(Jason Andrew for Wall Street Journal: photo of Park Slope, Brooklyn) The Evolution of Quasi-Linear...
If you can't read please download the document
(Jason Andrew for Wall Street Journal: photo of Park Slope, Brooklyn) The Evolution of Quasi-Linear Convective Systems Encountering the Northeastern US
(Jason Andrew for Wall Street Journal: photo of Park Slope,
Brooklyn) The Evolution of Quasi-Linear Convective Systems
Encountering the Northeastern US Coastal Marine Environment Kelly
Lombardo & Brian Colle Stony Brook University
Slide 2
31 MAY 2002 1700 UTC 01 JUN 2002 1000 UTC 23 JUL 2002 1600 UTC
24 JUL 2002 0400 UTC Lets compare the evolution of 2 different QLCS
events
Slide 3
31 MAY 2002 1700 UTC 01 JUN 2002 1000 UTC 23 JUL 2002 1600 UTC
24 JUL 2002 0400 UTC Lets compare the evolution of 2 different QLCS
events Why does one event survive over the Atlantic while the other
decays upon reaching the coastline?
Slide 4
Data & Methods: Composites Manually examined 2-km NOWrad
radar reflectivity for 6 warms seasons (May- Aug) 2002-2007;
Identified 73 QLCS that encountered the Atlantic coast. 65 QLCS
events were classified into 4 different categories based on their
evolution encountering the coastline. 32 decaying events: Decay at
the coastline. 18 slowly decaying events: Show no signs of decay at
the coast, but decay over the water within 100 km of the coast. 9
sustaining events: Maintain their intensity more than 100 km from
coastline. 6 organize events: Organize along the coastline (not
addressed in this study). Feature-based composites for decaying,
slowly decaying, and sustaining events using 32-km NARR data.
Centered on the point where the QLCS crosses the coast at the
closest 3-hr NARR time prior to the crossing. QLCS 0-100 km >100
km
Slide 5
MUCAPE (J kg -1 ), MSLP (hPa), 1000 theta (2 K), 10 m wnd (kts)
Decaying Sustaining Decaying: MUCAPE 1250 J kg -1 ; collocated with
a surface pressure trough & 1000 hPa thermal ridge. Geography
for reference only: Star center point for feature based composites.
Sustaining: MUCAPE 1000 J kg -1 ; surface pressure trough 300 km to
west; QLCS collocated with 1000 hPa baroclinic zone.
Slide 6
Decaying: MUCIN 15 J kg -1 and increases rapidly offshore; RH
of 68% (lowest 100 hPa); potential for evaporative cooling; Shear
15 kts. MUCIN (shaded, J kg -1 ), 1000 hPa RH (red, %), 0-3 km wind
shear (kts) DecayingSustaining Geography for reference only: Star
center point for feature based composites. Sustaining: MUCIN 35 J
kg -1 with a weak offshore gradient; RH 77%; less of a chance for
evaporative cooling; shear 25 kts. 70 80
Slide 7
900:800 frontogenesis (10 -2 K (100 km) -1 (3 hr) -1 ), 900 tmp
(black, o C), 900 tmp adv (10 -5 o C s -1 ), 900 winds (kts)
Decaying: QLCS on the warm side of a fronotogenesis maximum;
strengthening baroclinic zone/front. DecayingSustaining Geography
for reference only: Star center point for feature based composites.
Sustaining: QLCS within a region of WAA with little
frontogenesis.
Slide 8
Motivational Questions What is the role of warm air advection
during sustaining events? What is the role of the stable layer and
convective inhibition? How is the enhanced vertical wind shear
important to the maintenance of a QLCS? What role does low-level
diabatic cooling play in the evolution of QLCSs?
Slide 9
2 km 500 m 2 Case Studies Better understand the processes that
govern the maintenance and decay of a QLCS Simulations: WRF ARW
core Initial & Boundary Conditions: 32-km NARR Explicit
convection Morrison double-moment microphysics MYNN2.5 PBL Thermal
LSM 2002 Decaying: 23 JUL 0600 UTC 24 JUL 0300 UTC 2002 Sustaining:
31 MAY 1200 UTC 01 JUN 0600 UTC
Slide 10
31 May 2002 Sustaining Event 0100 UTC 01 JUN 2002
Slide 11
NARR: 300 wnd (shaded, m s -1 ), 500 hght (solid, dam), 500
Q-vect conv (dashed, 10 -15 K m -2 s -1 ), 500 wnd (m s -1 ) 2100
UTC 31 May 2002 300 hPa jet extending into base of an upper level
trough 500 hPa trough axis over eastern NY 500 hPa Q-vector
convergence over the Northeast coastal region Cold front and
prefrontal trough Cold front & prefrontal trough Convection
ahead of cold front, consistent with composites. Thermal ridge in
the Appalachian lee Coastal baroclinic zone Relatively moist air
along coast (dew points 17-18 o C) 2km WRF: mslp (solid, hPa), 2 m
tmp (dashed, o C), 2 m dwpt (shaded, o C), 10 m winds (m s -1
)
Slide 12
1500 UTC 31 May 20022100 UTC 31 May 2002 2km WRF: MUCAPE (J kg
-1 ), 925 hPa hght (solid, dam), 925 tmc (dashed, o C), 925 wnd( m
s -1 ) 900 hPa 700 hPa 500 m JFK: 1500 UTC 31 May500 m JFK: 2100
UTC 1 Jun T 925hPa ~22 o C LI CAPE 400-1600 J kg -1 WAA similar to
composites 1600-2000 J kg - 1 CAPE in lee T 925hPa ~18 o C MUCAPE
~200 J kg -1 MUCIN ~25-75 J kg -1 MUCAPE ~700 J kg -1 MUCIN
~25-100J kg -1
Slide 13
2258 UTC 31 May 0145 UTC 1 Jun 0200 UTC 1 Jun 2215 UTC 31 May
0300 UTC 1 Jun 0145 UTC 1 Jun 2 km WRF precip mixr (shaded, g kg -1
), 100 m omega (contour, 10 -2 m s -1 ), 100 m wnds Observed radar
reflectivity (dBZ)
Slide 14
23 July 2002 Decaying Event 2200 UTC 23 JUL 2002
Slide 15
NARR: 300 wnd (shaded, m s -1 ), 500 hght (solid, dam), 500
Q-vect conv (dashed, 10 -15 K m -2 s -1 ), 500 wnd (m s -1 ) 2100
UTC 23 July 2002 300 hPa jet core U.S.-Canada border Broad 500 hPa
trough Little 500 hPa Q-vector convergence over coastal region
Limited mid- and upper-level forcing 2km WRF: mslp (solid, hPa), 2
m tmp (dashed, o C), 2 m dwpt (shaded, o C), 10 m winds (m s -1 )
Convection collocated with surface cold front, consistent with
composites
Slide 16
1800 UTC 23 Jul 20022100 UTC 23 Jul 2002 500 m JFK: 1800 UTC500
m JFK: 2100 UTC 700 hPa 900 hPa Still 1200-1600 J kg -1 instability
along coast and offshore Little temperature advection similar to
composites 1600-2000 J kg -1 MUCAPE over coast Inversion becoming
reestablished 2km WRF: MUCAPE (J kg -1 ), 925 hPa hght (solid,
dam), 925 tmc (dashed, o C), 925 wnd( m s -1 ) MUCIN ~25-150 J kg
-1
Slide 17
Observed radar reflectivity (dBZ) 2015 UTC 23 Jul 2115 UTC 23
Jul 0000 UTC 24 Jul 2016 UTC 23 Jul 2115 UTC 23 Jul 0005 UTC 24 Jul
2 km WRF precip mixr (shaded, g kg -1 ), 100 m omega (contour, 10
-2 m s -1 ), 100 m wnds
Slide 18
Low-level Balance Theory for Long Lived Squall Lines (Weisman
& Rotunno 2004) vorticity generated by ambient low-level shear
in along line direction vorticity generated by buoyancy gradients
along leading edge of the cold pool = (Rotunno et al. 1988) QLCS
experiences variations in low-level winds and thermodynamics
Slide 19
Low-level Balance Theory for Long Lived Squall Lines (Weisman
& Rotunno 2004) vorticity generated by ambient low-level shear
in along line direction vorticity generated by buoyancy gradients
along leading edge of the cold pool = (Rotunno et al. 1988) QLCS
experiences variations in low-level winds and thermodynamics
Slide 20
Low-level Balance Theory for Long Lived Squall Lines (Weisman
& Rotunno 2004) vorticity generated by ambient low-level shear
in along line direction vorticity generated by buoyancy gradients
along leading edge of the cold pool = (Rotunno et al. 1988) QLCS
experiences variations in low-level winds and thermodynamics
Slide 21
500 m 0030 UTC 1 JUN (12.5h)2130 UTC 23 JUL (15.5h) 500 m
precip mixr (shaded, g kg -1 ), potential temp (solid, K), storm
relative circulation vectors C C = 3.75 K h c = 1.2 km C = 19.3 m s
-1 U 2.5km = 15.0 m s -1 = 4 K h c = 1.3 km C = 18.3 m s -1 U 2.5km
= 7.5 m s -1 C/U=1.3C/U=2.5
Slide 22
0100 UTC 1 JUN (13h) 2230 UTC 23 JUL (16.5h) 500 m precip mixr
(shaded, g kg -1 ), potential temp (solid, K), storm relative
circulation vectors
Slide 23
Response of QLCS to Low Level (Nocturnal) Cooling (Parker 2008)
Surface-based phase: Lifting by the surface cold pool. Stalling
phase: Mechanism for surface lifting disappears as the relative
strength of the cold pool approaches zero. Elevated phase:
Convection forced by a bore atop the stable layer. Limited cooling:
t=6h30m Unimited cooling: t=6h30m Unimited cooling: t=8h30m
Slide 24
precip mixr (shaded, g kg -1 ), potential temp (solid, K),
storm relative circulation vectors Sustaining Event Forcing similar
to a bore, though not purely bore driven. Stronger, deeper (up to
925 hPa; 750 m) temperature inversion (WAA) Moist Brunt-Vaisala
Frequency 0.04 s -1 Decaying Event More dominantly forced by a
surface based density current. More shallow inversion (975 hPa; 300
m) Moist Brunt-Vaisala Frequency 0.36 s -1
Slide 25
Sensitivity Experiments
Slide 26
t = 16 h t = 17 h t = 24 h 23 JULY 2002: Decrease Diabatic
Cooling At t = 13h, reduced the evaporative cooling to 15% of the
original value Convection more intense and moves over the coastal
waters 2 km 15%EVAP CTRL t=15h15%EVAP t=17h 4 K3 K hchc 1.5 km0.9
km C13.9 m s -1 13.2 m s -1 U 2.5km 4.0 m s -1 6.0 m s -1 C/U3.52.2
2km CTRL t=15h
Slide 27
23 JULY 2002: Remove Atlantic Ocean Ocean replaced with land
surface representative of the northeastern U.S. A few stronger
convective cores, but decay similar to CTRL t=16h CTRL-LAND RH (%)
at t=16hLAND precip mixr (g kg -1 ) and CTRL-LAND
line-perpendicular wind (m s -1 ) at t=16h t=17h Drier, warmer,
deeper boundary layer in LAND run. Increase offshore CAPE for LAND
run. Increase chance for evaporative cooling. Reduced vertical wind
shear for LAND run.
Slide 28
Summary In the mean, QLCSs that decay upon encountering the
northeastern U.S. coastline are collocated with frontal boundaries
and regions of 900:800 hPa frontogenesis, with little temperature
advection over the QLCS. Events that survive over the ocean waters
are associated with warm air advection (destabilize atmosphere and
strengthen low level temperature inversion: 31 May 2002 case) with
little 900:800 hPa frontogenesis associated with the QLCS. 31 May
2002 event Stronger vertical wind shear helps to balance the cold
pool, extending the longevity of the QLCS. Forcing transitions from
a surface-based cold pool to more of a bore type feature (perhaps
due to a stronger stable layer compared to 23 July?). 23 July 2002
event Reducing the diabatic cooling to 15% of the CTRL simulation
extended the longevity of the QLCS. Shows that diabatic processes
can be as important as the marine layer in influencing the
evolution of QLCS (though this may not always be the case).
Slide 29
extra slides
Slide 30
2km WRF: mslp (solid, hPa), 2 m tmp (dashed, o C), 2 m dwpt
(shaded, o C), 10 m winds (m s -1 ) Surface observations, mslp
(black, dam), surface temp (blue, o C) 2100 UTC 31 May 2002 Cold
front and prefrontal trough Convection ahead of cold front,
consistent with composites. Thermal ridge in Appalachian lee
Coastal baroclinic zone Relatively moist air along coast WRF ~1 o C
cooler compared to surface obs within thermal ridge WRF and obs
same at buoy 44025 WRF 0.5 o C too cool at Ambrose Light Tower
Slide 31
1500 UTC 31 May 2002 2100 UTC 31 May 2002 2km WRF: MUCAPE (J kg
-1 ), 925 hPa hght (dam), 925 tmc ( o C), 925 wnd( m s -1 ) 900 hPa
700 hPa 500 m OKX: 0000 UTC 31 MayKOKX: 0000 UTC 1 Jun 1200 UTC WRF
2-3 o C cooler than obs T 925hPa increases ~5 o C NARR MUCAPE is
~400 J kg -1 greater WAA similar to composites
Slide 32
2100 UTC 23 Jul 2002 2km WRF: mslp (solid, hPa), 2 m tmp
(dashed, o C), 2 m dwpt (shaded, o C), 10 m winds (m s -1 ) Surface
observations, mslp (black, dam), surface temp (blue, o C)
Convection collocated with surface cold front, consistent with
composites WRF does not capture mesoscale details of surface
pressure features WRF ~2 o C too warm in cold sector and ~2 o C too
cool in warm sector WRF 1 o C too cool at buoy 44025 WRF 100 m
winds 2.5 m s -1 too weak at Ambrose Light Tower H L
Slide 33
Lets compare the evolution of 2 different QLCS events 31 MAY
2002 1700 UTC 01 JUN 2002 1000 UTC 23 JUL 2002 1600 UTC 24 JUL 2002
0400 UTC