Discussion 



In reply to a query by Captain Best, Mr. Lillywhite said that tropical 

 continental air generally moved out from x\ustralia aloft in a north- 

 west to south-east direction. 



Some of the figures given by Mr. Lillywhite were confirmed by Mr. 

 Kerr, who presented similar results for the north Tasman Sea and 

 Tasmanian region. 



Captain Best then raised the question as to whether these depressions 

 might possibly develop aloft and not at the surface. Mr. Lillywhite 

 agreed that this was so, and Mr. Hutchings pointed out that the depres- 

 sions of the Lord Howe Island region very frequently developed aloft 

 over Northern Queensland. Mr. Hutchings pointed out that the northerly 

 component in the tracks of these lows indicated that they were possibly 

 of non-frontal origin. 



SOME MEASUREMENTS OF EARTH TEMPERATURE AND SOIL 

 CONDUCTIVITY IN NEW ZEALAND 



By J. W. Hutchings, New Zealand Meteorological Service 



Introduction 



It has often been emphasized that the standard meteorological practice 

 of measuring earth temperatures at a fixed hour of observation such as 

 9 a.m. fails to take account of the very large diurnal changes that occur 

 near the surface of the soil. It may also be pointed out that these changes 

 are of great importance to agriculture and in many other aspects of 

 the economic life of the country. Moreover, measured values of soil 

 temperature and conductivity are of interest in various geophysical 

 investigations and play an important part in certain meteorological 

 problems involving the exchange of heat between the earth and the 

 atmosphere. 



Part I — The Observations at Earnscleugh 

 Instruments and Site at Earnscleugh 

 As part of the investigation into frost forecasting in Central Otago 

 a Negretti and Zambra mercury-in-steel thermograph was installed at 

 the New Zealand Government Research Orchard at Earnscleugh, and 

 records from this instrument are now available from May, 1947. In 

 installing the bulbs of the thermograph in the earth a short trench 

 2 ft. or 3 ft. wide was dug, one side of the trench being 3 in. deep and 

 the other side 5 in. deep. The removed soil was then carefully filled in 

 so as to be packed around the elements, and the surface of the soil was 

 then pressed down and levelled. A sparse cover of short grass gradually 

 appeared as natural vegetation, and to all appearances the plot could 

 not be distinguished from the surrounding area of ground. Making 

 allowance for natural consohdation of the ground, it was thought that 

 the above procedure would result in the centres of the thermograph 

 bulbs being at depths of 3 in. and 5 in respectively in relatively undis- 

 turbed soil with a natural vegetation cover appropriate to climate of 

 the district. These values were later checked by excavation of the 

 elements and careful measurement of their depths. The centres were 

 found to be almost exactly 3 in. and 5 in. below the level surface of the 

 soil. As far as can be judged from working with the records, both ele- 

 ments have given a very satisfactory record of earth temperature. 



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