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Sea Breezes. Circulations, Forecasting, & More!. METEO 416/516 Matthew Greenstein March 31, 2004. Overview. Pressure gradient-driven wind from cooler water to warmer land Onset of sea breeze = sea breeze front

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slide1

Sea Breezes

Circulations, Forecasting, & More!

METEO 416/516

Matthew Greenstein

March 31, 2004

slide2

Overview

  • Pressure gradient-driven wind from cooler water to warmer land
  • Onset of sea breeze = sea breeze front
  • Front acts as a shallow cold front – a forcing mechanism for thunderstorms
  • Temperatures fall with its passage
slide3

Overview

March 26, 20043PM

slide5

Overview

ACY:

42oF on March 26

slide6

Circulation

Solenoid Circulation

  • Land heats more than water due toa smaller heat capacity
  • Hydrostatic high and low pressures form
slide7

Circulation

Mid - Late Morning

  • Sea Breeze begins once T(land)-T(water) > 6-10oF
  • Strength of the sea breeze is related to…
    • the temperature gradient between land and ocean
    • the synoptic flow
      • weak onshore  inland penetration
      • moderate offshore  prevents sea breeze
  • Some Cu form along the front
slide8

Circulation

Noon

  • Pressure over land decreases further
  • Pressure gradient force increases
  • Surface winds of 10-15 knots at the shoreline
  • Solenoidal circulation: 1500 to 3000 feet deep
  • Lake & River Breezes: Similar setup but weaker & less penetration inland
slide9

Circulation

Afternoon

  • Wind increases as pressure gradient increases
  • Temperature falls of 5oF to even 25oF possible with passage of sea breeze front
  • Depending on synoptic scale setup and other modifying factors (to be discussed later), the sea breeze pushes inland
  • Depending on stability and available moisture, more Cu form and grow deeper
slide10

Circulation

Afternoon (cont’d)

  • Depending on stability and available moisture, thunderstorms can develop – especially if the sea breeze front interacts with other fronts, convergence zones, outflows, and other sea breezes
  • Florida: Sea breezes off of the Atlantic & Gulf coasts, river breeze off the Banana River near Cape Canaveral, & lake breeze off Lake Okeechobee
  • Onshore advance of marine stratus on West Coast
slide11

Circulation

Evening & Night

  • Solenoid circulation gone 1 to 2 hours after sunset
  • Land cools  Land breeze  Nocturnal convection over water
slide12

Modifications

Coastline concavity

  • Convex coastline focuses convergence and enhances the lift along the sea breeze front
  • Concave coastline leads to divergence and a reduction in the lift along the sea breeze front
slide13

Modifications

Low-level inversion

  • Limits the vertical extend of heating, which reduces the strength of the sea breeze
  • Deeper moderate temperature rise leads to a stronger sea breeze than a shallow large temperature rise  stronger hydrostatic low pressure and a greater pressure gradient
slide14

Modifications

Synoptics

  • Weak offshore flow (< 10 knots): sea breeze can form with enough heating
  • Offshore flow > 10 knots: sea breeze won’t form
  • Weak flow in any direction: sea breeze can form
  • Strong along-shore flow can be turned with diurnal heating
    • LOW over land and HIGH over water is needed
    • HIGH over land and LOW over water will not turn properly
  • Strong on-shore flow will cool temperatures well-inland without any sea breeze
slide15

Modifications

Synoptics

slide16

Numerical Models

  • All models create sea breezes, but…
  • Resolution determines the placement and strength
    • MM5 does a good job
  • Since temperature gradient is only a few km wide, you’d need a 1-km resolution model to resolve the gradient properly
  • Gradient is smoothed weaker pressure gradient  weaker winds
slide17

Numerical Models

  • Resolution also affects how well coastline is modeled
  • Model will successfully predict if a sea breeze should develop, but details are not well forecast
  • See how well the models does in your forecasting area over time
slide18

Forecasting

  • Check the land-to-ocean forecasted temperature gradient – needs to be at least 6-10oF
  • Synoptic-scale flow needs to be weak, although onshore flow will, of course, lower temperatures
  • Know your coastline !
  • Use models as a guide to possible sea breeze formation
  • Dr. Markowski says to anticipate a sea breeze if…
  • |vg |2 / ΔT < 5
slide19

Real-time Forecasting

Clear-air

Mode

Radar

slide21

Real-time Forecasting

Visible Satellite Imagery

---------

Clear skies after front passage

&

Cu/Cb along front

slide22

Real-time Forecasting

  • Use a station model plot!
  • Look for the change in wind direction & temperature
  • This works especially well if you have a mesonet or tightly packed ASOS stations.
slide23

Upwelling

  • Upwelling leads to cooler water coming to the surface
  • This increases the land-ocean temperature gradient  promotes and strengthens the sea breeze
  • Can occur in localized areas, creating kinks in the sea breeze
  • Prolonged SW’erly flow off NJ, leads to upwelling
slide24

Additional Thoughts

  • You can see tell where the sea breeze has progressed to, based on how clear the skies are increased stability
slide25

Additional Thoughts

  • In NJ, the hottest days are on strong NW’erly flow
    • Strong downslope warming
    • Inhibits of sea breeze
    • Hot right at the water’s edge
  • Suppressed convection on cool side of sea breeze front
  • Harsh sea breezes in the spring with inland temperatures in the 70’s and ocean temperatures in the 40’s
slide26

Bibliography

COMET Meted: “Thermally-Forced Circulation I: Sea Breezes” @ http://www.meted.ucar.edu/mesoprim/seabreez/

Dr. Markowski’s METEO 414 notes

NJ State Climatologist @ http://climate.rutgers.edu/stateclim/

Rutgers Coastal Ocean Observation Lab (COOL) @ http://marine.rutgers.edu/cool/seabreeze/tutorial.html

University of Illinois Urbana-Champaign - WW2010: “Sea Breezes” @ http://ww2010.atmos.uiuc.edu/(Gl)/guides/mtr/fw/sea/htg.rxml