The Impact of Outflow Environment on Tropical Cyclone Intensification and Structure

Rappin, Eric D.; Morgan, Michael C.; Tripoli, Gregory J.

doi:10.1175/2009jas2970.1

Cited by 65 publications

(75 citation statements)

References 37 publications

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“…16a and 16b), the primary differences are found just north and northwest of the storm, with weakening storms characterized by a broad trough to the north or northeast of the storm and much stronger westerlies extending to near the storm center, while strengthening storms are located south of a ridge with westerlies displaced farther northward. Outflow from the strengthening storms is stronger and broader, which may reflect the more vigorous convection in those cases or a favorable interaction with the trough located poleward and to the west of the storm (Holland and Merrill 1984;Molinari and Vollaro 1989;Rappin et al 2010). By day 2 (Figs.…”

Section: A Composite View Of the Sal And Hurricanesmentioning

confidence: 98%

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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Section: A Composite View Of the Sal And Hurricanesmentioning

confidence: 98%

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

Braun

2010

Monthly Weather Review

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“…Although these results confirm that interaction favors TC intensification in a statistical sense, to identify whether or not a particular trough interaction is conducive to TC intensification is still not straightforward (Hanley et al, 2001;Leroux et al, 2013). Besides, these two studies ignored the role of upper-level inertial stability, emphasized in a number of other studies (e.g., Holland and Merrill, 1984;Rappin et al, 2011).…”

Section: Tc Interactionmentioning

confidence: 77%

“…High inertial stability means that strong forcing will result in limited responses. As a TC intensifies, especially when doing so rapidly, it requires low inertial stability (e.g., Rappin et al, 2011); the higher inertial stability shown here is partially responsible for reducing the positive effect of large EFC. Another reason is that TC intensity change is also controlled by two other environmental factors, i.e., SST and VWS.…”

Section: Relationship Between Efc and Other Environmental Factorsmentioning

confidence: 79%

“…One of the important factors concerning a TC's interaction with upper-level environmental flow, besides EFC, is the inertial stability, usually defined in the SEB theory (e.g., Rappin et al, 2011) as…”

Section: Methodsmentioning

confidence: 99%

“…Figure 6 shows the local inertial stability, i.e., ζ a superposed by the composite wind fields. In terms of local inertial stability, the role of each jet, located in different quadrants, could be different because relatively weak inertial stability over a certain quadrant of the TC could minimize the energy expenditure and facilitate the formation of an outflow channel in that quadrant (Rappin et al, 2011). From Fig.…”

Section: All Positive Interactionmentioning

confidence: 99%

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Upper-tropospheric environment–tropical cyclone interactions over the western North Pacific: A statistical study

Qian

Chen²,

Zhang³

et al. 2016

Adv. Atmos. Sci.

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Based on 25-year (1987-2011) tropical cyclone (TC) best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC-environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence (EFC) exceeding 10 m s −1 d −1 . Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach ∼120 m s −1 d −1 during the extratropical-cyclone (EC) stage, an order of magnitude larger than reported in previous studies. Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear (VWS). Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs (not in the EC stage), it was found that environments with a moderate EFC value generally below ∼25 m s −1 d −1 are more favorable for a TC's intensification than those with extremely large EFC.

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The impact of vertical shear on the sensitivity of tropical cyclogenesis to environmental rotation and thermodynamic state

Zhou

2015

J Adv Model Earth Syst

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The impact of vertical wind shear on the sensitivity of tropical cyclogenesis to environmental rotation and thermodynamic state is investigated through idealized cloud-resolving simulations of the intensification of an incipient vortex. With vertical shear, tropical cyclones intensify faster with a higher Coriolis parameter, f, irrespective of the environmental thermodynamic state. The vertical shear develops a vertically tilted vortex, which undergoes a precession process with the midlevel vortices rotating cyclonically around the surface center. With a higher f, the midlevel vortices are able to rotate continuously against the vertical shear, leading to the realignment of the tilted vortex and rapid intensification. With a lower f, the rotation is too slow such that the midlevel vortices are advected away from the surface center and the intensification is suppressed. The parameter, v b , measuring the effect from the low-entropy downdraft air on the boundary layer entropy, is found to be a good indicator of the environmental thermodynamic favorability for tropical cyclogenesis in vertical shear. Without vertical shear, tropical cyclones are found to intensify faster with a lower f by previous studies. We show this dependency on f is sensitive to the environmental thermodynamic state. The thermodynamical favorability for convection can be measured by v m , which estimates the time it takes for surface fluxes to moisten the midtroposphere. A smaller v m not only leads to a faster intensification due to a shorter period for moist preconditioning of the inner region but also neutralizes the faster intensification with a lower f due to enhanced peripheral convection.

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The Impact of Outflow Environment on Tropical Cyclone Intensification and Structure

Cited by 65 publications

References 37 publications

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

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

Upper-tropospheric environment–tropical cyclone interactions over the western North Pacific: A statistical study

The impact of vertical shear on the sensitivity of tropical cyclogenesis to environmental rotation and thermodynamic state

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