Jonathan L. Vigh

Rapid Development of the Tropical Cyclone Warm Core

This paper presents a simple theoretical argument to isolate the conditions under which a tropical cyclone can rapidly develop a warm-core thermal structure and subsequently approach a steady state. The theoretical argument is based on the balanced vortex model and, in particular, on the associated transverse circulation equation and the geopotential tendency equation. These second-order partial differential equations contain the diabatic forcing and three spatially varying coefficients: the static stability A, the baroclinity B, and the inertial stability C. Thus, the transverse circulation and the temperature tendency in a tropical vortex depend not only on the diabatic forcing but also on the spatial distributions of A, B, and C. Experience shows that the large radial variations of C are typically the most important effect. Under certain simplifying assumptions as to the vertical structure of the diabatic forcing and the spatial variability of A, B, and C, the transverse circulation equation and the geopotential tendency equation can be solved via separation of variables. The resultingradialstructureequationsretainthedynamicallyimportantradialvariationofCandcanbe solvedin terms of Green’s functions. These analytical solutions show that the vortex response to a delta function in the diabatic heating depends critically on whether the heating occurs in the low-inertial-stability region outside the radius of maximum wind or in the high-inertial-stability region inside the radius of maximum wind. This resultsuggeststhatrapidintensification isfavoredforstormsthathaveat leastsome oftheeyewallconvection inside the radius of maximum wind. The development of an eye partially removes diabatic heating from the high-inertial-stability region of the storm center; however, rapid intensification may continue if the eyewall heating continues to become more efficient. As the warm core matures and static stability increases over the inner core, conditions there become less favorable for deep upright convection and the storm tends to approach a steady state.

Revisiting the Relationship between Eyewall Contraction and Intensification

AbstractIn the widely accepted convective ring model of tropical cyclone intensification, the intensification of the maximum winds and the contraction of the radius of maximum winds (RMW) occur simultaneously. This study shows that in idealized numerical simulations, contraction and intensification commence at the same time, but that contraction ceases long before peak intensity is achieved. The rate of contraction decreases with increasing initial size, while the rate of intensification does not vary systematically with initial size. Utilizing a diagnostic expression for the rate of contraction, it is shown that contraction is halted in association with a rapid increase in the sharpness of the tangential wind profile near the RMW and is not due to changes in the radial gradient of the tangential wind tendency. It is shown that a number of real storms exhibit a relationship between contraction and intensification that is similar to what is seen in the idealized simulations. In particular, the statistical ...

A climatology of hurricane eye formation

AbstractThis paper presents a climatology of the initial eye formations of a broad set of Atlantic tropical cyclones (TCs) during 1989–2008. A new dataset of structure and intensity parameters is synthesized from the vortex data messages transmitted by routine aircraft reconnaissance. Using these data together with satellite imagery and other established datasets, the times when each TC achieved various stages of eye development are tabulated to form the basis of the climatology. About 60% of Atlantic TCs form eyes. Most often, aircraft observe the eye structure before it appears in IR satellite imagery. Eyes tend to form in high potential intensity environments characterized by high sea surface temperatures and low-to-moderate environmental vertical wind shear. A notable discovery is that most (67%) TCs that form eyes tend to do so within 48 h of the cyclone’s reaching tropical storm strength. This suggests the existence of an opportune time window during which a TC can readily form an eye. From the leng...

The Impact of Gradient Wind Imbalance on Potential Intensity of Tropical Cyclones in an Unbalanced Slab Boundary Layer Model

The assumption of gradient wind balance is customarily made so as to derive the theoretical upper-bound intensity of a mature tropical cyclone. Emanuel’s theory of hurricane potential intensity (E-PI) makes use of this assumption, whereas more recent studies by Bryan and Rotunno demonstrate that the effect of unbalanced flow can result in maximum winds that are well in excess of E-PI (superintensity). The existence of supergradient winds has been verified in a slab boundary layer model developed by Smith. Here, the authors apply the slab boundary layer model within the framework of classical E-PI theory to investigate the sensitivity of supergradient winds to the radius of maximum gradient wind (RMGW) and four nondimensional model parameters. The authors find that the Rossby number, the drag coefficient, and the modified Rankine decayparameterallhaveaconsiderableinfluenceonthestrengthoftheunbalancedflow.Incontrast,theratio of surface exchange coefficients has little noticeable effect on superintensity. The inclusion of horizontal momentum diffusion leads to a weaker superintensity, but the qualitative features of the model remain similar.To furtherelucidatethesefindings,theauthorsusetheboundarylayermodeltoexaminethemodified E-PI theoryproposedby Emanueland Rotunno.Theyassumea constantRichardsonnumberforthe outflow. The boundary layer model driven by the modified E-PI solution depends on just three model parameters rather than the four parameters used in the classical E-PI framework. Despite this apparent advantage, the resultsobtainedintheframeworkofthemodifiedE-PIarelessrealisticthanthosecomputedwiththeclassical E-PI approach.

Evaluating the Appropriateness of Downscaled Climate Information for Projecting Risks of Salmonella

Foodborne diseases have large economic and societal impacts worldwide. To evaluate how the risks of foodborne diseases might change in response to climate change, credible and usable climate information tailored to the specific application question is needed. Global Climate Model (GCM) data generally need to, both, be downscaled to the scales of the application to be usable, and represent, well, the key characteristics that inflict health impacts. This study presents an evaluation of temperature-based heat indices for the Washington D.C. area derived from statistically downscaled GCM simulations for 1971–2000—a necessary step in establishing the credibility of these data. The indices approximate high weekly mean temperatures linked previously to occurrences of Salmonella infections. Due to bias-correction, included in the Asynchronous Regional Regression Model (ARRM) and the Bias Correction Constructed Analogs (BCCA) downscaling methods, the observed 30-year means of the heat indices were reproduced reasonably well. In April and May, however, some of the statistically downscaled data misrepresent the increase in the number of hot days towards the summer months. This study demonstrates the dependence of the outcomes to the selection of downscaled climate data and the potential for misinterpretation of future estimates of Salmonella infections.

QSCAT-R: The QuikSCAT Tropical Cyclone Radial Structure Dataset

The Technical Notes series provides an outlet for a variety of NCAR Manuscripts that contribute in specialized ways to the body of scientific knowledge but that are not yet at a point of a formal journal, monograph or book publication. Reports in this series are issued by the NCAR scientific divisions, serviced by OpenSky and operated through the NCAR Library. Designation symbols for the series include: (UCAR) under the sponsorship of the National Science Foundation. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

A 10-year survey of tropical cyclone inner-core lightning bursts and their relationship to intensity change

AbstractThis study seeks to reconcile discrepancies between previous studies analyzing the relationship between lightning and tropical cyclone (TC) intensity change. Inner-core lightning bursts (ICLBs) were identified from 2005 to 2014 in North Atlantic (NA) and eastern North Pacific (ENP) TCs embedded in favorable environments (e.g., vertical wind shear ≤ 10 m s−1; sea surface temperatures ≥ 26.5°C) using data from the World Wide Lightning Location Network (WWLLN) transformed onto a regular grid with 8-km grid spacing to replicate the expected nadir resolution of the Geostationary Lightning Mapper (GLM). Three hypothesized factors that could impact the 24-h intensity change after a burst were tested: 1) prior intensity change, 2) azimuthal burst location, and 3) radial burst location. Most ICLBs occurred in weak TCs (tropical depressions and tropical storms), and most TCs intensified (remained steady) 24 h after burst onset in the NA (ENP). TCs were more likely to intensify 24 h after an ICLB if they wer...

Evaluation of a Multigrid Barotropic Tropical Cyclone Track Model

The performance of a multigrid barotropic tropical cyclone track model (MUDBAR) is compared to that of a current operational barotropic model (LBAR). Analysis of track forecast errors for the 2001 Atlantic hurricane season shows that MUDBAR gives accuracy similar to LBAR with substantially lower computational cost. Despite the use of a barotropic model, the MUDBAR forecasts show skill relative to climatology and persistence (CLIPER) out to 5 days.

Reply to "comments on 'revisiting the relationship between eyewall contraction and intensification'"

AbstractIn their comment, Kieu and Zhang critique the recent study of Stern et al. that examined the contraction of the radius of maximum wind (RMW) and its relationship to tropical cyclone intensification. Stern et al. derived a diagnostic expression for the rate of contraction and used this to show that while RMW contraction begins and accelerates as a result of an increasing negative radial gradient of tangential wind tendency inward of the RMW, contraction slows down and eventually ceases as a result of the increasing sharpness of the wind profile around the RMW during intensification. Kieu and Zhang claim that this kinematic framework does not yield useful understanding, that Stern et al. are mistaken in their favorable comparison of this framework to earlier work by Willoughby et al., and that Stern et al. are mistaken in their conclusion that an equation for the contraction of the RMW derived by Kieu is erroneous. This reply demonstrates that each of these claims by Kieu and Zhang is incorrect.

Desirability and Feasibility of a Global Reanalysis of Tropical Cyclones

What: Accurate records of historical tropical cyclones are invaluable for scientific research and risk quantification. Yet most tropical cyclone data were collected in aid of operational forecasting with mixed attention to their use as a climate archive. To remedy this, as far as possible, a comprehensive reanalysis of Atlantic tropical cyclones was undertaken and is enjoying widespread use. To explore the feasibility of undertaking a similar effort for the rest of the globe, covering about 88% of all tropical cyclones, a workshop was convened, involving 12 scientists from around the world, including researchers, data analysts, and forecasters. When: 22–23 May 2017 Where: Asheville, North Carolina ON THE DESIRABILITY AND FEASIBILITY OF A GLOBAL REANALYSIS OF TROPICAL CYCLONES