Atmospheric Circulation and Weather Phenomena

The climate in the Northern Hemisphere temperate zones is primarily determined by the position and interaction of the Polar Front and the Polar Front Jet Stream. These features represent the boundary between cold polar air masses and warm tropical air masses.

Key Atmospheric Factors

The Polar Front Jet Stream

The polar jet is described as "a swift river of wind that surrounds the Earth like a snake biting its tail, at altitudes of the tropopause. Its direction is from West to East" (Mariano Medina). This high-altitude current plays a crucial role in steering weather systems.

The Polar Front

The Polar Front is formed by a series of warm, cold, and occluded fronts that collectively surround the Earth, creating a continuous boundary. It is an imaginary zone separating two air masses of significantly different temperatures: cold air to the north and warm air to the south (in the Northern Hemisphere). Different types of winds converge in this boundary region.

The Circumpolar Vortex

The Circumpolar Vortex is a system of wave disturbances and storms associated with the Polar Front. It forms the boundary between cold polar air and warmer subtropical air masses in the mid-latitudes.

Blocking Anticyclones

Sometimes, the meanders of the jet stream become amplified and stationary without breaking off. This can lead to the formation of blocking anticyclones that remain motionless for days or even weeks. These blocks prevent the entry of rain-bearing weather systems, often causing severe droughts in affected areas, while diverting storms to other regions.

Weather Patterns in Spain

Weather in Spain is significantly influenced by its geographical position and the behavior of the Azores anticyclone.

• Summer: The Azores anticyclone moves northward and strengthens, blocking the entry of storms into Spain and diverting them towards northern Europe. Summer rainfall is typically convective, caused by clouds of vertical development (cumulonimbus). Winds often originate from the subtropical anticyclone over the Sahara Desert, bringing haze.
• Winter: The Azores anticyclone shifts southward. It can sometimes form a blocking anticyclone that diverts frontal rain systems towards the Cantabrian coast and northern Europe. Winter rains are primarily frontal.
• Spring and Autumn: The influence of the continental anticyclone diminishes, leading to more frequent entry of frontal wave storms.

Specific Weather Phenomena

Understanding Cold Drops (Gota Fría)

A cold drop originates from the entry of a mass of cold air at high altitude. When this cold air suddenly encounters warmer, less dense air below, it tends to spiral downwards towards the surface, creating intense instability. This instability, combined with the convective ascent of warm, moist air, can lead to the rapid formation of cumulonimbus clouds and result in very heavy rainfall or snowfall, particularly when the ascending air mass contains significant moisture.

Tornadoes

A tornado is a violently rotating column of wind and dust, typically about 50 meters wide, extending from the ground to the base of a cumulonimbus cloud. They are extremely dangerous, not only due to the intense winds but also the associated torrential rain and large hail. While they occur in many parts of the world, they are most common and severe in certain regions, such as the Great Plains of North America.