The Unconventional Eyewall Replacement Cycle of Hurricane Ophelia (2005)

Flight Level ◽

Intensive Observation ◽

Observation Period ◽

AbstractHurricane Ophelia (2005) underwent an unconventional eyewall replacement cycle (ERC) as it was a Category 1 storm located over cold sea surface temperatures near 23°C. The ERC was analyzed using airborne radar, flight-level, and dropsonde data collected during the Hurricane Rainband and Intensity Change Experiment (RAINEX) intensive observation period on 11 September 2005. Results showed that the spin-up of the secondary tangential wind maximum during the ERC can be attributed to the efficient convergence of absolute angular momentum by the mid-level inflow of Ophelia’s dominantly stratiform rainbands. This secondary tangential wind maximum strongly contributed to the azimuthal mean tangential wind field, which is conducive for increased low-level supergradient winds and corresponding outflow. The low-level supergradient forcing enhanced convergence to form a secondary eyewall. Ophelia provides a unique example of an ERC occurring in a weaker storm with predominantly stratiform rainbands, suggesting an important role of stratiform precipitation processes in the development of secondary eyewalls.

Essential Dynamics of Secondary Eyewall Formation

10.1175/jas-d-12-0318.1 ◽

2013 ◽

Vol 70 (10) ◽

pp. 3216-3230 ◽

Cited By ~ 54

Author(s):

Sergio F. Abarca ◽

Michael T. Montgomery

Keyword(s):

Boundary Layer ◽

Time Dependent ◽

Layer Model ◽

Mesoscale Simulation ◽

Wind Maximum ◽

Boundary Layer Model ◽

Secondary Eyewall Formation ◽

Tangential Wind ◽

Abstract The authors conduct an analysis of the dynamics of secondary eyewall formation in two modeling frameworks to obtain a more complete understanding of the phenomenon. The first is a full-physics, three-dimensional mesoscale model in which the authors examine an idealized hurricane simulation that undergoes a canonical eyewall replacement cycle. Analysis of the mesoscale simulation shows that secondary eyewall formation occurs in a conditionally unstable environment, questioning the applicability of moist-neutral viewpoints and related mathematical formulations thereto for studying this process of tropical cyclone intensity change. The analysis offers also new evidence in support of a recent hypothesis that secondary eyewalls form via a progressive boundary layer control of the vortex dynamics in response to a radial broadening of the tangential wind field. The second analysis framework is an axisymmetric, nonlinear, time-dependent, slab boundary layer model with radial diffusion. When this boundary layer model is forced with the aforementioned mesoscale model's radial profile of pressure at the top of the boundary layer, it generates a secondary tangential wind maximum consistent with that from the full-physics, mesoscale simulation. These findings demonstrate that the boundary layer dynamics alone are capable of developing secondary wind maxima without prescribed secondary heat sources and/or invocation of special inertial stability properties of the swirling flow either within or above the boundary layer. Finally, the time-dependent slab model reveals that the simulated secondary wind maximum contracts inward, as secondary eyewalls do in mesoscale models and in nature, pointing to a hitherto unrecognized role of unbalanced dynamics in the eyewall replacement cycle.

The role of outer rainband convection in governing the eyewall replacement cycle in numerical simulations of tropical cyclones

Journal of Geophysical Research Atmospheres ◽

10.1002/2014jd021899 ◽

2014 ◽

Vol 119 (13) ◽

pp. 8049-8072 ◽

Cited By ~ 26

Author(s):

Zhenduo Zhu ◽

Ping Zhu

Keyword(s):

Numerical Simulations ◽

Tropical Cyclones ◽

Asymmetric Rainband Processes Leading to Secondary Eyewall Formation in a Model Simulation of Hurricane Matthew (2016)

10.1175/jas-d-20-0061.1 ◽

2021 ◽

Vol 78 (1) ◽

pp. 29-49

Author(s):

Chau-Lam Yu ◽

Anthony C. Didlake ◽

Fuqing Zhang ◽

Robert G. Nystrom

Keyword(s):

Wind Field ◽

Model Simulation ◽

Wind Maximum ◽

Low Level ◽

Secondary Eyewall Formation ◽

Positive Acceleration ◽

Radial Extent ◽

Tangential Wind ◽

Low Levels ◽

Left Quadrant

AbstractThe dynamics of an asymmetric rainband complex leading into secondary eyewall formation (SEF) are examined in a simulation of Hurricane Matthew (2016), with particular focus on the tangential wind field evolution. Prior to SEF, the storm experiences an axisymmetric broadening of the tangential wind field as a stationary rainband complex in the downshear quadrants intensifies. The axisymmetric acceleration pattern that causes this broadening is an inward-descending structure of positive acceleration nearly 100 km wide in radial extent and maximizes in the low levels near 50 km radius. Vertical advection from convective updrafts in the downshear-right quadrant largely contributes to the low-level acceleration maximum, while the broader inward-descending pattern is due to horizontal advection within stratiform precipitation in the downshear-left quadrant. This broad slantwise pattern of positive acceleration is due to a mesoscale descending inflow (MDI) that is driven by midlevel cooling within the stratiform regions and draws absolute angular momentum inward. The MDI is further revealed by examining the irrotational component of the radial velocity, which shows the MDI extending downwind into the upshear-left quadrant. Here, the MDI connects with the boundary layer, where new convective updrafts are triggered along its inner edge; these new upshear-left updrafts are found to be important to the subsequent axisymmetrization of the low-level tangential wind maximum within the incipient secondary eyewall.

Secondary Eyewall Formation and Eyewall Replacement Cycles in a Simulated Hurricane: Effect of the Net Radial Force in the Hurricane Boundary Layer

10.1175/jas-d-12-017.1 ◽

2013 ◽

Vol 70 (5) ◽

pp. 1317-1341 ◽

Cited By ~ 26

Author(s):

Xingbao Wang ◽

Yimin Ma ◽

Noel E. Davidson

Keyword(s):

Boundary Layer ◽

Swirling Flow ◽

Mesoscale Model ◽

Radial Force ◽

Intensity Change ◽

Moist Convection ◽

Wind Maximum ◽

Mature Phase ◽

Tangential Wind ◽

Eyewall Replacement Cycles

Abstract Multiple secondary eyewall formations (SEFs) and eyewall replacement cycles (ERCs) are simulated with the fifth-generation Pennsylvania State University (PSU)–National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) at horizontal grid spacing of 0.67 km. The simulated hurricane is initialized from a weak, synthetic vortex in a quiescent environment on an f plane. After spinup and rapid intensification, the hurricane enters a mature phase during which the intensity change is relatively slow. Convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane’s primary eyewall. This secondary eyewall (SE) then contracts and strengthens. The primary eyewall weakens and is eventually replaced by the SE. The hurricane grows in size and the radius of maximum wind (RMW) increases as similar ERCs repeat 5 times during the simulation. Two existing hypotheses on SEF are evaluated using the simulation output. Then, model diagnostics are used to reveal that crucial linked components of SEF are (i) a broadening of the swirling flow, (ii) the structure of the evolving secondary circulation, and (iii) the structure of the net radial force (NRF) in the boundary layer (with largest contributions from the agradient and frictional forces). During SEF, there exists strong positive NRF in the region of the primary eyewall, a secondary positive maximum over the SEF region, and a minimum between the two. As a response of the boundary layer depth–integrated radial flow to the NRF, a secondary maximum convergence zone (SMCZ) in the boundary layer develops at the SEF radii. Eventually moist convection in the SMCZ becomes active as the SEF develops.

Are Eyewall Replacement Cycles Governed Largely by Axisymmetric Balance Dynamics?

10.1175/jas-d-14-0151.1 ◽

2015 ◽

Vol 72 (1) ◽

pp. 82-87 ◽

Cited By ~ 15

Author(s):

Sergio F. Abarca ◽

Michael T. Montgomery

Keyword(s):

Boundary Layer ◽

Recent Work ◽

Balance Model ◽

Tangential Wind ◽

Physics Simulation ◽

Physics Model ◽

Balance Dynamics ◽

Eyewall Replacement Cycles ◽

Abstract The authors question the widely held view that radial contraction of a secondary eyewall during an eyewall replacement cycle is well understood and governed largely by the classical theory of axisymmetric balance dynamics. The investigation is based on a comparison of the secondary circulation and derived tangential wind tendency between a full-physics simulation and the Sawyer–Eliassen balance model. The comparison is made at a time when the full-physics model exhibits radial contraction of the secondary eyewall during a canonical eyewall replacement cycle. It is shown that the Sawyer–Eliassen model is unable to capture the phenomenology of secondary eyewall radial contraction because it predicts a net spindown of the boundary layer tangential winds and does not represent the boundary layer spinup mechanism that has been articulated in recent work.

An ensemble study of HyMeX IOP6 and IOP7a: sensitivity to physical and initial and boundary condition uncertainties

Natural Hazards and Earth System Science ◽

10.5194/nhess-14-1071-2014 ◽

2014 ◽

Vol 14 (5) ◽

pp. 1071-1084 ◽

Cited By ~ 19

Author(s):

A. Hally ◽

E. Richard ◽

V. Ducrocq

Keyword(s):

Heavy Precipitation ◽

Low Level ◽

Mountainous Regions ◽

Model Skill ◽

Intensive Observation ◽

High Level ◽

Ctrl Simulation ◽

Level Of Agreement ◽

Precipitation Events ◽

Observation Period

Abstract. The first Special Observation Period of the HyMeX campaign took place in the Mediterranean between September and November 2012 with the aim of better understanding the mechanisms which lead to heavy precipitation events (HPEs) in the region during the autumn months. Two such events, referred to as Intensive Observation Period 6 (IOP6) and Intensive Observation Period 7a (IOP7a), occurred respectively on 24 and 26 September over south-eastern France. IOP6 was characterised by moderate to weak low-level flow which led to heavy and concentrated convective rainfall over the plains near the coast, while IOP7a had strong low-level flow and consisted of a convective line over the mountainous regions further north and a band of stratiform rainfall further east. Firstly, an ensemble was constructed for each IOP using analyses from the AROME, AROME-WMED, ARPEGE and ECMWF operational models as initial (IC) and boundary (BC) conditions for the research model Meso-NH at a resolution of 2.5 km. A high level of model skill was seen for IOP7a, with a lower level of agreement with the observations for IOP6. Using the most accurate member of this ensemble as a CTRL simulation, three further ensembles were constructed in order to study uncertainties related to cloud physics and surface turbulence parameterisations. Perturbations were introduced by perturbing the time tendencies of the warm and cold microphysical and turbulence processes. An ensemble where all three sources of uncertainty were perturbed gave the greatest degree of dispersion in the surface rainfall for both IOPs. Comparing the level of dispersion to that of the ICBC ensemble demonstrated that when model skill is low (high) and low-level flow is weak to moderate (strong), the level of dispersion of the ICBC and physical perturbation ensembles is (is not) comparable. The level of sensitivity to these perturbations is thus concluded to be case dependent.

Quadrant-Dependent Evolution of Low-Level Tangential Wind of a Tropical Cyclone in the Shear Flow

10.1175/jas-d-15-0165.1 ◽

2016 ◽

Vol 73 (3) ◽

pp. 1159-1177 ◽

Cited By ~ 10

Author(s):

Jian-Feng Gu ◽

Zhe-Min Tan ◽

Xin Qiu

Keyword(s):

Tropical Cyclone ◽

Shear Flow ◽

Vertical Wind Shear ◽

Intensity Change ◽

Low Level ◽

Budget Analysis ◽

Steady Stage ◽

Tangential Wind ◽

Low Level Jet ◽

The Right

Abstract This study investigates the quadrant-by-quadrant evolution of the low-level tangential wind near the eyewall of an idealized simulated mature tropical cyclone embedded in a unidirectional shear flow. It is found that the quadrant-averaged tangential wind in the right-of-shear quadrants weakens continuously, while that in the left-of-shear quadrants experiences a two-stage evolution: a quasi-steady stage followed by a weakening stage after the imposing of vertical wind shear. This leads to a larger weakening rate in the right-of-shear and a stronger jet in the left-of-shear quadrants. The budget analysis shows that the quadrant-dependent evolution of tangential wind is controlled through the balance between the generalized Coriolis force (GCF; i.e., the radial advection of absolute angular momentum) and the advection terms. The steady decreasing of the GCF is primarily responsible for the continuous weakening of jet strength in the right-of-shear quadrants. For the left-of-shear quadrants, the quasi-steady stage is due to the opposite contributions by the enhanced GCF and negative tendency of advections cancelling out each other. The later weakening stage is the result of both the decreased GCF and the negative tangential advection. The combination of storm-relative flows at vortex scale and the convection strength both within and outside the eyewall determines the evolution of boundary layer inflow asymmetries, which in turn results in the change of GCF, leading to the quadrant-dependent evolution of low-level jet strength and thus the overall storm intensity change.

Coherent Turbulence in the Boundary Layer of Hurricane Rita (2005) during an Eyewall Replacement Cycle

10.1175/jas-d-17-0347.1 ◽

2018 ◽

Vol 75 (9) ◽

pp. 3071-3093 ◽

Cited By ~ 4

Author(s):

Stephen R. Guimond ◽

Jun A. Zhang ◽

Joseph W. Sapp ◽

Stephen J. Frasier

Keyword(s):

Boundary Layer ◽

Doppler Radar ◽

Horizontal Wind ◽

Flux Analysis ◽

Hurricane Rita ◽

Turbulent Eddies ◽

Roll Vortices ◽

Flight Level ◽

Abstract The structure of coherent turbulence in an eyewall replacement cycle in Hurricane Rita (2005) is presented from novel airborne Doppler radar observations using the Imaging Wind and Rain Airborne Profiler (IWRAP). The IWRAP measurements and three-dimensional (3D) wind vector calculations at a grid spacing of 250 m in the horizontal and 30 m in the vertical reveal the ubiquitous presence of organized turbulent eddies in the lower levels of the storm. The data presented here, and the larger collection of IWRAP measurements, currently are the highest-resolution Doppler radar 3D wind vectors ever obtained in a hurricane over the open ocean. Coincident data from NOAA airborne radars, the Stepped Frequency Microwave Radiometer, and flight-level data help to place the IWRAP observations into context and provide independent validation. The typical characteristics of the turbulent eddies are the following: radial wavelengths of ~1–3 km (mean value is ~2 km), depths from the ocean surface up to flight level (~1.5 km), aspect ratio of ~1.3, and horizontal wind speed perturbations of 10–20 m s−1. The most intense eddy activity is located on the inner edge of the outer eyewall during the concentric eyewall stage with a shift to the inner eyewall during the merging stage. The evolving structure of the vertical wind shear is connected to this shift and together these characteristics have several similarities to boundary layer roll vortices. However, eddy momentum flux analysis reveals that high-momentum air is being transported upward, in contrast with roll vortices, with large positive values (~150 m2 s−2) found in the turbulent filaments. In the decaying inner eyewall, elevated tangential momentum is also being transported radially outward to the intensifying outer eyewall. These results indicate that the eddies may have connections to potential vorticity waves with possible modifications due to boundary layer shear instabilities.

Satellite and Aircraft Observations of the Eyewall Replacement Cycle in Typhoon Sinlaku (2008)

Monthly Weather Review ◽

10.1175/mwr-d-15-0066.1 ◽

2015 ◽

Vol 143 (9) ◽

pp. 3406-3420 ◽

Cited By ~ 4

Author(s):

Elizabeth R. Sanabia ◽

Bradford S. Barrett ◽

Nicholas P. Celone ◽

Zachary D. Cornelius

Keyword(s):

Inner Core ◽

Surface Wind ◽

Surface Winds ◽

Wind Speeds ◽

Radial Profiles ◽

Aircraft Observations ◽

Flight Level ◽

Cloud Tops ◽

Abstract Satellite and aircraft observations of the concurrent evolution of cloud-top brightness temperatures (BTs) and the surface and flight-level wind fields were examined before and during an eyewall replacement cycle (ERC) in Typhoon Sinlaku (2008) as part of The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC) and the Tropical Cyclone Structure 2008 (TCS08) field campaign. The structural evolution of deep convection through the life cycle of the ERC was clearly evident in the radial variation of positive water vapor (WV) minus infrared (IR) brightness temperature differences over the 96-h period. Within this framework, the ERC was divided into six broadly defined stages, wherein convective processes (including eyewall development and decay) were analyzed and then validated using microwave data. Dual maxima in aircraft wind speeds and geostationary satellite BTs along flight transects through Sinlaku were used to document the temporal evolution of the ERC within the TC inner core. Negative correlations were found between IR BTs and surface wind speeds, indicating that colder cloud tops were associated with stronger surface winds. Spatial lags indicated that the strongest surface winds were located radially inward of both the flight-level winds and coldest cloud tops. Finally, timing of the ERC was observed equally in IR and WV minus IR (WVIR) BTs with one exception. Decay of the inner eyewall was detected earlier in the WVIR data. These findings highlight the potential utility of WVIR and IR BT radial profiles, particularly so for basins without active aircraft weather reconnaissance programs such as the western North Pacific.

Convective-Scale Downdrafts in the Principal Rainband of Hurricane Katrina (2005)

Monthly Weather Review ◽

10.1175/2009mwr2827.1 ◽

2009 ◽

Vol 137 (10) ◽

pp. 3269-3293 ◽

Cited By ~ 58

Author(s):

Anthony C. Didlake ◽

Robert A. Houze

Keyword(s):

Hurricane Katrina ◽

Doppler Radar ◽

Extended Period ◽

Heavy Rain ◽

Radar Data ◽

Intensity Change ◽

Wind Maximum ◽

Tangential Wind ◽

Convective Scale ◽

Negative Buoyancy

Abstract Airborne Doppler radar data collected during the Hurricane Rainband and Intensity Change Experiment (RAINEX) document downdrafts in the principal rainband of Hurricane Katrina (2005). Inner-edge downdrafts (IEDs) originating at 6–8-km altitude created a sharp reflectivity gradient along the inner boundary of the rainband. Low-level downdrafts (LLDs) evidently driven by precipitation drag originated at 2–4 km within the heavy rain cells of each convective element. The IED and LLD were spatially separated by but closely associated with the updrafts within the rainband. The IED was forced aloft by pressure perturbations formed in response to the adjacent buoyant updrafts. Once descending, the air attained negative buoyancy via evaporative cooling from the rainband precipitation. A convective-scale tangential wind maximum tended to occur in the radial inflow at lower levels in association with the IED, which enhanced the inward flux of angular momentum at lower levels. Convergence at the base of the downdrafts on the upwind end of the principal rainband contributed to the principal rainband growing in length. New updraft elements triggered by this convergence led to the formation of new IED and LLD pockets, which were subsequently advected downwind around the storm by the vortex winds while additional new cells continued to form on the upwind end of the band. These processes sustained the principal rainband and helped to make it effectively stationary relative to the storm center, thus maintaining its impact on the hurricane dynamics over an extended period.