scholarly journals Forecast Uncertainty of Rapid Intensification of Typhoon Dujuan (201521) Induced by Uncertainty in the Boundary Layer

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1263
Author(s):  
Xiaohao Qin ◽  
Wansuo Duan
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Forecast Skill ◽  
Rapid Intensification ◽  
Strongly Correlated ◽  
Forecast Uncertainty ◽  
Cyclone Intensity ◽  
Tangential Wind ◽  
Typhoon Intensity

Using ensemble forecast experiments generated by the weather research and forecasting model, the forecast uncertainties of intensity and its rapid intensification (RI) induced by the uncertainty occurring in the boundary layer are investigated for Typhoon Dujuan (201521). The results show that the uncertainty in the boundary layer in the typhoon area, compared with that in other areas of the model domain, not only leads to a much larger forecast uncertainty of the typhoon intensity but also considerably perturbs the RI forecast uncertainty. Particularly, the uncertainty in the gale area in the boundary layer, compared with that in the inner-core and other areas, makes a much larger contribution to the forecast uncertainty of typhoon intensity, with the perturbations including moisture component being most strongly correlated with the occurrence of RI. Further analyses show that such perturbations increase the maximum tangential wind in the boundary layer and enhance the vorticity in the eyewall, which then facilitate the spin-up of the inner-core and induce the occurrence of RI. It is inferred that more observations, especially those associated with the moisture, should be preferentially assimilated in the gale area within the boundary layer of a tropical cyclone, which will help improve the forecast skill of the RI. These results also tell us that the boundary layer parameterization scheme should be further developed to improve the forecast skill of tropical cyclone intensity and its RI behavior.

Impact of Parameterized Boundary Layer Structure on Tropical Cyclone Rapid Intensification Forecasts in HWRF

2017 ◽  
Vol 145 (4) ◽  
pp. 1413-1426 ◽  
Author(s):  
Jun A. Zhang ◽  
Robert F. Rogers ◽  
Vijay Tallapragada
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Layer Structure ◽  
Intensity Change ◽  
Rapid Intensification ◽  
Near Surface ◽  
Boundary Layer Structure ◽  
Tangential Wind ◽  
The Impact

Abstract This study evaluates the impact of the modification of the vertical eddy diffusivity (Km) in the boundary layer parameterization of the Hurricane Weather Research and Forecasting (HWRF) Model on forecasts of tropical cyclone (TC) rapid intensification (RI). Composites of HWRF forecasts of Hurricanes Earl (2010) and Karl (2010) were compared for two versions of the planetary boundary layer (PBL) scheme in HWRF. The results show that using a smaller value of Km, in better agreement with observations, improves RI forecasts. The composite-mean, inner-core structures for the two sets of runs at the time of RI onset are compared with observational, theoretical, and modeling studies of RI to determine why the runs with reduced Km are more likely to undergo RI. It is found that the forecasts with reduced Km at the RI onset have a shallower boundary layer with stronger inflow, more unstable near-surface air outside the eyewall, stronger and deeper updrafts in regions farther inward from the radius of maximum wind (RMW), and stronger boundary layer convergence closer to the storm center, although the mean storm intensity (as measured by the 10-m winds) is similar for the two groups. Finally, it is found that the departure of the maximum tangential wind from the gradient wind at the eyewall, and the inward advection of angular momentum outside the eyewall, is much larger in the forecasts with reduced Km. This study emphasizes the important role of the boundary layer structure and dynamics in TC intensity change, supporting recent studies emphasizing boundary layer spinup mechanism, and recommends further improvement to the HWRF PBL physics.

scholarly journals The Role of Inner-Core Moisture in Tropical Cyclone Predictability and Practical Forecast Skill

2017 ◽  
Vol 74 (7) ◽  
pp. 2315-2324 ◽  
Author(s):  
Kerry Emanuel ◽  
Fuqing Zhang
Keyword(s):  
Tropical Cyclone ◽  
Wind Field ◽  
Inner Core ◽  
Forecast Skill ◽  
Initial Condition ◽  
Tropical Cyclone Intensity ◽  
Cyclone Intensity ◽  
Storm Intensity ◽  
Tropical Cyclone Intensity Forecasts

Abstract Errors in tropical cyclone intensity forecasts are dominated by initial-condition errors out to at least a few days. Initialization errors are usually thought of in terms of position and intensity, but here it is shown that growth of intensity error is at least as sensitive to the specification of inner-core moisture as to that of the wind field. Implications of this finding for tropical cyclone observational strategies and for overall predictability of storm intensity are discussed.

scholarly journals Sensitivity of Tropical Cyclone Intensity to Ventilation in an Axisymmetric Model

2012 ◽  
Vol 69 (8) ◽  
pp. 2394-2413 ◽  
Author(s):  
Brian Tang ◽  
Kerry Emanuel
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Mechanical Efficiency ◽  
Surface Fluxes ◽  
Tropical Cyclone Intensity ◽  
Cyclone Intensity ◽  
Thermal Wind ◽  
Convective Bursts ◽  
Upper Level

Abstract The sensitivity of tropical cyclone intensity to ventilation of cooler, drier air into the inner core is examined using an axisymmetric tropical cyclone model with parameterized ventilation. Sufficiently strong ventilation induces cooling of the upper-level warm core, a shift in the secondary circulation radially outward, and a decrease in the simulated intensity. Increasing the strength of the ventilation and placing the ventilation at middle to lower levels results in a greater decrease in the quasi-steady intensity, whereas upper-level ventilation has little effect on the intensity. For strong ventilation, an oscillatory intensity regime materializes and is tied to transient convective bursts and strong downdrafts into the boundary layer. The sensitivity of tropical cyclone intensity to ventilation can be viewed in the context of the mechanical efficiency of the inner core or a modified thermal wind relation. In the former, ventilation decreases the mechanical efficiency, as the generation of available potential energy is wasted by entropy mixing above the boundary layer. In the latter, ventilation weakens the eyewall entropy front, resulting in a decrease in the intensity by thermal wind arguments. The experiments also support the existence of a threshold ventilation beyond which a tropical cyclone cannot be maintained. Downdrafts overwhelm surface fluxes, leading to a precipitous drop in intensity and a severe degradation of structure in such a scenario. For a given amount of ventilation below the threshold, there exists a minimum initial intensity necessary for intensification to the quasi-steady intensity.

scholarly journals Lilly’s Model for Steady-State Tropical Cyclone Intensity and Structure

2020 ◽  
Vol 77 (11) ◽  
pp. 3701-3720
Author(s):  
Dandan Tao ◽  
Richard Rotunno ◽  
Michael Bell
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Cloud Model ◽  
Surface Boundary ◽  
Unpublished Manuscript ◽  
Tangential Wind ◽  
Radial Structure ◽  
Simplifying Assumptions

AbstractThis study revisits the axisymmetric tropical cyclone (TC) theory from D. K. Lilly’s unpublished manuscript (Lilly model) and compares it to axisymmetric TC simulations from a nonhydrostatic cloud model. Analytic solutions of the Lilly model are presented through simplifying assumptions. Sensitivity experiments varying the sea surface, boundary layer and tropopause temperatures, and the absolute angular momentum (M) at some outer radius in the Lilly model show that these variations influence the radial structure of the tangential wind profile V(r) at the boundary layer top. However, these parameter variations have little effect on the inner-core normalized tangential wind, V(r/rm)/Vm, where Vm is the maximum tangential wind at radius rm. The outflow temperature T∞ as a function of M (or saturation entropy s*) is found to be the only input that changes the normalized tangential wind radial structure in the Lilly model. In contrast with the original assumption of the Lilly model that T∞(s*) is determined by the environment, it is argued here that T∞(s*) is determined by the TC interior flow under the environmental constraint of the tropopause height. The present study shows that the inner-core tangential wind radial structure from the Lilly model generally agrees well with nonhydrostatic cloud model simulations except in the eyewall region where the Lilly model tends to underestimate the tangential winds due to its balanced-dynamics assumptions. The wind structure in temperature–radius coordinates from the Lilly model can largely reproduce the numerical simulation results. Though the Lilly model is based on a number of simplifying assumptions, this paper shows its utility in understanding steady-state TC intensity and structure.

scholarly journals How Much Does the Upward Advection of the Supergradient Component of Boundary Layer Wind Contribute to Tropical Cyclone Intensification and Maximum Intensity?

2020 ◽  
Vol 77 (8) ◽  
pp. 2649-2664 ◽  
Author(s):  
Yuanlong Li ◽  
Yuqing Wang ◽  
Yanluan Lin
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Numerical Experiments ◽  
Inner Core ◽  
Maximum Intensity ◽  
The Other ◽  
Wind Component ◽  
Tangential Wind ◽  
Tangential Momentum ◽  
Tc Model

Abstract Although the development of supergradient winds is well understood, the importance of supergradient winds in tropical cyclone (TC) intensification is still under debate. One view is that the spinup of the eyewall occurs by the upward advection of high tangential momentum associated with supergradient winds from the boundary layer. The other view argues that the upward advection of supergradient winds by eyewall updrafts results in an outward agradient force, leading to the formation of a shallow outflow layer immediately above the inflow boundary layer. As a result, the spinup of tangential wind in the eyewall by the upward advection of supergradient wind from the boundary layer is largely offset by the spindown of tangential wind due to the outflow resulting from the agradient force. In this study, the net contribution by the upward advection of the supergradient wind component from the boundary layer to the intensification rate and final intensity of a TC are quantified through ensemble sensitivity numerical experiments using an axisymmetric TC model. Results show that consistent with the second view above, the positive upward advection of the supergradient wind component from the boundary layer by eyewall updrafts is largely offset by the negative radial advection due to the outflow resulting from the outward agradient force. As a result, the upward advection of the supergradient wind component contributes little (often less than 4%) to the intensification rate and but it contributes about 10%–15% to the final intensity of the simulated TC due to the enhanced inner-core air–sea thermodynamic disequilibrium.

scholarly journals Reply to “Comments on ‘Revisiting the Balanced and Unbalanced Aspects of Tropical Cyclone Intensification’”

2018 ◽  
Vol 75 (7) ◽  
pp. 2497-2505 ◽  
Author(s):  
Junyao Heng ◽  
Yuqing Wang ◽  
Weican Zhou
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Model Simulation ◽  
Surface Friction ◽  
Fast Response ◽  
Tangential Wind ◽  
Physics Model ◽  
Balanced Dynamics ◽  
Balanced Solution

Abstract In their comment, Montgomery and Smith critique the recent study of Heng et al. that revisited the balanced and unbalanced aspects of tropical cyclone (TC) intensification based on diagnostics of a full-physics model simulation using the Sawyer–Eliassen equation. Heng et al. showed that the balanced dynamics reproduced to a large extent the secondary circulation in the full-physics model simulation and concluded that balanced dynamics can well explain TC intensification in their full-physics model simulation. Montgomery and Smith suspect the balanced solution in Heng et al. because the basic-state vortex is not exactly in thermal wind balance in the boundary layer and possibly a too-large diffusivity in the numerical model was used. In this reply, we first indicate that the boundary layer spinup mechanism proposed by Smith et al. is a fast response of the TC boundary layer to surface friction and should not be a major mechanism of TC intensification. We then evaluate the possible effect of imbalance in the basic state in the boundary layer on the balanced solution. The results show that although the removal of the imbalance in the boundary layer leads to about a one-third reduction in the maximum inflow near the surface in the inner-core region, the overall effect on the tangential wind budget is marginal because of other compensations. We also show that both the horizontal and vertical diffusivities in the model used in Heng et al. are reasonable based on previous observational studies. Therefore, we conclude that all results in Heng et al. are valid. Some related issues are also discussed.

Fluctuations in inner-core structure during the rapid intensification of Super Typhoon Nepartak (2016)

2020 ◽  
Author(s):  
Sam Hardy ◽  
Juliane Schwendike ◽  
Roger K. Smith ◽  
Chris J. Short ◽  
Michael J. Reeder ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Structural Changes ◽  
Inner Core ◽  
Single Case ◽  
Three Dimensional ◽  
Core Structure ◽  
Rapid Intensification ◽  
Budget Analysis ◽  
Tangential Wind ◽  
The Mean

AbstractThe key physical processes responsible for inner-core structural changes and associated fluctuations in the intensification rate for a recent, high-impact western North Pacific tropical cyclone that underwent rapid intensification (Nepartak, 2016) are investigated using a set of convection-permitting ensemble simulations. Fluctuations in the inner-core structure between ring-like and monopole states develop in 60% of simulations. A tangential momentum budget analysis of a single fluctuation reveals that during the ring-like phase, the tangential wind generally intensifies, whereas during the monopole phase, the tangential wind remains mostly constant. In both phases, the mean advection terms spin up the tangential wind in the boundary layer, whereas the eddy advection terms deepen the storm’s cyclonic circulation by spinning up the tangential wind between 1.5 and 4 km. Further calculations of the azimuthally-averaged, radially-integrated vertical mass flux suggest that periods of near-constant tangential wind tendency are accompanied by a weaker eyewall updraft, which is unable to evacuate all the mass converging in the boundary layer. Composite analyses calculated from 18 simulations produce qualitatively similar results to those from the single case, a finding that is also in agreement with some previous observational and modelling studies. Above the boundary layer, the integrated contribution of the eddy term to the tangential wind tendency is over 80% of the contribution from the mean term, irrespective of inner-core structure. Our results strongly indicate that to fully understand the storm’s three-dimensional evolution, the contribution of the eddies must be quantified.

scholarly journals Azimuthal Distribution of Deep Convection, Environmental Factors, and Tropical Cyclone Rapid Intensification: A Perspective from HWRF Ensemble Forecasts of Hurricane Edouard (2014)

2018 ◽  
Vol 75 (1) ◽  
pp. 275-295 ◽  
Author(s):  
Hua Leighton ◽  
Sundararaman Gopalakrishnan ◽  
Jun A. Zhang ◽  
Robert F. Rogers ◽  
Zhan Zhang ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Deep Convection ◽  
Environmental Flow ◽  
Core Structure ◽  
Ensemble Prediction ◽  
Rapid Intensification ◽  
Tangential Wind ◽  
Upper Level ◽  
Vorticity Flux

Forecasts from the operational Hurricane Weather Research and Forecasting (HWRF)-based ensemble prediction system for Hurricane Edouard (2014) are analyzed to study the differences in both the tropical cyclone inner-core structure and large-scale environment between rapidly intensifying (RI) and nonintensifying (NI) ensemble members. An analysis of the inner-core structure reveals that as deep convection wraps around from the downshear side of the storm to the upshear-left quadrant for RI members, vortex tilt and asymmetry reduce rapidly, and rapid intensification occurs. For NI members, deep convection stays trapped in the downshear/downshear-right quadrant, and storms do not intensify. The budget calculation of tangential wind tendency reveals that the positive radial eddy vorticity flux for RI members contributes significantly to spinning up the tangential wind in the middle and upper levels and reduces vortex tilt. The negative eddy vorticity flux for NI members spins down the tangential wind in the middle and upper levels and does not help the vortex become vertically aligned. An analysis of the environmental flow shows that the cyclonic component of the storm-relative upper-level environmental flow in the left-of-shear quadrants aids the cyclonic propagation of deep convection and helps establish the configuration that leads to the positive radial vorticity flux for RI members. In contrast, the anticyclonic component of the storm-relative mid- and upper-level environmental flow in the left-of-shear quadrants inhibits the cyclonic propagation of deep convection and suppresses the positive radial eddy vorticity flux for NI members. Environmental moisture in the downshear-right quadrant is also shown to be important for the formation of deep convection for RI members.

Adopting Model Uncertainties for Tropical Cyclone Intensity Prediction

2014 ◽  
Vol 142 (1) ◽  
pp. 72-78 ◽  
Author(s):  
Rosimar Rios-Berrios ◽  
Tomislava Vukicevic ◽  
Brian Tang
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Joint Probability ◽  
Parameter Estimates ◽  
Cyclone Intensity ◽  
Intensity Prediction ◽  
Tangential Wind ◽  
Parameter Values ◽  
Joint Probability Density

Abstract Quantifying and reducing the uncertainty of model parameterizations using observations is evaluated for tropical cyclone (TC) intensity prediction. This is accomplished using a nonlinear inverse modeling technique that produces a joint probability density function (PDF) for a set of parameters. The dependence of estimated parameter values and associated uncertainty on two types of observable quantities is analyzed using an axisymmetric hurricane model. When the observation is only the maximum tangential wind speed, the joint PDF of parameter estimates has large variance and is multimodal. When the full kinematic field within the inner core of the TC is used for the observations, however, the joint parameter estimates are well constrained. These results suggest that model parameterizations may not be optimized using the maximum wind speed. Instead, the optimization should be based on observations of the TC structure to improve the intensity forecasts.

scholarly journals Recent Advances in Our Understanding of Tropical Cyclone Intensity Change Processes from Airborne Observations

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 650
Author(s):  
Robert F. Rogers
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Vertical Shear ◽  
Intensity Change ◽  
Change Processes ◽  
Cyclone Intensity ◽  
Secondary Eyewall Formation ◽  
Warm Core ◽  
Major Hurricane ◽  
Upper Level

Recent (past ~15 years) advances in our understanding of tropical cyclone (TC) intensity change processes using aircraft data are summarized here. The focus covers a variety of spatiotemporal scales, regions of the TC inner core, and stages of the TC lifecycle, from preformation to major hurricane status. Topics covered include (1) characterizing TC structure and its relationship to intensity change; (2) TC intensification in vertical shear; (3) planetary boundary layer (PBL) processes and air–sea interaction; (4) upper-level warm core structure and evolution; (5) genesis and development of weak TCs; and (6) secondary eyewall formation/eyewall replacement cycles (SEF/ERC). Gaps in our airborne observational capabilities are discussed, as are new observing technologies to address these gaps and future directions for airborne TC intensity change research.

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