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THERMAP: Antarctic Shallow Firn Temperature Data
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Periodic Obiservations
At PS a joint coverage of deep firn temperatures was arranged between the glaciology, micrometeorology and United States Weather Bureau personnel. Micrometeorology and USWB were to record constantly the temperature at the following depths: 0, 2, 5, 10, 25, 100, 250, and 800 cm.
The temperature at 150, 200, 250, 300, 500, and 1200 cm depths was taken by glaciology. As the temperature at these depths was not as critical as the near surface temperature, readings were taken only every three days. Readings were taken for the period 19 January to 15 November and the schedule was met regularly except for January. On 15 January 1958, six thermohms were placed 120 m windward of PS at depths 10 cm above those indicated. A depth correction can be applied to each level for any observation by referring to the snow accumulation registered in network "A," noted earlier in this report. By 15 November 1958, the date of the last temperature reading, the thermohm leads were at depths 15 cm below those indicated. The area's snow accumulation for the period 15 January to 15 November was approximately 25 cm.
The six thermohm leads were placed in separate bored holes, 10 cm in diameter, and covered with dry powder snow up to the surface. They were connected to a junction box at the surface and a single thermohm wire 150 m long connected the system to a Wheatstone bridge inside a building where the temperatures were read.
The bridge dial is graduated to 0.2 degrees C; the observer visually narrowed the readings to eights of each division and the temperatures were noted to the nearest 0.025 degrees C, the reading accuracy being +/- 0.01 degrees C. Before being emplaced the thermohms were tested for accuracy in an alcohol bath at different temperatures between 0 and -25 degrees C in order to obtain a correction factor. The corrections varied from -0.08 to +0.12 degrees C Corrections have been applied to the values used in the following table and figures. The bridge was periodically checked with a calibration coil. Errors introduced, e.g., when the bridge is exposed to sudden air temperature changes,* when it is not level or it is shaken by the wind, were eliminated by its installation inside a building. The bridge dial would freeze at -50 degrees C and the junction box switch would become inoperative at -65 degrees C.
The temperature values given in the following table which were taken by micrometeorologist P. Dalrymple** and meteorologist K. Hanson*** are subject to revision by their respective agencies after further analysis. These temperatures were read to 0.1 degrees F. and converted to degrees centigrade to the nearest tenth.
In the following table, all temperatures are in degrees C; column 1 indicates month and day when observations were made; column 2, the time of observation, in GMT; column 3 indicates a depth correction to be applied for that day only to the shallow depths recorded by micrometeorology; other columns where temperature values are given, are headed by indications of depth and source.
* Uneven temperature distribution inside the bridge may affect the variable resistors.
** U.S. Army, Quartermaster Corps Research and Engineering Command.
*** United States Weather Bureau
