Thursday, January 25, 2007

Alice Hots up during the day only

Heading a little east we find another isolated weather station at the Alice Springs Airport. One of only 2 non urban stations in the Northern Territory with significant data, we shall analyse temperature data for this station alone.

Analysis in maximum and minimum temperatures over the years shows a very significant increase in maximum temperatures (t = 4.66, p < 0.01) at the rate of 0.02 degrees per year or 2.2 degrees per 100 years. The increase seems to have largely occurred from about 1978 onwards. With regards to minimum temperatures no significant increase or decrease was found (t = 0.36, p = 0.71) however there does seem to be a small case for cyclic behaviour.

When analysing temperatures at different times, data ranges back to 1952 for all cases with the exception of Midnight temperatures which start 12 years later. In tendem with a no significant minimum increase, no significant increases in temperature were found at Midnight (t = 0.66, p = 0.51), 3am (t = -1.87, p = 0.67), 6am (t = -1.4, p = 0.17), 6pm (t = 0.04, p = 0.97) and 9pm (t = -1.89, p = 0.06) when the sun is down. All these temperatures are highly correlated with each other, eg a 98.6% correlation occurs between Midnight and 3am. The years in which Midnight were missing from 1952 to 1964 showed significantly higher temperatures than normal at this time, hence like the other temperatures around this time we would most likely have a decreasing temperature trend when the sun is down.

Temperatures at 3am and 9pm have decreasing trends at a rate of 2.1 and 2.3 degrees per 100 years, however it should be noted that this decrease was not significant, albeit only marginally.

When the sun rises we see a significant increase in temperature. Temperatures at 9am (t = 6.2, p < 0.01), noon (t = 5.36, p < 0.01) and 3pm (t = 3.7, p < 0.01) all have a significant increasing trend. The rate of this increase has been recorded at 3.9, 3.35 and 2.6 degrees per 100 years respectively. This corresponds the significant maximum increase in temperature. The correlation between temperatures at 6am and 9am is not as strong (r = 28%) . Note that for the temperatures at 9am, noon and 3pm, a slight decrease in temperature is shown between the start of the records and the mid 1970s, from which temperatures increased.

So what does all this mean? It means that Alice Springs has seen a significant increase in temperatures when the sun is shining. When the sun is down, a decreasing temperature trend was found however not significant.

This differs from our previous analysis on Giles, which is not that far away from Alice Springs. The Alice does have more data, but still only 50 years of data is not ideal. It is strange that temperatures during the day would increase significantly at Alice Springs but not at Giles which is located moderately nearby. Both stations recorded no significant increases or decreases when the sun was down.

A hot looking Alice:


Anonymous said...

Perhaps you should look at the history of the Alice Springs Airport for physical changes such as new buildings, tarmac extensions, etc., and where these are in relation to the weather station, to see if these may have had an impact on daytime temperatures.

Jonathan Lowe said...

This is possible, but I'm not about to head all the way out to Alice Springs just to check. The theory of urban warming is one that has rarely been tested, which is surprising.