Thursday, 17 January 2013

Heat Waves of 5 days

 From Geoff Sherrington -

Brighton Beach Heat Wave.

Australias Bureau of Meteorology has issued nearly complete daily maximum temperatures from at or near its main Melbourne and Sydney sites, going back to the 1860s. Leaving the start to later (because of complications said to exist with screen variations), one can take groups of consecutive days, average the temperature over those days, then simply rank them from hottest down. 

Here is a graphical presentation for the month of January. The period is 5 days, but 6 readings contribute, because the start and end of the last day is included in case the last day was a short, early, hot spell. Readings are, to my knowledge, taken at 0900 hours and most here use the mercury thermometer with the peg to records the maximum. The graphs speak for themselves. There is a heat wave so defined about every 10 years in January. I have shown the hottest fifteen. Note that even with independent papers showing considerable Urban Heat Island effects, there seems to be an overall decrease in the maximum temperature over the 150 or so years though it is hard to confirm this effect because of the temperature changes being confused by noise and affected by the fine detail of the definition of heat wave used here. 

Data attributed to BOM online historic data files, calculated end Dec 2012.

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