Diurnal Variability of Soil and Air temperature as a function of time and depth, A case study of the cold wave that hit Zawia region during the period 1-5 February 1999

Abstract

Soil temperature is one of the important variables in agricultural studies, which is necessary to be measured and analyze. There are some major challenges facing a lot of agricultural studies focus on soil temperature in Libya, such as, the soil temperature is measured only at Agro meteorological stations in the country, the lack of stations, the measurement of soil temperature is a cumbersome business and not as simple as air temperature be noted by single thermometer, Separate thermometers are required to measure the temperature of the soil at different depths, the installation of thermometer sensor correctly in the soil is another very complicated technical matter. However, in Libya there are no enough studies into the pattern of hourly variation in soil temperature over twenty-four hours due to the lack of such measurements at agricultural lands. So that, this attempt has been made to diagnose the behavior of soil temperature and air temperature as a case study, This work was carried out by using the daily and hourly data recorded for the temperature in the standard depths of soil (5,10,20,30,50,100 cm), and the surface air temperature at heights of (5, 10, 15, 50, 100, 150, 200 cm), Data were measured, Reported and collected every three hours interval during the period from 01 to 05 February 1999, at Zawia Agro-Meteorological Station where the location of the station was under the effect of cold wave. The data were measured on a daily basis at 0000, 0300, 0600, 0900, 1200, 1500, 1800, 2100 UTC. The correlation coefficient between the hourly soil temperature and hourly air temperature at certain depths and heights were calculated using the Pearson’s Formula, then the matrix of correlation factors have been derived, The vertical profile for the hourly variation of temperature in the layer between 100 cm under the surface of soil and 200 cm above the surface of soil have been described, Graphs and tables were done to show more explanation. The analysis of the observation shows that soil temperature variability decreases with depth, the highest temperature variability in top soil, and the lowest one is deeper than 50 cm. These results were affected due to the prevailing weather situation because at night time there is no enough solar radiation and the ambient temperature is lower than soil temperature. As a result, the soil temperature transferred heat from soil to atmosphere above. In addition, the low thermal conductivity of the soil is also one important factor that affects heat storage. These results demonstrated the importance of monitoring the soil temperature as an important element for agricultural studies. The results of the present paper could fill in some of the gap related to the soil temperature studies in Libya, and can be used for planning agronomic and plant protection practices.