9.2 High and low pressure zones
Air pressure is one of the key observations that help meteorologists to make predictions about the weather. High and low air pressure are terms that describe the weight or pressure of the atmosphere per a unit of surface area. When evaluating the weather, changes in air pressure are more important than the exact values of air pressure measurements.
Usually, as a low pressure zone advances near our region, the weather will "get worse", meaning increased cloud cover and rainfall.
Conversely, when a high pressure zone begins to form near our region, the weather will "get better", meaning clear skies and sunshine.
Low pressure zones are formed when the surface of the Earth warms up. This causes the air mass directly above the planet's surface to grow warmer as well. Because warm air always rises above cold air, the warm air mass will begin to flow upwards. This air mass will move to high altitudes, lose its warmth, and begin to sink back towards the lower areas of the atmosphere. When an area accumulates new air mass due to this process, it will form a high pressure zone.
Wind is created by air moving from high pressure zones (where there is a lot of air) towards low pressure zones (where there is less air). The more significant the difference between the air pressures of high and low pressure zones is, the stronger the resulting wind will become. In the Northern Hemisphere, winds cycle around the center of the low pressure zone in a counterclockwise direction, whereas in the Southern Hemisphere they cycle the center in a clockwise direction. The direction of these winds is indicated by arrows on the weather map.
A day of high air pressure in Finland.
During the summer, the low pressure zones are often weaker than they are in winter, and they can bring long periods of rain with them. During the winter, low air pressure usually results in a grey and temperate weather suitable for outdoor activites.
High air pressure causes clear, sunny and warm weather during the summer. However, the coldest weather conditions during the year are also experienced during periods of high pressure. During the winter, high air pressure causes clear skies, which make warmth escape into space from the planet's atmosphere.
Earth's winds right now!
Usually, as a low pressure zone advances near our region, the weather will "get worse", meaning increased cloud cover and rainfall.
Conversely, when a high pressure zone begins to form near our region, the weather will "get better", meaning clear skies and sunshine.
Low pressure zones are formed when the surface of the Earth warms up. This causes the air mass directly above the planet's surface to grow warmer as well. Because warm air always rises above cold air, the warm air mass will begin to flow upwards. This air mass will move to high altitudes, lose its warmth, and begin to sink back towards the lower areas of the atmosphere. When an area accumulates new air mass due to this process, it will form a high pressure zone.
Wind is created by air moving from high pressure zones (where there is a lot of air) towards low pressure zones (where there is less air). The more significant the difference between the air pressures of high and low pressure zones is, the stronger the resulting wind will become. In the Northern Hemisphere, winds cycle around the center of the low pressure zone in a counterclockwise direction, whereas in the Southern Hemisphere they cycle the center in a clockwise direction. The direction of these winds is indicated by arrows on the weather map.
A day of high air pressure in Finland.
During the summer, the low pressure zones are often weaker than they are in winter, and they can bring long periods of rain with them. During the winter, low air pressure usually results in a grey and temperate weather suitable for outdoor activites.
High air pressure causes clear, sunny and warm weather during the summer. However, the coldest weather conditions during the year are also experienced during periods of high pressure. During the winter, high air pressure causes clear skies, which make warmth escape into space from the planet's atmosphere.
Earth's winds right now!