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 Front acts as a shallow cold front – a forcing mechanism for thunderstorms Temperatures fall with its passage

Overview March 26, PM

Overview

Overview ACY: 42 o F on March 26

Circulation Solenoid Circulation Land heats more than water due to a smaller heat capacity Hydrostatic high and low pressures form

Circulation Mid - Late Morning Sea Breeze begins once T(land)-T(water) > 6-10 o F 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

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

Circulation Afternoon Wind increases as pressure gradient increases Temperature falls of 5 o F to even 25 o F 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

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

Circulation Evening & Night Solenoid circulation gone 1 to 2 hours after sunset Land cools  Land breeze  Nocturnal convection over water

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

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

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

Modifications Synoptics

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

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

Forecasting Check the land-to-ocean forecasted temperature gradient – needs to be at least 6-10 o F 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… |v g | 2 / ΔT < 5

Real-time Forecasting Clear-air Mode Radar

Real-time Forecasting

Visible Satellite Imagery Clear skies after front passage & Cu/Cb along front

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.

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

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

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

Bibliography COMET Meted: “Thermally-Forced Circulation I: Sea Dr. Markowski’s METEO 414 notes NJ State Rutgers Coastal Ocean Observation Lab University of Illinois Urbana-Champaign - WW2010: “Sea