Meteorology

Question

How does things form in the atmosphere (like snow, rain, fog...)?

Answer

The dynamics of the earth's atmosphere is driven by incident solar radiation. Sunlight hits the earth's atmosphere and heats it to different temperature levels based on quantities such as cloud cover, surface texture, water vapor content, and chemical composition. This differential heating of the atmosphere results in buoyant flow or movement of different density air masses. These moving air masses then create an overall flow pattern in the atmosphere and in balance with the rotation of the earth result in flow structures such as the "jet stream" that flows across the United States. These flow patterns then interact with the ground surface and create our local weather. So, when a dense moist air mass interacts with a dry cold air mass it creates weather fronts where thunderstorms and tornados may result at the interface between the air masses, such as occurs in the Plains states of the US. Snow then results when a very cold air mass becomes saturated with water vapor. Rain and snow will also locally occur when an air mass with sufficient mositure is forced by mountains to change its elevation, resulting in rapid cooling and thus changing the saturation level and forcing water vapor into a liquid state (raindrops) or solid state (snow flakes). Fog occurs when the temperature of the moist air mass falls below the saturation temperature (dewpoint) and the water vapor condenses into small droplets resulting in fog. In addition to this daily cycle of heating and weather, there are longer period vairations in our weather which are tied to the cycle of sunspots on the sun. As you can see, the dynamics of our atmosphere is very complex and nonlinear. As such, to fully understand it one must be knowledgable in mathematics, fluid dynamics, thermodynamics, and chemistry.