Rubbish seabreezes

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Sputnik11 said..
Any ideas as to why the seabreezes are so crappy this summer. They never really fill in. Perfect weather for a good seabreeze and over and again, they don't get there. Wondering why its been so poor this year.

True...we have had very mild temperatures and perhaps no major differentials of temp between land and Sea.

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cameronil said..

matcoburn said..

Sputnik11 said..
Any ideas as to why the seabreezes are so crappy this summer. They never really fill in. Perfect weather for a good seabreeze and over and again, they don't get there. Wondering why its been so poor this year.

True...we have had very mild temperatures and perhaps no major differentials of temp between land and Sea.

Hit the nail on the head Matcoburn. Heating is what you want. Can have a gradient assisted seabreaze that is strong with less heating, or if no gradient you need more heating. You don't want a strong N'ly (opposing) gradient as it holds out the seabreeze. You don't want the seabreeze in too early (as recently in Melbourne) if heating and gradient are not working together as cooling occurs. You want general heating and ideally at least 28 degrees and an assisting gradient then she blows!!
In Perth for example, they get gradient assist and heating much of the time in summer giving the double wammy 20-30 knots, sometimes 35 knots.

OK - so today. 32 degrees. Breeze is there and building a bit as its warming. Gets really warm late - no seabreeze at all, it backs off to nothing. Today was your perfect seabreeze recipe. 32 degrees, no northerly. Breeze started building around midday, but nothing happened. In fact, it disappeared. Yesterday, it blew 2 knots one second and then 18 to 20 the next. And not for the first time this summer. There's something NQR about this summer.

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Sputnik11 said..

cameronil said..

matcoburn said..

Sputnik11 said..
Any ideas as to why the seabreezes are so crappy this summer. They never really fill in. Perfect weather for a good seabreeze and over and again, they don't get there. Wondering why its been so poor this year.

True...we have had very mild temperatures and perhaps no major differentials of temp between land and Sea.

Hit the nail on the head Matcoburn. Heating is what you want. Can have a gradient assisted seabreaze that is strong with less heating, or if no gradient you need more heating. You don't want a strong N'ly (opposing) gradient as it holds out the seabreeze. You don't want the seabreeze in too early (as recently in Melbourne) if heating and gradient are not working together as cooling occurs. You want general heating and ideally at least 28 degrees and an assisting gradient then she blows!!
In Perth for example, they get gradient assist and heating much of the time in summer giving the double wammy 20-30 knots, sometimes 35 knots.

OK - so today. 32 degrees. Breeze is there and building a bit as its warming. Gets really warm late - no seabreeze at all, it backs off to nothing. Today was your perfect seabreeze recipe. 32 degrees, no northerly. Breeze started building around midday, but nothing happened. In fact, it disappeared. Yesterday, it blew 2 knots one second and then 18 to 20 the next. And not for the first time this summer. There's something NQR about this summer.

Didn't you notice it was easterly that killed it.
We are getting way too many easterlys. Been happening for the last couple or so years.
Climate change perhaps ?

The heat differential between land and sea is definitely important but the seabreeze circulation is important too.
In the good true S-SSW seabreezes, you'll see a line of cloud 10-20km inland (say around the Airport), where the air rises to the mixing layer anywhere from 800m-1500m high. At this height the air then blows back as a gentle northerly to complete the circulation.

Strong high pressure (subsiding or descending air) is needed to help this circulation establish as it leaves this space of unstable air below 1500m where the seabreeze circulation can sit.
If it's unstable (low pressure) seabreezes can fail as air is rising to much preventing the circulation from forming. Similarly, if it's too warm (seemingly above about 25 deg), the mixing layer rises to a point (say>2km) that becomes too high for the seabreeze circulation to form.
The combination of heating, the circulation, wind flow and terrain are important. There's something about our warm still ENE flow days that stops any good seabreeze forming, prob as the mixing height is too high.
On really hot days, the seabreeze can load up out in Bass Strait like a rubber band and rush through as a squall, once the northerly eases.

Our best pure seabreezes seem to be from a gentle SSE-ESE flow as the shape of the bay bends it around into a SSW and the inland heat pulls it through.
Westerlies seem to be bad for seabreezes unless it is a pretty light flow - I think again the shape of the bay and westerly flow work against each other.

An extra tidbit about heating, is it is actually solar radiation, not temp in a screen that's important. Even if water temp is 19 and air temp 18 (less than water temp), direct summer sun on all that concrete in Melbourne can heat it to 40-50 degreesC, which can draw in a pretty decent seabreeze. These ones can be very up and down though, as the cool seabreeze air actually kills itself, then reforms and this repeats.

We don't actually get many pure seabreezes, with zero base flow.
Most build on the synoptic flow. Can be 10-15 knots southerly, which builds to 20-25 in the arvo with seabreeze effect, but also inland pull through Kilmore gap.

There's some good info by Kenn Batt:
http://www.bom.gov.au/nsw/amfs/Sea-Breeze.shtml
www.bom.gov.au/nsw/amfs/More-on-Sea-Breeze.shtml