Clouds Down Under
Guest Post by Willis Eschenbach
Sometimes climate research is just plain funny. I wrote before about Irish rain and investigated whether there is any effect on the rain from the solar variations linked to sunspots. I was looking for evidence that the Svensmark hypothesis is true. Svensmark said that changes in the heliomagnetic field related to the sunspot cycle affect the number of cosmic rays (true), and that this, in turn, affects the number of clouds (unproven). I found no evidence of any such effects in the Irish rainfall data.
In response, folks said a) rain is not the proper measure of the Svensmark effect, I should look at clouds instead, and b) I should look at some place that is drier than Ireland, where it’s basically all clouds all the time.
Fair enough, reasonable objections. So I thought I’d see what other cloud datasets I could find in drier areas. Since I’d already looked (unsuccessfully) for evidence of the Svensmark effect in US cloud data, I went to see what I could find about clouds in Australia. I found some good data, but along the way, I read something pretty hilarious. It had to do with what is called the “pan evaporation” data.
The idea behind pan evaporation is simple. Put some water in a pan. See how fast it evaporates. This measurement involves wind, temperature, humidity, solar input, and rainfall. It’s an important measure for farmers, who use it to determine when and how much to water their crops.
Figure 1. Flat pan-type container used to collect pan evaporation data, along with an anemometer to measure wind speed.
When I saw a link to the Australian pan evaporation data, I thought hmmm, that could be interesting. So I took a look … and found a truly funny statement, viz:
However, the installation of birdguards on the pans during the late 1960s and early 1970s is known to have created an inhomogeneity in the climate record.
Seriously, they put out pans of water to see how fast they evaporated and they didn’t do anything to stop birds from drinking the water? Gotta love climate science. But I digress …
I did find cloud data, from what is called the ACORN-SAT network of climate stations. This is a network of high-quality stations with longer-term records. The ACORN-SAT data is here. Figure 2 shows the locations of the ACORN-SAT stations.
Figure 2. Locations of the ACORN-SAT Australian climate stations
Now, the indefatigable Joanne Nova has done sterling work over at her blog showing that the temperature records from the ACORN-SAT networks have been … well … let me call it “massaged” and leave it at that. It’s a shame.
But I doubt greatly whether any such massaging has been done with the cloud data, because clouds are not political like the temperature data is.
So I went and got the cloud data. Actually, it is very detailed, in that they have recorded cloud coverage both in the morning (9AM) and the afternoon (3PM). I downloaded the data, which turns out to be a total of 888 separate files … urgg. So I girded my loins and started writing computer code. I identified all of the files containing monthly cloud data for both mornings and afternoons, that’s 260 files. I extracted them, did some simple QC on them, and saved them as a pair of CSV files (morning and afternoon clouds) so folks could look at them without the hassle I had extracting them. The data runs from July 1954 to April 2015.
Once I had the cloud data, I did a straight average on them. Yes, I could probably get a more refined answer by doing some kind of geographically-weighted average, but a straight average is generally more than adequate for this type of analysis.
Then I created a periodogram of the average Australian morning and afternoon clouds, and compared that to a periodogram of the sunspots for the same period. Figure 3 shows that result:
Figure 3. Periodograms, Australian clouds and sunspots.
Once again I don’t find any sign of any relationship between the sunspots and the clouds. The clouds have the usual variety of small cycles that you find in any natural dataset, including one at 12 years … but during the period the sunspot cycles were at ten and a half years. Close, but no cigar … and close only counts in horseshoes. And hand grenades. But this is neither one of those.
So, nothing to see regarding the Svensmark effect. However, there is more to be seen in the Aussie cloud data. For starters, my hypothesis that clouds and thunderstorms act to regulate the temperature implies that cloudiness should increase with temperature. And since temperatures are higher at 3PM than at 9AM, my hypothesis would suggest that there should be more clouds in the afternoon than in the morning. I’ve shown elsewhere that this is generally true in the wet tropics, but not in a mostly desert landmass like Australia. Here is the distribution of the morning and the afternoon Australian clouds …
Figure 4. Boxplots, Australian morning and afternoon clouds. Heavy black lines show medians. If the notches of two plots do not overlap this is ‘strong evidence’ that the two medians differ (Chambers et al, 1983, p. 62). “Whiskers” extend out 1.5 times the interquartile range. Circles are outliers.
Clearly, there are more clouds in Australia in the afternoon when it is warmer, as my hypothesis implies.
How much difference will the cloudiness make in the amount of sunlight that gets past the clouds to the surface? We can estimate this by using the CERES data. Here is the scatterplot of Australian cloud coverage (%) and Australian cloud solar reflections (W/m2).
Figure 5. Scatterplot, CERES monthly cloud coverage (%) and cloud solar reflections (W/m2) for Australia.
Now, the average difference between morning and afternoon clouds in Australia is 4.6% … which would imply a decrease in afternoon sunshine on the order of 4.6 W/m2. This is a significant amount of cooling.
There’s another way to consider this, again using the CERES data. This is to look at the relationship between the cloud reflections and the temperature.
Figure 6. Scatterplot, CERES monthly cloud coverage (%) and temperature (°C) for Australia.
This shows that in Australia when the temperature goes up by 1°C, the increased clouds reflect an additional 1.4 W/m2. Again, this is in agreement with my hypothesis about the clouds being part of the temperature regulating system.
Finally, note that this is just one of the ways that the cooling increases with the clouds. In addition to the change in the amount of reflected sunlight, there are the effects of rain and thunderstorms. Both of these cool the surface strongly through a variety of effects. See my post entitled Air Conditioning Nairobi, Refrigerating The Planet for a discussion of these effects.
So that’s the result of my wandering around the Australia outback … no sunspot effects on the clouds, and increasing clouds with temperature. Plus a good laugh about the birds drinking out of the Australian evaporation pans …
My best regards to all of my Aussie mates, it’s a great country with interesting folks. If you haven’t visited there you should … and if you are Down Under and you need a tattoo, and who doesn’t need one, go see my mate Tu and his lovely wife Ify, they are both fantastic artists.
And of course, warmest wishes to everyone,
PS: As always, I politely request that you quote the exact words that you are discussing, so we can all be clear who and what you are talking about. Misunderstandings are the bane of the internet. Plus, if you wish to refute something you need to quote exactly what it is that you are refuting. I ask politely, but if you don’t quote what you are talking about, I may indeed cast aspersions on your cranial horsepower or the personal habits of your antecedents …
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