As we mentioned briefly earlier, is one of the primary causes of the imbalance, which operates weather solar radiation. Tilt and the rotation of the Earth, not its surface is heated evenly. This, in turn, causes air masses over these cooler and warmer areas also will be cooler or hotter when the temperature in an air mass is determined to a large extent on the temperature of the surface under it. In addition to contributing to the different thermal characteristics of air masses, the influence of this uneven heating is also on the surrounding air pressure.
The air pressure is mainly a measure of the weight or thickness of the atmosphere over a given time. A thicker volume of atmosphere is heavier because it contains more air molecules, and vice versa for a thinner volume of the atmosphere. Temperature affects the pressure by a lot of air by expanding or contracting the. As a lot of the air gets warmer, it gets less dense and begins to increase and expand. High in the atmosphere the air begins to flow away from the rest of the mass of as it warms and expands, leaving less air under and create a lower air pressure. Conversely, a cooling air mass contracts and become more dense, providing extra air high in the atmosphere to flow inward, add extra weight to the mass of and create higher pressure.
As air rises in a low pressure system and flows outward high into the atmosphere, more air near the surface of the storm inwards to fill the vacuum. This air is lifted upward and also eventually dispersed, acts as a motor or pump continues to run until the surrounding atmosphere no longer are crooked. The same mechanism works vice versa in a high pressure system, where the air flows outward near the surface and more air rushes inward in the upper atmosphere. The air in the upper atmosphere will then run downwards against the surface, called subsidence, until it too finally reaches the surface and flowing outwards. But this inward and outward floating air does not flow in a straight line. Combined with the friction from the surface, the Earth’s rotation imparts rotational energy in the air, called the Coriolis force.
When low pressure areas cause air to be lifted higher in the atmosphere and high pressure areas cause air to sink, is low pressure generally associated with clouds and stormy weather while high pressure usually brings relatively calm, clear weather. Although high pressure areas plays an important role in weather, low pressure of most interest for our purposes. A typical low pressure system consists of a cool air mass to the North, a warm, moist air mass to the South and East and a cold, dry air mass to the West and North West. In an effort to maintain stability, the hot air flowing to the North, Southeast and cold, Northwestern air flows to the South. This configuration creates a warm front to the East of the high pressure and a trailing cold front to the South.
A final piece that often plays a role in hard weather, especially in the Great Plains, is a dry line. A dry line is a semi-permanent border, which often separates warm and moist air mass across the Southeast and central United States and warm, dry air mass originating from the desert Southwest and Northern Mexico. The boundary between very humid air and very dry air often acts as a focal point for storms when low pressure pass.