Global air circulation patterns are held to Earth's surface by gravity and heated by the planet. The Coriolis effect causes apparent deflections in moving air as seen from Earth's rotating frame of reference. Air pressure decreases with altitude due to the weight of air above, and wind occurs as air moves from high to low pressure areas. Air masses develop distinct characteristics over different surfaces and temperatures, influencing weather patterns as high or low pressure systems move across regions. Warm and cold fronts form at boundaries between air masses with differing temperatures and humidity levels.