Eastern Pacific Hurricanes Jimena of 1991 and Olivia of 1994: The Effect of Vertical Shear on Structure and Intensity

Black, Mark M.; Gamache, John F.; Marks, Frank D.; Samsury, Christopher E.; Willoughby, H. E.

doi:10.1175/1520-0493(2002)130<2291:ephjoa>2.0.co;2

Cited by 242 publications

(316 citation statements)

References 52 publications

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“…The calculation using a slab boundary layer model suggests that maximum convection preferably occurs in the front to right-front quadrants of the storm, in no shear situations. Although the results presented by Shapiro are consistent with some observational studies, recent observational works (e.g., Franklin et al 1993;Black et al 2002) suggest that the translation is not the sole cause of convective asymmetries in the inner-core region of TCs.…”

Section: Introductionsupporting

confidence: 86%

Observational Analysis and Numerical Evaluation of the Effects of Vertical Wind Shear on the Rainfall Asymmetry in the Typhoon Inner-Core Region

Ueno

2007

Journal of the Meteorological Society of Japan

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A number of observational and modeling studies have shown a tendency for typhoon strength vortices to develop upward motion and produce precipitation, particularly in the eyewall, on the downshear to downshear-left side of the tropical cyclones (TCs). However, the directional relationships obtained from the observational studies have been mostly confined to the TC cases in the Atlantic basin. Furthermore, little evidence has been presented so far for the relationship in magnitude, between shear and rainfall asymmetry.In the former part of the present study, the observational analysis on TC rainfall asymmetries is extended to the western North Pacific TCs in 2004, using the two types of rain-rate data, the RadarAMeDAS precipitation data, and satellite-based rainfall estimates, such as TMI and AMSR-E rain rates. It is well demonstrated from the analysis that rainfall in the inner-core region of a TC tends to occur on the downshear to downshear-left side, irrespective of data type used and latitudes where TCs are located. However, as far as the relationship between shear and storm motion is concerned, a sharp contrast is found between low and middle latitudes. In middle latitudes TCs have a tendency to move to the left of the shear, consistent with previous studies, while in low latitudes they tend to move to the right of the shear. The contrasting shear-relative storm heading between the two latitudes is attributed to the difference in vertical structure of the ambient wind.In the latter part of the study, to explore the quantitative relationship between shear and rainfall asymmetry, a formula for the shear-induced vertical motion is derived from the thermal wind balance equation for TC-like vortices. The formula states that the shear-induced vertical motion should be a function not only of shear magnitude, but also of vortex strength. To validate the formula a set of idealized numerical experiments are conducted, with realistic wind profiles, in which the initial environmental winds are specified from the 6-hourly JMA global analyses for two major typhoon cases in 2004. It is found from the numerical study that the magnitude of wavenumber-one vertical motion, predicted by the formula, is much more strongly correlated with that of model-produced rainfall asymmetry, than the shear alone, suggesting that the vortex strength is one of the main factors determining the magnitude of shear-induced rainfall asymmetry. The results from the idealized simulations also suggest that vortex tilt would have only a minor contribution to the rainfall asymmetry in the inner-core region, at least for well-developed TCs.

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Section: Introductionsupporting

confidence: 86%

Observational Analysis and Numerical Evaluation of the Effects of Vertical Wind Shear on the Rainfall Asymmetry in the Typhoon Inner-Core Region

Ueno

2007

Journal of the Meteorological Society of Japan

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“…By contrast, corresponding uniform-flow experiments tend to produce more symmetric rainfall pattern (not shown), suggesting that the ambient vertical shear is responsible for the asymmetric convective heating. Previous modeling studies with convective heating (Wang and Holland 1996a;Bender 1997), and observational studies (Franklin et al 1993;Corbosiero and Molinari 2002;Black et al 2002) also suggest that convective asymmetries in tropical cyclones are closely related to vertical wind shear. Frank and Ritchie (2001) speculated that differential vorticity advection with height caused by the shear could be the mechanism responsible for the asymmetry.…”

Section: Simulated Tracksmentioning

confidence: 87%

Steering Weight Concept and its Application to Tropical Cyclones Simulated in a Vertical Shear Experiment

Ueno

2003

Journal of the Meteorological Society of Japan

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A series of idealized numerical simulations of tropical cyclones is performed to enhance the knowledge on the mechanism of tropical cyclone (TC) motion in vertically sheared environments. The simulations are performed using an f -plane version of the typhoon track prediction model previously run at the Japan Meteorological Agency.A wide variety of TC tracks show up when the model is integrated repeatedly with different formulations of convective parameterization from an identical initial field. To account for the diversity of TC motion in vertically sheared environment, a steering-weight concept is introduced. The steeringweight is a set of weighting factors, mathematically derived from the surface pressure tendency equation, and can be a measure of how sensitive the motion of a TC is, to the steering flow at each vertical level. The experiments with different cumulus parameterizations show that the vertical profile of steering weight tends to strongly depend on the cumulus parameterization scheme used, but much less on the environment specified. This result implies that the axisymmetric thermal structure of modeled TCs, is mostly determined by parameterization schemes rather than environment in the model. And the longterm (say, 72 h mean) TC motion is well explained by the combination of steering weight, and large-scale flow fields.The result suggests that the differences in TC track among numerical prediction models, may be attributable to the differences in steering weight to some degree, given that there is no significant difference in the simulated large-scale flow fields among the models. Moreover, as long as the steering weight concept holds in nature, the steering-weighted deep layer mean flow, instead of the conventional and empirical pressure-weighted one, would work better in accounting for the motion of real tropical cyclones.

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“…Whether and by which means storms are detrimentally impacted by vertical shear on their periphery has not been well established. In most previous studies of vertical wind shear impacts on tropical cyclones, the ''detrimental'' shear was thought to be that existing over the core (the center and out to some specified radius) of the storm (Marks et al 1992;Franklin et al 1993;Reasor et al 2000;Black et al 2002;Corbosiero andMolinari 2002, 2003;Rogers et al 2003;Chan et al 2004;Braun et al 2006;Braun and Wu 2007;Chen et al 2006) and was often assumed to be horizontally uniform in modeling studies (Jones 1995;Frank andRitchie 1999, 2001;Wong and Chan 2004). For this study, we assume that the presence of an AEJ near the periphery of a storm is not necessarily detrimental to storm development.…”

Section: Vertical Shear and Increased Stabilitymentioning

confidence: 99%

Reevaluating the Role of the Saharan Air Layer in Atlantic Tropical Cyclogenesis and Evolution

Braun

2010

Monthly Weather Review

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The existence of the Saharan air layer (SAL), a layer of warm, dry, dusty air frequently present over the tropical Atlantic Ocean, has long been appreciated. The nature of its impacts on hurricanes remains unclear, with some researchers arguing that the SAL amplifies hurricane development and with others arguing that it inhibits it. The potential negative impacts of the SAL include 1) vertical wind shear associated with the African easterly jet; 2) warm air aloft, which increases thermodynamic stability at the base of the SAL; and 3) dry air, which produces cold downdrafts. Multiple NASA satellite datasets and NCEP global analyses are used to characterize the SAL's properties and evolution in relation to tropical cyclones and to evaluate these potential negative influences. The SAL is shown to occur in a large-scale environment that is already characteristically dry as a result of large-scale subsidence. Strong surface heating and deep dry convective mixing enhance the dryness at low levels (primarily below ;700 hPa), but moisten the air at midlevels. Therefore, mid-to-upper-level dryness is not generally a defining characteristic of the SAL, but is instead often a signature of subsidence. The results further show that storms generally form on the southern side of the jet, where the background cyclonic vorticity is high. Based upon its depiction in NCEP Global Forecast System meteorological analyses, the jet often helps to form the northern side of the storms and is present to equal extents for both strengthening and weakening storms, suggesting that jet-induced vertical wind shear may not be a frequent negative influence. Warm SAL air is confined to regions north of the jet and generally does not impact the tropical cyclone precipitation south of the jet.Composite analyses of the early stages of tropical cyclones occurring in association with the SAL support the inferences from the individual cases noted above. Furthermore, separate composites for strongly strengthening and for weakening storms show few substantial differences in the SAL characteristics between these two groups, suggesting that the SAL is not a determinant of whether a storm will intensify or weaken in the days after formation. Key differences between these cases are found mainly at upper levels where the flow over strengthening storms allows for an expansive outflow and produces little vertical shear, while for weakening storms, the shear is stronger and the outflow is significantly constrained.

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Eastern Pacific Hurricanes Jimena of 1991 and Olivia of 1994: The Effect of Vertical Shear on Structure and Intensity

Cited by 242 publications

References 52 publications

Observational Analysis and Numerical Evaluation of the Effects of Vertical Wind Shear on the Rainfall Asymmetry in the Typhoon Inner-Core Region

Observational Analysis and Numerical Evaluation of the Effects of Vertical Wind Shear on the Rainfall Asymmetry in the Typhoon Inner-Core Region

Steering Weight Concept and its Application to Tropical Cyclones Simulated in a Vertical Shear Experiment

Reevaluating the Role of the Saharan Air Layer in Atlantic Tropical Cyclogenesis and Evolution

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