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#3744 - 09/08/2009 02:00 Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
Re: whether a warm summer follows a warm winter, and such questions.
I have ten years data, beginning Autumn 1999, for 40 mean seasonal temperatures at Manilla. I found the 10-year mean for each season (Autumn, Winter, Spring, Summer) and subtracted it to get the anomaly for each of the 40 seasons. I smoothed the results (1:2:1)/4. A graph shows the following:

Seasonal temperature anomalies run from +1.05 degrees (Spring '02: the hottest spring) to -1.14 degrees (Summer '07'08: the coldest summer).

The curve is sinusoidal, with a period of about 1.6 years.

Peaks on the curve are:
Winter '99: +0.06
Spring '00: +0.25
Spring '02: +1.05
Autumn '04: +0.26
Spring '05: +0.61
Summer '06'07: +0.84
Spring '08: -0.01

Troughs on the curve are:
Summer '99: -0.61
Spring '01: -0.74
Winter '03: -0.37
Spring '04: -0.35
Winter '06: -0.22
Summer '07'08: -1.14

With 13 peaks and troughs, one might expect about 3 to occur in each season, but Spring has twice as many: 4 peaks and two troughs. Autumn has just the one peak.

There are two major sustained events: one warming and one cooling.
1. From Spring '01 to Spring '02 the anomaly rose by 1.79 degrees at the rate of 0.45 degrees per season.
2. From Summer '06'07 to Summer '07'08 the anomaly fell by 1.98 degrees at the rate of 0.5. degrees per season.

Do any of these observations ring any bells for anyone?

In case you are interested, the linear trendline has no slope at all.
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#3745 - 11/08/2009 15:41 Re: Observations of climate variation
Surly Bond Offline
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Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
A picture is worth a thousand words. (I just made that up laugh .)

I think there is no doubt that the temperature anomalies form a sine wave.
The period of the wave is a good deal longer than a year.
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#3746 - 11/08/2009 16:04 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
In the graph of the above post, each data point refers to a season. The four points in each year are Autumn, Winter, Spring, and Summer. Summer begins in December of a given year and extends into the next year.
On the smoothed curve, winter anomalies predict summer anomalies to some extent in half the years: 2000, 2001, 2002, 2005 and 2008. In each of these years except 2001 there is a peak anomaly in spring with winter and summer on the flanks of it. In 2001 spring marks a trough,not a peak.
In the other five years winter and summer anomalies are dissimilar, especially in 2006 and 2007.
Five successful forecasts out of ten is not a very good score. :rolleyes:
Perhaps data from other places might show a better success rate? :evillaugh:
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#3747 - 11/08/2009 16:16 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
I just noticed the strange repeated pattern of the peaks:
The first peak is low, the second peak is higher and broader with an up-slope on the crest, and the third peak is very high and sharp. Then the pattern repeats.
Any bets on whether it will repeat again? :nerd:
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#3748 - 12/08/2009 12:49 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
:wave: Hi, guys! :wave:
I would really appreciate comment on this graph.
Does the pattern relate to any data or model already discussed?
Is this the pattern of warm and cool seasons that you had at your place?

I now have data showing that autumn and (probably) winter this year have mean temps close to normal. That makes the current peak wider than the other two low peaks: winter '99 and spring '04.
All the same, the 1.6 year cycle is so strong, the graph suggests (to me) that the next few seasons are very likely to be cool.

Thanks.
laugh
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#3749 - 12/08/2009 16:40 Re: Observations of climate variation
Keith Offline
Meteorological Motor Mouth

Registered: 16/12/2001
Posts: 6453
Loc: Kings Langley, NSW
Excellent topic Surly..not sure that too many people have data.

I'll put my 30+ years of temperature data through some analysis and see what comes out. I've been distracted with trying to get a webpage to work properly. This would be a very welcome excuse to leave HTML etc behind!

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#3750 - 12/08/2009 17:31 Re: Observations of climate variation
Stratospear Offline
Weather Freak

Registered: 19/05/2008
Posts: 156
Loc: Lilydale
There is a strong El-Nino signature in that graph for the warmest periods (Spring in 2002 & 2006). Not surprising really.

The current mini-ElNino might be waning already, so a dip in temps may occur shortly although that could depend on where the warm water currently in the Pacific Ocean Tropics flows.

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#3751 - 13/08/2009 01:04 Re: Observations of climate variation
Arnost Offline
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Registered: 10/02/2007
Posts: 3908
Surly B

You can use your model to predict the future temps / trends at your site. But you have to wait years before you will find out if it has merit.

But you can also hindcast...

I have replicated your graph using Tamworth BoM data, and overlayed it over your graph:



Close - similar trends are evident.

Now, you can use the longer Tamworth dataset to see if what you have identifed holds in the past:



Hints of the identified pattern, but you have to say that it's not really there.

It's late - I'll post up my methodology and links tomorrow night if I get the chance.

cheers
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And this of course applies to scientific principles. Never compromise these. Never! [Follow the science and you will be shown correct in the end...]

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#3752 - 13/08/2009 10:47 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
Thanks for a great follow-through, Arnost.
I tried to count peaks and troughs (notoriously difficult frown ) on the 66(?) year Tamworth record that you have graphed.
I get 41 peaks and 38 troughs. That is a mean period for the cycle of 1.65 years. Is this a "well-known fact" that I haven't heard of?
I notice that there are a few peaks on the longer record that are a good deal warmer than those on my graph. I can't resolve them, but they seem to be in 1946, 1966 and 1981. The coldest time was about 1956.
I guess the major peaks and troughs will show up on annual figures as well. But to speak of a "hot year" clearly tells little of the story.
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#3753 - 13/08/2009 11:30 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
Just a thought: A cycle of 1.666... years would get into step with the seasonal cycle every seven years. If summer is a peak in one year, a summer peak might be expected seven years later.
My maths OK? :rolleyes:
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#3754 - 13/08/2009 11:42 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
My maths OK?
No. A 5-yr cycle.
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#3755 - 13/08/2009 11:44 Re: Observations of climate variation
roves Offline
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Registered: 02/02/2005
Posts: 1632
Loc: Paringa-Riverland
Interesting that the temp anomaly has been flat for the last 65years with variations up and down only.
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#3756 - 13/08/2009 13:13 Re: Observations of climate variation
Keith Offline
Meteorological Motor Mouth

Registered: 16/12/2001
Posts: 6453
Loc: Kings Langley, NSW
I'm probably getting thicker in the head with time..when I put a 1:2:1 filter on my data the result is virtually the same as the 3 month (seasonal) data.

I don't know where I may have gone wrong in the calculation.

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#3757 - 13/08/2009 18:41 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
Keith, are you using monthly data, perhaps? :nerd:
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#3758 - 13/08/2009 19:00 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
Re: the 5/3-year cycle getting in step with the seasons every five years:
I think I can see a 5-year cycle in Arnost's longer-term graph.
That would be expected only if one particular season were more liable to anomalies than the others. From my (very small) data set, I suspect that may be true of spring (see OP). If so, an enhanced peak or trough might occur when a 5/3-year peak or trough fell in spring.

This is clearly a case for spectral analysis. The only time I used that I had a famous statistician holding my hand. The programs are unbelievably fast now (used to take all night), but the traps for the unwary are still there. :evillaugh:

What climate forcing mechanism has a period of 5/3 years?
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#3759 - 13/08/2009 19:12 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
roves,
"Global warming" is almost certainly present in the Tamworth data set, but it is very hard to see on this graph. The trend line would rise only one degree in the width of the graph.
I intend to post later on a kind of graph that shows it better .
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#3760 - 13/08/2009 19:48 Re: Observations of climate variation
Keith Offline
Meteorological Motor Mouth

Registered: 16/12/2001
Posts: 6453
Loc: Kings Langley, NSW
Quote:
Originally posted by Surly Bond:
Keith, are you using monthly data, perhaps? :nerd:
Yes, to start with, then recalculated to seasonal.

Sorry for dumb questions but can you please briefly explain how you set up your calculations?

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#3761 - 13/08/2009 21:06 Re: Observations of climate variation
Arnost Offline
Weatherzone Addict

Registered: 10/02/2007
Posts: 3908
OK – here’s how I did it, so if anyone wants they can replicate…


The Tamworth temperatures can be obtained from:

http://www.bom.gov.au/climate/data/weather-data.shtml

where you can select various meteorological data.

Select Temperature, and then in the new box download both the monthly Maximum Mean and the Minimum Mean (the monthly mean is not available). The Tamworth station IDs are Tamworth AP (station 055054) and Tamworth AP AWS (station 055325).

Create a monthly mean from the above data by adding the maximum and minimum mean temps for each month and divide by two. I cross checked this against the data at GISS:

http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.501957620000.1.1/station.txt

which has what looks like the full Tamworth AP dataset. Note that the Tamworth AP data goes back to 1907 (as does the GISS data set) but there are a few gaps / missing months. Here is the difference between my mean and GISS:



Though there are a couple of downspikes, the vast majority is either the same or off by 0.05C attributable to rounding.

I then spliced the two datasets (the Tamworth AP and the Tamworth AP AWS) together without any adjustments. I guess that the temps should be identical as the AWS is basically at the same location as the screen that it replaces. There is a period of overlap and this is the difference.



The Airport AWS seems to run a bit cooler in the winter, and while purists may disagree as far as I’m concerned it’s negligible for this exercise.

The next step was to create a base from which an anomaly could be calculated. I decided to use the 1961-1990 period. (Note, if I used the same 10 year period as a base that Surly B used - the match may have been better…). To calculate the anomaly, I added every individual months means (i.e. added all the Jan’s, all the Feb’s etc) and divided by 30.

I then subtracted this monthly value from all the respective months to get the anomaly.

I then added the three months in each season (i.e. Mar, Apr & May for Autumn etc) and divided by three. This is the main (red) dataset in my graphs in my previous post.

I then did the 1:2:1 smoothing as follows (I think this is where you may have gone wrong Keith). The first value (Winter 1942) was:
(Autumn 1942 X 1 + Winter 1942 X 2 + Spring 1942 X 1) / 4,

and the next (Spring 1942) was:
(Winter 1942 X 1 + Spring 1942 X 2 + Summer 1943 X 1) / 4

This is the smoothed (blue) dataset in my graphs in my previous post.

And that’s it! If you have any questions let me know. I hope that this was usefull.
_________________________
“No. Not even in the face of Armageddon. Never compromise” ...

And this of course applies to scientific principles. Never compromise these. Never! [Follow the science and you will be shown correct in the end...]

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#3762 - 13/08/2009 21:32 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
My calculations are essentially the same as Arnost's, but I started from my own daily max and min temps at Manilla. That is where my interest lies.
I had already summarised my data by month and by season before I thought of doing this analysis. I do monthly and season reports for the local paper.
One could use monthly data directly with a wider smoothing window (half-width 8 months) for a similar result.
When I drew the graph, I used the whole 10 years of data as my base period. I intend to keep using that base period for the time being. Data for future seasons may well trend warmer or cooler than the chosen base.
I am glad Arnost stated his choice of base period, which saves me asking. smile
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#3763 - 13/08/2009 21:39 Re: Observations of climate variation
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 2060
Loc: Manilla, near Tamworth NSW
BTW Arnost, I believe the new Tamworth AWS is some kilometres from the old airport site.
The AWS is a "blasted heath" (without the witches). wink
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