Understanding Weather Phenomena: Fog, Frost, Humidity

Fog: Definition and Types

Fog is a dense air mass near the ground, often characterized by humidity. It forms through various processes:

• Irradiation Fog: Produced by nocturnal cooling due to the lack of solar radiation. The cold air mass condenses, leading to precipitation.
• Evaporation Fog: Occurs when warm water from lakes and rivers evaporates into cooler air, causing condensation.
• Marine Cooling Fog: Forms when a warm, moist air mass from the sea moves over a cooler continent.
• Dew: Forms when air is heated during the day, then cools and saturates at night due to increased solar irradiation and altitude, precipitating small water droplets.

Frost

Frost occurs when the soil surface temperature falls below 0°C (32°F), causing dew to freeze.

Thermal Oscillation

Thermal oscillation, or insolation, is the difference between the average temperature of the warmest and coldest months. In Spain, the lowest amplitudes are in the Canary Islands and coastal areas, while the highest are in the sub-plateau region.

Aridity

Aridity refers to the relationship between temperature and precipitation in a given area. An area is considered arid when it receives less precipitation than necessary, relative to its temperature. Various indices measure aridity, both monthly and overall.

Windward and Leeward

• Windward: The side of a geographical feature facing the direction from which the wind is blowing.
• Leeward: The direction towards which the wind is blowing; the side sheltered from the wind.

Rainfall Patterns

Rainfall patterns describe the distribution of rainfall during dry and wet seasons.

Relative and Absolute Humidity

Relative humidity is the ratio of the amount of water vapor in the air to the amount the air could hold at saturation. Absolute humidity is the quantity of water vapor in the air per cubic meter.

Geographical Latitude

Geographical latitude is the angular distance from any point on Earth to the Equator, measured in degrees (0° to 90°) along a meridian.

Convective Rain

Convective rain occurs when the ground heats up unevenly, transferring heat to the air mass above. This warmer, lighter air rises, cools, and condenses, forming clouds and potentially rain. This mechanism can also contribute to fog formation. Spontaneous ascent of moist air is characteristic of warm, moist areas and can occur during dry summers in temperate zones.

Orographic Rain

Orographic rain forms when moist winds from the sea encounter a mountain or high relief. The air is forced to ascend the windward slope, cooling and condensing to form clouds and rain. After passing the summit, the air descends the leeward side, warming and drying. Because there is no moisture source, the air is dry, and no rain occurs. This process creates rain shadow deserts.