Answer: Areas of high and low pressure are caused by ascending and descending air. As air warms it ascends, leading to low pressure at the surface. As air cools it descends, leading to high pressure at the surface.
Paragraph: High and low pressure systems cause day-to-day changes in our weather. In this article, we look at how they are defined and how they form.
What do we mean by 'pressure'?
The Earth's atmosphere exerts pressure on the surface. Pressure is measured in hectoPascals (hPa), also called millibars. Standard pressure at sea level is defined as 1013hPa, but we can see large areas of either high or low pressure. These areas are all relative to each other, so what defines a high will change depending on the area around it.
Weather chart
On a weather chart, lines joining places with equal sea-level pressures are called isobars. Charts showing isobars are useful because they identify features such as anticyclones (areas of high pressure) and depressions (areas of low pressure).
Ascending and descending air
Areas of high and low pressure are caused by ascending and descending air. As air warms it ascends, leading to low pressure at the surface. As air cools it descends, leading to high pressure at the surface.
In general, low pressure leads to unsettled weather conditions and high pressure leads to settled weather conditions.
Anticyclone (high pressure)
In an anticyclone (high pressure) the winds tend to be light and blow in a clockwise direction (in the northern hemisphere). Also, the air is descending, which reduces the formation of cloud and leads to light winds and settled weather conditions.
Depression (low pressure)
In a depression (low pressure), air is rising and blows in an anticlockwise direction around the low (in the northern hemisphere). As it rises and cools, water vapour condenses to form clouds and perhaps precipitation. This is why the weather in a depression is often unsettled, there are usually weather fronts associated with depressions.
Facts about air: The atmosphere of Earth, commonly known as air, is the layer of gases retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere.
There could be multiple answers to this due to where the hair like fibre is. if it is on a bacteria to aid movement it is called a flagella. if it is attached to a cell, for example in the throat or oviduct, it is called a cilia
High tides and low tides are caused by the Moon. The Moon's gravitational pull generates something called the tidal force. The tidal force causes Earth—and its water—to bulge out on the side closest to the Moon and the side farthest from the Moon.
