Sea Breezes Why What Where When How Sea

Sea Breezes Why, What, Where, When, How…

Sea Breeze • • • Wind blowing off the ocean onto the land Good for coastal soaring Limits thermal activity close to the coast Creates sea breeze front effect Can be caused by Synoptic forces or localised sea breeze effect

Synoptic Onshore Wind • Driven by nationally significant synoptic influences (i. e. High and Low pressure systems) • Large geographical effect (hundreds of kilometres) • High pressure system spins anticlockwise • Low pressure system spins clockwise • Wind travels along isobars

Synoptic Onshore Wind (cont. ) • Wide isobars mean low wind speed (shallow pressure gradient) • Tight isobars mean strong winds (sharp pressure gradient) • Wind system is thick: full troposphere = ~50, 000 feet, surface wind all boundary layers

Synoptic SE Wind • Classic Merewether and Strezzi days • Can turn east and NE as High moves into the Tasman Sea • More stable air mass than East Coast Low

Synoptic NE Wind • Classic Dudley days with reduced risk of wind shadow. • NE winds from early morning strengthening until after dark

Synoptic East Coast Low • Usually associated with cold air aloft which increases instability • Good for flights up the Hunter Valley • Classic Merewether and Strezzi days

Classic Sea Breeze Defined by BOM and various academics as; 1. Synoptic air mass moving offshore 2. Surface winds moving onshore generated by the difference in temperature between land sea

Theory – Basic Principles • Cool air is more dense than warm air. This is how a hot air balloon works and thermals rise. • The sun heats the ground, which heats the air close to the surface. • The heated air rises and leaves a localised low pressure area • Cool air moves in from the sea to equalise the pressure difference. • The warm ground heats the cool air.

Sea Breeze Schematic Re-circulation Warm air rises Sea Breeze Warm Land Cool Sea

Some Facts and Fables • Sea breeze thickness varies from 1000 to 3000 feet • The time of year can have a significant effect on thickness (heat transfer to the ground, max surface temp? ). • The re-circulation air can be very close to the top of the sea breeze.

Facts and Fables cont. • Sea breeze development can be enhanced or limited depending on the synoptic wind strength and direction. • Sea breeze penetration inland is dependant on difference between sea temp and maximum land temp • Can be felt ~100 kilometres inland • Sometimes less than 5 kilometres • Is influenced by topographic features (valleys, ranges)

Facts and Fables cont. • Imagine a bucket of water tipped onto the shoreline and where the water would run inland • Sea breeze starts perpendicular to the coast line and then gradually moves NE under the influence of the Coriolis force

Dudley effects What makes a good day and why can it go horribly wrong

Is it on ? The good signs • • Blowing onshore from sunrise ENE to NE Solid wind lines Wind lines all the way into the rocks below launch • Trees moving down the front on the cliff edge

The Warning Signs • A glassy section on the water close to the cliff • An off shore wind in the morning • Cu Nimbs drifting west towards the coast • Someone just launched and they are only getting 100 feet above launch

The Dudley Phenomenon Launch Still Dry Dense Air Glassy water surface Wind Moist Light Air Wind Lines

Sea Breeze Front Interactions

Effect on thermal conditions • The sea breeze front pushes inland • The front lifts the warm air off the ground and forces it upward over the cooler air mass moving in • A line of cumulus may develop along the front edge • The cool air mass cools the ground and inhibits the development of more thermals behind it • This is evident in a lack of cumulus behind the sea breeze front

References • Martin Babalkhan, Major Air Masses Over Australia • Dunsmuir, Spark, Kim, Chen; Statistical Prediction of Sea Breezes in Sydney Harbour • Kennet, Korb, Nickelson; Sea Breeze Prediction Using Bayesien Networks • Seabreeze. com. au; Wind Glorious Wind…