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Guifu Zhang - One of the best experts on this subject based on the ideXlab platform.
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evolution of microphysical structure of a subtropical Squall line observed by a polarimetric radar and a disdrometer during opacc in eastern china
Journal of Geophysical Research, 2017Co-Authors: Kun Zhao, Hao Huang, Bowen Zhou, Zhonglin Yang, Gang Chen, Mingjun Wang, Lili Xu, Guifu ZhangAbstract:The evolution of the microphysical structures of a subtropical Squall line observed during the Observation, Prediction and Analysis of Severe Convection of China (OPACC) field campaign in Eastern China is documented in this paper. The data collected from a C-band, polarimetric Doppler radar (reflectivity Z, differential reflectivity ZDR, and specific differential phase KDP) and a disdrometer are used to investigate the variations of microphysical characteristics within the convective region during the formative, intensifying, and mature stages of the Squall line. The microphysical characteristics of the Squall line are noticeably different among these three stages. When the Squall line develops from the formative stage to the mature stage, its radar-derived drop-size distribution (DSD) in the convective region evolves from continental-like convection to more maritime-like convection. Contrary to previous studies, the DSD characteristics of a convective line may not be simply locked to a geographical location but varied extensively throughout its life cycle. The polarimetric radar derived liquid water content below the freezing level in the convective region is three times higher than the ice water content above the freezing level. This, in conjunction with a low cloud base (~0.68 km) and a high freezing level (~5 km), indicates a deep warm cloud layer and the dominance of the warm rain process within this Squall line.
Matthew D Parker - One of the best experts on this subject based on the ideXlab platform.
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observations of a Squall line and its near environment using high frequency rawinsonde launches during vortex2
Monthly Weather Review, 2010Co-Authors: George H Bryan, Matthew D ParkerAbstract:Abstract Rawinsonde data were collected before and during passage of a Squall line in Oklahoma on 15 May 2009 during the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). Nine soundings were released within 3 h, allowing for unprecedented analysis of the Squall line’s internal structure and nearby environment. Four soundings were released in the prestorm environment and they document the following features: low-level cooling associated with the reduction of solar isolation by a cirrus anvil; abrupt warming (1.5 K in 30 min) above the boundary layer, which is probably attributable to a gravity wave; increases in both low-level and deep-layer vertical wind shear within 100 km of the Squall line; and evidence of ascent extending at least 75 km ahead of the Squall line. The next sounding was released ∼5 km ahead of the Squall line’s gust front; it documented a moist absolutely unstable layer within a 2-km-deep layer of ascent, with vertical air velocity of approximately 6 m s−1...
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relationship between system slope and updraft intensity in Squall lines
Monthly Weather Review, 2010Co-Authors: Matthew D ParkerAbstract:In recent years there has been debate about whether Squall lines have an ‘‘optimal state.’’ It has been repeatedly demonstrated that the slope of a Squall line’s convective region is related to the comparative magnitudes of the Squall line’s cold pool and the base-state vertical wind shear. The present work addresses a related assertion, that Squall-line intensity ought to be maximized for an upright updraft zone. A simple demonstration shows that upright systems realize more of their buoyancy because their attendant downwarddirected perturbation pressure gradient accelerations are weaker.
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a multimodel assessment of rkw theory s relevance to Squall line characteristics
Monthly Weather Review, 2006Co-Authors: George H Bryan, Jason C Knievel, Matthew D ParkerAbstract:Abstract The authors evaluate whether the structure and intensity of simulated Squall lines can be explained by “RKW theory,” which most specifically addresses how density currents evolve in sheared environments. In contrast to earlier studies, this study compares output from four numerical models, rather than from just one. All of the authors’ simulations support the qualitative application of RKW theory, whereby Squall-line structure is primarily governed by two effects: the intensity of the Squall line’s surface-based cold pool, and the low- to midlevel environmental vertical wind shear. The simulations using newly developed models generally support the theory’s quantitative application, whereby an optimal state for system structure also optimizes system intensity. However, there are significant systematic differences between the newer numerical models and the older model that was originally used to develop RKW theory. Two systematic differences are analyzed in detail, and causes for these differences ...
Mitchell W Moncrieff - One of the best experts on this subject based on the ideXlab platform.
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the two dimensional dynamics of west african Squall lines
Quarterly Journal of the Royal Meteorological Society, 2007Co-Authors: Jimy Dudhia, Mitchell W Moncrieff, D W K SoAbstract:The two-dimensional dynamics of multicell and unicell Squall lines are examined using a numerical model. Both types feature a convective jump updraught with extensive, deep, rearward-extending anvils. the multicell case contains travelling convection cells and is unsteady but persistent, whereas the unicell case is quasi-steady. In the multicell case, an extensive density current is produced by the evaporation and drag of rain falling from a succession of convection cells which travel rearwards relative to the density current head. the circulation within the density current is complex and consists of three mutually interactive branches: a rotor, a cold downdraught, and a subsidence region. In the unicell case, a density current is not produced and the updraught is forced by a propagating wave of elevation, generated as an interaction between the updraught, water loading and evaporation in a very localized area. The Squall line structure is compared with other models and it is shown that certain propagating two-dimensional tropical and mid-latitude Squall lines are dynamically similar, their detailed structure being controlled by the inflow wind profile. The multicell case is compared with a quasi-two-dimensional West African Squall line which occurred on 22 June 1981 during the Convection Profonde Tropicale (COPT 81) experiment performed in the northern part of the Ivory Coast. Good agreement is found between the model and the observations, and hence the dynamics of the observed Squall line is quantified. the unicell case, in which a density current and conventional downdraughts are absent, has yet to be identified in atmospheric observations.
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dynamical influence of microphysics in tropical Squall lines a numerical study
Monthly Weather Review, 1997Co-Authors: Mitchell W Moncrieff, Edward J ZipserAbstract:Abstract Based on environmental conditions of the 22 and 23 June Squall lines during the Convection Profonde Tropicale in 1981 (COPT81) experiment in West Africa, a series of numerical simulations are performed with a two-dimensional nonhydrostatic cloud model to examine the dynamical effect of microphysics in tropical Squall lines. The role of ice-phase microphysics strongly depends on ambient conditions. For the environment of strong convective instability, the ice phase is important regarding the system-scale structure but is not important to the convective-scale dynamics. On the other hand, the ice influence is crucial to the Squall-line convective system if the environment has a weak convective instability and is almost saturated at low levels.
Yunji Zhang - One of the best experts on this subject based on the ideXlab platform.
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general features of Squall lines in east china
Monthly Weather Review, 2013Co-Authors: Zhiyong Meng, Yunji ZhangAbstract:AbstractBased on mosaics of composite radar reflectivity patterns during the 2-yr period of 2008–09, a total of 96 Squall lines were identified in east China with a maximum frequency of occurrence in north China near the boundaries between Shandong, Henan, Anhui, and Jiangsu Provinces. The Squall lines form from March to October with a peak in July. Their diurnal variation shows a major peak in the early evening and two minor peaks in the early morning and early afternoon. The time between Squall-line formation and the first echo is about 4.8 h. The Squall lines have a dominant southwest–northeast orientation, an eastward motion at a speed of 14.4 m s−1, a maximum length of 243 km, a maximum intensity of 58–63 dBZ, and a duration of 4.7 h on average. The Squall lines commonly form in a broken-line mode, display a trailing-stratiform pattern, and dissipate in a reversed broken-line mode. Composite rawinsonde analyses show that Squall lines in midlatitude east China tend to form in a moister environment wit...
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on the Squall lines preceding landfalling tropical cyclones in china
Monthly Weather Review, 2012Co-Authors: Zhiyong Meng, Yunji ZhangAbstract:AbstractBased on a 3-yr (2007–09) mosaic of radar reflectivity and conventional surface and synoptic radiosonde observations, the general features of Squall lines preceding landfalling tropical cyclones (TCs) (pre-TC) in China are examined and compared with their midlatitude and subtropical counterparts. The results show that about 40% of landfalling TCs are associated with pre-TC Squall lines with high-occurring frequency in August and from late afternoon to midnight. Most pre-TC Squall lines form in a broken-line mode with a trailing-stratiform organization. On average, they occur about 600 km from the TC center in the front-right quadrant with a maximum length of 220 km, a maximum radar reflectivity of 57–62 dBZ, a life span of 4 h, and a moving speed of 12.5 m s−1. Pre-TC Squall lines are generally shorter in lifetime and length than typical midlatitude Squall lines.Pre-TC Squall lines tend to form in the transition area between the parent TC and subtropical high in a moist environment and with a weak...
D W K So - One of the best experts on this subject based on the ideXlab platform.
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the two dimensional dynamics of west african Squall lines
Quarterly Journal of the Royal Meteorological Society, 2007Co-Authors: Jimy Dudhia, Mitchell W Moncrieff, D W K SoAbstract:The two-dimensional dynamics of multicell and unicell Squall lines are examined using a numerical model. Both types feature a convective jump updraught with extensive, deep, rearward-extending anvils. the multicell case contains travelling convection cells and is unsteady but persistent, whereas the unicell case is quasi-steady. In the multicell case, an extensive density current is produced by the evaporation and drag of rain falling from a succession of convection cells which travel rearwards relative to the density current head. the circulation within the density current is complex and consists of three mutually interactive branches: a rotor, a cold downdraught, and a subsidence region. In the unicell case, a density current is not produced and the updraught is forced by a propagating wave of elevation, generated as an interaction between the updraught, water loading and evaporation in a very localized area. The Squall line structure is compared with other models and it is shown that certain propagating two-dimensional tropical and mid-latitude Squall lines are dynamically similar, their detailed structure being controlled by the inflow wind profile. The multicell case is compared with a quasi-two-dimensional West African Squall line which occurred on 22 June 1981 during the Convection Profonde Tropicale (COPT 81) experiment performed in the northern part of the Ivory Coast. Good agreement is found between the model and the observations, and hence the dynamics of the observed Squall line is quantified. the unicell case, in which a density current and conventional downdraughts are absent, has yet to be identified in atmospheric observations.
