In order to understand how altitude relates to climate and weather, it is necessary to explain the meaning of weather and climate. Weather refers to the conditions present in the atmosphere including humidity, temperature, wind, rainfall, atmospheric pressure, density among other meteorological factors, over a short period of time. Climate is how the weather pattern changes in a given region over long periods of time. The following explains how altitude relates to climate and weather.
When air is compressed, it acquires a higher temperature, and when air pressure is released, it gets colder. For instance, when air is pumped into a car tire, the tire tends to get hotter, whereas, if the air in a spray bottle is released, the bottle becomes cold. Low pressure, characteristic of high altitudes, causes temperature to drop. For this reason, temperature is colder in the mountains than at sea level.
The regions located above sea level are most commonly known as high altitude regions. High altitude is considered to start at 2,400 meters (788 feet) above sea level. At high altitudes, the atmospheric pressure is lower than at sea level. This is caused by gravity, which pulls air particles close to the ground, and to the atmospheric heat, which causes the air particles to bounce off each other and expand. The lower pressure causes air to cool. Cold air produces the characteristic highland climate where mean temperatures are no higher than 10° C (50° F).
The climate of the world can go through changes based on latitude, geologic terrain, altitude, and water currents. Climate tends to get colder at higher altitudes due to the lower air pressure and expansion of air particles. Under normal atmospheric conditions, the atmospheric lapse rate (increase or decrease of a parcel of air in relation to altitude) varies by 1.94° C (35.5° F) per 302 meters (1,000) of altitude.
Atmospheric lapse rate defines the way in which temperature varies at a given altitude. Meteorologists use the Environmental Lapse Rate (ELR) which varies from region to region and is affected by convection, radiation and condensation. The Dry Adiabatic Lapse Rate (DALR) and the saturated adiabatic Lapse Rate (SALR). A dry lapse rate of 5.5° F (3.05° C)/1,000 feet (304 meters) is used to calculate temperature changes in the air that is not saturated. A lapse wet rate of 3° F (1.66° C)/ 1,000 feet (304 meters) is used to calculate temperature changes in air that is saturated.
The ELR is most often used to describe the temperature changes that take place with increasing altitude. The DARL is the rate at which a parcel of dry air decreases under normal adiabatic (no heat transfer) conditions. Under these conditions, as the air raises, it expands, losing internal energy, thus, decreasing in temperature. The SARL varies strongly with temperature. In SARL, when latent heat is released, water condenses, decreasing the rate of temperature drop as altitude increases.
The varying environmental lapse rates in the Earth´s atmosphere extremely important in weather forecast. They´re used to predict if a parcel of air will rise to an altitude where it will condense, forming clouds, as well as to whether that parcel of air will continue rising, forming shower clouds or even bigger thunderous clouds. Meteorologists use radiosondes to measure atmospheric pressure, relative humidity, temperature, wind direction and speed to about 20 miles (32 km) altitude.