a multiscale analysis of the 23-24 november 2004 southeast united states tornado outbreak alicia c....
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A Multiscale Analysis of the A Multiscale Analysis of the 23-24 November 2004 23-24 November 2004
Southeast United States Southeast United States Tornado OutbreakTornado Outbreak
Alicia C. WasulaAlicia C. Wasula
Event SummaryEvent Summary
23/1700 UTC – 24/1300 UTC 23/1700 UTC – 24/1300 UTC (nocturnal)(nocturnal)
80 Tornadoes (17 F2 or greater)80 Tornadoes (17 F2 or greater) 3 Fatalities / 38 Injuries3 Fatalities / 38 Injuries 45% tornadoes close to Gulf coast 45% tornadoes close to Gulf coast
(south of 32 (south of 32 N)N)
MotivationMotivation
Examine tornado episode from Examine tornado episode from synoptic/mesoscale perspective to synoptic/mesoscale perspective to look for similarities/differences to look for similarities/differences to composite Gulf coast tornado composite Gulf coast tornado episodeepisode
0-2
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0 -3-3 s s -
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11))Convective Available Potential Energy (CAPE, Convective Available Potential Energy (CAPE, J/kg)J/kg)
Johns et Johns et al. 1993al. 1993
CAPE vs. Shear for Cold Season Tornado CAPE vs. Shear for Cold Season Tornado CasesCases
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km
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tive m
ean
sh
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(x 1
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-2 k
m p
osi
tive m
ean
sh
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(x 1
0 -3-3 s s -
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11))Convective Available Potential Energy (CAPE, Convective Available Potential Energy (CAPE, J/kg)J/kg)
Johns et Johns et al. 1993al. 1993
CAPE vs. Shear for Warm Season Tornado CAPE vs. Shear for Warm Season Tornado CasesCases
Tornado Episode Tornado Episode CompositesComposites
NCEP/NCAR 2.5NCEP/NCAR 2.5x 2.5x 2.5 Reanalysis Reanalysis datasetdataset
All tornado episodes 1950-2001All tornado episodes 1950-2001 ‘‘Episode-relative’ compositeEpisode-relative’ composite Grouped by start time: 0000-0600, Grouped by start time: 0000-0600,
0600-1200, 1200-1800, 1800-0000 0600-1200, 1200-1800, 1800-0000 UTCUTC
Will show 0600-1200 UTC onlyWill show 0600-1200 UTC only
200 hPa height (m), isotachs (m s200 hPa height (m), isotachs (m s-1-1))
500 hPa hgt (m), avor. (x 10500 hPa hgt (m), avor. (x 10-5-5 s s-1-1), vort. adv. (x 10), vort. adv. (x 10-10-10 s s-2-2))
850 hPa hgt (m), temp (850 hPa hgt (m), temp (C), temp. adv. (x 10C), temp. adv. (x 10-5-5 C sC s-1-1))
1000 hPa height (m), 1000-500 thck. (dam), 700 hPa RH (%)1000 hPa height (m), 1000-500 thck. (dam), 700 hPa RH (%)
700 hPa height (m), vertical motion (x 10700 hPa height (m), vertical motion (x 10-3-3 hPa s hPa s-1-1))
850 hPa winds, 850 hPa winds, ee (K), 850-500 lapse rate ( (K), 850-500 lapse rate (C)C)
Summary: CompositesSummary: Composites
Strong signal in spite of large sample size:Strong signal in spite of large sample size: ULJ entrance region at 200 hPaULJ entrance region at 200 hPa Vigorous upstream trough at 500 hPaVigorous upstream trough at 500 hPa Southwesterly LLJ at 850 hPaSouthwesterly LLJ at 850 hPa Low-level Low-level ee ridge ridge
Surface composites show 1Surface composites show 1stst tornado occurs: tornado occurs: At strongest At strongest TT On northern edge of moisture surge/southerly On northern edge of moisture surge/southerly
flowflow Dew point anomalies > +8 Dew point anomalies > +8 CC
22 November 2004 0000 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
22 November 2004 1200 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
23 November 2004 0000 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
23 November 2004 1200 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
23 November 2004 1800 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
24 November 2004 0000 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
24 November 2004 0600 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
24 November 2004 1200 UTC
SLP, 1000-500 THCK 500 hPa HGHT, AVOR
200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS
ConclusionsConclusions
Tornado episode occurred:Tornado episode occurred: In presence of strong synoptic-scale In presence of strong synoptic-scale
forcing for ascent (in warm sector)forcing for ascent (in warm sector) LLJ strength increased overnightLLJ strength increased overnight Surface winds stayed south or southeast Surface winds stayed south or southeast
as surface low rapidly deepened to the as surface low rapidly deepened to the northnorth
Ample moisture and instabilityAmple moisture and instability
ConclusionsConclusions
Case study shows similarities to composite Case study shows similarities to composite tornado episodetornado episode Strong shear/ULJ/LLJStrong shear/ULJ/LLJ Deepening surface cycloneDeepening surface cyclone Ample low-level moisture (esp. close to coast)Ample low-level moisture (esp. close to coast) Surface winds ‘back’ with time ahead of Surface winds ‘back’ with time ahead of
surface lowsurface low Difference:Difference:
Mesoscale thermal gradient?Mesoscale thermal gradient?
Future WorkFuture Work
Question:Question: Did isallobaric effects help to keep flow Did isallobaric effects help to keep flow
in warm sector southerly/southeasterly in warm sector southerly/southeasterly and allow warm moist Gulf air to remain and allow warm moist Gulf air to remain in place close to coast?in place close to coast?
Why did LLJ increase in strength so Why did LLJ increase in strength so rapidly?rapidly? Dynamically driven?Dynamically driven?