The Role of Boundary-Layer Convergence Zones and Horizontal Rolls in the Initiation of Thunderstorms: A Case Study

Wilson, James W.; Foote, G. Brant; Cṙook, N. Andrew; Fankhauser, J. C.; Wade, Charles G.; Tuttle, John D.; Mueller, Cynthia K.; Krueger, Steven K.

doi:10.1175/1520-0493(1992)120<1785:troblc>2.0.co;2

Cited by 123 publications

(88 citation statements)

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“…Many studies have demonstrated that misocyclones along air mass boundaries distort the boundaries and produce local maxima of low-level convergence and vertical velocity in their vicinity, which often could be preferred regions to form clouds and/or radar reflectivity cores (e.g., Wilson et al 1992;Atkins et al 1995;Lee and Wilhelmson 1997b;Friedrich et al 2005;Arnott et al 2006;Murphey et al 2006;Marquis et al 2007;Wakimoto and Murphey 2009). Although well-defined vortices with quasi-circular vorticity contours do not develop in the present simulations, it is suggested that in the U15-S2 and U20-S2 cases the concentrated vertical vorticity distorted the horizontal wind field and enhanced the low-level convergence in the vicinity of the vorticity maxima, leading to formation of the precipitation maxima north of the bow apexes.…”

Section: ) Stably Stratified Casesmentioning

confidence: 99%

Numerical Study of Horizontal Shear Instability Waves along Narrow Cold Frontal Rainbands

Kawashima

2011

Journal of the Atmospheric Sciences

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The effects of variations in low-level ambient vertical shear and horizontal shear on the alongfront variability of narrow cold frontal rainbands (NCFRs) that propagate into neutral and slightly unstable environments are investigated through a series of idealized cloud-resolving simulations.In cases initialized with slightly unstable sounding and weak ambient cross-frontal vertical shears, core-gap structures of precipitation along NCFRs occur that are associated with wavelike disturbances that derive their kinetic energy mainly from the mean local vertical shear and buoyancy. However, over a wide range of environmental conditions, core-gap structures of precipitation occur because of the development of a horizontal shear instability (HSI) wave along the NCFRs.The growth rate and amplitude of the HSI wave decrease significantly as the vertical shear of the ambient cross-front wind is reduced. These decreases are a consequence of the enhancement of the low-level local vertical shear immediately behind the leading edge. The strong local vertical shear acts to damp the vorticity edge wave on the cold air side of the shear zone, thereby suppressing the growth of the HSI wave through the interaction of the two vorticity edge waves. It is also noted that the initial wavelength of the HSI wave increases markedly with increasing horizontal shear. The local vertical shear around the leading edge is shown to damp long HSI waves more strongly than short waves, and the horizontal shear dependency of the wavelength is explained by the decrease in the magnitude of the vertical shear relative to that of the horizontal shear.

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Section: ) Stably Stratified Casesmentioning

confidence: 99%

Numerical Study of Horizontal Shear Instability Waves along Narrow Cold Frontal Rainbands

Kawashima

2011

Journal of the Atmospheric Sciences

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“…Besides convection forced by synoptic-scale processes, the boundary-layer conditions often play an important role for both the evolution of the pre-convective environment (Parker, 2002;Khodayar et al, 2010) and the initiation of convective precipitation (Wilson et al, 1992;Weckwerth, 2000;Kottmeier et al, 2008;Hauck et al, 2011). The evolution and state of the convective boundary layer (CBL), in turn, depends considerably on the transformation of the available energy at the Earth's surface into sensible and latent heat fluxes (Stull, 1988;Garratt, 1994).…”

Section: Introductionmentioning

confidence: 99%

The dependence of convection‐related parameters on surface and boundary‐layer conditions over complex terrain

Kalthoff

Köhler

Barthlott

et al. 2010

Quart J Royal Meteoro Soc

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The field campaign 'Convective and Orographically-induced Precipitation Study' (COPS) was performed in south-western Germany and eastern France in summer 2007. Within the COPS context this study focused on the process chain of soil moisture, surface fluxes, conditions of the convective boundary layer (CBL), and convection-related parameters.The results were different for valley and mountain sites. Only in the Rhine valley did the ratios of sensible and latent heat to the net radiation at the surface, H 0 /Q 0 and E 0 /Q 0 respectively, reveal a weak dependence on soil moisture. H 0 /Q 0 was lower and E 0 /Q 0 was higher at higher soil moisture. The correlation of the diurnal increase of the equivalent potential temperature, e , with the energy supplied by H 0 and E 0 was found to be lower for higher surface inhomogeneity. Furthermore, only a weak dependence of the CBL depth on the sensible surface heat flux was found for valley sites and was non-existent for the mountain crest.The convective indices in the whole COPS domain were found to depend on e in the CBL. The absolute values of conditional and potential instability are not necessarily the decisive parameters for convection to occur, because highest instability was observed in the Rhine valley while convection was preferably initiated over the mountains. Convective inhibition (CIN) was positively correlated with the capping strength and negatively with the CBL height: the higher the CBL, the lower the upper threshold of CIN. The frequency of low CIN was higher in the Black Forest mountains than in the Rhine valley, which facilitates convection initiation over the mountain sites.

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“…These radars also record echoes in the optically clear boundary layer (e.g., Clothiaux et al 2000), as do the operational scanning weather radars, which are centimeter wave. These clear-air echoes occur mainly in the warm season and mainly over land (Wilson et al 1994). They are a nuisance for radar-based studies of continental boundary layer clouds since they may contaminate the true cloud echo and hide the cloud base (e.g., Martner and Moran 2001).…”

Section: Introductionmentioning

confidence: 99%

The Use of Millimeter Doppler Radar Echoes to Estimate Vertical Air Velocities in the Fair-Weather Convective Boundary Layer

Geerts

Miao

2005

Journal of Atmospheric and Oceanic Technology

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Vertical velocity characteristics of the optically clear convective boundary layer (CBL) are examined by means of profiling airborne radar data collected in the central Great Plains during the International H 2 O Project, May-June 2002 (IHOP 2002. Clear-air echoes are sufficiently strong for the radar, a 95-GHz cloud radar, to detect most of the CBL at a resolution of ϳ30 m. Vertical radar transects across the CBL are remarkably dominated by well-defined plumes of higher reflectivity. These echo plumes occupy most of the depth of the CBL in the developing and mature stages of the CBL. Gust probe data indicate that the plumes tend to correspond with ascending motion. Evidence exists in the literature, and arises from this study, that the clear-air scatterers are mostly small insects.The close-range Doppler radar velocities, some 100 m above and below the aircraft, are compared to gust probe vertical velocities after both are corrected for aircraft motion.It is found that the radar vertical velocities have a downward bias of 0.5 Ϯ 0.2 m s Ϫ1 on average. This bias is of the same sign as that reported in wind profiler data in the CBL, but it is larger. The difference between aircraft and radar vertical velocities becomes larger in stronger updrafts. This does not happen in cases where the scatterers are hydrometeors: hydrometeors fall out at their terminal velocity, which does not directly depend on updraft speed.The existence of the CBL echo plumes and radar "fine lines," sustained by low-level air convergence, has long been attributed to a biotic response to updrafts. This response has been assumed to be controlled by air temperature; that is, insects subside when they encounter cold air in the upper CBL. The authors propose that the biotic response is not temperature controlled but, rather, is dependent on the vertical displacement.

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The Role of Boundary-Layer Convergence Zones and Horizontal Rolls in the Initiation of Thunderstorms: A Case Study

Cited by 123 publications

References 0 publications

Numerical Study of Horizontal Shear Instability Waves along Narrow Cold Frontal Rainbands

Numerical Study of Horizontal Shear Instability Waves along Narrow Cold Frontal Rainbands

The dependence of convection‐related parameters on surface and boundary‐layer conditions over complex terrain

The Use of Millimeter Doppler Radar Echoes to Estimate Vertical Air Velocities in the Fair-Weather Convective Boundary Layer

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