Why are the highs stronger in winter

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Why are the highs stronger in winter

Postby Vinny » Sat Jun 04, 2011 4:29 pm

Why are the high pressures stronger in winter than in summer ?

eg 1038hp in June , vs less than that in January ?
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Re: Why are the highs stronger in winter

Postby Cmon Aussie Cmon » Sat Jun 04, 2011 5:07 pm

There's a bigger pressure gradient in winter than in summer. My guess is there is stronger, sustained lows in winter like 970hpa vs summer 995hpa and the odd cyclone. Remember air flows out of high pressure into low pressure to restore equilibrium. The stronger the low is, the stronger the high has to be. Not sure if that's right though...

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Re: Why are the highs stronger in winter

Postby Fu Manchu » Sat Jun 04, 2011 6:01 pm

I'll look into it for you Vinny.
I recall similar discussion last year and the year before.
Pretty sure we worked out that Siberia has the strongest Highs, but we surely must be close in recent years.

Good topic :)

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Re: Why are the highs stronger in winter

Postby Cmon Aussie Cmon » Sat Jun 04, 2011 8:16 pm

Fu Manchu wrote:I'll look into it for you Vinny.
I recall similar discussion last year and the year before.
Pretty sure we worked out that Siberia has the strongest Highs, but we surely must be close in recent years.

Good topic :)

Siberia get like 1060hpa highs.

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Re: Why are the highs stronger in winter

Postby Pete » Sat Jun 04, 2011 8:17 pm

In a typical May/June pattern strong high pressure systems follow deep low pressure systems and vice versa. High pressure systems are stronger in winter because they at first they form nearer to the Antarctic and are stronger because high pressure systems form in cold air; the colder the air the stronger the high. As the belt of subtropical belt of high pressure systems drift north during the winter they weaken in the warmer air over the Australian continent and a replaced sub-polar low pressure cells.

If the sea surface temperatures are warmer won't the highs, when they finally move north, be weaker than normal this year, allowing the westerly air flow to be stronger and the more dominant feature affecting south Australia? How will current state of the southern oscillation index in a weak La Nina pattern affect the climate of WA this winter? The current Indian Ocean Dipole (IOD) favours a drier than normal winter over southern WA now. :(

http://www.bom.gov.au/climate/ahead/rain.wa.shtml

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Re: Why are the highs stronger in winter

Postby Vinny » Mon Jun 06, 2011 6:31 pm

The highs will stay south forever .....
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Re: Why are the highs stronger in winter

Postby Fu Manchu » Mon Jun 06, 2011 6:38 pm

We will get more feedback possibly and so far Neil Bennett says,

"Highs form due to subsiding air, and are aided by regions of convergence in the upper atmosphere. Combinations of both lead to very strong High Pressure."

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Why are the highs stronger in winter

Postby Fu Manchu » Tue Jun 07, 2011 5:15 pm

From BoM
"The strong high pressure systems have been impressive south of the state over the last month"...

ftp://ftp.bom.gov.au/anon/home/ncc/www/ ... 110531.gif

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Re: Why are the highs stronger in winter

Postby Vinny » Wed Jun 08, 2011 4:07 pm

I think the highs were stronger last year , if I recall correctly sometimes up to 1044hp !
Yeppoon Annual Average Rainfall is (BOM) = 982.5mm
2012 Yeppoon 976.8mm
2014:1114.2mm

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Why are the highs stronger in winter

Postby Fu Manchu » Wed Jun 08, 2011 5:23 pm

You'd be right but either way, 1038/9 or 1040-44 they are bloody strong.

When I was a grommet checking weather maps for surf (before technology) a 1024 or 1026 was a strong high if it featured on the synoptic.

Things are changing.

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Re: Why are the highs stronger in winter

Postby Pete » Fri Jun 17, 2011 9:57 pm

THE COMPLETE BOOK OF AUSTRALIAN WEATHER wrote:The lowest mean sea level pressure ever recorded was 870hPa in 1976 in typhoon Tip and the highest mean sea level pressure was 1084hPa in Siberia in 1968.
In Australia, strong high-pressure cells occasionally register 1040hPa, and intense lows, often tropical cyclones can go below 950hPa .

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Re: Why are the highs stronger in winter

Postby MetRep » Wed Jun 22, 2011 5:58 pm

Highs are stronger in winter because the surface weather pattern represents air pressure which could be simply defined as the weight of air above a particular point. Cold air is heavier (more dense). So as the sun goes north in winter the Australian region cools, especially over the land and the pressures as a whole are higher than they would otherwise be. In summer the region warms up and pressures drop, especially in the tropics.

In July almost the whole Australian region has a mean pressure over 1015hpa (including northern Tasmania) whilst in January almost the entire region has a pressure below 1015 hpa.
See here: http://www.bom.gov.au/jsp/ncc/climate_a ... period=jan

However, the mean pressure at any place is also determined by the location of the major pressure systems which also move north with the sun. So the regions to the south of the continent have lower pressures in winter than they would in summer as the lows move north as also the high pressure ridge moves north.

If we do get a high in winter, it will be more intense than a high in summer.

The coldest temperatures and the highest pressures are in Siberia in winter.

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Re: Why are the highs stronger in winter

Postby Pete » Wed Jun 22, 2011 6:20 pm

Thanks for the explanation MetRep. :)

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Re: Why are the highs stronger in winter

Postby Vinny » Thu Jun 23, 2011 10:52 pm

So with NZ being further south than Australia , would this be why it gets more cold fronts and lows ?
Yeppoon Annual Average Rainfall is (BOM) = 982.5mm
2012 Yeppoon 976.8mm
2014:1114.2mm

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