Multi-sensor observations of a wave beneath an impacting rear-inflow jet in an elevated mesoscale convective system

Marsham, John H.; Browning, K. A.; Nicol, John; Parker, Douglas J.; Norton, E. G.; Blyth, Alan; Corsmeier, U.; Perry, Felicity

doi:10.1002/qj.669

Cited by 22 publications

(57 citation statements)

References 47 publications

(82 reference statements)

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“…Evaporative cooling in the wide cold frontal rainband (e.g., Matejka et al 1980;Ferris 1989;Browning 1990), is one mechanism by which stronger postfrontal winds could develop; locally enhanced cooling and associated descent could increase low-level divergence behind the line, thereby increasing rear inflow in the zone between the region of maximum divergence and the NCFR. The existence of a stronger pressure surge behind the NCFR in the type-A LV cases (Table 1) would be consistent with the idea of stronger evaporative cooling in these cases than for type-B events, since hydrostatic pressure increases would be expected where cooling occurs, and possibly even nonhydrostatic pressure increases, as described by Marsham et al (2010). The mean value, over the seven type-A LV cases analyzed, of the largest observed pressure increase over a line-normal distance of 10 km postfront was 2.61 hPa.…”

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confidence: 79%

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

Clark

Parker

2014

Monthly Weather Review

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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.

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confidence: 79%

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

Clark

Parker

2014

Monthly Weather Review

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“…It was probably also influenced by the combined effects of MCS B and another MCS behind it. It has been shown by Marsham et al (2010) that gravity waves associated with another MCS on this day caused considerable variation in the depth of the undercurrent near the core of that MCS, as well as strengthening the shear and triggering billows behind the storm. In that case, the billows were observed near where the depth of the undercurrent was reduced by an impacting rear-inflow jet; in the present case, however, the billows occurred in an area where the undercurrent was deepening.…”

Section: Effect Of Deepening Undercurrent On Elevated Convectionmentioning

confidence: 90%

“…Several MCSs are depicted in this figure. The MCS analysed by Browning et al (2010) and Marsham et al (2010), which they designated MCS C, is the one in the bottom left-hand corner, mostly beyond the range circle during this period. The billows analysed in the present paper were associated with an earlier MCS, referred to as MCS B.…”

Section: Location and Extent Of The Billowsmentioning

confidence: 97%

“…This was so on the occasion studied by Browning et al (2010) and Marsham et al (2010). They focused on a single intense MCS for which the billows appeared to be a secondary issue; however, another MCS on the same day was associated with a large coherent patch of billows that appeared to be interacting with overlying elevated convection.…”

Section: Introductionmentioning

confidence: 99%

“…There have been many studies of KH billows, both in the clear air, where they are responsible for clear air turbulence (CAT), and in cloud and precipitation. Recent examples of situations in which billows were observed within precipitation include the studies of a wintertime storm by Houser and Bluestein (2011) and of a summertime mesoscale convective system (MCS) by Browning et al (2010) and Marsham et al (2010).…”

Section: Introductionmentioning

confidence: 99%

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A case study of a large patch of billows surmounted by elevated convection

Browning¹,

Marsham²,

White³

et al. 2012

Quart J Royal Meteoro Soc

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A region of large-amplitude Kelvin-Helmholtz billows, of area 2000 km2 , was observed in a region of moderate rain at the rear of a mesoscale convective system on a day during the Convective Storm Initiation Project in southern England. The mesoscale convective system (MCS) was characterized by elevated convection above a layer of cool air, separated by a sloping statically stable layer characterized by strong wind shear. Doppler radar observations showed that the large patch of billows was situated within this shear layer and that it persisted over the 2 h period of observation, maintaining its position with respect to the MCS and producing surface pressure perturbations of ± 0.3 hPa. Potentially unstable air above the sloping shear layer reached its level of free convection while ascending above this layer. The resulting elevated convection was in the form of cells whose spacing appeared to be influenced by the underlying billows. Results from large-eddy model simulations are shown to support the hypothesis that, although the large-scale ascent alone would have triggered the elevated convection, the billows exerted a secondary forcing effect on the convection.

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Precipitation

2016

Hydrometeorology

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Multi-sensor observations of a wave beneath an impacting rear-inflow jet in an elevated mesoscale convective system

Cited by 22 publications

References 47 publications

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

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

A case study of a large patch of billows surmounted by elevated convection

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