Key Concepts in Meteorology and Climatology
Key Meteorological and Climatological Terms
Time and Climate
Time refers to the atmospheric conditions at a specific moment. Climate is the sequence of weather types that occur over a period of 30 years of observation in a given territory. Meteorology is the science that studies weather, while climatology studies climate.
Jet Stream and Action Centers
A jet stream is a strong wind current with a tubular structure, circulating between 9-11km in altitude. No difference exists between the equatorial and polar tropopause, and it is responsible for the weather on the surface. An action center is an area of high or low pressure.
Air Masses and Fronts
An air mass is a portion of air with specific characteristics of pressure, temperature, and humidity, acquired in its area of origin. These characteristics may vary if the air mass travels great distances. The surface that separates two air masses with distinct characteristics is called a front, along which an abrupt change in air properties occurs. The largest in Spain is the polar front, an area north of the Pacific and Atlantic oceans over which polar and subtropical maritime air masses meet.
Anticyclones and Depressions
An anticyclone is an area surrounded by high pressures, with lower pressure in its immediate vicinity. The wind circulates in the direction of the clock’s needles, producing dry weather. A depression, storm, or cyclone is a low-pressure area surrounded by higher pressure. The wind circulates in the opposite direction of the clock’s needles, producing unstable weather.
Temperature and Humidity
Temperature is the degree of heat in the air and is measured in degrees Celsius (°C) with a mercury thermometer. Humidity is the quantity of water vapor contained in the air. It increases as the temperature decreases.
Wind and Evaporation
Wind is the horizontal movement of air. It always goes from high to low pressure. Evaporation is the physical process of a liquid changing to a gaseous state at ambient temperature, especially favored by high temperatures.
Dew and Drought
Dew is water droplets deposited on the ground’s surface, originating from the condensation of water vapor in the atmosphere. A drought is a shortage of water at a specific moment or period.
Isohyets, Isotherms, and Isobars
Isohyets are lines that join points of equal precipitation. Isotherms represent temperature on maps by connecting points with equal temperatures. Isobars are lines joining points with the same pressure.
Heat Stroke and Annual Temperature Range
Heat stroke is the amount of solar radiation received by the Earth’s surface. The annual temperature range is the difference between the average temperature of the warmest and coldest months.
Frost and Fog
Frosts occur when the air temperature drops to 0°C. It may be by irradiation (cooling of the soil, which is passed to the air that is in contact with it) or advection (arrival of a very cold air mass). Fog is the suspension of water droplets in the lower layer of the atmosphere, limiting visibility to less than 1 km. It occurs when moist air condenses on the lower layer of the atmosphere. It can be caused by irradiation (loss of heat from the ground) or advection (arrival of masses of warm, moist air on a cold floor, or a cold air mass over a warmer and wetter soil).
Haze and Atmospheric Pressure
Haze is a phenomenon that reduces visibility. It is caused by the presence of many fine dust particles in the lower layers of the atmosphere. Atmospheric pressure depends on the characteristics of air masses that are located in Spain. In winter and summer, high pressures dominate; otherwise, low pressures dominate in spring and autumn.
Evapotranspiration and Aridity
Evapotranspiration is the moisture loss from the land surface due to sunstroke and transpiration from plants. There are two types: actual evapotranspiration and potential evapotranspiration. Aridity is the relationship between heat and humidity. Aridity increases with temperature and decreases with precipitation. Various indices are used to calculate it:
- Gaussen Index: Measures monthly aridity. A month is considered arid when twice its average temperature is greater than or equal to its total rainfall.
- Lautensacg-Meyer Index: Determines the general aridity of a zone, based on the number of months with a water deficit (less than 30 mm precipitation). Depending on the number of arid months, we can talk about dryness or humidity, semi-arid zones (1-3 dry months), and extreme semi-arid zones (7-11 dry months).