Table Vni. Sample computer output for canopy, leaf and soil temperatures. 



AVE - PACE AVE 



AVE* • CUMULATIVE DAY AVE 



- DEPTH INDICATES SENS ABOVE GROUND 



Data tapes were air mailed to USA CRREL, Hanover, New Hampshire, every several days. 

 These tapes were run through a standard computer program, the data for each temperature level 

 per core printed and summarized for every 6 hours and for every 24 hours, and the printout returned 

 to Barrow usually within 5 days after the data were recorded in the field. A sample 6-hour output 

 for soil, plant canopy and leaf temperatures is given in Table VIII. The thaw adjacent to each 

 core was probed on a regular basis so that measured degrees Centigrade could be compared with 

 physically probed thaw. Both values were then compared with the thaw model that will be dis- 

 cussed later in this section. 



The results of soil thaw under the various manipulations will be discussed mae fully in a later 

 section of this report. The seasonal progressions of thaw for site 1 and site 2 plots are presented 

 in Figures 10 and 11. Soil thaw is most rapid in the initial 2 to 3 weeks of thaw. At site 1, 50% 

 or more of the thaw occurred by 4 July. Site 1 with its more dense canopy had a considerably 

 shallower thaw than site 2 control plots: approximately 20 cm for site 1 vs 26 cm for site 2, Both 

 these values are significantly less than those for site 8, which averaged 36 cm in 1970. The site 

 1 and site 2 soils were on the more shallow end of the thaw gradient. 



Heat and mass transports are two important physical processes in the arctic tundra soils. 

 Understanding of the mechanisms of the transport phenomena is the basis upon which a sound 

 mathematical model is built. Despite extensive research on the exchange of heat and mass at the 

 air/soil interface, the degree of accuracy in the determination of exchanged quantities is less 

 than adequate. In order to concentrate on the transport phenomena in the soil, the air/soil inter- 

 face was chosen as the upper boundary condition. Variables such as temperature and moisture 

 content at and below the interface were measured in the field. Although from the microscopic 

 viewpoint the mechanism of heat transfer in soils is not by conduction alone, it is possible and 

 practical to define the effective conductivity of soils and to formulate the problem as one of 

 pure conductive heat transfer with phase changes. This is the basic assumption adopted in the 

 thaw-temperature model. 



22 



