPFs that are hot towers in the IC region.