Streamwise Vorticity Effects on Supercell Morphology and Persistence

Brandes, Edward A.; Davies‐Jones, Robert; Johnson, Brenda C.

doi:10.1175/1520-0469(1988)045<0947:sveosm>2.0.co;2

Cited by 37 publications

(14 citation statements)

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“…Thus, supercell storms can propagate long distances at a direction often to the right (and occasionally left) of the mean wind (e.g., Browning 1964;Marwitz 1972;Doswell and Burgess 1993). The behavior described above are confirmed by observations (e.g., Charba and Sasaki 1971;Brandes et al 1988;Cai and Wakimoto 2001;Edwards and Hodanish 2006), while reviews on the detailed dynamics can be found in Davies-Jones et al (2001) and Wilhelmson and Wicker (2001).…”

Section: Background On Supercell Thunderstormssupporting

confidence: 67%

Wintertime Supercell Thunderstorms in a Subtropical Environment: A Diagnostic Study

Wang

Chen

Yang

et al. 2009

Monthly Weather Review

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The present study documents the environment, initiation, and evolution of three isolated supercell storms on 19 December 2002, as the first case near Taiwan reported in the literature, mainly using radar data and manual and gridded analyses. In a subtropical environment, the supercells occurred behind a winter cold front that provided a large west-southwesterly vertical wind shear of 6.4 ϫ 10 Ϫ3 s Ϫ1 at 0-3 km. This combined with weak-to-moderate instability (CAPE ϭ 887 J kg Ϫ1 ) above the shallow surface cold air to yield a favorable environment for supercells. An approaching upper-level jet (ULJ) at 200 hPa also provided strong shear through deep layers farther aloft. Prior to storm initiation, significant daytime solar heating occurred over the mountain slopes along the coast of southeastern China, leading to development of local circulation and onshore/upslope winds, resulting in convergence and uplifting. Three storms were initiated about 80 km inland around 1400 LST near the peaks of local terrain with a northeast-southwest alignment. After formation, the three storms evolved into isolated supercells and each experienced multiple splits. The right-moving storms were usually stronger than left-moving ones and traveled eastward rapidly at about 18 m s Ϫ1 across the Taiwan Strait. The storms reached their maximum strength over the strait where low-level shear intensified during the day due to cold air surge. The northern storm also registered a peak reflectivity of 72 dBZ, the strongest ever recorded by any radar in Taiwan. Eventually, the three supercell storms made landfall over Taiwan, producing swaths of rain, hail, and property damages. Before they diminished after midnight, each of the three storms had lasted for about 10 h and propagated for over 550 km. and tornadoes (e.g., Lemon and Doswell 1979;Weisman and Klemp 1986).Supercell storms are predominantly a midlatitude phenomenon and occur most frequently over the U.S. Great Plains in spring and summer, when the two necessary ingredients (i.e., large vertical wind shear and instability) are readily available (e.g., Barber and Mahrt 1981;Doswell 2001). In the cold season, their frequencies drop dramatically (e.g., Moller et al. 1994) and few such events were studied (e.g., Monteverdi and Johnson 1996;Kulie and Lin 1998). Outside the United States, supercells are also found over land areas in Europe, East Asia, and the Southern Hemisphere as well, although much less severe on average (e.g.,

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Section: Background On Supercell Thunderstormssupporting

confidence: 67%

Wintertime Supercell Thunderstorms in a Subtropical Environment: A Diagnostic Study

Wang

Chen

Yang

et al. 2009

Monthly Weather Review

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“…2) Helicity is used in this study not to understand how the cells themselves evolve, but rather as a scalar marker indicating the probability of supercell occurrence. Numerous papers have verified the value of helicity for such purposes in middle latitudes (e.g., Brandes et al 1988;Davies-Jones et al 1990;Johns and Doswell 1992;Kerr and Darkow 1996;Thompson et al 2003).…”

Section: Role Of Individual Cells In Tropical Cyclonesmentioning

confidence: 86%

Distribution of Helicity, CAPE, and Shear in Tropical Cyclones

Molinari

Vollaro

2010

Journal of the Atmospheric Sciences

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The previous study of helicity, CAPE, and shear in Hurricane Bonnie (1998) was extended to all eight tropical cyclones sampled by NASA during the Convection and Moisture Experiments (CAMEX). Storms were categorized as having large or small ambient vertical wind shear, with 10 m s 21 as the dividing line. In strongly sheared storms, the downshear mean helicity exceeded the upshear mean by a factor of 4. As in the previous study, the helicity differences resulted directly from the tropical cyclone response to ambient shear, with enhanced in-up-out flow and veering of the wind with height present downshear. CAPE in strongly sheared storms was 60% larger downshear. Mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear. At more than 30% of observation points outside the 100-km radius in the downshear right quadrant, midlatitude empirical parameters indicated a strong likelihood of supercells. No such points existed upshear in highly sheared storms. Much smaller upshear-downshear differences and little likelihood of severe cells occurred in storms with ambient wind shear below 10 m s 21 . In addition to these azimuthal asymmetries, highly sheared storms produced 30% larger area-averaged CAPE and double the area-averaged helicity versus relatively unsheared storms. The vortex-scale increase in these quantities lessens the negative impact of large vertical wind shear.

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“…(6) is found, for example, in Brandes et al (1988) and Davies-Jones (2002). The anelastic value of Ј is that which globally causes (5) and (6) to possess the same common value, which we will refer to as G. In the anelastic case G Ͼ 0 implies a positive horizontal convergence tendency, and G Ͻ 0 implies a negative horizontal convergence tendency.…”

Section: Dpe and Pressure Tendenciesmentioning

confidence: 95%

“…This has been termed the "occlusion downdraft" (Klemp and Rotunno 1983), and has been seen in both models and observations as an extension of the RFD (see the review by Markowski 2002). Observations have lent support to the idea that these downdrafts are driven at least in part by near-surface low pressure associated with increased rotation (Brandes 1978;Wakimoto and Liu 1998). During the downdraft descent vertical vorticity acquires the form of a thin ring or horseshoe, which then becomes dynamically unstable and breaks down into subvortices, one of which becomes the "parent circulation" of the tornado (Rotunno 1984).…”

mentioning

confidence: 99%

Low-Level Mesocyclonic Concentration by Nonaxisymmetric Transport. Part I: Supercell and Mesocyclone Evolution

Gaudet

Cotton

2006

Journal of the Atmospheric Sciences

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An idealized simulation of a supercell using the Regional Atmospheric Modeling System (RAMS) was able to produce a low-level mesocyclone near the intersection of the forward-and rear-flank downdrafts. The creation of the low-level mesocyclone is similar to previous studies. After 3600 s, the low-level mesocyclone underwent a period of rapid intensification, during which its form changed from an elongated patch to a compact center. This transition was also accompanied by a sudden decrease in pressure (to 12 mb below that of the neighboring flow), and was found to occur even in the absence of nested grids.It is shown that the stage of strong intensification does not begin aloft, as in the dynamic pipe effect, and then descend to the surface. Rather, the vortex is initiated near the surface, and then builds upward. The process is completed in 5 min, and the final vortex can be clearly distinguished from the larger-scale mesocyclone at the cloud base. The reduction of pressure can be explained as a consequence of the evacuation of mass in the horizontal convergence equation. This is in contrast to axisymmetric models of vortex intensification, which generally rely on the evacuation of mass in the vertical divergence equation. In the latter cases a positive horizontal convergence tendency is what initiates the concentrated vortex. However, nondivergent models prove that vorticity concentration can occur in the absence of any horizontal convergence. Here the concentration is associated with a negative horizontal convergence tendency.

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Streamwise Vorticity Effects on Supercell Morphology and Persistence

Cited by 37 publications

References 0 publications

Wintertime Supercell Thunderstorms in a Subtropical Environment: A Diagnostic Study

Wintertime Supercell Thunderstorms in a Subtropical Environment: A Diagnostic Study

Distribution of Helicity, CAPE, and Shear in Tropical Cyclones

Low-Level Mesocyclonic Concentration by Nonaxisymmetric Transport. Part I: Supercell and Mesocyclone Evolution

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