Low vs High Pressure Systems
In the meteorological reports, in the news, the word pressure system is a common term and often indicates something is out of place. It is a major factor influencing the local weather.
In general, a pressure system is a region of the Earth’s atmosphere where air pressure is a relative peak or calm in the sea level pressure distribution.
Low Pressure System
A region in the atmosphere where air is rising is known as a low pressure system. They are also called lows, depressions, or cyclones. A low pressure system is developed when the air gets hot and moist compared to the surrounding air. The expansion from the heat and the decrease in weight due to water vapor creates the air to move upwards. As the air moves up, it cools down, and clouds form. If it continues to cool, it may develop into rain or snow, under favourable conditions. The low pressure regions experience strong winds, cloudy skies, rain, snow, and unpredictable changes in the weather.
At the sections closer to the ground, the air of the cyclone tends to spiral inwards, helped by the rotation of the earth. If the pressure becomes sufficiently low, these winds can develop into a storm or hurricane. Therefore, cyclones are related to storm originated from the low pressure systems.
High Pressure System
A region in the atmosphere where the air is sinking is known as high pressure system. These systems are also called highs or anticyclones. Anticyclones are descending air after getting cooled in the upper atmosphere. The temperature of the gas increase as the relative humidity decreases. As a result, the water in the air mass is vaporized, and dry weather conditions are created. High pressure regions create calm and unchanging weather. High frequency systems are more frequent than the low pressure systems and cover a greater area of the atmosphere. They also have a longer lifetime compared to low pressure systems
The sinking air stops the warm air from rising and stabilizes the atmosphere. This also stops the cloud formation and cyclone formation. Anticyclones are larger than the cyclones and have the ability to block the movement of the depressions. Therefore, the high pressure zones help fair, calm weather prevail for days, sometimes even for weeks.
However, in summer time, when the solar radiation is at its peak, the air is dry and high pressure zones increase the dryness leading to droughts.
What is the difference between High Pressure and Low Pressure Systems?
• Low pressure systems are zones where air is rising, and high pressure systems are when the air is descending. A low pressure system is known as a cyclone and high pressure system as an anti-cyclone.
• Low pressure systems create moist weather, cloudy conditions, and changing weather, whereas high pressure systems support low humidity, dry and warm, fair weather.
• High pressure systems are larger than low pressure systems and more frequent, hence covers a greater area than the low pressure systems.
• High pressure systems have a longer atmospheric lifetime compared to low pressure systems.