Thermal signal propagation in soils in Romania: conductive and non-conductive processes

Temperature data recorded in 2002 and 2003 at 10 stations out of the 70 of the Romanian automatic weather stations network are presented and analyzed in terms of the heat transfer from air to underground. The air temperature at 2 m, the soil temperatures at 0, 5, 10, 20, 50 and 100 cm below soil surface as well as precipitation and snow thickness have been monitored. The selected locations sample various climate environments in Romania. First order modelling confirm that at certain locations and for certain time intervals soil temperatures track air temperature variations and consequently the heat transfer is by conduction, while at others, processes such as soil freezing and/or solar radiation heating play an important part in the heat flux balance at the air/soil interface. However, the propagation of the annual thermal signal in the first meter of soil is through conduction; the effective thermal diffusivity for 8 stations with continuous time series at all depth levels ranges from 3 to 10×10?6m2s?1.