METEOROLOGY OF AMERICAN ANTARCTIC 309 



every day. The difiference between the maximum and minimum of 

 each day, which is sometimes called the diurnal amplitude and should 

 not be confused with the amplitude of the diurnal variations, attains 

 a mean value of 7° to S° at the stations in the American quadrant of 

 the Antarctic. At Snow Hill there was observed an amplitude of 33.9° 

 one day in July, and in two years 16 days were counted on which the 

 daily amplitude was more than 20°. At the South Orkneys the highest 

 observed daily amplitude was 27°, and amplitudes greater than 20° 

 are observed every year. At Petermann Island the greatest daily 

 amplitude was 18.6° in July, and only nine times did the amplitude 

 exceed 15°. 



In the Antarctic, temperature changes of more than 20° in an 

 hour are occasionally observed; for example at Snow Hill on May 8, 

 1903, the thermometer fell from -0.8° to -21.5° between 6:45 and 

 7:45 p. M. 



VARIABILITY OF THE TEMPERATURE 



Another datum which serves as a criterion for an evaluation of the 

 climate is the variability of the temperature, i. e.the difference between 

 the mean temperatures of two successive days. Temperature varia- 

 bility is less at maritime stations than at continental stations. It 

 varies inversely with the moisture of the air. An important factor 

 to consider is the position of the station with regard to the pathways 

 of atmospheric lows, as the variability depends in a large measure on 

 changes in the wind direction. 



The mean variability of temperature is as follows in the American 

 quadrant of the Antarctic : 



Stations 



Ushuaia ... 

 Orange Bay 

 Falkland Islands 

 South Georgia 

 South Orkneys 

 Snow Hill . . 

 Belgica ... 



Mean Variability of Temperature 



i.9°C. 



1.7° 

 1.2° 

 2.1° 

 3.0° 

 3.1° 

 3.3° 



Whereas the maximum variability at the Falkland Islands is 6°, 

 it is 12° at South Georgia, 19° at the South Orkneys, 22° at Snow Hill, 

 15° at Wandel Island, 14° at Petermann Island, and 21° in the region 

 where the drift of the Belgica took place. 



In comparison it may be said that at Verkhoyansk in Siberia, the 

 continental-climate station par excellence, the mean variability is 4.8°, 

 with a maximum of 29°. 



