On the Mesoscale Structure of Surface Wind and Pressure Fields near Tornadic and Nontornadic Cold Fronts

Abstract

Article:Clark, MR and Parker, DJ (2014) On the mesoscale structure of surface wind and pressure fields near tornadic and nontornadic cold fronts. Monthly Weather Review, 142 (10). https://doi.org/10.1175/MWR-D-13-00395.1 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. ABSTRACTObservations from a mesoscale network of automatic weather stations are analyzed for 15 U.K. cold fronts exhibiting narrow cold frontal rainbands (NCFRs). Seven of the NCFRs produced tornadoes. A timecompositing approach is applied to the minute-resolution data using the radar-observed motion vectors of NCFR precipitation segments. Interpolated onto a 5-km grid, the analyses resolve much of the smallmesoscale structure in surface wind, temperature, and pressure fields. Postfrontal winds varied substantially between cases. Tornadic NCFRs exhibited a near-908 wind veer and little or no reduction in wind speed on NCFR passage; these attributes were generally associated with large vertical vorticity, horizontal convergence, and vorticity stretching at the NCFR. Nontornadic NCFRs exhibited smaller wind veers and/or marked decreases in wind speed across the NCFR, and weaker vorticity, convergence, and vorticity stretching. In at least four tornadic NCFRs, increases in vorticity stretching preceded tornadogenesis. Doppler radar observations of two tornadic NCFRs revealed the development of misocyclones, some tornadic, during the latter stages of vorticity-stretching increase. The presence of cyclonic vortices only, in one case occurring at regular intervals along the NCFR, provides limited circumstantial evidence for horizontal shearing instability (HSI), though other vortex-genesis mechanisms cannot be discounted. Vorticity-stretching increases were associated with coherent mesoscale structures in the postfrontal wind field, which modified the crossfrontal convergence. Where cross-frontal convergence was large, extremely narrow, intense shear zones were observed; results suggest that tornadoes occurred when such shear zones developed in conjunction with conditional instability in the prefrontal environment.

Development of localized damaging wind gusts associated with a frontal wave and mesoscale vortex across south Wales on 18 May 2015

“…Misocyclones have been observed on numerous occasions along cold fronts and other zones of strong horizontal shear, and have occasionally been associated with tornadoes and other instances of highly localized wind damage (e.g. Carbone, , ; Wakimoto and Wilson, ; Clark and Parker, ). The radar‐observed features in the present case are strikingly similar to another well‐documented event on 3 November 2009 (Clark, ).…”

“…In a system-relative reference frame, these flows comprise a convergent, cyclonic flow about the centre of the mesolow (the grey arrows in Figure 10 instances of highly localized wind damage (e.g. Carbone, 1982Carbone, , 1983Wakimoto and Wilson, 1989;Clark and Parker, 2014). The radar-observed features in the present case are strikingly similar to another well-documented event on 3 November 2009 (Clark, 2012).…”

Features of Urban Heat Island in Mountainous Chongqing from a Dense Surface Monitoring Network

“…A proper way is to compare the potential temperature of each station at a same level, but it is infeasible because of lack of surface pressure observations. Here, a simple method based on sounding data is implemented [31]. The near-surface lapse rate at a certain day is firstly calculated, i.e.,…”

“…As a local factor, the urbanization is elucidated to impact near-surface winds in two ways. The first is to increase surface roughness and reduce the wind speed through drag effect, and the second is to enhance the downward transport of momentum and strength the near-surface winds through vertical mixing [31]. The observed mean wind speed at urban sites is generally lower than the rural throughout the day (Figure 6a).…”

The relationships between temperature gradient and wind during cold frontal passages in the eastern United States: a numerical modeling study

“…Sharp gradients in temperature, moisture, precipitation, and wind direction are well-documented (e.g. Brundidge, 1965;Shapiro, 1984;Moore, 1985;Crook, 1987;Smith and Reeder, 1988;Mass and Schultz, 1993;Sanders, 1999;Schultz, 2004;Zhang et al, 2009;Payer et al, 2011;Sinclair et al, 2012;Sinclair, 2013;Clark and Parker, 2014). However, relatively little research is available on the relationships between these quantities -in particular between temperature gradient and wind -along the cold-frontal interface.…”