The Evolution of Quasi-Linear Convective Systems Encountering the Northeastern US Coastal Marine Environment

receptivetrucksMechanics

Oct 27, 2013 (3 years and 10 months ago)

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(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


31 MAY 2002 1700 UTC



01 JUN 2002 1000 UTC

23 JUL 2002 1600 UTC



24 JUL 2002 0400 UTC

Let’s 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

Let’s compare the evolution of 2 different QLCS events…

Why does one event survive over the Atlantic

while the other decays upon reaching the coastline?

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

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.

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)

Decaying

Sustaining

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

70

80

80

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.

Decaying

Sustaining

Geography for reference only: Star center point for feature
based composites.

Sustaining
: QLCS within a region of WAA with
little frontogenesis.

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?

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

31 May 2002

Sustaining Event

0100 UTC 01 JUN 2002

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
)

1500 UTC 31 May 2002

2100 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

900 hPa

700 hPa

700 hPa

500 m JFK: 1500 UTC 31 May

500 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



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)

23 July 2002
Decaying Event

2200 UTC 23 JUL 2002

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




1800 UTC 23 Jul 2002

2100 UTC 23 Jul 2002

500 m JFK: 1800 UTC

500 m JFK: 2100 UTC

700 hPa

700 hPa

900 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


MUCIN ~25
-
150 J kg
-
1


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


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


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


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

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

θ’ = 3.75 K

h
c

= 1.2 km

C = 19.3 m s
-
1

ΔU
2.5km
= 15.0 m s
-
1

θ’ = 4 K

h
c

= 1.3 km

C = 18.3 m s
-
1

ΔU
2.5km
= 7.5 m s
-
1

C/ΔU=1.3

C/ΔU=2.5

0100 UTC 1 JUN (13h)

2230 UTC 23 JUL (16.5h)

500 m

500 m

precip mixr (shaded, g kg
-
1
), potential temp (solid, K), storm relative circulation vectors

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

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


Sensitivity Experiments


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=15h

15%EVAP t=17h

θ’

4 K

3 K

h
c

1.5 km

0.9 km

C

13.9 m s
-
1

13.2 m s
-
1


ΔU
2.5km

4.0 m s
-
1


6.0 m s
-
1


C/ΔU

3.5

2.2

2km CTRL t=15h

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=16h

LAND 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.



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).


extra slides

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

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

900 hPa

700 hPa

700 hPa

500 m OKX: 0000 UTC 31 May

KOKX: 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

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

Let’s 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