An analysis of the Northern Gulf of MexicoAn analysis of the Northern Gulf of Mexicosea breeze and associated thunderstormssea breeze and associated thunderstorms

Mississippi State UniversityMississippi State University

January 17, 2007January 17, 20071616thth Conference on Applied ClimatologyConference on Applied Climatology

Christopher M. HillChristopher M. HillYee H. LauYee H. Lau

SachinSachin K. K. BhateBhate

Patrick J. FitzpatrickPatrick J. FitzpatrickJames H. CorbinJames H. CorbinP. Grady DixonP. Grady Dixon

Overview

•• The sea breeze is commonly observed along the northern Gulf coasThe sea breeze is commonly observed along the northern Gulf coast during t during the summer (June, July, August)the summer (June, July, August)

•• Intersection of a sea breeze front with boundary layer perturbatIntersection of a sea breeze front with boundary layer perturbations (i.e. ions (i.e. horizontal convective rolls) will trigger convection (horizontal convective rolls) will trigger convection (FovellFovell 2005)2005)

The exact orientation and migration of the sea (land) breeze froThe exact orientation and migration of the sea (land) breeze front, and nt, and the focus of associated convection, depends upon:the focus of associated convection, depends upon:

•• the temperature gradient between land and waterthe temperature gradient between land and water•• the prevailing boundary layer flowthe prevailing boundary layer flow•• land elevationland elevation•• shape of the coastlineshape of the coastline

Medlin and Croft 1998Medlin and Croft 1998

(PM) SB(PM) SB

(AM) LB(AM) LB

Methodology

•• Surface observations, upper air observations at KLIX,Surface observations, upper air observations at KLIX, andandNEXRAD data at KLIX collected for:NEXRAD data at KLIX collected for:June, July, and August of 2003 June, July, and August of 2003 –– 2005 ( 2005 ( 276 days276 days ))

•• Reduced dataset to Reduced dataset to ““sea breezesea breeze”” days with the following criteria:days with the following criteria:

–– wind speed at land stations does not exceed 7.5 mph (or 3.4 m swind speed at land stations does not exceed 7.5 mph (or 3.4 m s--11) ) at 00 UTC or 12 UTCat 00 UTC or 12 UTC

–– no precipitation event generated by a synoptic system or by no precipitation event generated by a synoptic system or by widespread air mass thunderstorm activity, as discerned from widespread air mass thunderstorm activity, as discerned from NEXRAD dataNEXRAD data

•• 33--year averages of meteorological quantities computed for year averages of meteorological quantities computed for remaining days ( remaining days ( 168168 ) by month) by month

Observing stations

Red squares Red squares -- NOAA stationsNOAA stationsBlue circles Blue circles -- Mississippi RAWS stationsMississippi RAWS stations

Green triangles Green triangles -- buoysbuoys

KLIXKLIX

JUNEJUNE JULYJULY AUGUSTAUGUST

Monthly composites of convective rain pixels for 2003 Monthly composites of convective rain pixels for 2003 –– 2005 2005 on on ““sea breezesea breeze”” ( 168 of 276 ) days( 168 of 276 ) days

0 20 40 60 80 100 120 1400 20 40 60 80 100 120 140 160160

20

20 --

00 U

TC00

UTC

12

12 --

16 U

TC16

UTC

total radar pixels total radar pixels ≥≥ 30 30 dBZdBZ

2

4

1

3

Average WIND DIR and SPEEDAverage WIND DIR and SPEED

for 2003 for 2003 –– 20052005on on ““sea breezesea breeze”” ( 168 of 276 ) days( 168 of 276 ) days

KGPT (orange line), Buoy 42007 (blue line)KGPT (orange line), Buoy 42007 (blue line)

1.00

1.50

2.00

2.503.00

3.50

4.00

4.50

5.00

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00

C D T

KGPT (SB) 42007 (SB) KGPT (all) 42007 (all)

0.030.060.090.0

120.0150.0180.0210.0240.0270.0300.0330.0360.0

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00CD T

KGPT (SB) 42007 (SB) KGPT (all) 42007 (all)

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00

C DT

0.030.060.090.0

120.0150.0180.0210.0240.0270.0300.0330.0360.0

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00CDT

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00

CDT

0.030.060.090.0

120.0150.0180.0210.0240.0270.0300.0330.0360.0

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00CDT

JUNEJUNE JULYJULY AUGUSTAUGUST

win

d sp

eed

win

d sp

eed

win

d di

r.w

ind

dir.

KGPTKGPT

4200742007

Average AIR DENSITY DIFF.Average AIR DENSITY DIFF.

for 2003 for 2003 –– 20052005on on ““sea breezesea breeze”” ( 168 of 276 ) days( 168 of 276 ) days

KGPTKGPT

4200742007

-0.020

-0.016

-0.012

-0.008

-0.004

0.000

0.004

0.008

0.012

0.016

0.020

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00

t i me ( CDT )

-0.020

-0.016

-0.012

-0.008

-0.004

0.000

0.004

0.008

0.012

0.016

0.020

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00

t i me ( CDT )

-0.020

-0.016

-0.012

-0.008

-0.004

0.000

0.004

0.008

0.012

0.016

0.020

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00

t i me ( CDT )

Dark blue line:Dark blue line:Density difference of KGPT Density difference of KGPT –– 4200742007

AUGUSTAUGUSTJUNEJUNE

JULYJULY

HH

LL

LL

HH

LLHH

Flow distribution

Afternoon sea breezeAfternoon sea breeze

-- flow primarily from the southflow primarily from the south-- resulting front runs westresulting front runs west--easteast

Morning land breezeMorning land breeze

-- flow from north and westflow from north and west-- resulting front converges overresulting front converges overbarrier islandsbarrier islands

Methodology, cont.

•• Assess predictive capability of upperAssess predictive capability of upper--air air parameters for parameters for arealareal precipitation coverage precipitation coverage (APC)(APC)

–– Compare 00 UTC and 12 UTC parameters against Compare 00 UTC and 12 UTC parameters against following 4following 4--hr composites of APChr composites of APC

•• KK--indexindex–– 700700--hPa Dew. Dep.hPa Dew. Dep.

–– 850 850 -- 500 500 hPahPa ΓΓ

•• CAPECAPE•• 850850--hPa wind dir.hPa wind dir.•• PW (1000 PW (1000 -- 300 300 hPahPa))

12 12 -- 16 UTC16 UTC 20 20 -- 00 UTC00 UTC

SE s

ecto

r (2)

SE s

ecto

r (2)

NE

sect

or (4

)N

E se

ctor

(4)

12 UTC K12 UTC K--index versus 4index versus 4--hr hr ArealAreal Precipitation CoveragePrecipitation Coverage

12 12 -- 16 UTC16 UTC 20 20 -- 00 UTC00 UTC

SE s

ecto

r (2)

SE s

ecto

r (2)

NE

sect

or (4

)N

E se

ctor

(4)

12 UTC Dewpoint Depression at 700 12 UTC Dewpoint Depression at 700 hPahPa versus 4versus 4--hr hr ArealAreal Precipitation CoveragePrecipitation Coverage

12 12 -- 16 UTC16 UTC 20 20 -- 00 UTC00 UTC

SE s

ecto

r (2)

SE s

ecto

r (2)

NE

sect

or (4

)N

E se

ctor

(4)

12 UTC 12 UTC PrecipitablePrecipitable Water versus 4Water versus 4--hr hr ArealAreal Precipitation CoveragePrecipitation Coverage

ConclusionsConclusions

•• As expected, precipitation forms at coast along As expected, precipitation forms at coast along sea breeze frontsea breeze front

•• The land breeze front converges near barrier The land breeze front converges near barrier islands, providing focus for precipitationislands, providing focus for precipitation

•• Linear trends of 700Linear trends of 700--hpa dewpoint depression hpa dewpoint depression and and precipitableprecipitable water with precipitation water with precipitation coverage coverage