Mesoscale Convective Vortex Formation in a Weakly Sheared Moist Neutral Environment

Abstract

Idealized simulations of a diabatic Rossby vortex (DRV) in an initially moist neutral baroclinic environment are performed using the fifth-generation National Center for Atmospheric Research-Pennsylvania State University (NCAR-PSU) Mesoscale Model (MM5). The primary objective is to test the hypothesis that the formation and maintenance of midlatitude warm-season mesoscale convective vortices (MCVs) are largely influenced by balanced flow dynamics associated with a vortex that interacts with weak vertical shear. As a part of this objective, the simulated DRV is placed within the context of the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) field campaign by comparing its tangential velocity, radius of maximum winds, CAPE, and shear with the MCVs observed in BAMEX.The simulations reveal two distinct scales of development. At the larger scale, the most rapidly growing moist baroclinic mode is excited, and exponential growth of this mode occurs during the simulation. Embedded within the large-scale baroclinic wave is a convective system exhibiting the characteristic DRV development, with a positive potential vorticity (PV) anomaly in the lower troposphere and a negative PV anomaly in the upper troposphere, and the positive/negative PV doublet tilted downshear with height. The DRV warm-air advection mechanism is active, and the resulting deep convection helps to reinforce the DRV against the deleterious effects of environmental shear, causing an eastward motion of the convective system as a whole.The initial comparisons between the simulated DRVs and the BAMEX MCVs show that the simulated DRVs grew within background conditions of CAPE and shear similar to those observed for BAMEX MCVs and suggest that the same dynamical mechanisms are active. Because the BAMEX field campaign sampled MCVs in different backgrounds of CAPE and shear, the comparison also demonstrates the need to perform additional simulations to explore these different CAPE and shear regimes and to understand their impacts on the intensity and longevity of MCVs. Such a study has the additional benefit of placing MCV dynamics in an appropriate context for exploring their relevance to tropical cyclone formation.

The Integral Role of a Diabatic Rossby Vortex in a Heavy Snowfall Event

“…Given that it has been previously argued that a mesoscale convective vortex in the presence of vertical shear can be thought of as a DRV (Raymond and Jiang 1990;Conzemius et al 2007), it is possible to hypothesize that the DRV growth mechanism played an important role during this stage of the storm evolution.…”

“…On the one hand, diagnosis of a limited number of diabatically generated low-level positive PV anomalies using a PV inversion technique (see Davis and Emanuel 1991, hereinafter DE91) suggests that while moist effects invariably contribute to a more intense disturbance, the basic dry development mechanism is largely unaltered (DE91; Reed et al 1992;Davis 1992;Davis et al 1993;Stoelinga 1996). On the other hand, the DRV concept has been linked with or invoked to account for numerous atmospheric vortex phenomena [e.g., explosive cyclogenesis (Wernli et al 2002 and MM04); mesoscale convective vortices in baroclinic environments (Raymond and Jiang 1990, Davis and Weisman 1994, Jiang and Raymond 1995, and Conzemius et al 2007); squall lines (PT95); and polar lows (Montgomery and Farrell 1992, Fantini and Buzzi 1993, and Mak 1994]. …”

A diagnostic study of convective environment leading to heavy rainfall during the summer monsoon 2010 over Pakistan

“…(1), the MPV is theoretically defined as Benard et al (1992) remark that PV or MPV is a significant dynamical variable to understand the atmospheric flow both at the synoptic scale as well as at the mesoscale. The PV and MPV concepts have been widely used by the researchers in the last several decades to understand their roles in the genesis and development of severe weather system (Emanuel, 1979;Bennetts and Sharp, 1982;Hoskins and Berrisford, 1988;Robinson, 1989;Thorpe, 1985Thorpe, , 1990Gao et al, 1990Gao et al, , 2005Davis and Emanuel, 1991;Montgomery and Farrell, 1993;Davis et al, 1993;Jiang and Raymond, 1995;Stoelinga, 1996;Cho and Cao, 1998;Gray, 1999;Schultz and Schumacher, 1999;Conzemius et al, 2007;Liang et al, 2010;Gray et al, 2011). However, the use of dry PV is only applicable in a dry air, while the use of MPV assumes completely saturated atmosphere, especially, in the rainfall area.…”

Convection-Allowing and Convection-Parameterizing Ensemble Forecasts of a Mesoscale Convective Vortex and Associated Severe Weather Environment

“…Because convection-allowing simulations better depict convective processes (e.g., Weisman et al 2008), this is the type of case in which convection-allowing guidance could be most beneficial relative to guidance using CP. In addition, although many previous works have used numerical modeling to study various aspects of MCV formation and maintenance mechanisms (e.g., Rogers and Fritsch 2001;Davis and Trier 2002;Conzemius et al 2007;DG09), only a few have examined the skill of numerical models in predicting MCVs within an operationally relevant context (e.g., Davis et al 2002;Hawblitzel et al 2007;Xue et al 2009). …”