An anticyclone is a weather system of high atmospheric pressure (generally above 1013 hPa) in which air slowly descends from the upper atmosphere toward the surface. This descending motion — called subsidence — compresses and warms the air, dissolving clouds and producing stable, sunny weather with light winds. In the Northern Hemisphere, winds circulate clockwise around the centre; in the Southern Hemisphere, anticlockwise.
Several types exist based on origin. Subtropical anticyclones (like the Azores High) are semi-permanent and regulate the climate of vast regions. Thermal anticyclones form in winter over cold continental masses (Siberia, Canada), creating persistent cold, clear conditions. Blocking anticyclones can stall for weeks, diverting depressions and causing prolonged droughts or heatwaves. Anticyclones are usually larger and more persistent than low-pressure systems, sometimes spanning thousands of kilometres.
In Spain, the Azores High is the main weather regulator in summer, bringing clear skies and heat. When it weakens, Atlantic cold fronts can push through. In winter, thermal anticyclones over the central plateau can trap fog and pollution beneath temperature inversions for days. Learning to identify anticyclones on a weather map — marked with H or A — is the first step in understanding synoptic meteorology.