I live in Boston and the heat has me wondering. What makes one day 97 and the next day 79 if both days are sunny and clear?
While energy from the sun does serve to warm the air, other factors affect air temperature, especially the direction of the wind. A process called advection, in which the wind transports a colder or warmer air mass into an area, can sometimes overwhelm the heating of the sun. That is to say, a cold wind from the north can lower the temperatures during a day that is sunny. Likewise, a warm southerly breeze can make the mercury climb, even on an overcast day. Existing soil conditions also contribute to how quickly the mercury rises on a sunny day. Much of the solar energy that moves through the atmosphere does not directly heat the air. Rather, the sunshine reaches the ground and warms it, which in turn heats the air near the surface. If the soil is dry without much green vegetation, the sun quickly warms it and air temperatures climb quickly. If there has been a recent rain and soils are wet, much of the solar energy goes into evaporating water in the soil, rather than heating the soil.
