@InProceedings{RibeiroSelu:2015:AnSe'c,
author = "Ribeiro, Bruno Zanetti and Seluchi, Marcelo Enrique",
affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto
Nacional de Pesquisas Espaciais (INPE)}",
title = "Analysis of a severe 'comma-shaped' bow echo in southern Brazil",
year = "2015",
organization = "Conference on Mesoscale Processes, 16.",
abstract = "On 19 October 2014, a squall line with an embedded 'comma-shaped'
bow echo (inverted comma in Southern Hemisphere) impacted Southern
Brazil, causing material damage due to severe straight-line winds.
The damaging-wind path and duration suggest this event was a
derecho. Storm morphology was analyzed using a S-band radar in the
city of Santiago, Southern Brazil. Synoptic and thermodynamic
environments were analyzed through surface stations and sounding
data, as well as the CFSR reanalysis fields preceding the event.
Several intense storms formed along an outflow boundary over
Northern Argentina, where a tornado was reported, and then moved
east toward Brazil organized as a squall line. Most severe wind
gusts were associated with embedded bow echoes, and the most
intense measured gust, of 60 kt, occurred near the head of the
comma-shaped bow echo. Moreover, the damage registered in some
locations lead to estimates of 80-100 kt wind gusts. The squall
line formed under weak forcing, in the left entrance of an
upper-level jet streak and ahead of a surface cold front. A
sounding launched just before the squall line passage showed
intense low-level vertical wind shear (17 m/s 0-1-km and 15 m/s
0-3-km line-perpendicular shear), favoring bowing segments within
the squall line. Below approximately 2.5 km above ground level the
shear was mostly directional, becoming predominantly a speed shear
above this height. Most unstable CAPE was 2100 J/kg, indicating
moderate thermodynamic instability, but precipitable water was
more than 50 mm, which favors heavy precipitation and strong cold
pools. 250-hPa winds of more than 85 kt were observed, coherent
with a leading-line propagation at approximately 50 kt. The
comma-shaped bow echo formed in response to strengthening of the
cyclonic bookend vortex associated with the bow echo. The
high-precipitation supercell responsible for the tornado in
Argentina possibly provided cyclonic vorticity to the bookend
vortex. The supercell formed before the squall-line organization
and may have played an important role in creating the cold pool
responsible for driving the system. Evolution of the comma-shaped
system follows theoretical models for the Northern Hemisphere. The
bowing segment moved faster than other sectors of the squall line,
which might have been caused by acceleration of the Rear-Inflow
Jet. After bookend vortex formation, the northern flank of the
squall line caused wind gusts of more than 50 kt in other
locations, while the southern flank weakened, causing wind gusts
of less than 25 kt. This study describes a classic case of a
strong comma-shaped bow echo embedded in a squall line, and it is
the first of this kind realized in Southern Brazil. Future work on
numerical simulations of bow echoes is required to elucidate the
behavior of these systems in this region.",
conference-location = "Boston, MA",
conference-year = "3-6 Aug.",
urlaccessdate = "27 abr. 2024"
}