Diurnal Temperature Variation

Diurnal temperature variation is the difference between the highest and lowest air temperature recorded at a location during the same day. Peak temperatures usually arrive after noon because the atmosphere keeps absorbing more solar energy than it loses through the early afternoon, and the daily low usually comes in the early morning rather than at midnight because heat continues to escape through the night, an effect known as temperature lag or thermal inertia; solar heating of a thin one to three centimetre layer of air right above the ground, combined with inefficient heat transfer to the cooler air above it, can create temperature differences of over 16 degrees Celsius within just a few feet of height. The size of the daily swing depends on humidity, which reduces it, nearby large bodies of water, which moderate it, elevation, which increases it, cloud cover and soil type, and urbanization, which tends to narrow the range in cities compared with the surrounding countryside; temperatures typically settle into equilibrium in the mid-to-late afternoon.