The diurnal and annual cycle in solar radiation is reflected into air temperature by the absorption of solar radiation. Soil temperature follows the changes in the air temperature with a time lag that increases with soil depth. Close to the soil surface, the variation in temperature is larger than, for example, half a meter deep in the soil. In summertime the soil surface warms up much more than the deeper soil layers. In summer the temperature in soil surface can reach 15 to 20 °C, while in deeper soil layers the temperature stays around 10°C. In midwinter, the temperature remains above zero in deeper soil layers, approximately at +1–2°C. The snow cover efficiently insulates the soil surface keeping the temperature close to zero.