Initiation of Deep Convection along Boundary Layer Convergence Lines in a Semitropical Environment

Fankhauser, J. C.; Cṙook, N. Andrew; Tuttle, John D.; Miller, L. Jay; Wade, Charles G.

doi:10.1175/1520-0493(1995)123<0291:iodcab>2.0.co;2

Cited by 61 publications

(31 citation statements)

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“…One phenomenon that bares some similarity to the triggering of convection ahead of an advancing density current (e.g., Simpson et al 1980) is the effect of sea-breeze front (SBF), which in Florida has been studied extensively (e.g., Pielke 1974;Wakimoto and Atkins 1994;Kingsmill 1995). In several studies, deep convection (often associated with roll clouds) can be initiated at a short distance (within about 20 km) ahead of the advancing SBF (e.g., Nicholls et al 1991;Fovell and Dailey 2001), or before the collision with an outflow boundary (e.g., Fankhauser et al 1995).…”

Section: Discussionmentioning

confidence: 99%

Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

2011

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In this study, the heavy-rainfall event over central Taiwan during the mei-yu season on 8 June 2007 is investigated, with an emphasis on the triggering mechanism for the deep convection that produced the rain. Observations indicate that there existed two lines of forcing with convection prior to the rain: one over the northern Taiwan Strait along the mei-yu front and the other over the southern Taiwan Strait. Yet, the convection in question developed over the central strait between these two lines, in an unstable environment with strong westerly vertical wind shear. This motivated the authors to carry out the present study.The Cloud-Resolving Storm Simulation (CReSS) of Nagoya University was used and the event was reproduced at a horizontal grid size of 2 km, including the initiation of new convection over the central strait at the correct location and time. The model results suggest a crucial role played by the series of active, persistent, and propagating storms in the southern strait (along the aforementioned second forcing line). On their back (northern) side, these storms repeatedly produced pulses of cold outflow that traveled toward the north-northeast with positive pressure perturbation. With characteristics of gravity waves, the perturbation propagated faster than the cold air and the associated increase in forward-directed (horizontal) pressure gradient force led to northward acceleration of near-surface flow (by up to 4-5 m s 21 h 21 ). The stronger southerly flow in turn enhanced downstream convergence, and the deep convection was triggered in the central strait near the arrival of the gravity wave ahead of the cold air. When the convection moved eastward over Taiwan, heavy rainfall resulted. The mechanism presented here for remote triggering of convection over the ocean has not been documented near Taiwan during the mei-yu season. With a better understanding about the behavior of convection, these results can contribute to the improvement of quantitative precipitation forecasts and hazard prevention and reduction.

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Section: Discussionmentioning

confidence: 99%

Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

2011

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“…Before proceeding further it is necessary to introduce a quantitative measure of roll properties including roll orientation, wavelength, and linearity. A two-dimensional correlation analysis on vertical velocity (w) fields, as described by Weckwerth et al (1999) and Fankhauser et al (1995) is used (however, in this study, all the correlation analysis are performed on vertical velocity fields in a Cartesian coordinate system, rather than a polar coordinate system). The vertical velocity (w) field in any x-y slice can be treated as a linear wave in the roll case, so the correlation between w and a cosine function of the form cos(2 x/), where x is the distance in the cross-roll direction from one grid point to the next one, can be used to determine the orientation and wavelength of rolls.…”

Section: Factors Controlling the Formation And Breakup Of Rollsmentioning

confidence: 99%

A Comparison of Roll and Nonroll Convection and the Subsequent Deepening Moist Convection: An LEM Case Study Based on SCMS Data

Huang

Marsham

Parker

et al. 2009

Monthly Weather Review

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Rolls observed during the Small Cumulus Microphysical Study (SCMS) field campaign are simulated using a large eddy model (LEM). The simulated boundary layer properties were in a good agreement with sounding profiles and aircraft observations, and the observed boundary layer rolls were reproduced by the model. Rolls started to decay when ϪZ i /L exceeded a threshold, with a value between 5 and 45. Here Z i and L refer to the height of the top of convective boundary layer and the Monin-Obukhov length, respectively. This value was found to depend on a nondimensional combination of the low-level wind shear, the height of the CBL, and the eddy velocity scale. Larger surface buoyancy fluxes and smaller shears gave higher thresholds. For the case modeled, rolls persisted for surface buoyancy fluxes less than 110 W m Ϫ2 , and formed for boundary layer wind shears greater than 5 ϫ 10 Ϫ3 s Ϫ1 , which is consistent with previous studies.The simulated roll convection was compared with a nonroll simulation, which was identical except for the wind and the wind shear used. In both the roll and nonroll cases the variability in convective inhibition (CIN) was dominated by the variability in the source air, rather than the lifting of the top of the boundary layer by the convection. Stronger moist updrafts existed in the nonroll convection, whereas roll convection gave a more symmetrical distribution of up and downdrafts, with stronger downdrafts than the nonroll case. The nonroll convection simulations have lower minimum values of CIN and clouds develop 15 min earlier in this case.

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“…More information on the CaPE experiment and its data sources can be found in Atkins et al (1995), Frankhauser et al (1995, Kingsmill (1995), Laird et al (1995), Wakimoto and Kingsmill (1995), Yuter and Houze (1995), Weckwerth et al (1996), Wilson and Megenhardt (1997), Weckwerth (2000), and Kingsmill and Crook (2003) among other studies. The key observing systems used in this investigation are the CP3 and CP4 Doppler radar systems operated by the National Center for Atmospheric Research (NCAR) and the FL2 Doppler radar system sponsored by the Federal Aviation Administration (FAA).…”

Section: Observing Systems and Data Processingmentioning

confidence: 99%

Misocyclone Characteristics along Florida Gust Fronts during CaPE

Friedrich

Kingsmill

Young

2005

Monthly Weather Review

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Multiple-Doppler radar and rawinsonde data are used to examine misocyclone characteristics along gust fronts observed during the Convection and Precipitation/Electrification (CaPE) project in Florida. The objective of this study is to investigate the observational representativeness of previous numerical simulations of misocyclones by employing a consistent analysis strategy to 11 gust fronts observed in the same region. The investigation focuses on the intensity range of misocyclones and their organization along gust fronts; the relationship between misocyclone intensity and horizontal wind shear, vertical wind shear, and static stability; and the relationship between misocyclones and convection initiation.The intensity of misocyclones, as indicated by the maximum values of vertical vorticity, varied from 2.8 ϫ 10 Ϫ3 to 13.9 ϫ 10 Ϫ3 s Ϫ1 , although all but one case exhibited values less than 6.4 ϫ 10 Ϫ3 s Ϫ1 . Organized misocyclone patterns were only found along small segments of gust fronts. Within those segments misocyclones were spaced between 3 and 7 km. Results show that the intensity of misocyclones was most closely related to the strength of horizontal wind shear across the gust front. The relationship between misocyclone intensity and vertical wind shear and static stability was not as clear. Although convection was initiated along the gust front in 7 of the 11 cases, those regions were not collocated with or in close proximity to misocyclones.

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Initiation of Deep Convection along Boundary Layer Convergence Lines in a Semitropical Environment

Cited by 61 publications

References 0 publications

Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

A Comparison of Roll and Nonroll Convection and the Subsequent Deepening Moist Convection: An LEM Case Study Based on SCMS Data

Misocyclone Characteristics along Florida Gust Fronts during CaPE

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