Orientation & strength of sea breezes
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Orientation & strength of sea breezes
OK, here's a nerdy question that's been nagging at me. I think I have an idea of the answer, but wondering what those of you more knowledgeable about met think....
It's about the orientation and strength of sea breezes in various locations.
Let's say there are three cases:
1. The "classic" case, perpendicular to the coastline, where there is a gentle offshore breeze overnight and early morning and then onshore as the land warms up.
e.g. Cannes, Clacton in UK, ?Cape Town
2. Where you have same effect but more oblique to the coastline, e.g. Perth in Australia in the Summer
3. Where, despite being close to the sea, there is no obvious strong sea breeze effect. I'm thinking particularly of Bournemouth here in the UK. Equally, I presume in the tropics the trades are so strong there is little effect too?
Realise there's a seasonal aspect to this and sometimes due to the orientation of the coastline to prevailing wind direction there is an over-printing that occurs.
So, what is happening in cases 2. or 3.?
My guess is that it must have something to do with topography (e.g. role of Darling Range or even the Swan River in Perth, the presence of the Bay next to Bournemouth), but is it that right?
What goes on at places with complex coastlines like the US NE seaboard cities? How far inland can a sea breeze have an effect, especially if there's a topographic funneling effect? What happens at lakeside airports?
It's about the orientation and strength of sea breezes in various locations.
Let's say there are three cases:
1. The "classic" case, perpendicular to the coastline, where there is a gentle offshore breeze overnight and early morning and then onshore as the land warms up.
e.g. Cannes, Clacton in UK, ?Cape Town
2. Where you have same effect but more oblique to the coastline, e.g. Perth in Australia in the Summer
3. Where, despite being close to the sea, there is no obvious strong sea breeze effect. I'm thinking particularly of Bournemouth here in the UK. Equally, I presume in the tropics the trades are so strong there is little effect too?
Realise there's a seasonal aspect to this and sometimes due to the orientation of the coastline to prevailing wind direction there is an over-printing that occurs.
So, what is happening in cases 2. or 3.?
My guess is that it must have something to do with topography (e.g. role of Darling Range or even the Swan River in Perth, the presence of the Bay next to Bournemouth), but is it that right?
What goes on at places with complex coastlines like the US NE seaboard cities? How far inland can a sea breeze have an effect, especially if there's a topographic funneling effect? What happens at lakeside airports?
Last edited by betterfromabove; 20th Feb 2018 at 22:05.
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I'll guess at Bournemouth. You'll have the same effect, sea breeze, trying to be generated by Studland and Isle of Wight, both are southerly of Bournemouth and one to the west and one to the east. Their sea breezes could be taking the air before it has chance to reach Bournemouth.
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As ever, RAT has a sensible answer. As for the Freemantle Doctor (the sea breeeze off the Indian Ocean around Perth) that starts off perpendicular to the coast. As the day moves on, apparently due to Coriolis Effect, the wind backs so it becomes a southerly until the sun goes down. When you leave the pub in the evening at Swanbourne it’s virtually calm. At Hobart airport a strange phenomena sometimes occurs. Both ends of the runway can have a tailwind as the air above the isthmus on which the airport is built rises. As the day continues to heat up this micro-sea breeze is killed by the overall effect of the island. The controllers there do not take the wind for granted. As for topology, I’ve regularly seen days that had a slightly westerly turn into an easterly as the sun sets. One evening at Dunstable I was passenger in balloon that did a vertical circuit. We landed back within 10 metres from where we took off. The upper air was still westerly but the colder, lower layers flowed against the prevailing wind to lower levels as it sank.
It would therefore be safe to say topology, surface, albido, latitude are all factors (with many others) that control sea breezes.
It would therefore be safe to say topology, surface, albido, latitude are all factors (with many others) that control sea breezes.
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The Fremantle Doctor's strange behaviour finally explained - thanks! Never would have thought the Coriolis would have been involved, but learn a new thing, etc. etc.
There are also days when it never kicks in at all, the N flow persists all day and you can add 10C to the mercury....
Almost feels like there's a quirky book like Cloudspotting to be written on this!
There are also days when it never kicks in at all, the N flow persists all day and you can add 10C to the mercury....
Almost feels like there's a quirky book like Cloudspotting to be written on this!
To be classed as a 'sea breeze', the airflow must be onshore irrespective of the direction of the isobars.
It is caused by unequal heating during daytime, the land mass heats up quicker than the sea; the air over the land rises and cool air from the sea rushes in to replace it.
It is caused by unequal heating during daytime, the land mass heats up quicker than the sea; the air over the land rises and cool air from the sea rushes in to replace it.
Or the increase in temp over the land causes the column of air to expand leading to a pressure differential at about 500' causing a flow of air from land to sea at height. This in turn leads to a pressure differential on the surface (slightly higher over the sea) and starts the onshore breeze. With time the Coriolis force sets in and slowly diverts the onshore breeze to the right (N hemisphere).
