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#1414119 - 22/03/2017 09:29 MSLP anomaly
CaptainAhab Offline
Cloud Gazer

Registered: 20/03/2017
Posts: 3
I live on the South Coast of SA. In the last three years I have documented massive sea level pressure(MSLP) anomalies in South Eastern AU. I remember in 2015 that one of the yearly graphics depicting the world wide impacts of Climate Change. It had drought almost everywhere and an occasional flood. But the most standout feature was the anomaly of pressure in the Great Australian Bight. It had its own symbol of mslpa.

It was like somebody changed the pressures. They no longer matched the weather. The pressure rarely went above 1015(more or less the normal middle of the scale). We used to frequently have those lovely 1035 blue sky 20kt dry days. No longer. Even now 3yrs later, we have finally had 6 weeks of blue skies in Adelaide, but the pressure is still wrong.

In 2016 it was common to not see the pressure go above 1010 for weeks at a time, regardless of weather. I believe it is the result of the Antarctic jet stream coming north near AU and causing a consistent low pressure area. The higher pressure on the continent are only 10-15 hPA higher than the 1000 low just south of us. The 1040 amazing AU days have not happened in 3 yrs. 1020 is the new high pressure for AU. Its been common to have the entire country under 1010 for a few days at a time. I don't recall this happening in the past.

How have the baro pressures been around AU for the last 3 yrs. Does anyone know if this is happening anywhere else on the planet? Is this the new normal? The scientists have focused on the screwed up northern hemisphere jet streams. What are they saying about the southern?


Edited by CaptainAhab (22/03/2017 09:32)

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#1414125 - 22/03/2017 09:53 Re: MSLP anomaly [Re: CaptainAhab]
Snowy Hibbo Offline
Weather Freak

Registered: 30/12/2016
Posts: 314
Loc: Matlock, Victoria.
1040+ highs are very stable airmasses. As energy increases in the atmosphere, airmasses will get less stable. Hence lower than normal MSLP in high pressure airmasses. But this should be happening over time, not 3 years.
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#1414174 - 22/03/2017 12:31 Re: MSLP anomaly [Re: CaptainAhab]
retired weather man Offline
Weatherzone Addict

Registered: 01/07/2007
Posts: 4325
Loc: Wynnum
The SAM situation is one indicator.
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#1414348 - 22/03/2017 20:38 Re: MSLP anomaly [Re: CaptainAhab]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 7155
Loc: Adelaide Hills.
This is my perspective smile :

In general, barometric pressure at Southern Hemispheric Mediterranean latitudes is higher (with more sharp, dramatic changes) in winter, and lower (with less sharp, dramatic changes) in summer.

If the [barometric] pressure is getting affected [falling], per the Gas Laws (e.g. P*V = n*R*T), we would be talking about changes in-situ, where it happens. If we theoretically pump more water-vapour (mass per cubic metre) into the atmosphere, the overall air-density, pressure, and temperature would fall. This is because:

A. Water is about 18 atomic mass units (grams per mole), whereas dry-air is about 29. Therefore water-vapour is lighter than dry air.
B. Falling temperatures are capable of increasing cloud cover at these latitudes.
C. The higher the temperature, the more molecular kinetic energy there is (molecules travel further before they collide with each other, and release heat they have more momentum), and vice versa.

There are a few caveats, but that's the general picture as far as I can tell smile . As this is a mostly weather-based forum, I won't be elaborating on the science of this unless a request is made.

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#1414388 - 22/03/2017 23:09 Re: MSLP anomaly [Re: retired weather man]
CaptainAhab Offline
Cloud Gazer

Registered: 20/03/2017
Posts: 3
I'm familiar with the positive/negative aspects of the SAM. Definitely a shift over the same time frame. The jet streams bring the storms closer to the continent. This explains part of the situation. The pressure not matching the weather is a bit more complicated.

I was amazed how many of the fronts(most of them) turned cyclonic in 2016. Many took a similar storm track to the one in September that hit Adelaide and took out the power.

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#1414405 - 23/03/2017 07:18 Re: MSLP anomaly [Re: CaptainAhab]
Funkyseefunkydo Offline
Weather Freak

Registered: 30/04/2007
Posts: 487
Loc: East Lake Macquarie
This may help. Hadley cell effect

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#1416313 - 26/03/2017 21:41 Re: MSLP anomaly [Re: CaptainAhab]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 7155
Loc: Adelaide Hills.
So long as one understands correlation does not necessarily indicate cause, I think one will be ok smile .

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