What causes horizontal pressure variations in the atmosphere both aloft and at the surface?

Horizontal pressure variations in the atmosphere, both aloft and at the surface, are primarily caused by temperature differences in air columns. When air is heated, it expands and becomes less dense, leading to lower pressure in that area. Conversely, when air cools, it contracts and becomes denser, resulting in higher pressure. This creates pressure gradients, which are essential in generating wind.

Temperature differences are influenced by various factors, including solar heating, geographical features, and time of day. As warm air rises and cooler air sinks, this sets up a flow of air from high-pressure areas to low-pressure areas, establishing the wind patterns we observe.

While other factors such as wind patterns, humidity variations, and topography can influence weather and contribute to pressure changes, it is the temperature differences in air columns that fundamentally drive the creation of horizontal pressure variations. Recognizing this relationship is crucial for understanding larger weather systems and phenomena.