Impact of Upper-Tropospheric Temperature Anomalies and Vertical Wind Shear on Tropical Cyclone Evolution Using an Idealized Version of the Operational GFDL Hurricane Model

Abstract The GFDL hurricane modeling system, initiated in the 1970s, has progressed from a research tool to an operational system over four decades. This system is still in use today in research and operations, and its evolution will be briefly described. This study used an idealized version of the 2014 GFDL model to test its sensitivity across a wide range of three environmental factors that are often identified as key factors in tropical cyclone (TC) evolution: SST, atmospheric stability (upper-air thermal anomalies), and vertical wind shear (westerly through easterly). A wide range of minimum central pressure intensities resulted (905–980 hPa). The results confirm that a scenario (e.g., global warming) in which the upper troposphere warms relative to the surface will have less TC intensification than one with a uniform warming with height. The TC rainfall is also investigated for the SST–stability parameter space. Rainfall increases for combinations of SST increase and increasing stability similar to global warming scenarios, consistent with climate change TC downscaling studies with the GFDL model. The forecast system’s sensitivity to vertical shear was also investigated. The idealized model simulations showed weak disturbances dissipating under strong easterly and westerly shear of 10 m s−1. A small bias for greater intensity under easterly sheared versus westerly sheared environments was found at lower values of SST. The impact of vertical shear on intensity was different when a strong vortex was used in the simulations. In this case, none of the initial disturbances weakened, and most intensified to some extent.

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A Balanced Tropical Cyclone Test Case for AGCMs with Background Vertical Wind Shear

Monthly Weather Review ◽

10.1175/mwr-d-14-00366.1 ◽

2015 ◽

Vol 143 (5) ◽

pp. 1762-1781 ◽

Cited By ~ 4

Author(s):

Fei He ◽

Derek J. Posselt ◽

Colin M. Zarzycki ◽

Christiane Jablonowski

Keyword(s):

Tropical Cyclone ◽

Wind Shear ◽

General Circulation ◽

Vertical Wind Shear ◽

Circulation Model ◽

Background Field ◽

Vertical Wind ◽

Intensity Change ◽

Test Case ◽

The Impact

Abstract This paper presents a balanced tropical cyclone (TC) test case designed to improve current understanding of how atmospheric general circulation model (AGCM) configurations affect simulated TC development and behavior. It consists of an analytic initial condition comprising two independently balanced components. The first provides a vortical TC seed, while the second adds a planetary-scale zonal flow with height-dependent velocity and imposes background vertical wind shear (VWS) on the TC seed. The environmental flow satisfies the steady-state hydrostatic primitive equations in spherical coordinates and is in balance with other background field variables (e.g., temperature, surface geopotential). The evolution of idealized TCs in the test case framework is illustrated in 10-day simulations performed with the Community Atmosphere Model, version 5.1.1 (CAM 5.1.1). Environmental wind profiles with different magnitudes, directions, and vertical inflection points are applied to ensure that the technique is robust to changes in the VWS characteristics. The well-known shear-induced intensity change and structural asymmetry in tropical cyclones are well captured. Sensitivity of TC evolution to small perturbations in the initial vortex is also quantitatively addressed to validate the numerical robustness of the technique. It is concluded that the enhanced TC test case can be used to evaluate the impact of model choice (e.g., resolution, physical parameterizations) on the simulation and representation of TC-like vortices in AGCMs.

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Idealized Tropical Cyclone Responses to the Height and Depth of Environmental Vertical Wind Shear

Monthly Weather Review ◽

10.1175/mwr-d-15-0320.1 ◽

2016 ◽

Vol 144 (6) ◽

pp. 2155-2175 ◽

Cited By ~ 39

Author(s):

Peter M. Finocchio ◽

Sharanya J. Majumdar ◽

David S. Nolan ◽

Mohamed Iskandarani

Keyword(s):

Tropical Cyclone ◽

Wind Shear ◽

Large Scale ◽

Deep Layer ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Polynomial Expansions ◽

The Impact ◽

Tilt Response ◽

Left Quadrant

Abstract Three sets of idealized, cloud-resolving simulations are performed to investigate the sensitivity of tropical cyclone (TC) structure and intensity to the height and depth of environmental vertical wind shear. In the first two sets of simulations, shear height and depth are varied independently; in the third set, orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis. Despite all simulations having the same westerly deep-layer (200–850 hPa) shear of 10 m s−1, different intensity and structural evolutions are observed, suggesting the deep-layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on TCs. In general, vertical wind shear that is shallower and lower in the troposphere is more destructive to model TCs because it tilts the TC vortex farther into the downshear-left quadrant. The vortices that tilt the most are unable to precess upshear and realign, resulting in their failure to intensify. Shear height appears to modulate this tilt response by modifying the thermodynamic environment above the developing vortex early in the simulations, while shear depth modulates the tilt response by controlling the vertical extent of the convective vortex. It is also found that TC intensity predictability is reduced in a narrow range of shear heights and depths. This result underscores the importance of accurately observing the large-scale environmental flow for improving TC intensity forecasts, and for anticipating when such forecasts are likely to have large errors.

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Environmental Flow Impacts on Tropical Cyclone Structure Diagnosed from Airborne Doppler Radar Composites

Monthly Weather Review ◽

10.1175/mwr-d-12-00334.1 ◽

2013 ◽

Vol 141 (9) ◽

pp. 2949-2969 ◽

Cited By ~ 113

Author(s):

Paul D. Reasor ◽

Robert Rogers ◽

Sylvie Lorsolo

Keyword(s):

Tropical Cyclone ◽

Wind Shear ◽

Doppler Radar ◽

Statistical Significance ◽

Three Dimensional ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Asymmetric Structure ◽

The Impact ◽

Airborne Doppler Radar

Abstract Following a recent demonstration of multicase compositing of axisymmetric tropical cyclone (TC) structure derived from airborne Doppler radar measurements, the authors extend the analysis to the asymmetric structure using an unprecedented database from 75 TC flights. In particular, they examine the precipitation and kinematic asymmetry forced by the TC's motion and interaction with vertical wind shear. For the first time they quantify the average magnitude and phase of the three-dimensional shear-relative kinematic asymmetry of observed TCs through a composite approach. The composite analysis confirms principal features of the shear-relative TC asymmetry documented in prior numerical and observational studies (e.g., downshear tilt, downshear-right convective initiation, and a downshear-left precipitation maximum). The statistical significance of the composite shear-relative structure is demonstrated through a stratification of cases by shear magnitude. The impact of storm motion on eyewall convective asymmetry appears to be secondary to the much greater constraint placed by vertical wind shear on the organization of convection, in agreement with prior studies using lightning and precipitation data.

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Secondary Circulation of Tropical Cyclones in Vertical Wind Shear: Lagrangian Diagnostic and Pathways of Environmental Interaction

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0350.1 ◽

2015 ◽

Vol 72 (9) ◽

pp. 3517-3536 ◽

Cited By ~ 25

Author(s):

Michael Riemer ◽

Frédéric Laliberté

Keyword(s):

Tropical Cyclones ◽

Wind Shear ◽

Vertical Wind Shear ◽

Secondary Circulation ◽

Vertical Wind ◽

Vertical Shear ◽

Intensity Change ◽

Cold Temperatures ◽

Environmental Interaction ◽

The Impact

Abstract This study introduces a Lagrangian diagnostic of the secondary circulation of tropical cyclones (TCs), here defined by those trajectories that contribute to latent heat release in the region of high inertial stability of the TC core. This definition accounts for prominent asymmetries and transient flow features. Trajectories are mapped from the three-dimensional physical space to the (two dimensional) entropy–temperature space. The mass flux vector in this space subsumes the thermodynamic characteristics of the secondary circulation. The Lagrangian diagnostic is then employed to further analyze the impact of vertical wind shear on TCs in previously published idealized numerical experiments. One focus of this analysis is the classification and quantitative depiction of different pathways of environmental interaction based on thermodynamic properties of trajectories at initial and end times. Confirming results from previous work, vertical shear significantly increases the intrusion of low–equivalent potential temperature () air into the eyewall through the frictional inflow layer. In contrast to previous ideas, vertical shear decreases midlevel ventilation in these experiments. Consequently, the difference in eyewall between the no-shear and shear experiments is largest at low levels. Vertical shear, however, significantly increases detrainment from the eyewall and modifies the thermodynamic signature of the outflow layer. Finally, vertical shear promotes the occurrence of a novel class of trajectories that has not been described previously. These trajectories lose entropy at cold temperatures by detraining from the outflow layer and subsequently warm by 10–15 K. Further work is needed to investigate in more detail the relative importance of the different pathways for TC intensity change and to extend this study to real atmospheric TCs.

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A Statistical Perspective on Wind Profiles and Vertical Wind Shear in Tropical Cyclone Environments of the Northern Hemisphere

Monthly Weather Review ◽

10.1175/mwr-d-16-0221.1 ◽

2017 ◽

Vol 145 (1) ◽

pp. 361-378 ◽

Cited By ~ 15

Author(s):

Peter M. Finocchio ◽

Sharanya J. Majumdar

Keyword(s):

Tropical Cyclone ◽

Northern Hemisphere ◽

Wind Shear ◽

Deep Layer ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Vertical Shear ◽

Intensity Change ◽

Upper Level ◽

Wind Profiles

Abstract A statistical analysis of tropical cyclone (TC) environmental wind profiles is conducted in order to better understand how vertical wind shear influences TC intensity change. The wind profiles are computed from global atmospheric reanalyses around the best track locations of 7554 TC cases in the Northern Hemisphere tropics. Mean wind profiles within each basin exhibit significant differences in the magnitude and direction of vertical wind shear. Comparisons between TC environments and randomly selected “non-TC” environments highlight the synoptic regimes that support TCs in each basin, which are often characterized by weaker deep-layer shear. Because weaker deep-layer shear may not be the only aspect of the environmental flow that makes a TC environment more favorable for TCs, two new parameters are developed to describe the height and depth of vertical shear. Distributions of these parameters indicate that, in both TC and non-TC environments, vertical shear most frequently occurs in shallow layers and in the upper troposphere. Linear correlations between each shear parameter and TC intensity change show that shallow, upper-level shear is slightly more favorable for TC intensification. But these relationships vary by basin and neither parameter independently explains more than 5% of the variance in TC intensity change between 12 and 120 h. As such, the shear height and depth parameters in this study do not appear to be viable predictors for statistical intensity prediction, though similar measures of midtropospheric vertical wind shear may be more important in particularly challenging intensity forecasts.

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A Ventilation Index for Tropical Cyclones

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-11-00165.1 ◽

2012 ◽

Vol 93 (12) ◽

pp. 1901-1912 ◽

Cited By ~ 82

Author(s):

Brian Tang ◽

Kerry Emanuel

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Wind Shear ◽

Large Scale ◽

Environmental Control ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Vertical Shear ◽

Tropical Cyclogenesis ◽

Model Errors

An important environmental control of both tropical cyclone intensity and genesis is vertical wind shear. One hypothesized pathway by which vertical shear affects tropical cyclones is midlevel ventilation—or the flux of low-entropy air into the center of the tropical cyclone. Based on a theoretical framework, a ventilation index is introduced that is equal to the environmental vertical wind shear multiplied by the nondimensional midlevel entropy deficit divided by the potential intensity. The ventilation index has a strong influence on tropical cyclone climatology. Tropical cyclogenesis preferentially occurs when and where the ventilation index is anomalously low. Both the ventilation index and the tropical cyclone's normalized intensity, or the intensity divided by the potential intensity, constrain the distribution of tropical cyclone intensification. The most rapidly intensifying storms are characterized by low ventilation indices and intermediate normalized intensities, while the most rapidly weakening storms are characterized by high ventilation indices and high normalized intensities. Since the ventilation index can be derived from large-scale fields, it can serve as a simple and useful metric for operational forecasts of tropical cyclones and diagnosis of model errors.

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Dynamically Derived Tropical Cyclone Intensity Changes over the Western North Pacific

Journal of Climate ◽

10.1175/2011jcli4139.1 ◽

2012 ◽

Vol 25 (1) ◽

pp. 89-98 ◽

Cited By ~ 51

Author(s):

Liguang Wu ◽

Haikun Zhao

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Wind Shear ◽

Western North Pacific ◽

Vertical Wind Shear ◽

Vertical Wind ◽

China Meteorological Administration ◽

Cyclone Intensity ◽

Intensity Changes ◽

The Impact

Abstract The study of the impact of global warming on tropical cyclone (TC) intensity is subject to uncertainty in historical datasets, especially in the western North Pacific (WNP) basin, where conflicting results have been found with the TC datasets archived in different organizations. In this study the basinwide TC intensity in the WNP basin is derived dynamically with a TC intensity model, based on the track data from the Joint Typhoon Warning Center (JTWC), the Regional Specialized Meteorological Center (RSMC) of Tokyo, and the Shanghai Typhoon Institute (STI) of the China Meteorological Administration. The dynamically derived TC intensity is compared to the three datasets and used to investigate trends in TC intensity. The associated contributions of changes in SST, vertical wind shear, and prevailing tracks are also examined. The evolution of the basinwide TC intensity in the JTWC best-track dataset can be generally reproduced over the period 1975–2007. Dynamically derived data based on the JTWC, RSMC, and STI track datasets all show an increasing trend in the peak intensity and frequency of intense typhoons, mainly because of the combined effect of changes in SST and vertical wind shear. This study suggests that the increasing intensity trend in the JTWC dataset is real, but that it may be overestimated. In contrast, the TC intensity trends in the RSMC and STI intensity datasets are dynamically inconsistent. Numerical simulations also suggest that the frequency of intense typhoons is more sensitive to changes in SST and vertical wind shear than the peak and average intensities defined in previous studies.

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Tropical Cyclone Climatology from Satellite Passive Microwave Measurements

Remote Sensing ◽

10.3390/rs12213610 ◽

2020 ◽

Vol 12 (21) ◽

pp. 3610

Author(s):

Song Yang ◽

Richard Bankert ◽

Joshua Cossuth

Keyword(s):

Southern Hemisphere ◽

Northern Hemisphere ◽

Wind Shear ◽

Vertical Wind Shear ◽

Passive Microwave ◽

Vertical Wind ◽

Vertical Shear ◽

Shear Direction ◽

Motion Direction ◽

Horizontal Structure

The satellite passive microwave (PMW) sensor brightness temperatures (TBs) of all tropical cyclones (TCs) from 1987–2012 have been carefully calibrated for inter-sensor frequency differences, center position fixing using the Automated Rotational Center Hurricane Eye Retrieval (ARCHER) scheme, and application of the Backus–Gilbert interpolation scheme for better presentation of the TC horizontal structure. With additional storm motion direction and the 200–850 hPa wind shear direction, a unique and comprehensive TC database is created for this study. A reliable and detailed climatology for each TC category is analyzed and discussed. There is significant annual variability of the number of storms at hurricane intensity, but the annual number of all storms is relatively stable. Results based on the analysis of the 89 GHz horizontal polarization TBs over oceans are presented in this study. An eyewall contraction is clearly displayed with an increase in TC intensity. Three composition schemes are applied to present a reliable and detailed TC climatology at each intensity category and its geographic characteristics. The global composition relative to the North direction is not able to lead a realistic structure for an individual TC. Enhanced convection in the down-motion quadrants relative to direction of TC motion is obvious for Cat 1–3 TCs, while Cat 4–5 TCs still have a concentric pattern of convection within 200 km radius. Regional differences are evident for weak storms. Results indicate the direction of TC movement has more impact on weak storms than on Cat 4–5 TCs. A striking feature is that all TCs have a consistent pattern of minimum TBs at 89 GHz in the downshear left quadrant (DSLQ) for the northern hemisphere basins and in the downshear right quadrant (DSRQ) for the southern hemisphere basin, regarding the direction of the 200–850 hPa wind shear. Tropical depression and tropical storm have the minimum TBs in the downshear quadrants. The axis of the minimum TBs is slightly shifted toward the vertical shear direction. There is no geographic variation of storm structure relative to the vertical wind shear direction except over the southern hemisphere which shows a mirror image of the storm structure over the northern hemisphere. This study indicates that regional variation of storm structure relative to storm motion direction is mainly due to differences of the vertical wind shear direction among these basins. Results demonstrate the direction of the 200–850 hPa wind shear plays a critical role in TC structure.

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Some Effects of Vertical Wind Shear on Thunderstorm Structure *

Bulletin of the American Meteorological Society ◽

10.1175/1520-0477-30.5.168 ◽

1949 ◽

Vol 30 (5) ◽

pp. 168-175 ◽

Cited By ~ 21

Author(s):

Horace R. Byers ◽

Louis J. Battan

Keyword(s):

Cross Sections ◽

Wind Shear ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Vertical Shear ◽

Radar Cross Sections ◽

Almost All

Observations of thunderclouds obtained with a 3-cm height-finding radar set are used to obtain a description of the vertical shear of thunderclouds. Several photographs are given which show the shearing of the radar clouds. A scattergram of wind shear plotted against echo shear is presented and shows that the two variables are related, with the former exceeding the latter in almost all cases. Scatter-diagrams are given which verify that strong vertical wind shear tends to restrict the growth of thunderstorms. A series of radar cross sections illustrates the displacement of the upper part of a thundercloud which is subjected to wind shear, and the growth of another cloud column from the lower part of the thundercloud.

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