Climate Factors and Atmospheric Dynamics in Spain

Factors Influencing the Climate

Astronomical factors are constant, such as latitude or those dependent on the territory's rotation and translation movements of the Earth, including the amount of solar radiation. Geographic factors modify the influence of astronomical factors; the main ones are maritime and continental influence and altitude. Thermodynamic factors are related to atmospheric dynamics.

Altitude and Location

The Iberian Peninsula is located between 36º and 44º North, in the temperate zone, but it receives many hours of sunshine throughout the year.

The Relief and the Föhn Effect

The relief (the highlight of the terrain) means that territories at higher altitudes have lower than average temperatures compared to the plains. It impedes the entry of air masses. Changes in temperature and humidity occur when air masses collide with a mountain range; they are forced to rise and cool, discharging precipitation. As the air goes down the other side, the dry air is heated, producing what is called the Föhn effect.

Fronts and the Jet Stream

Fronts are surfaces that separate air masses of different characteristics. The most important for Spain is the polar front, which separates tropical and polar air masses. The Jet Stream (stream in blast) is a strong current with a circular structure moving in an eastbound direction. The jet separates the low pressure at the pole (to the left of its path) from the tropical high pressure (to the right). The jet stream is responsible for surface weather.

Jet Stream Velocity and Action Centers

The current has a velocity of 180 km/h with gentle undulations. Seasonal movements in the latitude of the jet hit Spain especially in winter. Centers of action are areas of high and low pressure. Atmospheric pressure is the weight of air over a unit area; it is measured in millibars (mb) with a barometer and plotted on maps with isobars.

Anticyclones and Air Masses

A thermal anticyclone forms when an air mass is cooled; cold air weighs more, descends, and exerts high pressure. A thermal low forms when the air is heated; hot air weighs less, rises, and exerts downward pressure. Air masses are portions of air with specific characteristics of temperature, humidity, and pressure, which they acquire from their regions of origin.

Insolation, Cloudiness, and Fog

Insolation (often referred to as heat stroke in radiation terms) is a measure of solar radiation, expressed as the number of hours during which the sun's rays reach the ground. This varies greatly throughout the year due to astronomical causes, such as the different lengths of day and night or the change in the sun's angle. Cloudiness is measured as a percentage of covered days per year; the highest value of cloudiness is found in the north of the peninsula, specifically in Asturias. The presence of clouds attenuates thermal fluctuations and reduces the risk of frost. Fog is a common phenomenon in mountainous areas, valleys, and river basins. It forms when the soil temperature drops below the temperature of the lower layer of air.