What is the explanation for the fact that the desert sand is very hot in the day and very cool at night?

Tropical desert regions have a high diurnal temperature range. This means that there is a relatively large difference in the temperature during the day and the night. This occurs because desert environments have little water vapor in the atmosphere. This means that the desert heats up very quickly during the day and will lose heat rapidly during the night.  

Answerfur trade;

5×^2+20-15 or -(5x^2-20+15)