Rain, clouds, and temperature

Looking at the continent of Australia as a whole, and using 12 month running means to smooth the very noisy data, we can see some intriguing patterns.

Firstly, here is a comparison of tropospheric temperatures above Australia from the University of Alabama- Huntsville (UAH), with surface air temperatures from the Bureau of Meteorology’s ACORN-SAT database.   To be comparable, both datasets are in anomalies from their 1981 – 2010 means.  The data are monthly since December 1978, with a 12 month running mean.

Fig. 1

uah v mean

Both datasets show concurrent rises and falls and are very similar (though not always).  Note how Acorn means were very much cooler in 2011 -2012 and much hotter in 2013.  Note also that 2014 has Buckley’s of being the hottest year on record.

Mean equals the average of maximum and minimum, so let’s look at maxima and minima.

Fig. 2

uah v max & min

Note that UAH usually tracks Acorn maxima, except when it doesn’t- shown above by the Xes.

Perhaps it has something to do with rainfall, or lack of it.  In the next plot, rainfall is inverted, so dry is at the top, wet at the bottom.

Fig. 3

uah v rain inv

Incidentally, the Bureau also has 9 a.m. and 3 p.m. cloud data available.  Note how closely both cloud datasets match, and how rainfall largely corresponds.

Fig. 4

rain v cloud

And the Southern Oscillation Index runs in close partnership with rainfall- sometimes SOI leads rain, sometimes rain leads SOI.

Fig. 5

rain v soi

Which is why I don’t take a lot of notice of predictions based on SOI.

Now see what happens when we plot inverted rainfall (dry at the top, wet at the bottom) and maxima.

Fig. 6

rain v max

Only once does 12 month mean maximum temperature precede 12 month rainfall (1991-1992).  At all other times, rainfall peaks or troughs occur before maxima (or at most, simultaneously).

With minima, the lead is even more obvious, however there are apparent exceptions in 1982 and 1994-1995, although these may be further examples of rain leading minima by more than a year (marked with “?”).

Fig. 7

rain v min

When we compare maxima with minima, the pattern is clear.

Fig. 8

max v min

Only in the summer of 1994-1995 do the records diverge.

Generalisations (and farmers have known about these rules of thumb for years):

  1. Climate is cyclical.  Rain and temperature rise and fall in roughly two or three year cycles.
  2. It always rains after a drought.
  3. Dry years are followed by spikes in maximum and minimum temperatures, from one to several months later.
  4. Wet years, with heavy cloud and rain, cause sharp drops in minimum and maximum temperatures, from one to several months later.
  5. Maximum temperatures lead minimum temperatures by several months in wet years, and by a shorter period in dry years.
  6. There are exceptions to all of the above.

Next step: Australia is a large continent with several distinct climatic regions.  I will next look at smaller regions to see if the above generalisations hold true and indeed may be modified or enhanced.

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One Response to “Rain, clouds, and temperature”

  1. paul Says:

    i have just read that BOM have called spring 2014 as the hottest on record. whats the bet that no individual temp gauges recorded a hottest for sept or oct or November record.

    I will have a go at checking this but you might have stats already.

    keep up the good work

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