scholarly journals On the Secondary Eyewall Formation of Hurricane Edouard (2014)

2016 ◽  
Vol 144 (9) ◽  
pp. 3321-3331 ◽  
Author(s):  
Sergio F. Abarca ◽  
Michael T. Montgomery ◽  
Scott A. Braun ◽  
Jason Dunion
Keyword(s):  
Boundary Layer ◽  
Vertical Structure ◽  
Potential Temperature ◽  
Wind Maximum ◽  
Gradient Wind ◽  
Secondary Eyewall Formation ◽  
Equivalent Potential ◽  
Unstable Environment ◽  
Time Periods ◽  
Second Period

A first observationally based estimation of departures from gradient wind balance during secondary eyewall formation is presented. The study is based on the Atlantic Hurricane Edouard (2014). This storm was observed during the National Aeronautics and Space Administration’s (NASA) Hurricane and Severe Storm Sentinel (HS3) experiment, a field campaign conducted in collaboration with the National Oceanic and Atmospheric Administration (NOAA). A total of 135 dropsondes are analyzed in two separate time periods: one named the secondary eyewall formation period and the other one referred to as the decaying double eyewalled storm period. During the secondary eyewall formation period, a time when the storm was observed to have only one eyewall, the diagnosed agradient force has a secondary maximum that coincides with the radial location of the secondary eyewall observed in the second period of study. The maximum spinup tendency of the radial influx of absolute vertical vorticity is within the boundary layer in the region of the eyewall of the storm and the spinup tendency structure elongates radially outward into the secondary region of supergradient wind, where the secondary wind maximum is observed in the second period of study. An analysis of the boundary layer averaged vertical structure of equivalent potential temperature reveals a conditionally unstable environment in the secondary eyewall formation region. These findings support the hypothesis that deep convective activity in this region contributed to spinup of the boundary layer tangential winds and the formation of a secondary eyewall that is observed during the decaying double eyewalled storm period.

Low-Level Wind Maxima and Structure of the Stably Stratified Boundary Layer in the Coastal Zone

2014 ◽  
Vol 53 (2) ◽  
pp. 363-376 ◽  
Author(s):  
L. Mahrt ◽  
Dean Vickers ◽  
Edgar L Andreas
Keyword(s):  
Boundary Layer ◽  
Land Surface ◽  
Vertical Structure ◽  
The United States ◽  
Sea Surface ◽  
Temperature Structure ◽  
Wind Maximum ◽  
Low Level ◽  
Weakly Stable ◽  
Northeastern Coast

AbstractA Rutan Aircraft Factory Long-EZ aircraft flew numerous low-level slant soundings on two summer days in 2001 off the northeastern coast of the United States. The soundings are analyzed here to study the nonstationary vertical structure of the wind, temperature, and turbulence. An error analysis indicates that fluxes computed from the aircraft slant soundings are unreliable. The first day is characterized by a weakly stable boundary layer in onshore flow capped by an inversion. A low-level wind maximum formed at about 100 m above the sea surface. The second day is characterized by stronger stability due to advection of warm air from the upwind land surface. On this more stable day, the wind maxima are very sharp and the speed and height of the wind maxima increase with distance from the coast. Although trends in the vertical structure are weak, variations between subsequent soundings are large on time scales of tens of minutes or less. The vertical structure of the wind and turbulence is considerably more nonstationary than the temperature structure, although the existence of the wind maximum is persistent. Causes of the wind maxima and their variability are examined but are not completely resolved.

scholarly journals Evolution of Pre- and Postconvective Environmental Profiles from Mesoscale Convective Systems during PECAN

2019 ◽  
Vol 147 (7) ◽  
pp. 2329-2354 ◽  
Author(s):  
Stacey M. Hitchcock ◽  
Russ S. Schumacher ◽  
Gregory R. Herman ◽  
Michael C. Coniglio ◽  
Matthew D. Parker ◽  
...  
Keyword(s):  
Potential Temperature ◽  
Cold Pool ◽  
Temperature Perturbation ◽  
Convective System ◽  
Equivalent Potential Temperature ◽  
Wind Maximum ◽  
Low Level ◽  
Equivalent Potential ◽  
Mesoscale Convective ◽  
Low Levels

Abstract During the Plains Elevated Convection at Night (PECAN) field campaign, 15 mesoscale convective system (MCS) environments were sampled by an array of instruments including radiosondes launched by three mobile sounding teams. Additional soundings were collected by fixed and mobile PECAN integrated sounding array (PISA) groups for a number of cases. Cluster analysis of observed vertical profiles established three primary preconvective categories: 1) those with an elevated maximum in equivalent potential temperature below a layer of potential instability; 2) those that maintain a daytime-like planetary boundary layer (PBL) and nearly potentially neutral low levels, sometimes even well after sunset despite the existence of a southerly low-level wind maximum; and 3) those that are potentially neutral at low levels, but have very weak or no southerly low-level winds. Profiles of equivalent potential temperature in elevated instability cases tend to evolve rapidly in time, while cases in the potentially neutral categories do not. Analysis of composite Rapid Refresh (RAP) environments indicate greater moisture content and moisture advection in an elevated layer in the elevated instability cases than in their potentially neutral counterparts. Postconvective soundings demonstrate significantly more variability, but cold pools were observed in nearly every PECAN MCS case. Following convection, perturbations range between −1.9 and −9.1 K over depths between 150 m and 4.35 km, but stronger, deeper stable layers lead to structures where the largest cold pool temperature perturbation is observed above the surface.

The Structure and Evolution of Hurricane Elena (1985). Part I: Symmetric Intensification

2005 ◽  
Vol 133 (10) ◽  
pp. 2905-2921 ◽  
Author(s):  
Kristen L. Corbosiero ◽  
John Molinari ◽  
Michael L. Black
Keyword(s):  
Inner Core ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
Equivalent Potential Temperature ◽  
Constructive Interference ◽  
Wind Maximum ◽  
Radial Gradient ◽  
Equivalent Potential ◽  
Tangential Wind

Abstract One of the most complete aircraft reconnaissance and ground-based radar datasets of a single tropical cyclone was recorded in Hurricane Elena (1985) as it made a slow, 3-day anticyclonic loop in the Gulf of Mexico. Eighty-eight radial legs and 47 vertical incidence scans were collected aboard NOAA WP-3D aircraft, and 1142 ground-based radar scans were made of Elena’s eyewall and inner rainbands as the storm intensified from a disorganized category 2 to an intense category 3 hurricane. This large amount of continuously collected data made it possible to examine changes that occurred in Elena’s inner-core symmetric structure as the storm intensified. On the first day of study, Elena was under the influence of vertical wind shear from an upper-tropospheric trough to the west. The storm was disorganized, with no discernable eyewall and nearly steady values of tangential wind and relative vorticity. Early on the second day of study, a near superposition and constructive interference occurred between the trough and Elena, coincident with upward vertical velocities and the radial gradient of reflectivity becoming concentrated around the 30-km radius. Once an inner wind maximum and eyewall developed, the radius of maximum winds contracted and a sharp localized vorticity maximum emerged, with much lower values on either side. This potentially unstable vorticity profile was accompanied by a maximum in equivalent potential temperature in the eyewall, deeper and stronger inflow out to 24 km from the eyewall, and mean outflow toward the eyewall from the eye. Within 6–12 h, intensification came to an end and Elena began to slowly weaken. Vorticity and equivalent potential temperature at 850 hPa showed indications of prior mixing between the eye and eyewall. During the weakening stage, an outflow jet developed at the eyewall radius. A strong 850-hPa updraft accompanied the outflow jet, yet convection was less active aloft than before. This feature appeared to represent a shallow, outward-sloping updraft channel associated with the spindown of the storm.

Essential Dynamics of Secondary Eyewall Formation

2013 ◽  
Vol 70 (10) ◽  
pp. 3216-3230 ◽  
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 ◽  
Eyewall Replacement Cycle ◽  
Replacement Cycle

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.

scholarly journals Observed development of the vertical structure of the marine boundary layer during the LASIE experiment in the Ligurian Sea

2010 ◽  
Vol 28 (1) ◽  
pp. 17-25 ◽  
Author(s):  
A. M. Sempreviva ◽  
M. E. Schiano ◽  
S. Pensieri ◽  
A. Semedo ◽  
R. Tomé ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Structure ◽  
Marine Boundary Layer ◽  
Potential Temperature ◽  
Internal Boundary Layer ◽  
Surface Flow ◽  
Internal Boundary ◽  
Research Centre ◽  
Ligurian Sea ◽  
Entire Depth

Abstract. In the marine environment, complete datasets describing the surface layer and the vertical structure of the Marine Atmospheric Boundary Layer (MABL), through its entire depth, are less frequent than over land, due to the high cost of measuring campaigns. During the seven days of the Ligurian Air-Sea Interaction Experiment (LASIE), organized by the NATO Undersea Research Centre (NURC) in the Mediterranean Sea, extensive in situ and remote sensing measurements were collected from instruments placed on a spar buoy and a ship. Standard surface meteorological measurements were collected by meteorological sensors mounted on the buoy ODAS Italia1 located in the centre of the Gulf of Genoa. The evolution of the height (zi) of the MABL was monitored using radiosondes and a ceilometer on board of the N/O Urania. Here, we present the database and an uncommon case study of the evolution of the vertical structure of the MABL, observed by two independent measuring systems: the ceilometer and radiosondes. Following the changes of surface flow conditions, in a sequence of onshore – offshore – onshore wind direction shifting episodes, during the mid part of the campaign, the overall structure of the MABL changed. Warm and dry air from land advected over a colder sea, induced a stably stratified Internal Boundary Layer (IBL) and a consequent change in the structure of the vertical profiles of potential temperature and relative humidity.

scholarly journals Thermodynamic structure of the convective boundary layer (CBL) over the Indian monsoon region during CAIPEEX campaigns

2017 ◽  
Vol 35 (6) ◽  
pp. 1361-1379 ◽  
Author(s):  
Sanjay Kumar Mehta ◽  
Devendra Ojha ◽  
Shyam Mehta ◽  
Devarajan Anand ◽  
Daggumati Narayana Rao ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Indian Monsoon ◽  
Potential Temperature ◽  
Equivalent Potential Temperature ◽  
Monsoon Region ◽  
Convective Boundary ◽  
Clear Sky ◽  
Equivalent Potential ◽  
Indian Monsoon Region

Abstract. Spatial and temporal variability in the convective boundary layer (CBL) height for the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) study period are examined using the data collected from high-resolution radiosondes during May–September 2009 over the Indian monsoon region. In total, 57 radiosonde launchings were carried out at ∼ 11:00–17:00 IST over six different stations covering a large geographical region, ranging from latitude ∼ 13 to 32° N and longitude 73 to 92° E. Of the total 57 launchings, 17 were made during cloudy conditions during which relative humidity (RH) was found to be greater than 83 % for an ∼ 1.0 km layer at various altitudes below 6 km. Within the layer the difference between saturated equivalent potential temperature and equivalent potential temperature is small, and it satisfies the condition that RH > 83 % for about 1 km is considered as the cloudy layer. There are eight cases when the cloud-topped boundary layer (CTBL) and 19 cases when fair-weather boundary layer (FWBL) is observed. The CBL heights are obtained using thermodynamic profiles, which vary from ∼ 0.4 to 2.5 km a. g. l.  The formation of the cloud layers above the boundary layer generally lowers the CBL height and is responsible for its day-to-day variability. The development of the cloud beneath the boundary layer generally elevates the CBL, which is also responsible for the large day-to-day variability in the CBL. The FWBL identified using relative invariance of the thermodynamic profiles varies from ∼ 2.0 to 5.5 km, which is clearly marked by a local minimum in the refractivity gradient. During cloudy days, the CBL is found to be shallow and the surface temperature lower when compared to clear-sky days. The CBL and the lifting condensation level (LCL) heights are randomly related and are found to be at a lower height during cloudy days when compared to clear-sky days. Finally, the typical comparison between the CBL height obtained using thermodynamic profiles and backscattering profiles using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is examined.

Finescale Vertical Structure and Dynamics of Some Dryline Boundaries Observed in IHOP

2007 ◽  
Vol 135 (12) ◽  
pp. 4161-4184 ◽  
Author(s):  
Qun Miao ◽  
Bart Geerts
Keyword(s):  
Boundary Layer ◽  
Great Plains ◽  
Vertical Structure ◽  
Potential Temperature ◽  
Convective Boundary ◽  
Fine Line ◽  
Millimeter Wave Radar ◽  
Structure And Dynamics ◽  
Wave Radar ◽  
Virtual Potential Temperature

Abstract Several radar fine lines, all with a humidity contrast, were sampled in the central Great Plains during the 2002 International H2O Project (IHOP). This study primarily uses aircraft and airborne millimeter-wave radar observations to dynamically interpret the presence and vertical structure of these fine lines as they formed within the well-developed convective boundary layer. In all cases the fine line represents a boundary layer convergence zone. This convergence sustains a sharp contrast in humidity, and usually in potential temperature, across the fine line. The key question addressed herein is whether, at the scale examined here (∼10 km), the airmass contrast itself, in particular the horizontal density (virtual potential temperature) difference and resulting solenoidal circulation, is responsible for the sustained convergence and the radar fine line. For the 10 cases examined herein, the answer is affirmative.

scholarly journals Outer Rainbands–Driven Secondary Eyewall Formation of Tropical Cyclones

2020 ◽  
Vol 77 (6) ◽  
pp. 2217-2236
Author(s):  
Yi-Fan Wang ◽  
Zhe-Min Tan
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclones ◽  
Positive Feedback ◽  
Outer Core ◽  
Relative Vorticity ◽  
Wind Maximum ◽  
Formation Pathway ◽  
Physical Conditions ◽  
Secondary Eyewall Formation ◽  
Tangential Wind

Abstract Secondary eyewall formation (SEF) could be considered as the aggregation of a convective-ring coupling with a tangential wind maximum outside the primary eyewall of a tropical cyclone (TC). The dynamics of SEF are investigated using idealized simulations based on a set of triplet experiments, whose differences are only in the initial outer-core wind speed. The triplet experiments indicate that the unbalanced boundary layer (BL) process driven by outer rainbands (ORBs) is essential for the canonical SEF. The developments of a secondary tangential wind maximum and a secondary convective ring are governed by two different pathways, which are well coupled in the canonical SEF. Compared with inner/suppressed rainbands, the downwind stratiform sectors of ORBs drive significant stronger BL convergence at its radially inward side, which fastens up the SEF region and links the two pathways. In the wind-maximum formation pathway, the positive feedback among the BL convergence, supergradient force, and relative vorticity within the BL dominates the spinup of a secondary tangential wind maximum. In the convective-ring formation pathway, the BL convergence contributes to the ascending motion through the frictional-forced updraft and accelerated outflow associated with the supergradient force above the BL. Driven only by inner rainbands, the simulated vortex develops a fake SEF with only the secondary convective ring since the rainband-driven BL convergence is less enhanced and thus fails to maintain the BL positive feedback in the wind-maximum pathway. Therefore, only ORBs can promote the canonical SEF. It also infers that any environmental/physical conditions favorable for the development of ORBs will ultimately contribute to SEF.

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.

Sign in / Sign up

Export Citation Format

Share Document