Environmental Helicity and Its Effects on Development and Intensification of Tropical Cyclones

2014 ◽  
Vol 71 (11) ◽  
pp. 4308-4320 ◽  
Author(s):  
Matthew J. Onderlinde ◽  
David S. Nolan
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Local Scale ◽  
Intensity Change ◽  
Forecast System ◽  
Negative Helicity ◽  
Idealized Modeling ◽  
Time Periods ◽  
Wind Profiles ◽  
The Impact

Abstract Much attention has been given to the impact of environmental wind shear in the 850–200-hPa layer on tropical cyclones (TCs). However, even with the same magnitude of shear, helicity in this layer can vary significantly. A new parameter is presented, the tropical cyclone–relative environmental helicity (TCREH). Positive TCREH leads to a tilted storm that enhances local storm-scale helicity in regions of convection within the TC. This enhanced local-scale helicity potentially allows for more robust and longer-lasting convection, which is more effective at generating latent heat and subsequent TC intensification. TC vertical tilt is often attributed to wind shear. Different values of helicity modulate this tilt and certain tilt configurations are more favorable for development or intensification than others, suggesting that mean positive environmental helicity is more favorable for development and intensification than mean negative helicity. Idealized modeling simulations demonstrate the impact of environmental helicity on TC development and intensification. Results show that wind profiles with the same 850–200-hPa wind shear but different values of helicity lead to different rates of development. TCREH also is computed from the Interim ECMWF Re-Analysis (1979–2011) and Global Forecast System analyses (2004–11) to determine if a significant signal exists between TCREH and TC intensification. Mean annular helicity is averaged over various time periods and correlated with the TC intensity change during those periods. Results suggest a weak but statistically significant correlation between environmental helicity and TC intensity change with positive helicity being more favorable for intensification.

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

2015 ◽  
Vol 72 (9) ◽  
pp. 3517-3536 ◽  
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.

scholarly journals Influence of Environmental Vertical Wind Shear on the Intensity of Hurricane-Strength Tropical Cyclones in the Australian Region

2005 ◽  
Vol 133 (12) ◽  
pp. 3644-3660 ◽  
Author(s):  
Linda A. Paterson ◽  
Barry N. Hanstrum ◽  
Noel E. Davidson ◽  
Harry C. Weber
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Time Lag ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Intensity Change ◽  
Negative Effects ◽  
Australian Region ◽  
Upper Level ◽  
The Impact

Abstract NCEP–NCAR reanalyses have been used to investigate the impact of environmental wind shear on the intensity change of hurricane-strength tropical cyclones in the Australian region. A method of removing a symmetric vortex from objective analyses is used to isolate the environmental flow. A relationship between wind shear and intensity change is documented. Correlations between wind shear and intensity change to 36 h are of the order of 0.4. Typically a critical wind shear value of ∼10 m s−1 represents a change from intensification to dissipation. Wind shear values of less than ∼10 m s−1 favor intensification, with values between ∼2 and 4 m s−1 favoring rapid intensification. Shear values greater than ∼10 m s−1 are associated with weakening, with values greater than 12 m s−1 favoring rapid weakening. There appears to be a time lag between the onset of increased vertical wind shear and the onset of weakening, typically between 12 and 36 h. A review of synoptic patterns during intensification-weakening cycles revealed the juxtaposition of a low-level anticyclone on the poleward side of the storm and an approaching 200-hPa trough to the west. In most cases, intensification commences under weak shear with the approach of the trough, but just prior to the onset of high shear. Further, based on described cases when wind shear was weak but no intensification occurred, it is suggested that weak shear is a necessary but not a sufficient condition for intensification. It is illustrated here that the remote dynamical influence of upper-level potential vorticity anomalies may offset the negative effects of environmental shear.

scholarly journals The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part I: Overview and Observations

2018 ◽  
Vol 146 (11) ◽  
pp. 3773-3800 ◽  
Author(s):  
David R. Ryglicki ◽  
Joshua H. Cossuth ◽  
Daniel Hodyss ◽  
James D. Doyle
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Convective Cloud ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Brightness Temperatures ◽  
Idealized Modeling ◽  
Hurricane Prediction ◽  
Upper Level

Abstract A satellite-based investigation is performed of a class of tropical cyclones (TCs) that unexpectedly undergo rapid intensification (RI) in moderate vertical wind shear between 5 and 10 m s−1 calculated as 200–850-hPa shear. This study makes use of both infrared (IR; 11 μm) and water vapor (WV; 6.5 μm) geostationary satellite data, the Statistical Hurricane Prediction Intensity System (SHIPS), and model reanalyses to highlight commonalities of the six TCs. The commonalities serve as predictive guides for forecasters and common features that can be used to constrain and verify idealized modeling studies. Each of the TCs exhibits a convective cloud structure that is identified as a tilt-modulated convective asymmetry (TCA). These TCAs share similar shapes, upshear-relative positions, and IR cloud-top temperatures (below −70°C). They pulse over the core of the TC with a periodicity of between 4 and 8 h. Using WV satellite imagery, two additional features identified are asymmetric warming/drying upshear of the TC relative to downshear, as well as radially thin arc-shaped clouds on the upshear side. The WV brightness temperatures of these arcs are between −40° and −60°C. All of the TCs are sheared by upper-level anticyclones, which limits the strongest environmental winds to near the tropopause.

scholarly journals A Comparison of the Downstream Predictability Associated with ET and Baroclinic Cyclones

2017 ◽  
Vol 145 (11) ◽  
pp. 4651-4672 ◽  
Author(s):  
Ryan D. Torn
Keyword(s):  
Standard Deviation ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Ensemble Forecast ◽  
Latent Heat Release ◽  
Propagation Characteristics ◽  
Forecast System ◽  
The Impact

The impact of the extratropical transition (ET) of tropical cyclones and baroclinic cyclogenesis in the western North Pacific (WNP), Atlantic, and southern Indian Ocean (SIO) basins on the predictability of the downstream midlatitude flow is assessed using 30 years of cases from the Global Ensemble Forecast System (GEFS) Reforecast, version 2. In all three basins, ET is associated with statistically larger 500-hPa geopotential height forecast standard deviation (SD) compared to the forecast climatology. The higher SD values originate from where the TC enters the midlatitudes and spread downstream at the group velocity of the associated wave packet. Of the three basins, WNP ET is associated with the largest amplitude and longest-lasting SD anomalies. Forecasts initialized 2–4 days prior to the onset of ET have larger SD anomalies compared to forecasts initialized during or after the onset of ET. By contrast, the region of positive SD anomaly associated with winter baroclinic cyclones is confined to the upstream trough, with fall cyclones exhibiting some downstream propagation characteristics similar to ET. The ET cases with the larger downstream SD anomaly are characterized by a more amplified ridge downstream of the TC as it enters the midlatitudes. By contrast, ET cases with an upstream trough, large TC position variability at the onset of ET, latent heat release, or upper-tropospheric PV advection by the irrotational wind are not characterized by significantly larger downstream SD compared to cases without an upstream trough or smaller values of these quantities.

scholarly journals Increasing vertical resolution in US models to improve track forecasts of Hurricane Joaquin with HWRF as an example

2016 ◽  
Vol 113 (42) ◽  
pp. 11765-11769 ◽  
Author(s):  
Banglin Zhang ◽  
Richard S. Lindzen ◽  
Vijay Tallapragada ◽  
Fuzhong Weng ◽  
Qingfu Liu ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Forecast Model ◽  
Vertical Resolution ◽  
Global Forecast System ◽  
Forecast System ◽  
Atlantic Basin ◽  
Hurricane Track ◽  
Environmental Prediction ◽  
The Impact ◽  
Positive Impacts

The atmosphere−ocean coupled Hurricane Weather Research and Forecast model (HWRF) developed at the National Centers for Environmental Prediction (NCEP) is used as an example to illustrate the impact of model vertical resolution on track forecasts of tropical cyclones. A number of HWRF forecasting experiments were carried out at different vertical resolutions for Hurricane Joaquin, which occurred from September 27 to October 8, 2015, in the Atlantic Basin. The results show that the track prediction for Hurricane Joaquin is much more accurate with higher vertical resolution. The positive impacts of higher vertical resolution on hurricane track forecasts suggest that National Oceanic and Atmospheric Administration/NCEP should upgrade both HWRF and the Global Forecast System to have more vertical levels.

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

2015 ◽  
Vol 143 (5) ◽  
pp. 1762-1781 ◽  
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.

scholarly journals Further examination of the thermodynamic modification of the inflow layer of tropical cyclones by vertical wind shear

2013 ◽  
Vol 13 (1) ◽  
pp. 327-346 ◽  
Author(s):  
M. Riemer ◽  
M. T. Montgomery ◽  
M. E. Nicholls
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Numerical Experiments ◽  
Structural Changes ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Experimental Setup ◽  
Power Machine ◽  
The Impact

Abstract. Recent work has developed a new framework for the impact of vertical wind shear on the intensity evolution of tropical cyclones. A focus of this framework is on the frustration of the tropical cyclone's power machine by shear-induced, persistent downdrafts that flush relatively cool and dry (lower equivalent potential temperature, θe) air into the storm's inflow layer. These previous results have been based on idealised numerical experiments for which we have deliberately chosen a simple set of physical parameterisations. Before efforts are undertaken to test the proposed framework with real atmospheric data, we assess here the robustness of our previous results in a more realistic and representative experimental setup by surveying and diagnosing five additional numerical experiments. The modifications of the experimental setup comprise the values of the exchange coefficients of surface heat and momentum fluxes, the inclusion of experiments with ice microphysics, and the consideration of weaker, but still mature tropical cyclones. In all experiments, the depression of the inflow layer θe values is significant and all tropical cyclones exhibit the same general structural changes when interacting with the imposed vertical wind shear. Tropical cyclones in which strong downdrafts occur more frequently exhibit a more pronounced depression of inflow layer θe outside of the eyewall in our experiments. The magnitude of the θe depression underneath the eyewall early after shear is imposed in our experiments correlates well with the magnitude of the ensuing weakening of the respective tropical cyclone. Based on the evidence presented, it is concluded that the newly proposed framework is a robust description of intensity modification in our suite of experiments.

scholarly journals A Hydrodynamical Atmosphere/Ocean Coupled Modeling System for Multiple Tropical Cyclones

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 869
Author(s):  
Ghassan J. Alaka ◽  
Dmitry Sheinin ◽  
Biju Thomas ◽  
Lew Gramer ◽  
Zhan Zhang ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Sea Surface ◽  
Intensity Change ◽  
Coupling Scheme ◽  
Sea Surface Temperatures ◽  
Improvement Program ◽  
Surface Temperatures ◽  
Skill Scores ◽  
Basin Scale ◽  
The Impact

The goal of this paper is to introduce a new multi-storm atmosphere/ocean coupling scheme that was implemented and tested in the Basin-Scale Hurricane Weather Research and Forecasting (HWRF-B) model. HWRF-B, an experimental model developed at the National Oceanic and Atmospheric Administration (NOAA) and supported by the Hurricane Forecast Improvement Program, is configured with multiple storm-following nested domains to produce high-resolution predictions for several tropical cyclones (TCs) within the same forecast integration. The new coupling scheme parallelizes atmosphere/ocean interactions for each nested domain in HWRF-B, and it may be applied to any atmosphere/ocean coupled system. TC forecasts from this new hydrodynamical modeling system were produced in the North Atlantic and eastern North Pacific from 2017–2019. The performance of HWRF-B was evaluated, including forecasts of TC track, intensity, structure (e.g., surface wind radii), and intensity change, and simulated sea-surface temperatures were compared with satellite observations. Median forecast skill scores showed significant improvement over the operational HWRF at most forecast lead times for track, intensity, and structure. Sea-surface temperatures cooled by 1–8 °C for the five HWRF-B case studies, demonstrating the utility of the model to study the impact of the ocean on TC intensity forecasting. These results show the value of a multi-storm modeling system and provide confidence that the multi-storm coupling scheme was implemented correctly. Future TC models within NOAA, especially the Unified Forecast System’s Hurricane Analysis and Forecast System, would benefit from the multi-storm coupling scheme whose utility and performance are demonstrated in HWRF-B here.

scholarly journals Lightning in Eastern North Pacific Tropical Cyclones: A Comparison to the North Atlantic

2015 ◽  
Vol 144 (1) ◽  
pp. 225-239 ◽  
Author(s):  
Stephanie N. Stevenson ◽  
Kristen L. Corbosiero ◽  
Sergio F. Abarca
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
North Pacific ◽  
Wind Shear ◽  
Inner Core ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Intensity Change ◽  
The North ◽  
The North Atlantic

Abstract As global lightning detection has become more reliable, many studies have analyzed the characteristics of lightning in tropical cyclones (TCs); however, very few studies have examined flashes in eastern North Pacific (ENP) basin TCs. This study uses lightning detected by the World Wide Lightning Location Network (WWLLN) to explore the relationship between lightning and sea surface temperatures (SSTs), the diurnal cycle, the storm motion and vertical wind shear vectors, and the 24-h intensity change in ENP TCs during 2006–14. The results are compared to storms in the North Atlantic (NA). Higher flash counts were found over warmer SSTs, with 28°–30°C SSTs experiencing the highest 6-hourly flash counts. Most TC lightning flashes occurred at night and during the early morning hours, with minimal activity after local noon. The ENP peak (0800 LST) was slightly earlier than the NA (0900–1100 LST). Despite similar storm motion directions and differing vertical wind shear directions in the two basins, shear dominated the overall azimuthal lightning distribution. Lightning was most often observed downshear left in the inner core (0–100 km) and downshear right in the outer rainbands (100–300 km). A caveat to these relationships were fast-moving ENP TCs with opposing shear and motion vectors, in which lightning peaked downmotion (upshear) instead. Finally, similar to previous studies, higher flash densities in the inner core (outer rainbands) were associated with nonintensifying (intensifying) TCs. This last result constitutes further evidence in the efforts to associate lightning activity to TC intensity forecasting.

scholarly journals The Influence of Environments on the Intensity Change of Typhoon Soudelor

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 162
Author(s):  
Leo Oey ◽  
Yuchen Lin
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Intensity Variation ◽  
Vertical Wind ◽  
Intensity Change ◽  
Rapid Intensification ◽  
Philippine Sea ◽  
Anomalous Anticyclone ◽  
Upper Level

Previous studies have shown that background oceanic and atmospheric environments can influence not only the formation but also the intensity of tropical cyclones. Typhoon Soudelor in August 2015 is notable in that it underwent two rapid intensifications as the storm passed over the Philippine Sea where the 26 °C isotherm (Z26) was deeper than 100 m and warm eddies abounded. At the same time, prior to the storm’s arrival, an anomalous upper-level anticyclone developed south of Japan and created a weakened vertical wind shear (Vs) environment that extended into the Philippine Sea. This study examines how the rapid intensification of Typhoon Soudelor may be related to the observed variations of Z26, Vs and other environmental fields as the storm crossed over them. A regression analysis indicates that the contribution to Soudelor’s intensity variation from Vs is the largest (62%), followed by Z26 (27%) and others. Further analyses using composites then indicate that the weak vertical wind shear produced by the aforementioned anomalous anticyclone is a robust feature in the western North Pacific during the developing summer of strong El Ninos with Oceanic Nino Index (ONI) > 1.5.

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