Moreover, the Coriolis force and strong cold pools were also found favorable for the genesis of strong MVs ( Atkins and St. Conversely, MVs were weak, shallow, and short lived in the case of weak wind shear. Moderate-to-strong vertical wind shear at low to midlevels was found conductive to the formation of strong, deep, and long-lived MVs. Laurent (2009a) through a series of idealized numerical simulations. The impact of ambient wind shear on MV structure and strength was assessed by Weisman and Trapp (2003) and Atkins and St. Low-level MVs were found to originate from downward or upward tilting of baroclinic horizontal vorticity generated along the cold outflow boundary and in general intensify as a result of vertical stretching ( Trapp and Weisman 2003 Atkins and St. In light of their damage potential, MVs within QLCSs have also been studied through high-resolution numerical simulations. (2006) through the investigation of five bow-echo events during BAMEX it was found that most significant wind damage was typically associated with MVs in the bow-echo systems. More observational evidence was provided by Wheatley et al. (2006b) based on airborne Doppler radar analysis of a bow echo observed near Omaha, Nebraska, on 5 July 2003 (also a BAMEX case). The important role of bow-echo MVs in determining the locations of intense straight-line wind damage was also documented by Wakimoto et al. (2005) revealed the strongest winds were associated with MVs. 2004) and detailed radar analyses and damage surveys performed by Atkins et al. This case was observed by the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment (BAMEX Davis et al. This was true in a severe bow echo that occurred near Saint Louis, Missouri, on 10 June 2003. However, the strongest straight-line wind damage may not be directly associated with the RIJ itself, but with low-level MVs along the bow echo, sometimes away from the bow apex. Additionally, the RIJ strength had been found to be sensitive to ice microphysical processes as well as the environmental humidity ( Yang and Houze 1995 Mahoney and Lackmann 2011). Various factors have been implicated in the development of RIJs, such as the hydrostatically induced midlevel pressure minimum behind the leading convective updrafts ( Lafore and Moncrieff 1989), horizontal buoyancy gradients related to the upshear-tilting convective circulation ( Weisman 1992, 1993), and bookend (or line-end) vortices ( Skamarock et al. The production of damaging winds within QLCSs has long been linked to the descent to the surface of a rear-inflow jet (RIJ) at the bow apex ( Fujita 1978, 1979). Moreover, bow-echo MVs have been observed to spawn tornadoes ( Forbes and Wakimoto 1983 Przybylinski 1995). Recently, MVs have received increasing attention, owing to their propensity to produce damaging straight-line winds near the surface ( Weisman and Trapp 2003 Atkins et al. Low-level, meso- γ-scale mesovortices (MVs) are frequently observed at the leading edge of quasi-linear convective systems (QLCSs) like squall lines and bow echoes (e.g., Funk et al. The locally enhanced descent of the rear-inflow jet near the mesovortex is forced primarily by the dynamically induced downward vertical pressure gradient force while the buoyancy force only plays a minor role there. These high winds are mainly caused by the descent of the rear-inflow jet at the bow apex, but the MV-induced vortical flow also has a considerable contribution. Moreover, the model results show that these bow-apex MVs are accompanied with damaging straight-line winds near the surface. MVs located at (or near) the bow apex are found to persist for a notably longer lifetime than the other MVs. Vortex mergers occur between MVs during their forward movement, which causes redevelopment of some MVs in the decaying stage of the bow echo. MVs that develop on the southern bow tend to be weaker and shorter-lived than their northern counterparts. Both the observed and simulated bow-echo MVs predominantly form north of the bow apex. Significant MVs are detected from the radar radial velocity using a linear least squares derivatives (LLSD) method, and from the model simulation based on calculated vorticity. The genesis of near-surface high winds within the system is also investigated. Emphasis is placed on documenting the existence, evolution, and characteristics of low-level mesovortices (MVs) that form along the leading edge of the bowing system. A derecho-producing bow-echo event over the central United States on is analyzed based on radar observations and a successful real-data WRF simulation at 0.8-km grid spacing.
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