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What is a Bow Echo?• Bowing pattern on radar
• Severe straight-line winds at the surfaceo Cause about 1/3 severe wind reports in US
• Have a specific structure with rear-inflow jet reaching the surface
• Originate from various storm modes
• Typically need >2,000J/kg CAPE
• Move quickly and acceleratehttp://www.crh.noaa.gov/dmx/?n=preparesvrintro
StructureNote:• Strong rear inflow
jet reaching the surface
• Mid-level low pressure
• Surface high pressure (by cold pool)
• Most lift near leading edge of cold pool = strongest updrafts
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Cross section taken from case-study of June 10, 2003 bow echo during near NE/IA border during BAMEX (Bow Echo and Mesoscale Convective Vortex Experiment)
Initial Stages and Types
• BE = classic bow echo• BEC = bow echo complex
(bow echo with other storm type embedded, ie. supercell)
• CBE = cell bow echo (small scale bow echo)
• SLBE = squall line bow echo, also known as line echo wave pattern. Part of elongated linear convective system.Klimowski et al. 2004
Kilmowski et al. Data and Summary
• Used 273 scenarios between 1996-2003 in US
• More squall line bow echoes as you head further east
• Thunderstorm mergers likely to play a role in BE development - consolidating cold pools, but need more data• Also suggests that when initial cell that merges with another,
the speed and direction is maintained by BE
• Average life span higher further south in the plains• CAPE and LLJ could be the reasoning for this – easier to get
widespread high value CAPEs in the region and a strong low-level jet
Mesovortices• Play a role in the production of straight-line winds
and even tornadoes in bow echo eventso Straight-line winds enhanced on south side of mesovortex because
horizontal pressure gradient
• Most often observed near the apex of the bow
• Depends on the low level wind shear and strength (temperature contrast) of cold pool
• Few to tens of kilometres in size• Observed while rear inflow jets are strengthening• Causes still under research
Mesovortices (cont.)Note:
• The location of the mesovortice, just north of the apex of the bow
• The damaging part of the mesovortex (strongest straight-line winds) is on the south side as it wraps around the descending rear inflow jet Nolan Atkins & St. Laurent 2009
Mesovortice TheoriesTheory 1: o Horizontal vorticity from downdraft gets tilted, stretched by
updraft along gust front creating the vortice
Theory 2: o Along the apex of bow echo stronger updrafts are produced
(by either stronger downdrafts prior, or rear inflow jet)
o Horizontal vorticity just behind gust front is tilted by the stronger updraft, which produces a cyclonic vortice just north of apex and anticyclonic one south of apex• Anticyclonic one not observed as much
Other Bow Echo Characteristics• Can have bookend vortices during mature stage –
also caused by tilting of horizontal vorticity by updrafto Larger in scale than mesovortices
• Bow echoes can become derechos if they have path >400km and meet wind criteria
• Shelf clouds will typically be visible along gust front of bow echo
http://en.wikipedia.org/wiki/Bow_echo#mediaviewer/File:Bow_echo_diagram.svg
Bow Echo Summary• Produce strong winds, sometimes tornadoes
• Rear inflow jet creates the strong winds
• Bow echoes transition from other types of storms, some cases include cold pool consolidation
• Can acquire characteristics that enhance tornado threat and winds locally (mesovortices)
References:• Atkins, N. T & St. Laurent, M. (2009). Bow Echo Mesovortices. Part
I: Processes That Influence Their Damaging Potential. Monthly Weather Review, 137, 1498-1513. doi:10.1175/2008MWR2649.1
• Atkins, N.T & St. Laurent, M. (2009, May). Bow Echo Mesovortices. Part II: Their Genesis. Monthly Weather Review, 137, 1514-1532. doi:10.1175/2008MWR2650.1
• Davis, C et al. (2014, August). The Bow Echo and MCV Experiment. BAMS, 1075-1093. doi:10.1175/BAMS-85-8-1075
• Klimowski, B. A et al. (2004, February). Radar Observations of the Early Evolution of Bow Echoes. Weather and Forecasting (AMS), 19, 727-734.