Squall

Abstract: This paper describes the two different kinds of downdraft air frequently observed to the rear of some squall lines at low levels. The primary data source is measurements taken during aircraft penetrations of certain low-latitude squall lines; they are supplemented by satellite data, radar data, surface meteorological data, and soundings ahead of and behind the squall lines. A shallow layer of cool, near-saturated air occupies the lowest few hundred meters and is separated by a marked stable layer from a deep layer of highly unsaturated air. The lowest layer is hypothesized to be the product of convective-scale saturated downdrafts, and the drier air is shown to be the result of mesoscale unsaturated downdrafts as described by Zipser (1969). Over a warm ocean, there is a large latent and sensible heat flux from the surface into the lowest layer, which rapidly becomes a new mixed layer and incorporates the drier air from above by entrainment. Mesoscale sinking in the post-squall region is shown to ...

Abstract: A tropical squall-line system which moved over the observational network of the Global Atmospheric Research Programme's Atlantic Tropical Experiment (GATE) was investigated using rawinsonde, weather radar, satellite, surface meteorological, acoustic sounder and cloud photographic data. Combining these data led to a detailed synthesis of the three-dimensional structure, dynamics and life cycle of the disturbance. The squall-line system consisted of a squall line forming the leading edge of the system and a trailing anvil cloud region. The squall line was made up of discrete active centers of cumulonimbus convection, referred to as line elements (LE's). New LE's formed ahead of the squall line. Old LE's weekened toward the rear of the line and blended into the trailing anvil region as they dissipated. Each LE progressed through a period of rapid growth, with echo tops penetrating the tropopause to maximum heights of 16–17 km, then decreasing to heights of 13–14 km, which corresponds to the height o...

Abstract: Idealizedsimulations ofthe 15May2009 squalllinefromthe SecondVerification ofthe OriginsofRotation in Tornadoes Experiment (VORTEX2) are evaluated in this study Four different microphysical setups are used, with either single-moment (1M) or double-moment (2M) microphysics, and either hail or graupel as the dense (rimed) ice species Three different horizontal grid spacings are used: Dx 5 4, 1, or 025 km (with identical vertical grids) Overall, results show that simulated squall lines are sensitive to both microphysical setupandhorizontalresolution,althoughsomequantities(ie,surfacerainfall)aremoresensitiveto Dxinthis study Simulations with larger Dx are slower to develop, produce more precipitation, and have higher cloud tops, all of which are attributable to larger convective cells that do not entrain midlevel air The highestresolution simulations have substantially more cloud water evaporation, which is partly attributable to the development of resolved turbulence For a given Dx, the 1M simulations produce less rain, more intense cold pools, and do not have trailing stratiform precipitation at the surface, owing to excessive rainwater evaporation The simulations with graupel as the dense ice species have unrealistically wide convective regions Comparison against analyses from VORTEX2 data shows that the 2M setup with hail and Dx 5 025 km producesthemostrealisticsimulationbecause(i)thissimulationproducesrealisticdistributionsofreflectivity associatedwithconvective,transition,andtrailingstratiformregions,(ii)thecoldpoolpropertiesarereasonably close to analyses from VORTEX2, and (iii) relative humidity in the cold pool is closest to observations

Abstract: The utility of color displays of Doppler-radar data in revealing real-time kinematic information has been demonstrated in past studies, especially for extratropical cyclones and severe thunderstorms. Such displays can also indicate aspects of the circulation within a certain type of mesoscale convective system—the squall line with trailing “stratiform” rain. Displays from a single Doppler radar collected in two squall-line storms observed during the Oklahoma-Kansas PRE-STORM project conducted in May and June 1985 reveal mesoscale-flow patterns in the stratiform rain region of the squall line, such as front-to-rear storm-relative flow at upper levels, a subsiding storm-relative rear inflow at middle and low levels, and low-level divergent flow associated with strong mesoscale subsidence. “Dual-Doppler” analysis further illustrates these mesoscale-flow features and, in addition, shows the structure of the convective region within the squall line and a mesoscale vortex in the “stratiform” region tra...