scholarly journals Secondary Eyewall Formation and Concentric Eyewall Replacement in Association with Increased Low-Level Inner-Core Diabatic Cooling

2018 ◽  
Vol 75 (8) ◽  
pp. 2659-2685 ◽  
Author(s):  
Guanghua Chen
Keyword(s):  
Boundary Layer ◽  
Inner Core ◽  
Outer Core ◽  
Core Region ◽  
Large Radius ◽  
Strong Wind ◽  
Low Level ◽  
Secondary Eyewall Formation ◽  
Tangential Wind ◽  
Radial Outflow

Abstract The role of increased diabatic cooling in secondary eyewall formation (SEF) and eyewall replacement cycle (ERC) is examined using idealized numerical simulation. The experiment with the low-level inner-core diabatic cooling increased by 30% features the low-entropy air and downward motion in the inner-core region whereas the convergence and active convective updrafts are in the outer-core region. In collaboration with the favorable ambient dynamical conditions and boundary layer dynamical processes, the concentric convective ring is initiated with the aid of the outward expansion of strong wind field, and then contracts inward to replace the inner eyewall. Subsequently, the deep-tropospheric radial outflows driven by the large outward-directed agradient force related to the massive strong tangential wind generate a largely outward-tilted eyewall, eventually forming a large-eyed storm. The sensitivity to the strength and radial location of diabatic cooling shows that neither the 20% increase nor 10-km radially inward shift of the low-level cooling produces a pronounced SEF and ERC because of the lack of an evident moat region. In contrast, both the 40% increase and 10-km radially outward shift of cooling lead to the active outer rainbands occurring at a larger radius. In the former case, because of the deep-layer radial outflow above the boundary layer, the largely outward-tilted concentric eyewall shrinks slowly, directly creating a large-eyed structure. In the latter case, the formation of concentric eyewall is delayed because of the low inertial stability at a large radius, but experiences an expeditious ontraction because of the strong radial inflow.

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.

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 Revisiting the Balanced and Unbalanced Aspects of Tropical Cyclone Intensification

2017 ◽  
Vol 74 (8) ◽  
pp. 2575-2591 ◽  
Author(s):  
Junyao Heng ◽  
Yuqing Wang ◽  
Weican Zhou
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Model Simulation ◽  
Surface Friction ◽  
Core Region ◽  
Physics Model ◽  
The One ◽  
Balanced Dynamics ◽  
Balanced Solution

Abstract The balanced and unbalanced aspects of tropical cyclone (TC) intensification are revisited with the balanced contribution diagnosed with the outputs from a full-physics model simulation of a TC using the Sawyer–Eliassen (SE) equation. The results show that the balanced dynamics can well capture the secondary circulation in the full-physics model simulation even in the inner-core region in the boundary layer. The balanced dynamics can largely explain the intensification of the simulated TC. The unbalanced dynamics mainly acts to prevent the boundary layer agradient flow in the inner-core region from further intensification. Although surface friction can enhance the boundary layer inflow and make the inflow penetrate more inward into the eye region, contributing to the eyewall contraction, the net dynamical effect of surface friction on TC intensification is negative. The sensitivity of the balanced solution to the procedure used to ensure the ellipticity condition for the SE equation is also examined. The results show that the boundary layer inflow in the balanced response is very sensitive to the adjustment to inertial stability in the upper troposphere and the calculation of radial wind at the surface with relatively coarse vertical resolution in the balanced solution. Both the use of the so-called global regularization and the one-sided finite-differencing scheme used to calculate the surface radial wind in the balanced solution as utilized in some previous studies can significantly underestimate the boundary layer inflow. This explains why the boundary layer inflow in the balanced response is too weak in some previous studies.

scholarly journals An Idealized Numerical Study of Shear-Relative Low-Level Mean Flow on Tropical Cyclone Intensity and Size

2019 ◽  
Vol 76 (8) ◽  
pp. 2309-2334 ◽  
Author(s):  
Buo-Fu Chen ◽  
Christopher A. Davis ◽  
Ying-Hwa Kuo
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Numerical Study ◽  
Vertical Wind Shear ◽  
Development Stage ◽  
Surface Fluxes ◽  
Mean Flow ◽  
Low Level ◽  
Core Convection

Abstract Given comparable background vertical wind shear (VWS) magnitudes, the initially imposed shear-relative low-level mean flow (LMF) is hypothesized to modify the structure and convective features of a tropical cyclone (TC). This study uses idealized Weather Research and Forecasting Model simulations to examine TC structure and convection affected by various LMFs directed toward eight shear-relative orientations. The simulated TC affected by an initially imposed LMF directed toward downshear left yields an anomalously high intensification rate, while an upshear-right LMF yields a relatively high expansion rate. These two shear-relative LMF orientations affect the asymmetry of both surface fluxes and frictional inflow in the boundary layer and thus modify the TC convection. During the early development stage, the initially imposed downshear-left LMF promotes inner-core convection because of high boundary layer moisture fluxes into the inner core and is thus favorable for TC intensification because of large radial fluxes of azimuthal mean vorticity near the radius of maximum wind in the boundary layer. However, TCs affected by various LMFs may modify the near-TC VWS differently, making the intensity evolution afterward more complicated. The TC with a fast-established eyewall in response to the downshear-left LMF further reduces the near-TC VWS, maintaining a relatively high intensification rate. For the upshear-right LMF that leads to active and sustained rainbands in the downshear quadrants, TC size expansion is promoted by a positive radial flux of eddy vorticity near the radius of 34-kt wind (1 kt ≈ 0.51 m s−1) because the vorticity associated with the rainbands is in phase with the storm-motion-relative inflow.

scholarly journals Wind profiler observations of a monsoon low-level jet over a tropical Indian station

2007 ◽  
Vol 25 (10) ◽  
pp. 2125-2137 ◽  
Author(s):  
M. C. R. Kalapureddy ◽  
D. N. Rao ◽  
A. R. Jain ◽  
Y. Ohno
Keyword(s):  
Boundary Layer ◽  
Mutual Influence ◽  
Boreal Summer ◽  
Wind Profiler ◽  
Strong Wind ◽  
Height Range ◽  
Diurnal Variability ◽  
Low Level ◽  
Low Level Jet ◽  
Wind Shears

Abstract. Three-year high-resolution wind observations of the wind profiler have been utilized to characterize the diurnal and seasonal features of the monsoon Low-Level Jet (LLJ) over a tropical station, Gadanki (13.5° N, 79.2° E), with a focus on the diurnal variability of low-level winds. The Boreal summer monsoon winds show a conspicuously strong westerly LLJ with average wind speed exceeding 20 m s−1. The L-band wind profiler measurements have shown an advantage of better height and time resolutions over the conventional radiosonde method for diurnal wind measurements. An interesting diurnal oscillation of LLJ core has been observed. It is varying in the height range of 1.8±0.6 km with the maximum and minimum intensity noticed during the early morning and afternoon hours, respectively. The jet core (wind maxima) height is observed to coincide with the inversion height. Strong wind shears are normally located beneath the LLJ core. The sole wind profiler observations are capable of identifying the monsoon phases, such as onset, break and active spells, etc. The mutual influence between the LLJ and the boundary layer has been discussed. One notices that the observed LLJ diurnal structures depend on the local convective activity, wind shears and turbulence activity associated with boundary layer winds. The day-to-day change in the LLJ structure depends on the latitudinal position of the LLJ core.

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

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.

Microheterogeneity of Sodium Dodecylsulfate Micelles Probed by Frequency-Domain Fluorometry

1992 ◽  
Vol 46 (2) ◽  
pp. 329-339 ◽  
Author(s):  
Jingfan Huang ◽  
Frank V. Bright
Keyword(s):  
Inner Core ◽  
Global Analysis ◽  
Sodium Dodecylsulfate ◽  
Outer Core ◽  
Core Region ◽  
Fluorescence Lifetimes ◽  
Decay Kinetics ◽  
Sds Micelles ◽  
Counter Ions ◽  
Compositional Diversity

The microenvironment of sodium dodecylsulfate (SDS) micelles has been examined with the use of two fluorescent probes, 2-anilinonaphthalene-6-sulfonic acid (2,6-ANS) and N-phenyl-naphthylamine (1-AN). The fluorescence lifetimes are recovered from multifrequency phase and modulation data with the use of a global analysis protocol. The fluorescence decay kinetics of 2,6-ANS, which probes the outer-core region (i.e., the palisade layer) of SDS micelles, is characterized by a Lorentzian distribution. In contrast, a single discrete excited-state lifetime is observed for 1-AN, which is expected to position itself in the inner-core region of the micelle. Fluorescence lifetimes of these probes are investigated also as functions of temperature, concentration of counter ions (Na+ and Mg2+) and linear alcohols ( n-BuOH, n-PeOH, n-HeOH, and n-HepOH). The collective results confirm that the outer-core region of SDS micelles is microheterogeneous and the inner core is essentially homogeneous. In addition, the lifetimes and the partitioning of the outer-core probe, 2,6-ANS, appear to be more sensitive to variations in temperature and counter ions in comparison to those of the inner-core probe, 1-AN. The microenvironment of 2,6-ANS is found to be more heterogeneous at high temperature and low salt concentrations. This observation, we propose, is a result of different degrees of water penetration in the outer-core region. In the SDS system, the effects of micelle polydispersity and compositional diversity, on the environmental microheterogeneity of the fluorescent probe, seem to be minimal in comparison to water gradient effects.

scholarly journals A High-Resolution Simulation of Asymmetries in Severe Southern Hemisphere Tropical Cyclone Larry (2006)

2009 ◽  
Vol 137 (12) ◽  
pp. 4171-4187 ◽  
Author(s):  
Hamish A. Ramsay ◽  
Lance M. Leslie ◽  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Southern Hemisphere ◽  
Inner Core ◽  
Mesoscale Model ◽  
Deep Convection ◽  
Vertical Motion ◽  
Vertical Shear ◽  
Low Level ◽  
Frictional Convergence

Abstract Advances in observations, theory, and modeling have revealed that inner-core asymmetries are a common feature of tropical cyclones (TCs). In this study, the inner-core asymmetries of a severe Southern Hemisphere tropical cyclone, TC Larry (2006), are investigated using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and the Kepert–Wang boundary layer model. The MM5-simulated TC exhibited significant asymmetries in the inner-core region, including rainfall distribution, surface convergence, and low-level vertical motion. The near-core environment was characterized by very low environmental vertical shear and consequently the TC vortex had almost no vertical tilt. It was found that, prior to landfall, the rainfall asymmetry was very pronounced with precipitation maxima consistently to the right of the westward direction of motion. Persistent maxima in low-level convergence and vertical motion formed ahead of the translating TC, resulting in deep convection and associated hydrometeor maxima at about 500 hPa. The asymmetry in frictional convergence was mainly due to the storm motion at the eyewall, but was dominated by the proximity to land at larger radii. The displacement of about 30°–120° of azimuth between the surface and midlevel hydrometeor maxima is explained by the rapid cyclonic advection of hydrometeors by the tangential winds in the TC core. These results for TC Larry support earlier studies that show that frictional convergence in the boundary layer can play a significant role in determining the asymmetrical structures, particularly when the environmental vertical shear is weak or absent.

scholarly journals Controlled meteorological (CMET) balloon profiling of the Arctic atmospheric boundary layer around Spitsbergen compared to a mesoscale model

2015 ◽  
Vol 15 (19) ◽  
pp. 27539-27573 ◽  
Author(s):  
T. J. Roberts ◽  
M. Dütsch ◽  
L. R. Hole ◽  
P. B. Voss
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Sea Ice ◽  
Mesoscale Model ◽  
Potential Temperature ◽  
The Arctic ◽  
Strong Wind ◽  
Free Atmosphere ◽  
Low Level ◽  
Free Region

Abstract. Observations from CMET (Controlled Meteorological) balloons are analyzed in combination with mesoscale model simulations to provide insights into tropospheric meteorological conditions (temperature, humidity, wind-speed) around Svalbard, European High Arctic. Five Controlled Meteorological (CMET) balloons were launched from Ny-Ålesund in Svalbard over 5–12 May 2011, and measured vertical atmospheric profiles above Spitsbergen Island and over coastal areas to both the east and west. One notable CMET flight achieved a suite of 18 continuous soundings that probed the Arctic marine boundary layer over a period of more than 10 h. The CMET profiles are compared to simulations using the Weather Research and Forecasting (WRF) model using nested grids and three different boundary layer schemes. Variability between the three model schemes was typically smaller than the discrepancies between the model runs and the observations. Over Spitsbergen, the CMET flights identified temperature inversions and low-level jets (LLJ) that were not captured by the model. Nevertheless, the model largely reproduced time-series obtained from the Ny-Ålesund meteorological station, with exception of surface winds during the LLJ. Over sea-ice east of Svalbard the model underestimated potential temperature and overestimated wind-speed compared to the CMET observations. This is most likely due to the full sea-ice coverage assumed by the model, and consequent underestimation of ocean–atmosphere exchange in the presence of leads or fractional coverage. The suite of continuous CMET soundings over a sea-ice free region to the northwest of Svalbard are analysed spatially and temporally, and compared to the model. The observed along-flight daytime increase in relative humidity is interpreted in terms of the diurnal cycle, and in the context of marine and terrestrial air-mass influences. Analysis of the balloon trajectory during the CMET soundings identifies strong wind-shear, with a low-level channeled flow. The study highlights the challenges of modelling the Arctic atmosphere, especially in coastal zones with varying topography, sea-ice and surface conditions. In this context, CMET balloons provide a valuable technology for profiling the free atmosphere and boundary layer in remote regions where few other observations are available for model validation.

scholarly journals Observed Kinematic and Thermodynamic Structure in the Hurricane Boundary Layer during Intensity Change

2019 ◽  
Vol 147 (8) ◽  
pp. 2765-2785 ◽  
Author(s):  
Kyle Ahern ◽  
Mark A. Bourassa ◽  
Robert E. Hart ◽  
Jun A. Zhang ◽  
Robert F. Rogers
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Inner Core ◽  
Intensity Change ◽  
Conditional Stability ◽  
Thermodynamic Structure ◽  
Wind Structure ◽  
Tangential Wind ◽  
Axisymmetric Structure ◽  
Hurricane Boundary Layer

Abstract The axisymmetric structure of the inner-core hurricane boundary layer (BL) during intensification [IN; intensity tendency ≥20 kt (24 h)−1, where 1 kt ≈ 0.5144 m s−1], weakening [WE; intensity tendency <−10 kt (24 h)−1], and steady-state [SS; the remainder] periods are analyzed using composites of GPS dropwindsondes from reconnaissance missions between 1998 and 2015. A total of 3091 dropsondes were composited for analysis below 2.5-km elevation—1086 during IN, 1042 during WE, and 963 during SS. In nonintensifying hurricanes, the low-level tangential wind is greater outside the radius of maximum wind (RMW) than for intensifying hurricanes, implying higher inertial stability (I2) at those radii for nonintensifying hurricanes. Differences in tangential wind structure (and I2) between the groups also imply differences in secondary circulation. The IN radial inflow layer is of nearly equal or greater thickness than nonintensifying groups, and all groups show an inflow maximum just outside the RMW. Nonintensifying hurricanes have stronger inflow outside the eyewall region, likely associated with frictionally forced ascent out of the BL and enhanced subsidence into the BL at radii outside the RMW. Equivalent potential temperatures (θe) and conditional stability are highest inside the RMW of nonintensifying storms, which is potentially related to TC intensity. At greater radii, inflow layer θe is lowest in WE hurricanes, suggesting greater subsidence or more convective downdrafts at those radii compared to IN and SS hurricanes. Comparisons of prior observational and theoretical studies are highlighted, especially those relating BL structure to large-scale vortex structure, convection, and intensity.

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