Analysis of a Dryline during IHOP: Implications for Convection Initiation

Abstract

A detailed analysis of a dryline that formed on 22 May 2002 during the International H 2 O Project (IHOP) is presented. The dryline was classified as a null case since air parcels lifted over the convergence boundary were unable to reach the level of free convection preventing thunderstorms from forming. A secondary dryline associated with a distinct moisture discontinuity developed to the west of the primary dryline. The primary dryline exhibited substantial along-frontal variability owing to the presence of misocyclones. This nonlinear pattern resembled the precipitation core/gap structure associated with cold fronts during one of the analysis times although the misocyclones were positioned within the gap regions. Radar refractivity has been recently shown to accurately retrieve the low-level moisture fields within the convective boundary layer; however, its use in forecasting the initiation of convection has been restricted to qualitative interpretations. This study introduces the total derivative of radar refractivity as a quantitative parameter that may improve nowcasts of convection. Although no storms developed on this day, there was a tendency for maxima of the total derivative to be near regions where cumulus clouds were developing near a convergence boundary.

Numerical Study of Horizontal Shear Instability Waves along Narrow Cold Frontal Rainbands

“…The PCs are typically aligned at a clockwise angle with respect to the synoptic-scale cold front (e.g., Hobbs and Persson 1982;Parsons and Hobbs 1983a;Wakimoto and Bosart 2000). Horizontal shear instabilities (HSIs) along the leading edge of a cold front or their coupling with a convective instability have frequently been proposed as mechanisms that lead to the alongfront variability (AFV) of NCFRs (e.g., Matejka 1980;Hobbs and Persson 1982;Moore 1985, Carbone 1982Parsons and Hobbs 1983b;Wakimoto and Bosart 2000;Smart and Browning 2009).…”

Understanding Radar Refractivity: Sources of Uncertainty

“…Since that innovation, radar refractivity experiments have been conducted in the Oklahoma Panhandle (Weckwerth et al 2005;Fabry 2006;Wakimoto and Murphey 2009), northeast Colorado (Roberts et al 2008), and southwest and central Oklahoma (Cheong et al 2008;Heinselman et al 2009;Bodine et al 2010). Moreover, radar refractivity studies have become global, as the United Kingdom (Nicol et al 2008) and France (Boudjabi and Parent du Châtelet 2008) are conducting radar refractivity experiments on operational magnetron radars.…”

“…Several radar refractivity studies have shown that high-resolution refractivity data could potentially improve convection initiation nowcasting by identifying boundaries not observed in reflectivity (Weckwerth et al 2005;Roberts et al 2008) and identifying areas of small-scale moistening unobserved by surface stations (Bodine et al 2010). Wakimoto and Murphey (2009) showed that maxima of the total derivative of radar refractivity (DN/Dt) tended to be collocated with cumulus development. While these studies have identified possible forecasting applications, an operational evaluation of refractivity at the Norman, Oklahoma, Weather Forecast Office (WFO) determined that the utility of refractivity data for forecasting was limited because the WFO had access to relatively high-resolution surface observations from the Oklahoma Mesonetwork (hereinafter ''Mesonet'') ).…”

The coastal convective interactions experiment

“…Previously documented similarities between the gust-front and theoretical gravity currents was also concluded by Wakimoto. More recent studies have confirmed that detached gust fronts continue propagating long after the parent cell dissipates and are critically important for understanding the initiation of new cells through the lifting of boundary layer air (Goff 1975;Nicholls et al 1991;Wakimoto and Murphey 2009) and interactions with PBL circulations (Kingsmill 1995;Wilson and Megenhardt 1997). Simulations of multicell storms by (Fovell and Ogura 1989) showed a systemic relationship between gust front propagation speed and increasing environment shear, with the rear inflow jet contributing to colder subcloud layers and faster propagation.…”

“…The most comprehensive reconstructions are derived from remotely sensed products, including geostationary satellite images of the cloud field (e.g., King et al 2003;Azorin-Molina et al 2009), clear air retrievals from weather radar (e.g., Wilson and Schreiber 1986;Wilson et al 1994), and radar refractivity (Wakimoto and Murphey 2009). Given the significant processing difficulties and limited availability of these datasets across multi-years, the most robust long-term sea breeze climatologies are still developed using weather station sites through the automated detection of changes associated with the arrival of the maritime air mass (Biggs and Graves 1962;Simpson et al 1977;Azorin-Molina et al 2011).…”