TITLE

Low-Level Mesovortices within Squall Lines and Bow Echoes. Part II: Their Genesis and Implications

AUTHOR(S)
Trapp, Robert J.; Weisman, Morris L.
PUB. DATE
November 2003
SOURCE
Monthly Weather Review;Nov2003, Vol. 131 Issue 11, p2804
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
This two-part study proposes a fundamental explanation of the genesis, structure, and implications of low-level, meso-γ-scale vortices within quasi-linear convective systems (QLCSs) such as squall lines and bow echoes. Such “mesovortices” are observed frequently, at times in association with tornadoes. Idealized experiments with a numerical cloud model show that significant low-level mesovortices develop in simulated QLCSs, especially when the environmental vertical wind shear is above a minimum threshold and when the Coriolis forcing is nonzero. As illustrated by a QLCS simulated in an environment of moderate vertical wind shear, mesovortexgenesis is initiated at low levels by the tilting, in downdrafts, of initially crosswise horizontal baroclinic vorticity. Over a 30-min period, the resultant vortex couplet gives way to a dominant cyclonic vortex as the relative and, more notably, planetary vorticity is stretched vertically; hence, the Coriolis force plays a direct role in the low-level mesovortexgenesis. A downward-directed vertical pressure-gradient force is subsequently induced within the mesovortices, effectively segmenting the previously (nearly) continuous convective line. In moderate-to-strong environmental shear, the simulated QLCSs evolve into bow echoes with “straight line” surface winds found at the bow-echo apex and additionally in association with, and in fact induced by, the low-level mesovortices. Indeed, the mesovortex winds tend to be stronger, more damaging, and expand in area with time owing to a mesovortex amalgamation or “upscale” vortex growth. In weaker environmental shear—in which significant low-level mesovortices tend not to form—damaging surface winds are driven by a rear-inflow jet that descends and spreads laterally at the ground, well behind the gust front.
ACCESSION #
11280259

 

Related Articles

  • Hook Echoes and Rear-Flank Downdrafts: A Review. Markowski, Paul M. // Monthly Weather Review;Apr2002, Vol. 130 Issue 4, p852 

    Nearly 50 years of observations of hook echoes and their associated rear-flank downdrafts (RFDs) are reviewed. Relevant theoretical and numerical simulation results also are discussed. For over 20 years, the hook echo and RFD have been hypothesized to be critical in the tornadogenesis process....

  • Low-Level Mesovortices within Squall Lines and Bow Echoes. Part I: Overview and Dependence on Environmental Shear. Weisman, Morris L.; Trapp, Robert J. // Monthly Weather Review;Nov2003, Vol. 131 Issue 11, p2779 

    This two-part study proposes fundamental explanations of the genesis, structure, and implications of low-level meso-γ-scale vortices within quasi-linear convective systems (QLCSs) such as squall lines and bow echoes. Such “mesovortices” are observed frequently, at times in...

  • Heat, Moisture, and Momentum Budgets of Isolated Deep Midlatitude and Tropical... Schlesinger, Robert // Journal of the Atmospheric Sciences;10/15/99, Vol. 56 Issue 20, p3520 

    Presents information on a study which evaluated the feedback of isolated deep convective clouds over a horizontal scale comparable to one grid cell in typical mesoscale numerical prediction models. Sensitivity of the feedback to modest changes in the initial vertical wind shear intensity and...

  • Probability of Tornado Occurrence across Canada*. Cheng, Vincent Y. S.; Arhonditsis, George B.; Sills, David M. L.; Auld, Heather; Shephard, Mark W.; Gough, William A.; Klaassen, Joan // Journal of Climate;Dec2013, Vol. 26 Issue 23, p9415 

    The number of tornado observations in Canada is believed to be significantly lower than the actual occurrences. To account for this bias, the authors propose a Bayesian modeling approach founded upon the explicit consideration of the population sampling bias in tornado observations and the...

  • Thick Anvils as Viewed by the TRMM Precipitation Radar. Wei Li; Schumacher, Courtney // Journal of Climate;Mar2011, Vol. 24 Issue 6, p1718 

    This study investigates anvils from thick, nonprecipitating clouds associated with deep convection as observed in the tropics by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) during the 10-yr period, 1998--2007. Anvils observable by the PR occur, on average, 5 out of...

  • Cold-Frontal Potential Vorticity Maxima, the Low-Level Jet, and Moisture Transport in Extratropical Cyclones. Lackmann, Gary M. // Monthly Weather Review;Jan2002, Vol. 130 Issue 1, p59 

    An elongated cold-frontal maximum in the lower-tropospheric potential vorticity (PV) field accompanies some midlatitude cyclones. These PV maxima are often of diabatic origin, and are hypothesized to contribute substantially to the strength of the low-level jet (LLJ) and moisture transport in...

  • Environmental Vertical Wind Shear with Hurricane Bertha (1996). Zehr, Raymond M. // Weather & Forecasting;Apr2003, Vol. 18 Issue 2, p345 

    Hurricane Bertha (1996) was influenced by vertical wind shear with highly variable direction and magnitude. The paper describes a unique method for determining the vertical tilt of a tropical cyclone vortex using satellite and aircraft data. Hurricane Bertha's vortex tracks at three levels are...

  • Microburst Detection Using Agent Networks. Dance, Sandy; Potts, Rodney // Journal of Atmospheric & Oceanic Technology;May2002, Vol. 19 Issue 5, p646 

    Focuses on a study which discussed the automatic detection of microbursts from Doppler and reflectivity radar data using agent networks. Information on microbursts; Description of agent networks in image processing; Information on the agent network architecture; Conclusions.

  • Cloud-environment interface instability. Part III: Direct influence of environmental shear. Grabowski, Wojciech W.; Clark, Terry L. // Journal of the Atmospheric Sciences;12/1/93, Vol. 50 Issue 23, p3821 

    Investigates the direct effect of vertical shear of the horizontal wind for the unperturbed environment on the cloud-environment interface instability. Review of related literature; Assumptions of the numerical model; Consideration of thermal rising in a shear environment.

Share

Read the Article

Courtesy of THE LIBRARY OF VIRGINIA

Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics