Effects of Vertical Wind Shear on the Predictability of Tropical Cyclones

2013 ◽  
Vol 70 (3) ◽  
pp. 975-983 ◽  
Author(s):  
Fuqing Zhang ◽  
Dandan Tao
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Small Amplitude ◽  
Wind Shear ◽  
Random Noise ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Small Scale ◽  
Rapid Intensification ◽  
Moist Convection

Abstract Through cloud-resolving simulations, this study examines the effect of vertical wind shear and system-scale flow asymmetry on the predictability of tropical cyclone (TC) intensity during different stages of the TC life cycle. A series of ensemble experiments is performed with varying magnitudes of vertical wind shear, each initialized with an idealized weak TC-like vortex, with small-scale, small-amplitude random perturbations added to the initial conditions. It is found that the environmental shear can significantly affect the intrinsic predictability of tropical cyclones, especially during the formation and rapid intensification stage. The larger the vertical wind shear, the larger the uncertainty in the intensity forecast, primarily owing to the difference in the timing of rapid intensification. In the presence of environmental shear, initial random noise may result in changes in the timing of rapid intensification by as much as 1–2 days through the randomness (and chaotic nature) of moist convection. Upscale error growth from differences in moist convection first alters the tilt amplitude and angle of the incipient tropical storms, which leads to significant differences in the timing of precession and vortex alignment. During the precession process, both the vertical tilt of the storm and the effective (local) vertical wind shear are considerably decreased after the tilt angle reaches 90° to the left of the environmental shear. The tropical cyclone intensifies immediately after the tilt and the effective local shear reach their minima. In some instances, small-scale, small-amplitude random noise may also limit the intensity predictability through altering the timing and strength of the eyewall replacement cycle.

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 The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part II: Vortex Tilt

2018 ◽  
Vol 146 (11) ◽  
pp. 3801-3825 ◽  
Author(s):  
David R. Ryglicki ◽  
James D. Doyle ◽  
Yi Jin ◽  
Daniel Hodyss ◽  
Joshua H. Cossuth
Keyword(s):  
Tropical Cyclones ◽  
Wind Shear ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Model Simulations ◽  
Observational Analysis ◽  
Idealized Model ◽  
Cold Anomaly

Abstract We investigate a class of tropical cyclones (TCs) that undergo rapid intensification (RI) in moderate vertical wind shear through analysis of a series of idealized model simulations. Two key findings derived from observational analysis are that the average 200–850-hPa shear value is 7.5 m s−1 and that the TCs displayed coherent cloud structures, deemed tilt-modulated convective asymmetries (TCA), which feature pulses of deep convection with periods of between 4 and 8 h. Additionally, all of the TCs are embedded in an environment that is characterized by shear associated with anticyclones, a factor that limits depth of the strongest environmental winds in the vertical. The idealized TC develops in the presence of relatively shallow environmental wind shear of an anticyclone. An analysis of the TC tilt in the vertical demonstrates that the source of the observed 4–8-h periodicity of the TCAs can be explained by smaller-scale nutations of the tilt on the longer, slower upshear precession. When the environmental wind shear occurs over a deeper layer similar to that of a trough, the TC does not develop. The TCAs are characterized as collections of updrafts that are buoyant throughout the depth of the TC since they rise into a cold anomaly caused by the tilting vortex. At 90 h into the simulation, RI occurs, and the tilt nutations (and hence the TCAs) cease to occur.

Distribution of Helicity, CAPE, and Shear in Tropical Cyclones

2010 ◽  
Vol 67 (1) ◽  
pp. 274-284 ◽  
Author(s):  
John Molinari ◽  
David Vollaro
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Wind Shear ◽  
Negative Impact ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Ambient Wind ◽  
Hurricane Bonnie ◽  
Azimuthal Asymmetries ◽  
Dividing Line

Abstract The previous study of helicity, CAPE, and shear in Hurricane Bonnie (1998) was extended to all eight tropical cyclones sampled by NASA during the Convection and Moisture Experiments (CAMEX). Storms were categorized as having large or small ambient vertical wind shear, with 10 m s−1 as the dividing line. In strongly sheared storms, the downshear mean helicity exceeded the upshear mean by a factor of 4. As in the previous study, the helicity differences resulted directly from the tropical cyclone response to ambient shear, with enhanced in-up-out flow and veering of the wind with height present downshear. CAPE in strongly sheared storms was 60% larger downshear. Mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear. At more than 30% of observation points outside the 100-km radius in the downshear right quadrant, midlatitude empirical parameters indicated a strong likelihood of supercells. No such points existed upshear in highly sheared storms. Much smaller upshear–downshear differences and little likelihood of severe cells occurred in storms with ambient wind shear below 10 m s−1. In addition to these azimuthal asymmetries, highly sheared storms produced 30% larger area-averaged CAPE and double the area-averaged helicity versus relatively unsheared storms. The vortex-scale increase in these quantities lessens the negative impact of large vertical wind shear.

scholarly journals Changes in Characteristics of Rapidly Intensifying Western North Pacific Tropical Cyclones Related to Climate Regime Shifts

2018 ◽  
Vol 31 (19) ◽  
pp. 8163-8179 ◽  
Author(s):  
Haikun Zhao ◽  
Xingyi Duan ◽  
G. B. Raga ◽  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclones ◽  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
Regime Shift ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Climate Regime ◽  
Climate Regime Shift

A significant increase in the proportion of tropical cyclones undergoing rapid intensification at least once during their lifetime (RITCs) over the western North Pacific (WNP) is observed since 1998 when an abrupt climate regime shift occurred. Changes of large-scale atmospheric and oceanic conditions affecting TC activity are compared between two subperiods: one before and one since 1998. Results suggest that both a significant decrease in the number of TCs and a nearly unchanged number of RITCs since 1998 caused a significant increase in the frequency of RITCs. The decrease in TC numbers is likely driven by considerably increased vertical wind shear and decreased low-level vorticity. In contrast, the unchanged RITC counts and thus increased ratio of RITCs during the recent decades are largely attributed to the dominance of a more conducive ocean environment with increased TC heat potential and warmer sea surface temperature anomalies. These associated decadal changes are closely associated with the recent climate regime shift. During the recent decades with a mega–La Niña–like pattern, stronger easterly trade winds have caused increased vertical wind shear and a weakened monsoon trough, thus hampering TC formation ability over the WNP. In addition, a steeper thermocline slope that hampered the eastward migration of warm water along the equatorial Pacific has generated a more favorable thermodynamic environment supporting TC rapid intensification over the WNP.

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.

scholarly journals A Ventilation Index for Tropical Cyclones

2012 ◽  
Vol 93 (12) ◽  
pp. 1901-1912 ◽  
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.

The Intensity- and Size-Dependent Response of Tropical Cyclones to Increasing Vertical Wind Shear

2021 ◽  
Author(s):  
Peter M. Finocchio ◽  
Rosimar Rios-Berrios
Keyword(s):  
Wind Field ◽  
Wind Shear ◽  
Diabatic Heating ◽  
Inner Core ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Rapid Intensification ◽  
Vertical Coupling ◽  
Tangential Wind

AbstractThis study describes a set of idealized simulations in which westerly vertical wind shear increases from 3 to 15 m s−1 at different stages in the lifecycle of an intensifying tropical cyclone (TC). The TC response to increasing shear depends on the intensity and size of the TC’s tangential wind field when shear starts to increase. For a weak tropical storm, increasing shear decouples the vortex and prevents intensification. For Category 1 and stronger storms, increasing shear causes a period of weakening during which vortex tilt increases by 10–30 km before the TCs reach a near-steady Category 1–3 intensity at the end of the simulations. TCs exposed to increasing shear during or just after rapid intensification tend to weaken the most. Backward trajectories reveal a lateral ventilation pathway between 8–11 km altitude that is capable of reducing equivalent potential temperature in the inner core of these TCs by nearly 2°C. In addition, these TCs exhibit large reductions in diabatic heating inside the radius of maximum winds (RMW) and lower-entropy air parcels entering downshear updrafts from the boundary layer, which further contributes to their substantial weakening. The TCs exposed to increasing shear after rapid intensification and an expansion of the outer wind field reach the strongest near-steady intensity long after the shear increases because of strong vertical coupling that prevents the development of large vortex tilt, resistance to lateral ventilation through a deep layer of the middle troposphere, and robust diabatic heating within the RMW.

scholarly journals Multidecadal Variability of Tropical Cyclone Rapid Intensification in the Western North Pacific

2015 ◽  
Vol 28 (9) ◽  
pp. 3806-3820 ◽  
Author(s):  
Xidong Wang ◽  
Chunzai Wang ◽  
Liping Zhang ◽  
Xin Wang
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Trade Wind ◽  
Rapid Intensification ◽  
Multidecadal Variability ◽  
Heat Potential

Abstract This study investigates the variation of tropical cyclone (TC) rapid intensification (RI) in the western North Pacific (WNP) and its relationship with large-scale climate variability. RI events have exhibited strikingly multidecadal variability. During the warm (cold) phase of the Pacific decadal oscillation (PDO), the annual RI number is generally lower (higher) and the average location of RI occurrence tends to shift southeastward (northwestward). The multidecadal variations of RI are associated with the variations of large-scale ocean and atmosphere variables such as sea surface temperature (SST), tropical cyclone heat potential (TCHP), relative humidity (RHUM), and vertical wind shear (VWS). It is shown that their variations on multidecadal time scales depend on the evolution of the PDO phase. The easterly trade wind is strengthened during the cold PDO phase at low levels, which tends to make equatorial warm water spread northward into the main RI region rsulting from meridional ocean advection associated with Ekman transport. Simultaneously, an anticyclonic wind anomaly is formed in the subtropical gyre of the WNP. This therefore may deepen the depth of the 26°C isotherm and directly increase TCHP over the main RI region. These thermodynamic effects associated with the cold PDO phase greatly support RI occurrence. The reverse is true during the warm PDO phase. The results also indicate that the VWS variability in the low wind shear zone along the monsoon trough may not be critical for the multidecadal modulation of RI events.

scholarly journals The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part III: Outflow–Environment Interaction

2019 ◽  
Vol 147 (8) ◽  
pp. 2919-2940 ◽  
Author(s):  
David R. Ryglicki ◽  
James D. Doyle ◽  
Daniel Hodyss ◽  
Joshua H. Cossuth ◽  
Yi Jin ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Environmental Flow ◽  
Vertical Wind ◽  
Environment Interaction ◽  
Rapid Intensification ◽  
Field Matching ◽  
Upper Level ◽  
Bernoulli Flow ◽  
Dynamic High Pressure

Abstract Interactions between the upper-level outflow of a sheared, rapidly intensifying tropical cyclone (TC) and the background environmental flow in an idealized model are presented. The most important finding is that the divergent outflow from convection localized by the tilt of the vortex serves to divert the background environmental flow around the TC, thus reducing the local vertical wind shear. We show that this effect can be understood from basic theoretical arguments related to Bernoulli flow around an obstacle. In the simulation discussed, the environmental flow diversion by the outflow is limited to 2 km below the tropopause in the 12–14-km (250–150 hPa) layer. Synthetic water vapor satellite imagery confirms the presence of upshear arcs in the cloud field, matching satellite observations. These arcs, which exist in the same layer as the outflow, are caused by slow-moving wave features and serve as visual markers of the outflow–environment interface. The blocking effect where the outflow and the environmental winds meet creates a dynamic high pressure whose pressure gradient extends nearly 1000 km upwind, thus causing the environmental winds to slow down, to converge, and to sink. We discuss these results with respect to the first part of this three-part study, and apply them to another atypical rapid intensification hurricane: Matthew (2016).

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