Numerical Simulation of Hurricane Bonnie (1998). Part II: Sensitivity to Varying Cloud Microphysical Processes

2006 ◽  
Vol 63 (1) ◽  
pp. 109-126 ◽  
Author(s):  
Tong Zhu ◽  
Da-Lin Zhang
Keyword(s):  
Large Scale ◽  
Structural Changes ◽  
Inner Core ◽  
Cloud Microphysics ◽  
Cloud Water ◽  
Heat Of Fusion ◽  
Hurricane Intensity ◽  
Cloud Band ◽  
Intensity Changes ◽  
Hurricane Bonnie

Abstract In this study, the effects of various cloud microphysics processes on the hurricane intensity, precipitation, and inner-core structures are examined with a series of 5-day explicit simulations of Hurricane Bonnie (1998), using the results presented in Part I as a control run. It is found that varying cloud microphysics processes produces little sensitivity in hurricane track, except for very weak and shallow storms, but it produces pronounced departures in hurricane intensity and inner-core structures. Specifically, removing ice microphysics produces the weakest (15-hPa underdeepening) and shallowest storm with widespread cloud water but little rainwater in the upper troposphere. Removing graupel from the control run generates a weaker hurricane with a wider area of precipitation and more cloud coverage in the eyewall due to the enhanced horizontal advection of hydrometeors relative to the vertical fallouts (or increased water loading). Turning off the evaporation of cloud water and rainwater leads to the most rapid deepening storm (i.e., 90 hPa in 48 h) with the smallest radius but a wider eyewall and the strongest eyewall updrafts. The second strongest storm, but with the most amount of rainfall, is obtained when the melting effect is ignored. It is found that the cooling due to melting is more pronounced in the eyewall where more frozen hydrometeors, especially graupel, are available, whereas the evaporative cooling occurs more markedly when the storm environment is more unsaturated. It is shown that stronger storms tend to show more compact eyewalls with heavier precipitation and more symmetric structures in the warm-cored eye and in the eyewall. It is also shown that although the eyewall replacement scenarios occur as the simulated storms move into weak-sheared environments, the associated inner-core structural changes, timing, and location differ markedly, depending on the hurricane intensity. That is, the eyewall convection in weak storms tends to diminish shortly after being encircled by an outer rainband, whereas both the cloud band and the inner eyewall in strong storms tend to merge to form a new eyewall with a larger radius. The results indicate the importance of the Bergeron processes, including the growth and rapid fallout of graupel in the eyewall, and the latent heat of fusion in determining the intensity and inner-core structures of hurricanes, and the vulnerability of weak storms to the influence of large-scale sheared flows in terms of track, inner-core structures, and intensity changes.

Sensitivity of Idealized Hurricane Intensity and Structures under Varying Background Flows and Initial Vortex Intensities to Different Vertical Resolutions in HWRF

2015 ◽  
Vol 143 (3) ◽  
pp. 914-932 ◽  
Author(s):  
Da-Lin Zhang ◽  
Lin Zhu ◽  
Xuejin Zhang ◽  
Vijay Tallapragada
Keyword(s):  
Structural Changes ◽  
Inner Core ◽  
Vertical Wind Shear ◽  
Initial Time ◽  
Mean Flow ◽  
Hurricane Intensity ◽  
Vertical Grid ◽  
Hurricane Intensification ◽  
Intensity Fluctuations ◽  
Upper Level

Abstract A series of 5-day numerical simulations of idealized hurricane vortices under the influence of different background flows is performed by varying vertical grid resolution (VGR) in different portions of the atmosphere with the operational version of the Hurricane Weather Research and Forecasting Model in order to study the sensitivity of hurricane intensity forecasts to different distributions of VGR. Increasing VGR from 21 to 43 levels produces stronger hurricanes, whereas increasing it further to 64 levels does not intensify the storms further, but intensity fluctuations are much reduced. Moreover, increasing the lower-level VGRs generates stronger storms, but the opposite is true for increased upper-level VGRs. On average, adding mean flow increases intensity fluctuations and variability (between the strongest and weakest hurricanes), whereas adding vertical wind shear (VWS) delays hurricane intensification and then causes more rapid growth in intensity variability. The stronger the VWS, the larger intensity variability and bifurcation rate occur at later stages. These intensity differences are found to be closely related to inner-core structural changes, and they are attributable to how much latent heat could be released in higher-VGR layers, followed by how much moisture content in nearby layers is converged. Hurricane intensity with higher VGRs is shown to be much less sensitive to varying background flows, and stronger hurricane vortices at the model initial time are less sensitive to the vertical distribution of VGR; the opposite is true for relatively uniform VGRs or weaker hurricane vortices. Results reveal that higher VGRs with a near-parabolic or Ω shape tend to produce smoother intensity variations and more typical inner-core structures.

scholarly journals On the Rapid Intensification of Hurricane Wilma (2005). Part I: Model Prediction and Structural Changes

2011 ◽  
Vol 26 (6) ◽  
pp. 885-901 ◽  
Author(s):  
Hua Chen ◽  
Da-Lin Zhang ◽  
James Carton ◽  
Robert Atlas
Keyword(s):  
Model Prediction ◽  
Structural Changes ◽  
Inner Core ◽  
Initial Conditions ◽  
Single Case ◽  
Inversion Layer ◽  
Rapid Intensification ◽  
Structural Variations ◽  
Hurricane Wilma ◽  
Intensity Changes

Abstract In this study, a 72-h cloud-permitting numerical prediction of Hurricane Wilma (2005), covering its initial 18-h spinup, an 18-h rapid intensification (RI), and the subsequent 36-h weakening stage, is performed using the Weather Research Forecast Model (WRF) with the finest grid length of 1 km. The model prediction uses the initial and lateral boundary conditions, including the bogus vortex, that are identical to the Geophysical Fluid Dynamics Laboratory’s then-operational data, except for the time-independent sea surface temperature field. Results show that the WRF prediction compares favorably in many aspects to the best-track analysis, as well as satellite and reconnaissance flight-level observations. In particular, the model predicts an RI rate of more than 4 hPa h−1 for an 18-h period, with the minimum central pressure of less than 889 hPa. Of significance is that the model captures a sequence of important inner-core structural variations associated with Wilma’s intensity changes, namely, from a partial eyewall open to the west prior to RI to a full eyewall at the onset of RI, rapid eyewall contraction during the initial spinup, the formation of double eyewalls with a wide moat area in between during the most intense stage, and the subsequent eyewall replacement leading to the weakening of Wilma. In addition, the model reproduces the boundary layer growth up to 750 hPa with an intense inversion layer above in the eye. Recognizing that a single case does not provide a rigorous test of the model predictability due to the stochastic nature of deep convection, results presented herein suggest that it is possible to improve forecasts of hurricane intensity and intensity changes, and especially RI, if the inner-core structural changes and storm size could be reasonably predicted in an operational setting using high-resolution cloud-permitting models with realistic initial conditions and model physical parameterizations.

scholarly journals Influence of Rain-Rate Initialization, Cloud Microphysics, and Cloud Torques on Hurricane Intensity

2011 ◽  
Vol 139 (2) ◽  
pp. 627-649 ◽  
Author(s):  
S. Pattnaik ◽  
C. Inglish ◽  
T. N. Krishnamurti
Keyword(s):  
Angular Momentum ◽  
Rain Rate ◽  
Velocity Structure ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Cloud Microphysics ◽  
Hurricane Intensity ◽  
Storm Intensity ◽  
Intensity Changes ◽  
The Impact

Abstract This study examines the impact of rain-rate initialization (RINIT), microphysical modifications, and cloud torques (in the context of angular momentum) on hurricane intensity forecasts using a mesoscale model [the Advanced Research Weather Research and Forecasting model (ARW-WRF)] at a cloud-resolving resolution of 2.7 km. The numerical simulations are performed in a triple-nested manner (25, 8.3, and 2.7 km) for Hurricane Dennis of 2005. Unless mentioned otherwise, all the results discussed are from the innermost grid with finest resolution (2.7 km). It is found that the model results obtained from the RINIT technique demonstrated robust improvement in hurricane structure, track, and intensity forecasts compared to the control experiment (CTRL; i.e., without RINIT). Thereafter, using RINIT initial conditions datasets three sensitive experiments are designed by modifying specific ice microphysical parameters (i.e., temperature-independent snow intercept parameter, doubling number of concentrations of ice, and ice crystal diameter) within the explicit parameterization scheme [i.e., the WRF Single-Moment 6-class (WSM6)]. It is shown that the experiment with enhanced ice mass concentration and temperature-independent snow intercept parameter produces the strongest and weakest storms, respectively. The results suggest that the distributions of hydrometeors are also impacted by the limited changes introduced in the microphysical scheme (e.g., the quantitative amount of snow drastically reduced to 0.1–0.2 g kg−1 when the intercept parameter of snow is made independent of temperature). It is noted that the model holds ice at a warmer temperature for a longer time with a temperature-independent intercept parameter. These variations in hydrometeor distribution in the eyewall region of the storm affect diabatic heating and vertical velocity structure and modulated the storm intensity. However, irrespective of the microphysical changes the quantitative amount of graupel hydrometeors remained nearly unaffected. Finally, the indirect effect of microphysical modifications on storm intensity through angular momentum and cloud torques is examined. A formulation to predict the short-term changes in the storm intensity using a parcel segment angular momentum budget method is developed. These results serve to elucidate the indirect impact of microphysical modifications on tropical cyclone intensity changes through modulation in cloud torque magnitude.

scholarly journals On the Rapid Weakening of Very Intense Tropical Cyclone Hellen (2014)

2019 ◽  
Vol 147 (8) ◽  
pp. 2717-2737 ◽  
Author(s):  
Adrien Colomb ◽  
Tarik Kriat ◽  
Marie-Dominique Leroux
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Large Scale ◽  
Inner Core ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Warm Core ◽  
Operational Forecasting ◽  
Intensity Changes ◽  
The Impact

Abstract In late March 2014, very intense Tropical Cyclone Hellen threatened the Comoros Archipelago and the Madagascan northwest coastline as it became one of the strongest tropical cyclones (TCs) ever observed over the Mozambique Channel. Its steep intensity changes were not well anticipated by operational forecasting models or by La Reunion regional specialized meteorological center forecasters. In particular, the record-setting rapid weakening over the open ocean was not supported by usual large-scale predictors. AROME, a new nonhydrostatic finescale model, is able to closely reproduce these wide intensity changes. When benchmarked against available observations, the model is also consistent in terms of inner-core structure, environmental features, track, and intensity. In the simulation, a northwesterly 400-hPa environmental wind is associated with unsaturated air, while the classic 200–850-hPa wind shear remains weak, and does not suggest a specifically unfavorable environment. The 400-hPa constraint affects the simulated storm through two pathways. Air with low equivalent potential temperature (θe) is flushed downward into the inflow layer in the upshear semicircle, triggering the decay of the storm. Then, direct erosion of the upper half of the warm core efficiently increases the surface pressure and also plays an instrumental role in the rapid weakening. When the storm gets closer to the Madagascan coastline, low-θe air can be directly advected within the inflow layer. Results illustrate on a real TC case the recently proposed paradigm for TC intensity modification under vertical wind shear and highlight the need for innovative tools to assess the impact of wind shear at all vertical levels.

scholarly journals Numerical Simulation of Hurricane Bonnie (1998). Part III: Energetics

2009 ◽  
Vol 66 (9) ◽  
pp. 2678-2696 ◽  
Author(s):  
Wallace Hogsett ◽  
Da-Lin Zhang
Keyword(s):  
Structural Changes ◽  
Inner Core ◽  
Vertical Shear ◽  
High Resolution Data ◽  
Fourier Decomposition ◽  
Large Intensity ◽  
Considerable Research ◽  
Core Energy ◽  
Intensity Fluctuations ◽  
Hurricane Bonnie

Abstract Despite considerable research on tropical cyclones (TCs), few studies have been performed to examine inner-core energy conversions because of the lack of high-resolution data. In this study, the TC energetic characteristics in relation to intensity and structural changes under different sheared environments are investigated using a 5-day cloud-resolving simulation of Hurricane Bonnie (1998). Results show that in the presence of intense vertical shear Bonnie undergoes high-frequency fluctuations in intensity and energy conversions (at a time scale of 3 h) during the partial eyewall stage. The fluctuations are closely related to the life cycle of individual convective elements that propagate cyclonically around the downshear portion of the eyewall. The energy conversions are shown to be maximized in the vicinity of the radius of maximum wind (RMW), thus affecting strongly TC intensity. On average, about 2% of latent energy can be converted to kinetic energy to increase TC intensity. After the vertical shear subsides below a threshold, intensity fluctuations become small as convective elements reorganize into an axisymmetric eyewall in which energy conversions are more evenly distributed. Fourier decomposition is conducted to separate the wavenumber-0, -1, and -2 components of inner-core energetics. Whereas wavenumber-1 perturbations dominate the partial eyewall stage, the propagation of wavenumber-2 perturbations is shown to be closely related to individual convective elements during both the partial eyewall and axisymmetric stages. The wavenumber-2 perturbations can be traced as they move around the eyewall in the form of vortex–Rossby waves, and they play a role in determining the large intensity fluctuations during the partial eyewall stage and the formation of an outer eyewall to replace the partial inner eyewall at the later stage.

Droplet dynamics and fine-scale structure in a shearless turbulent mixing layer with phase changes

2017 ◽  
Vol 814 ◽  
pp. 452-483 ◽  
Author(s):  
Paul Götzfried ◽  
Bipin Kumar ◽  
Raymond A. Shaw ◽  
Jörg Schumacher
Keyword(s):  
Large Scale ◽  
Mixing Layer ◽  
Domain Size ◽  
Cloud Microphysics ◽  
Cloud Water ◽  
Phase Changes ◽  
Small Scale ◽  
Air Interface ◽  
Scale Properties ◽  
Set Up

Three-dimensional direct numerical simulations of a shearless mixing layer in a small fraction of the cloud–clear air interface are performed to study the response of an ensemble of cloud water droplets to the turbulent entrainment of clear air into a cloud filament. The main goal of this work is to understand how mixing of cloudy and clear air evolves as turbulence and thermodynamics interact through phase changes, and how the cloud droplets respond. In the main simulation case, mixing proceeds between a higher level of turbulence in the cloudy filament and a lower level of turbulence in the clear air environment – the typical shearless mixing layer set-up. Fluid turbulence is driven solely by buoyancy, which incorporates feedbacks from the temperature, the vapour content and the liquid water content fields. Two different variations on the core set of shearless mixing layer simulations are discussed, a simulation in a larger domain and a simulation with the same turbulence level inside the filament and its environment. Overall, it is found that, as evaporation occurs for the droplets that enter subsaturated clear air regions, buoyancy comes to dominate the subsequent evolution of the mixing layer. The buoyancy feedback leads initially to downdraughts at the cloudy–clear air interface and to updraughts in the bulk regions. The strength of the turbulence after initial transients depends on the domain size, showing that the range of scales is an important parameter in the shearless mixing layer set-up. In contrast, the level of turbulence in the clear air is found to have little effect on the evolution of the mixing process. The distributions of cloud water droplet size, supersaturation at the droplet positions and vertical velocity are more sensitive to domain size than to the details of the turbulence profile, suggesting that the evolution of cloud microphysics is more sensitive to large-scale as opposed to small-scale properties of the flow.

scholarly journals A Numerical Study of Typhoon Megi (2010). Part I: Rapid Intensification

2014 ◽  
Vol 142 (1) ◽  
pp. 29-48 ◽  
Author(s):  
Hui Wang ◽  
Yuqing Wang
Keyword(s):  
Large Scale ◽  
Structural Changes ◽  
Inner Core ◽  
Numerical Study ◽  
Convective Available Potential Energy ◽  
Heat Content ◽  
Vertical Shear ◽  
Rapid Intensification ◽  
Upper Troposphere ◽  
Spiral Rainbands

Abstract Typhoon Megi (15W) was the most powerful and longest-lived tropical cyclone (TC) over the western North Pacific during 2010. While it shared many common features of TCs that crossed Luzon Island in the northern Philippines, Megi experienced unique intensity and structural changes, which were reproduced reasonably well in a simulation using the Advanced Research Weather Research and Forecasting Model (ARW-WRF) with both dynamical initialization and large-scale spectral nudging. In this paper processes responsible for the rapid intensification (RI) of the modeled Megi before it made landfall over Luzon Island were analyzed. The results show that Megi experienced RI over the warm ocean with high ocean heat content and decreasing environmental vertical shear. The onset of RI was triggered by convective bursts (CBs), which penetrate into the upper troposphere, leading to the upper-tropospheric warming and the formation of the upper-level warm core. In turn, CBs with their roots inside of the eyewall in the boundary layer were buoyantly triggered/supported by slantwise convective available potential energy (SCAPE) accumulated in the eye region. During RI, convective area coverage in the inner-core region was increasing while the updraft velocity in the upper troposphere and the number of CBs were both decreasing. Different from the majority of TCs that experience RI with a significant eyewall contraction, the simulated Megi, as the observed, rapidly intensified without an eyewall contraction. This is attributed to diabatic heating in active spiral rainbands, a process previously proposed to explain the inner-core size increase, enhanced by the interaction of the typhoon vortex with a low-level synoptic depression in which Megi was embedded.

scholarly journals An Ensemble Approach to Investigate Tropical Cyclone Intensification in Sheared Environments. Part II: Ophelia (2011)

2016 ◽  
Vol 73 (4) ◽  
pp. 1555-1575 ◽  
Author(s):  
Rosimar Rios-Berrios ◽  
Ryan D. Torn ◽  
Christopher A. Davis
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Inner Core ◽  
Deep Convection ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Wind Fields ◽  
Convective Scale ◽  
Intensity Changes ◽  
Large Scale Flow

Abstract The mechanisms leading to tropical cyclone (TC) intensification amid moderate vertical wind shear can vary from case to case, depending on the vortex structure and the large-scale conditions. To search for similarities between cases, this second part investigates the rapid intensification of Hurricane Ophelia (2011) in an environment characterized by 200–850-hPa westerly shear exceeding 8 m s−1. Similar to Part I, a 96-member ensemble was employed to compare a subset of members that predicted Ophelia would intensify with another subset that predicted Ophelia would weaken. This comparison revealed that the intensification of Ophelia was aided by enhanced convection and midtropospheric moisture in the downshear and left-of-shear quadrants. Enhanced left-of-shear convection was key to the establishment of an anticyclonic divergent outflow that forced a nearby upper-tropospheric trough to wrap around Ophelia. A vorticity budget showed that deep convection also contributed to the enhancement of vorticity within the inner core of Ophelia via vortex stretching and tilting of horizontal vorticity enhanced by the upper-tropospheric trough. These results suggest that TC intensity changes in sheared environments and in the presence of upper-tropospheric troughs highly depend on the interaction between convective-scale processes and the large-scale flow. Given the similarities between Part I and this part, the results suggest that observations from the three-dimensional moisture and wind fields could improve both forecasting and understanding of TC intensification in moderately sheared environments.

scholarly journals Intensification of Tropical Cyclone FANI Observed by INSAT-3DR Rapid Scan Data

2021 ◽  
Author(s):  
Neeru Jaiswal ◽  
Sanjib K. Deb ◽  
Chandra M. Kishtawal
Keyword(s):  
Large Scale ◽  
Structural Changes ◽  
Inner Core ◽  
Operation Mode ◽  
Radial Distance ◽  
Extreme Weather Events ◽  
Small Scale ◽  
High Temporal Resolution ◽  
Rapid Scan ◽  
Scan Data

Abstract Geo-stationary satellite images are one of the primary tool for real-time monitoring and intensity analysis of Tropical Cyclones (TCs) in spite of other complimentary remote sensing sensors like scatterometers, microwave imagers and sounders, mounted on the polar orbiting satellites. The weather activities over Indian region are continuously monitored by two Indian geostationary satellites viz., INSAT-3D and INSAT-3DR for every 15 minutes in staggered mode. During extreme weather events like TCs, INSAT-3DR is operated in rapid scan operation mode by taking observations over the system in every 4-minutes interval. These observations are highly useful in understating the instantaneous structural changes during evolution, intensification and landfall of TC. The salient observations over the cloud systems by visible, thermal infrared (TIR1), and water vapour imageries of INSAT-3DR satellite during the life cycle of the TC FANI are presented in this paper. The rapidly evolving small-scale features inside the inner core of TC FANI in high temporal resolution images were examined. The large-scale circulation features are analysed by atmospheric motion winds generated using rapid scan infrared images of INSAT-3DR. The relationship between TC intensity and inner core TIR1 BT, number of overshooting top clouds in the differenced TIR1-WV BT have been presented by analysing the sequence of INSAT-3DR imageries. The strong correlation (r2=0.74) was obtained between the TC eye temperature and radial distance of first overshooting cloud top. The 1 km x 1 km visible images of TC were found to have the presence of small-scale mesovortices in the eye region, which are a typical characteristic of intense TC system. The rapid scan operation mode generated sequence of images have been presented to show their application to identify the signatures of TC intensification.

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