scholarly journals Reintensification and Eyewall Formation in Strong Shear: A Case Study of Typhoon Noul (2015)

2018 ◽  
Vol 146 (9) ◽  
pp. 2799-2817 ◽  
Author(s):  
Udai Shimada ◽  
Takeshi Horinouchi
Keyword(s):  
Doppler Radar ◽  
Vertical Wind Shear ◽  
Vertical Shear ◽  
Tangential Wind ◽  
Strong Shear ◽  
Vertically Aligned ◽  
Mean Structure ◽  
Convection Dominated ◽  
Left Quadrant

Abstract Strong vertical wind shear produces asymmetries in the eyewall structure of a tropical cyclone (TC) and is generally a hostile environment for TC intensification. Typhoon Noul (2015), however, reintensified and formed a closed eyewall despite 200–850-hPa vertical shear in excess of 11 m s−1. Noul’s reintensification and eyewall formation in strong shear were examined by using Doppler radar and surface observations. The evolution of the azimuthal-mean structure showed that the tangential wind at 2-km altitude increased from 30 to 45 m s−1 in only 5 h. During the first half of the reintensification, the azimuthal-mean inflow penetrated into the ~40-km radius, well inside the radius of maximum wind (RMW), at least below 4-km altitude, and reflectivity inside the RMW increased. As for the asymmetric evolution, vigorous convection, dominated by an azimuthal wavenumber-1 asymmetry, occurred in the downshear-left quadrant when shear started to increase and then moved upshear. A mesovortex formed inside the convective asymmetry on the upshear side. The direction of vortex tilt between the 1- and 5-km altitudes rotated cyclonically from the downshear-left to the upshear-right quadrant as the vortex was vertically aligned. In conjunction with the alignment, the amplitude of the wavenumber-1 convective asymmetry decreased and a closed eyewall formed. These features are consistent with the theory that a vortex can be vertically aligned through upshear precession. The analysis results suggest that the vortex tilt, vigorous convection, and subsequent intensification were triggered by the increase in shear in a convectively favorable environment.

scholarly journals Polar Lows – Moist Baroclinic Cyclones Developing in Four Different Vertical Wind Shear Environments

2020 ◽  
Author(s):  
Patrick Johannes Stoll ◽  
Thomas Spengler ◽  
Annick Terpstra ◽  
Rune Grand Graversen
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Vertical Shear ◽  
Polar Lows ◽  
North East ◽  
The North ◽  
Strong Shear ◽  
Polar Low ◽  
Mesoscale Cyclones

Abstract. Polar lows are intense mesoscale cyclones that develop in polar marine air masses. Motivated by the large variety in their proposed intensification mechanisms, cloud structure, and ambient sub-synoptic environment, we use self-organising maps to classify polar lows. The method is applied to 370 polar lows in the North-East Atlantic, which were obtained by matching mesoscale cyclones from the ERA-5 reanalysis to polar lows registered by the Norwegian Meteorological Institute in the STARS dataset. ERA-5 reproduces 93 % of the STARS polar lows. We identify five different polar-low configurations, which are characterised by the vertical wind shear vector relative to the propagation direction. Four categories feature a strong shear with different orientations of the shear vector, whereas the fifth category contains conditions with weak shear. The orientation of the vertical-shear vector for the strong shear categories determines the dynamics of the systems, confirming the relevance of the previously identified categorisation into forward and reverse-shear polar lows. In addition, we expand the categorisation with right and left-shear polar lows that propagate towards colder and warmer environments, respectively. Polar lows in the four strong shear categories feature an up-shear tilt in the vertical, typical for the intensification through moist baroclinic processes. As weak-shear conditions mainly occur at the mature or lysis stage of polar lows, we find no evidence for hurricane-like development and propose that spirali-form PLs are most likely associated with a warm seclusion process.

scholarly journals Reexamining the Near-Core Radial Structure of the Tropical Cyclone Primary Circulation: Implications for Vortex Resiliency

2005 ◽  
Vol 62 (2) ◽  
pp. 408-425 ◽  
Author(s):  
Kevin J. Mallen ◽  
Michael T. Montgomery ◽  
Bin Wang
Keyword(s):  
Tropical Cyclone ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Core Region ◽  
Vertical Shear ◽  
Theoretical Studies ◽  
True Nature ◽  
Radial Profiles ◽  
Tangential Wind ◽  
Radial Structure

Abstract Recent theoretical studies, based on vortex Rossby wave (VRW) dynamics, have established the importance of the radial structure of the primary circulation in the response of tropical cyclone (TC)–like vortices to ambient vertical wind shear. Linear VRW theory suggests, in particular, that the degree of broadness of the primary circulation in the near-core region beyond the radius of maximum wind strongly influences whether a tilted TC vortex will realign and resist vertical shear or tilt over and shear apart. Fully nonlinear numerical simulations have verified that the vortex resiliency is indeed sensitive to the initial radial structure of the idealized vortex. This raises the question of how well the “true” nature of a TC’s primary circulation is represented by idealized vortices that are commonly used in some theoretical studies. In this paper the swirling wind structure of TCs is reexamined by utilizing flight-level observations collected from Atlantic and eastern Pacific storms during 1977–2001. Hundreds of radial profiles of azimuthal-mean tangential wind and relative vorticity are constructed from over 5000 radial flight leg segments and compared with some standard idealized vortex profiles. This analysis reaffirms that real TC structure in the near-core region is characterized by relatively slow tangential wind decay in conjunction with a skirt of significant cyclonic relative vorticity possessing a negative radial gradient. This broadness of the primary circulation is conspicuously absent in some idealized vortices used in theoretical studies of TC evolution in vertical shear. The relationship of the current findings to the problem of TC resiliency is discussed.

scholarly journals The Structure and Evolution of Hurricane Elena (1985). Part II: Convective Asymmetries and Evidence for Vortex Rossby Waves

2006 ◽  
Vol 134 (11) ◽  
pp. 3073-3091 ◽  
Author(s):  
Kristen L. Corbosiero ◽  
John Molinari ◽  
Anantha R. Aiyyer ◽  
Michael L. Black
Keyword(s):  
Deep Convection ◽  
Vertical Wind Shear ◽  
Wave Theory ◽  
Azimuthal Velocity ◽  
Vertical Shear ◽  
Fourier Decomposition ◽  
The Core ◽  
Tangential Wind ◽  
Spiral Rainbands ◽  
Reflectivity Data

Abstract A portable data recorder attached to the Weather Surveillance Radar-1957 (WSR-57) in Apalachicola, Florida, collected 313 radar scans of the reflectivity structure within 150 km of the center of Hurricane Elena (in 1985) between 1310 and 2130 UTC 1 September. This high temporal and spatial (750 m) resolution dataset was used to examine the evolution of the symmetric and asymmetric precipitation structure in Elena as the storm rapidly strengthened and attained maximum intensity. Fourier decomposition of the reflectivity data into azimuthal wavenumbers revealed that the power in the symmetric (wavenumber 0) component dominated the reflectivity pattern at all times and all radii by at least a factor of 2. The wavenumber 1 asymmetry accounted for less than 20% of the power in the reflectivity field on average and was found to be forced by the environmental vertical wind shear. The small-amplitude wavenumber 2 asymmetry in the core was associated with the appearance and rotation of an elliptical eyewall. This structure was visible for nearly 2 h and was noted to rotate cyclonically at a speed equal to half of the local tangential wind. Outside of the eyewall, individual peaks in the power in wavenumber 2 were associated with repeated instances of cyclonically rotating, outward-propagating inner spiral rainbands. Four separate convective bands were identified with an average azimuthal velocity of 25 m s−1, or ∼68% of the local tangential wind speed, and an outward radial velocity of 5.2 m s−1. The azimuthal propagation speeds of the elliptical eyewall and inner spiral rainbands were consistent with vortex Rossby wave theory. The elliptical eyewall and inner spiral rainbands were seen only in the 6-h period prior to peak intensity, when rapid spinup of the vortex had produced an annular vorticity profile, similar to those that have been shown to support barotropic instability. The appearance of an elliptical eyewall was consistent with the breakdown of eyewall vorticity into mesovortices, asymmetric mixing between the eye and eyewall, and a slowing of the intensification rate. The inner spiral rainbands might have arisen from high eyewall vorticity ejected from the core during the mixing process. Alternatively, because the bands were noted to emanate from the vertical shear-forced deep convection in the northern eyewall, they could have formed through the axisymmetrization of the asymmetric diabatically generated eyewall vorticity.

scholarly journals Rapidly Intensifying Hurricane Guillermo (1997). Part I: Low-Wavenumber Structure and Evolution

2009 ◽  
Vol 137 (2) ◽  
pp. 603-631 ◽  
Author(s):  
Paul D. Reasor ◽  
Matthew D. Eastin ◽  
John F. Gamache
Keyword(s):  
Doppler Radar ◽  
Deep Layer ◽  
Structural Evolution ◽  
Relative Vorticity ◽  
Vertical Shear ◽  
Doppler Observation ◽  
Convective Bursts ◽  
Airborne Doppler Radar ◽  
Left Quadrant ◽  
Observation Period

Abstract The structure and evolution of rapidly intensifying Hurricane Guillermo (1997) is examined using airborne Doppler radar observations. In this first part, the low-azimuthal-wavenumber component of the vortex is presented. Guillermo’s intensification occurred in an environmental flow with 7–8 m s−1 of deep-layer vertical shear. As a consequence of the persistent vertical shear forcing of the vortex, convection was observed primarily in the downshear left quadrant of the storm. The greatest intensification during the ∼6-h Doppler observation period coincided with the formation and cyclonic rotation of several particularly strong convective bursts through the left-of-shear semicircle of the eyewall. Some of the strongest convective bursts were triggered by azimuthally propagating low-wavenumber vorticity asymmetries. Mesoscale budget analyses of axisymmetric angular momentum and relative vorticity within the eyewall are presented to elucidate the mechanisms contributing to Guillermo’s structural evolution during this period. The observations support a developing conceptual model of the rapidly intensifying, vertically sheared hurricane in which shear-forced mesoscale ascent in the downshear eyewall is modulated by internally generated vorticity asymmetries yielding episodes of anomalous intensification.

Intensity and Inner-Core Structure of Typhoon Haiyan (2013) near Landfall: Doppler Radar Analysis

2018 ◽  
Vol 146 (2) ◽  
pp. 583-597 ◽  
Author(s):  
Udai Shimada ◽  
Hisayuki Kubota ◽  
Hiroyuki Yamada ◽  
Esperanza O. Cayanan ◽  
Flaviana D. Hilario
Keyword(s):  
Wind Speed ◽  
Inner Core ◽  
Doppler Radar ◽  
Core Structure ◽  
Maximum Wind Speed ◽  
Vertical Shear ◽  
Doppler Velocity ◽  
Maximum Wind ◽  
Tangential Wind ◽  
The Right

Abstract The intensity and inner-core structure of an extremely intense tropical cyclone, Typhoon Haiyan (2013), were examined using real-time ground-based Doppler radar products from the Guiuan radar over the period of about 2.5 h immediately before the storm approached Guiuan in Eastern Samar, Philippines. Haiyan’s wind fields from 2- to 6-km altitude were retrieved by the ground-based velocity track display (GBVTD) technique from the Doppler velocity data. The GBVTD-retrieved maximum wind speed reached 101 m s−1 at 4-km altitude on the right side of the track. The relatively fast forward speed of Haiyan, about 11 m s−1, increased maximum wind speed on the right-hand side of the storm. Azimuthal mean tangential wind increased with height from 2 to 5 km, and a local maximum of 86 m s−1 occurred at 5-km altitude. The central pressure was estimated as 906 hPa with an uncertainty of ±4 hPa by using the GBVTD-retrieved tangential wind and by assuming gradient wind balance. The radius of maximum radar reflectivity was about 23 km from the center, a few kilometers inside the radius of maximum wind. The reflectivity structure was highly asymmetric at and above 3-km altitude, and was more symmetric below 3-km altitude in the presence of relatively weak vertical shear (~4 m s−1). The center of the eyewall ring was tilted slightly downshear with height.

scholarly journals The Relationship between Spatial Variations in the Structure of Convective Bursts and Tropical Cyclone Intensification as Determined by Airborne Doppler Radar

2018 ◽  
Vol 146 (3) ◽  
pp. 761-780 ◽  
Author(s):  
Joshua B. Wadler ◽  
Robert F. Rogers ◽  
Paul D. Reasor
Keyword(s):  
Diabatic Heating ◽  
Radial Flow ◽  
Doppler Radar ◽  
Deep Layer ◽  
Vertical Wind Shear ◽  
Intensity Change ◽  
Convective Bursts ◽  
Tangential Wind ◽  
The Relationship ◽  
Airborne Doppler Radar

Abstract The relationship between radial and azimuthal variations in the composite characteristics of convective bursts (CBs), that is, regions of the most intense upward motion in tropical cyclones (TCs), and TC intensity change is examined using NOAA P-3 tail Doppler radar. Aircraft passes collected over a 13-yr period are examined in a coordinate system rotated relative to the deep-layer vertical wind shear vector and normalized by the low-level radius of maximum winds (RMW). The characteristics of CBs are investigated to determine how the radial and azimuthal variations of their structures are related to hurricane intensity change. In general, CBs have elevated reflectivity just below the updraft axis, enhanced tangential wind below and radially outward of the updraft, enhanced vorticity near the updraft, and divergent radial flow at the top of the updraft. When examining CB structure by shear-relative quadrant, the downshear-right (upshear left) region has updrafts at the lowest (highest) altitudes and weakest (strongest) magnitudes. When further stratifying by intensity change, the greatest differences are seen upshear. Intensifying storms have updrafts on the upshear side at a higher altitude and stronger magnitude than steady-state storms. This distribution provides a greater projection of diabatic heating onto the azimuthal mean, resulting in a more efficient vortex spinup. For variations based on radial location, CBs located inside the RMW show stronger updrafts at a higher altitude for intensifying storms. Stronger and deeper updrafts inside the RMW can spin up the vortex through greater angular momentum convergence and a more efficient vortex response to the diabatic heating.

scholarly journals The Retrieval of Asymmetric Tropical Cyclone Structures Using Doppler Radar Simulations and Observations with the Extended GBVTD Technique

2006 ◽  
Vol 134 (4) ◽  
pp. 1140-1160 ◽  
Author(s):  
Yu-Chieng Liou ◽  
Tai-Chi Chen Wang ◽  
Wen-Chau Lee ◽  
Ya-Ju Chang
Keyword(s):  
Doppler Radar ◽  
Flat Surface ◽  
Circulation Model ◽  
Wind Component ◽  
Topographic Effects ◽  
Wind Fields ◽  
Radar Systems ◽  
Tangential Wind

Abstract The ground-based velocity track display (GBVTD) technique is extended to two Doppler radars to retrieve the structure of a tropical cyclone’s (TC’s) circulation. With this extension, it is found that the asymmetric part of the TC radial wind component can be derived up to its angular wavenumber-1 structure, and the accuracy of the retrieved TC tangential wind component can be further improved. Although two radar systems are used, a comparison with the traditional dual-Doppler synthesis indicates that this extended GBVTD (EGBVTD) approach is able to estimate more of the TC circulation when there are missing data. Previous research along with this study reveals that the existence of strong asymmetric radial flows can degrade the quality of the GBVTD-derived wind fields. When a TC is observed by one radar, it is suggested that the GBVTD method be applied to TCs over a flat surface (e.g., the ocean) where the assumption of relatively smaller asymmetric radial winds than asymmetric tangential winds is more likely to be true. However, when a TC is observed by two radar systems, especially when the topographic effects are expected to be significant, the EGBVTD rather than the traditional dual-Doppler synthesis should be used. The feasibility of the proposed EGBVTD method is demonstrated by applying it to an idealized TC circulation model as well as a real case study. Finally, the possibility of combining EGBVTD with other observational instruments, such as dropsonde or wind profilers, to recover the asymmetric TC radial flow structures with even higher wavenumbers is discussed.

scholarly journals Dynamics of the Transition from Spiral Rainbands to a Secondary Eyewall in Hurricane Earl (2010)

2018 ◽  
Vol 75 (9) ◽  
pp. 2909-2929 ◽  
Author(s):  
Anthony C. Didlake ◽  
Paul D. Reasor ◽  
Robert F. Rogers ◽  
Wen-Chau Lee
Keyword(s):  
Boundary Layer ◽  
Inner Core ◽  
Doppler Radar ◽  
Buoyant Jet ◽  
Wind Maximum ◽  
Low Level ◽  
Secondary Eyewall Formation ◽  
Tangential Wind ◽  
Negatively Buoyant ◽  
Left Quadrant

Abstract Airborne Doppler radar captured the inner core of Hurricane Earl during the early stages of secondary eyewall formation (SEF), providing needed insight into the SEF dynamics. An organized rainband complex outside of the primary eyewall transitioned into an axisymmetric secondary eyewall containing a low-level tangential wind maximum. During this transition, the downshear-left quadrant of the storm exhibited several notable features. A mesoscale descending inflow (MDI) jet persistently occurred across broad stretches of stratiform precipitation in a pattern similar to previous studies. This negatively buoyant jet traveled radially inward and descended into the boundary layer. Farther inward, enhanced low-level inflow and intense updrafts appeared. The updraft adjacent to the MDI was likely triggered by a region of convergence and upward acceleration (induced by the negatively buoyant MDI) entering the high-θe boundary layer. This updraft and the MDI in the downshear-left quadrant accelerated the tangential winds in a radial range where the axisymmetric wind maximum of the secondary eyewall soon developed. This same quadrant eventually exhibited the strongest overturning circulation and wind maximum of the forming secondary eyewall. Given these features occurring in succession in the downshear-left quadrant, we hypothesize that the MDI plays a significant dynamical role in SEF. The MDI within a mature rainband complex persistently perturbs the boundary layer, which locally forces enhanced convection and tangential winds. These perturbations provide steady low-level forcing that projects strongly onto the axisymmetric field, and forges the way for secondary eyewall development via one of several SEF theories that invoke axisymmetric dynamical processes.

Precipitation Processes and Vortex Alignment during the Intensification of a Weak Tropical Cyclone in Moderate Vertical Shear

2020 ◽  
Vol 148 (5) ◽  
pp. 1899-1929 ◽  
Author(s):  
Robert F. Rogers ◽  
Paul D. Reasor ◽  
Jonathan A. Zawislak ◽  
Leon T. Nguyen
Keyword(s):  
Mass Flux ◽  
Structural Changes ◽  
Doppler Radar ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Cooperative Interaction ◽  
Vertical Shear ◽  
Low Level ◽  
Flux Profile

Abstract The mechanisms underlying the development of a deep, aligned vortex, and the role of convection and vertical shear in this process, are explored by examining airborne Doppler radar and deep-layer dropsonde observations of the intensification of Hurricane Hermine (2016), a long-lived tropical depression that intensified to hurricane strength in the presence of moderate vertical wind shear. During Hermine’s intensification the low-level circulation appeared to shift toward locations of deep convection that occurred primarily downshear. Hermine began to steadily intensify once a compact low-level vortex developed within a region of deep convection in close proximity to a midlevel circulation, causing vorticity to amplify in the lower troposphere primarily through stretching and tilting from the deep convection. A notable transition of the vertical mass flux profile downshear of the low-level vortex to a bottom-heavy profile also occurred at this time. The transition in the mass flux profile was associated with more widespread moderate convection and a change in the structure of the deep convection to a bottom-heavy mass flux profile, resulting in greater stretching of vorticity in the lower troposphere of the downshear environment. These structural changes in the convection were related to a moistening in the midtroposphere downshear, a stabilization in the lower troposphere, and the development of a mid- to upper-level warm anomaly associated with the developing midlevel circulation. The evolution of precipitation structure shown here suggests a multiscale cooperative interaction across the convective and mesoscale that facilitates an aligned vortex that persists beyond convective time scales, allowing Hermine to steadily intensify to hurricane strength.

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.

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