Cyclones and Anticyclones

Cyclones Explained

Cyclones are regions of low atmospheric pressure with air converging towards the center and rising. In the northern hemisphere, winds circulate anti-clockwise around cyclones due to the Coriolis effect. Cyclones are linked to cloud development, precipitation, and often poor visibility—conditions that can challenge flight operations. Tropical cyclones, also known as hurricanes or typhoons depending on the region, are intense examples that pose significant hazards.

Anticyclones Explained

Anticyclones are high-pressure systems where air diverges outward from the center and descends, suppressing cloud formation. In the northern hemisphere, airflow circulates clockwise around anticyclones. These systems are generally associated with settled weather, light winds, and good visibility. However, under certain conditions—especially over moist surfaces—fog or low cloud can develop beneath the inversion layer.

Types of Anticyclones

• Warm Anticyclones: The core temperature is higher than the surrounding air. These typically form over warm surfaces and promote stable, fair weather, but can generate afternoon cumulus clouds due to surface heating.
• Cold Anticyclones: The core temperature is lower than the surrounding air. Often found over cold landmasses, they can be very dry and stable, but may become unstable if moisture and surface heating are present.
• Blocking Anticyclones: These are quasi-stationary, often warm, and can persist for days or weeks, especially between 50°N and 70°N. They block the movement of cyclones and frontal systems, leading to prolonged periods of the same weather.

Formation Mechanisms

High-level convergence aloft (air coming together at altitude) leads to subsidence and the development of surface high-pressure areas. Conversely, divergence aloft supports cyclone formation. Ridges are elongated areas of high pressure extending from anticyclones, while troughs are elongated lows from cyclones.

Weather Associated

• Cyclones: Cloudy, rainy, windy, sometimes severe weather.
• Anticyclones: Clear skies, light winds, potential for fog or low cloud, especially in the morning or over moist ground.

Aviation Relevance

Pilots must recognize the presence and movement of these systems to anticipate weather changes, turbulence, icing, and visibility issues, all of which impact flight safety and planning.