examining sea breeze frontogenesis using petterssen’s frontogenetical function

Examining Sea Breeze Examining Sea Breeze Frontogenesis Using Frontogenesis Using

Petterssen’s Frontogenetical Petterssen’s Frontogenetical FunctionFunction

Brian C. ZachryBrian C. ZachryDepartment of Marine and Environmental SystemsDepartment of Marine and Environmental Systems

Florida Institute of TechnologyFlorida Institute of TechnologyMelbourne, FL 32901Melbourne, FL 32901

OVERVIEWOVERVIEW

• Fronts and FrontogenesisFronts and Frontogenesis

• Petterssen’s Frontogenetical FunctionPetterssen’s Frontogenetical Function

• Rapid Update Cycle (RUC)Rapid Update Cycle (RUC)

• Analyze Each DayAnalyze Each Day

• ConclusionsConclusions

BACKGROUND INFORMATIONBACKGROUND INFORMATION

• A front is the interface between two air masses of A front is the interface between two air masses of different density (most often a front separates air different density (most often a front separates air masses of different temperatures). masses of different temperatures).

• Frontogenesis is the formation of a front or frontal Frontogenesis is the formation of a front or frontal zone.zone.– It is an increase in the horizontal temperature gradient.It is an increase in the horizontal temperature gradient.

• Frontolysis is the dissipation of a front or frontal zone.Frontolysis is the dissipation of a front or frontal zone.– It is a decrease in the horizontal temperature gradient.It is a decrease in the horizontal temperature gradient.

• Temperature gradientTemperature gradient– GenerationGeneration– MovementMovement– Enhancement Enhancement

Frontogenesis is an increase in the temperature Frontogenesis is an increase in the temperature gradientgradient

• Petterssen’s Frontogenetical Function is a kinematic measure of the Petterssen’s Frontogenetical Function is a kinematic measure of the tendency of the flow in an airmass to increase the horizontal tendency of the flow in an airmass to increase the horizontal temperature gradient:temperature gradient:

it quantifies the amount of change in the potential temperature it quantifies the amount of change in the potential temperature gradient following air-parcel motion. gradient following air-parcel motion.

• The function is simplified to:The function is simplified to:

where δ and D are horizontal divergence and resultant deformation. where δ and D are horizontal divergence and resultant deformation. • Resultant deformation was neglected in the interpretation but was Resultant deformation was neglected in the interpretation but was

included in the calculated surface frontogenesis by the atmospheric included in the calculated surface frontogenesis by the atmospheric model.model.

• Q represents diabatic heating and was neglected entirely, but can be Q represents diabatic heating and was neglected entirely, but can be important near the surface. important near the surface.

Impact of Convergence and Divergence on Impact of Convergence and Divergence on the Temperature Gradientthe Temperature Gradient

• Convergence acts to compress Convergence acts to compress the temperature gradient.the temperature gradient.– StrengtheningStrengthening

• Divergence acts to Divergence acts to decompress the temperature decompress the temperature gradient.gradient.– WeakeningWeakening

Frontogenesis and FrontolysisFrontogenesis and Frontolysis

• Frontogenesis occurs when convergence and the Frontogenesis occurs when convergence and the temperature gradient correspond.temperature gradient correspond.– Convergence acts to increase the temperature gradient.Convergence acts to increase the temperature gradient.– The stronger the temperature gradient being The stronger the temperature gradient being

compressed, the stronger the frontogenesis. compressed, the stronger the frontogenesis.

• Frontolysis occurs when divergence and the Frontolysis occurs when divergence and the temperature gradient correspond.temperature gradient correspond.– Divergence acts to decrease temperature gradient.Divergence acts to decrease temperature gradient.– The weaker the temperature gradient being The weaker the temperature gradient being

decompressed, the stronger the frontolysis. decompressed, the stronger the frontolysis.

Weak Moderate

Strong

• Study the intensity of the sea breeze frontStudy the intensity of the sea breeze front– How it varied each dayHow it varied each day– Why a stronger front occurred on May 27Why a stronger front occurred on May 27

MethodsMethods

• The analysis of the RUC model (plotted on “Garp”) The analysis of the RUC model (plotted on “Garp”) was used to obtain:was used to obtain:– Temperature Gradient (Temperature Gradient (°C/m)°C/m): Scaled 10: Scaled 10-5-5

– Convergence (- values) (sConvergence (- values) (s-1-1): Scaled 10): Scaled 10-5-5

– Frontogenesis (+ values) (K/100km*3h)Frontogenesis (+ values) (K/100km*3h)

• The Rapid Update Cycle (RUC) is an atmospheric The Rapid Update Cycle (RUC) is an atmospheric model. model. – Grid point model that covers the lower 48 states. Grid point model that covers the lower 48 states. – Horizontal resolution of 20km (resolution of local circulations)Horizontal resolution of 20km (resolution of local circulations)

Meteorological ScenarioMeteorological Scenario • The meteorological scenario differed each day based on The meteorological scenario differed each day based on

synoptic conditions. synoptic conditions. – Easterly flow on May 25Easterly flow on May 25– Light, westerly flow on May 26Light, westerly flow on May 26– Westerly flow on May 27Westerly flow on May 27

• Easterly synoptic flow: Easterly synoptic flow: – Weakens the temperature gradientWeakens the temperature gradient– Very little frontogenesis forming a weak frontVery little frontogenesis forming a weak front– Deep inland penetration of the sea breeze frontDeep inland penetration of the sea breeze front

• Westerly synoptic flow:Westerly synoptic flow:– Tightens the temperature gradientTightens the temperature gradient– Strong frontogenesis forming a well-defined frontStrong frontogenesis forming a well-defined front– Limited inland penetration of the sea breeze frontLimited inland penetration of the sea breeze front

• Meteorological conditions at 18Z (1:00 EST) and Meteorological conditions at 18Z (1:00 EST) and 23Z (7:00 EST) were used to compare each day. 23Z (7:00 EST) were used to compare each day. – Location of the sea breeze frontLocation of the sea breeze front– Locations of convergence/divergenceLocations of convergence/divergence– Strongest temperature gradientsStrongest temperature gradients– Cold/warm air advectionCold/warm air advection

18Z May 25

18Z May 26

18Z May 27

23Z May 25

23Z May 26

23Z May 27

Grid Point AnalysisGrid Point Analysis• Four grid points on the RUC were analyzed for Four grid points on the RUC were analyzed for

temperature gradient, convergence and temperature gradient, convergence and frontogenesis.frontogenesis.

Temperature Gradient on May 25, 2004

0

5

10

15

20

25

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Tem

pera

ture

Gra

dien

t (de

g C/

m)

Scal

e (1

0^-5

)

Point 1

Point 2

Point 3

Point 4

Temperature Gradient on May 26, 2004

0

5

10

15

20

25

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Tem

pera

ture

Gra

dien

t (de

g C

/m)

Sc

ale

(10^

-5)

Point 1

Point 2

Point 3

Point 4

Temperature Gradient on May 27, 2004

0

5

10

15

20

25

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Tem

pera

ture

Gra

dien

t (de

g C

/m)

Scal

e (1

0^-5

)

Point 1

Point 2

Point 3

Point 4

Convergence on May 25, 2004

-15

-10

-5

0

5

10

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Con

verg

ence

(s^-

1)Sc

ale

(10^

-5)

Point 1

Point 2

Point 3

Point 4

Convergence on May 26, 2004

-15

-10

-5

0

5

10

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Con

verg

ence

(s^-

1)Sc

ale

(10^

-5)

Point 1

Point 2

Point 3

Point 4

Convergence on May 27, 2004

-15

-10

-5

0

5

10

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Con

verg

ence

(s^-

1)Sc

ale

(10^

-5)

Point 1

Point 2

Point 3

Point 4

Frontogenesis on May 25, 2004

-100

0

100

200

300

400

500

600

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Fron

toge

nesi

s (K

/100

km*3

hr)

Point 1

Point 2

Point 3

Point 4

Frontogenesis on May 26, 2004

-100

0

100

200

300

400

500

600

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Fron

toge

nesi

s (K

/100

km*3

hr)

Point 1

Point 2

Point 3

Point 4

Frontogenesis on May 27, 2004

-100

0

100

200

300

400

500

600

10Z 11Z 12Z 13Z 14Z 15Z 16Z 17Z 18Z 19Z 20Z 21Z 22Z 23Z

Time (Z)

Fron

toge

nesi

s (K

/100

km*3

hr)

Point 1Point 2Point 3Point 4

ConclusionsConclusions

• May 25, 2004May 25, 2004 – Temperature gradients were weakened by Temperature gradients were weakened by

easterly synoptic flow and did not correspond easterly synoptic flow and did not correspond to areas of convergence.to areas of convergence.

– Minimal frontogenesis only over a short time Minimal frontogenesis only over a short time period.period.

– Frontal boundary was advection inland shortly Frontal boundary was advection inland shortly after it formed.after it formed.

– Inland penetration was much further this day Inland penetration was much further this day than the other two days. than the other two days.

• May 26, 2004May 26, 2004 – Temperature gradients were slightly Temperature gradients were slightly

strengthened by a weak synoptic flow regime strengthened by a weak synoptic flow regime turning westerly.turning westerly.

– Horizontal temperature gradients and Horizontal temperature gradients and convergence corresponded better than the 25convergence corresponded better than the 25th. th.

– Stronger frontogenesis and subsequent strength Stronger frontogenesis and subsequent strength of the sea breeze front.of the sea breeze front.

– Inland penetration was less than on the 25Inland penetration was less than on the 25thth and and advection of the front occurred later in the day.advection of the front occurred later in the day.

• May 27, 2004May 27, 2004 – Temperature gradients were strengthened and Temperature gradients were strengthened and

compressed by 5 to 10 knot westerly flow.compressed by 5 to 10 knot westerly flow.– Horizontal temperature gradients and Horizontal temperature gradients and

convergence corresponded from 15Z to 23Z. convergence corresponded from 15Z to 23Z. – Strong frontogenesis over a longer period Strong frontogenesis over a longer period

formed a well-defined front. formed a well-defined front. – Inland advection of the developed sea breeze Inland advection of the developed sea breeze

front was minimal and occurred late in the day.front was minimal and occurred late in the day.– This allowed a strong front to develop and This allowed a strong front to develop and

remain in an area of frontogenesis throughout remain in an area of frontogenesis throughout most of the day. most of the day.

AcknowledgementsAcknowledgements

• Mr. Splitt for all his time and energy put Mr. Splitt for all his time and energy put into this presentation.into this presentation.

• My fellow MPF students for all their hard My fellow MPF students for all their hard work during this study and all the other work during this study and all the other studies conducted during MFP. studies conducted during MFP.

Questions?Questions?

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