In my last post I showed how in Australia more than three quarters of the difference between surface maxima and tropospheric anomalies can be explained by variation in rainfall alone. Figure 12 from that post showed that clearly:
Fig. 1: 12 month rainfall vs surface maxima – TLT difference: Australia
In this post I am looking at the different contributions made by the north and the south of Australia. This map shows the regions used for climate analysis by the Bureau.
Fig. 2: Climate regions
Northern Australia and Southern Australia have vastly different climates, as shown by the following graphs of mean monthly rainfall:
Fig. 3: Mean Monthly Rainfall: Northern Australia
Fig. 4: Mean Monthly Rainfall: Southern Australia
The sheer volume of wet season rain in the north dominates, and distorts, the national means, therefore it is sensible to analyse northern and southern influences separately.
Northern Australia, north of 26 degrees South, has less than 3 degrees outside the Tropics, so may be considered the tropical northern half of Australia. Do not think of this as a lush tropical paradise. Far from it. There are a couple of very small areas of wet tropics, and some softer country in the far south-east, but the rest is either monsoonal wet/dry (very wet summers, almost completely dry for the rest of the year), or desert. The rainfall graph for Northern Australia is for the whole region- most of which is desert. If the monsoon is weak or fails altogether we get drought.
Southern Australia is largely influenced by the Southern Annular Mode. Each winter the southern high pressure systems move north, and cold fronts sweep across the south bringing winter rains. If these systems don’t move far enough north, the rain systems dodge the bottom of the continent, resulting in drought conditions. The far north-east of Southern Australia (southern Queensland and northern New South Wales) gets a wet summer/ dry winter pattern, and Tasmania and coastal New South Wales get rain in all seasons.
Comparing the influences of northern and southern rainfall on the national surface- TLT differences:
Fig. 5: Northern rain vs national maxima- TLT difference
More than two thirds of the national maxima-TLT difference can be explained by variation in the northern rainfall alone.
Southern rainfall has a much weaker correlation with national maxima- TLT difference:
Fig. 6: Southern rain vs national maxima- TLT difference
Now let’s plot Northern rain vs northern maxima- TLT (for the whole of Australia) difference, firstly for each month:
Fig. 7: Northern rain vs northern maxima- national TLT difference: monthly
Nearly two thirds of the monthly difference can be explained by monthly rainfall alone.
Fig. 8: Northern rain vs northern maxima- national TLT difference: 3 monthly
Three quarters of the 3 month mean surface maxima minus national TLT difference can be explained by rainfall.
Fig. 9: Northern rain vs northern maxima- national TLT difference: 12 monthly
R squared value of 0.8348 corresponds to a correlation of -0.91! But wait- there’s more! The 24 month means give an even better fit!
Fig. 10: Northern rain vs northern maxima- national TLT difference: 24 monthly
And 120 month means show an extremely close fit:
Fig. 11: Northern rain vs northern maxima- national TLT difference: decadal
97% of decadal northern surface maxima- national TLT difference is explained by decadal northern rainfall variation.
Fig. 12: Southern rain vs southern maxima- TLT difference: monthly
Fig. 13: Southern rain vs southern maxima- TLT difference: 3 monthly
Fig. 14: Southern rain vs southern maxima- TLT difference: 12 monthly
More than half the difference between southern Australian maxima and TLT can be explained by southern rainfall variation.
However, 24 month means are not as good a fit:
Fig. 15: Southern rain vs southern maxima- TLT difference: 24 monthly
And the long term means are a much poorer fit:
Fig. 16: Southern rain vs southern maxima- TLT difference: decadal
Only 34% of the decadal southern Australian maxima-TLT difference is due to rainfall variation.
In tabular form:
Fig. 17: Range of rainfall anomalies and R-squared values for regional rainfall vs regional surface maxima- national TLT differences
Australian climate is dominated by the tropics, and tropical rainfall variation dominates the national surface- troposphere differences, and even more so the tropical surface – national troposphere temperature differences: the greater the rainfall variation, the greater the difference between surface and tropospheric temperatures.
For a better analysis, we would need UAH anomalies for Australia separated into north and south of 26 degrees South.