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

Abstract

On 24-25 February 2005, a significant East Coast cyclone deposited from 4 to nearly 12 in. (ϳ10-30 cm) of snow on parts of the northeastern United States. The heaviest snowfall and most rapid deepening of the cyclone coincided with the favorable positioning of an upper-level, short-wave trough immediately upstream of a preexisting surface cyclone. The surface cyclone in question formed approximately 15 h before the heaviest snowfall along a coastal front in a region of frontogenesis and heavy precipitation. The incipient surface cyclone subsequently intensified as it moved to the northeast, consistently generating the strongest convection to the east-northeast of the low-level circulation center. The use of potential vorticity (PV) inversion techniques and a suite of mesoscale model simulations illustrates that the early intensification of the incipient surface cyclone was primarily driven by diabatic effects and was not critically dependent on the upper-level wave. These facts, taken in conjunction with the observed structure, energetics, and Lagrangian evolution of the incipient surface disturbance, identify it as a diabatic Rossby vortex (DRV). The antecedent surface vorticity spinup associated with the DRV phase of development is found to be integral to the subsequent rapid growth. The qualitative similarity with a number of observed cases of explosive cyclogenesis leaves open the possibility that a DRV-like feature comprises the preexisting positive low-level PV anomaly in a number of cyclogenetic events that exhibit a two-stage evolution.

Moist versus Dry Baroclinic Instability in a Simplified Two-Layer Atmospheric Model with Condensation and Latent Heat Release

“…First, we confirm the temporal enhancement of the growth rate of the instability due to the condensation that was found by other idealized studies (e.g., Emanuel et al 1987) or case studies (e.g., Wernli et al 2002;Moore et al 2008). Despite this enhancement, we observed that the perturbation energy (diagnosed with different norms) is almost the same after nonlinear saturation of the instability.…”

Numerical Investigation of Development Processes of Baiu Frontal Depressions Part I: Case Studies

“…The NOUL is a simulation without upper-level disturbances. According to Moore et al (2008), upper-level PV anomalies from 500 hPa to the top of the model, which are defined as deviations from the 15-day mean, are excluded from initial and boundary conditions in NOUL using the piecewise PV inversion technique (Davis and Emanuel 1991).…”

Excitation of Deep Convection to the North of Tropical Storm Bebinca (2006)

“…Recent studies have indicated that severe convection is excited by a diabatic Rossby vortex (DRV) in a baroclinic zone (Moore et al 2008;Boettcher and Wernli 2011). Parker and Thorpe (1995) presented the first description of the dynamics of DRVs.…”

“…Using idealized two-and three-dimensional models, theoretical studies of DRVs by Montgomery (2004, 2005) determined that a low-level, moisture-rich baroclinic field is a key environmental condition for excitation of DRV. Moore and Montgomery (2008) and Boettcher and Wernli (2011) conducted case studies of rapidly intensifying extratropical cyclones, and reported that DRV systems are highly significant in these events.…”