The key difference between low and high pressure systems is that low pressure systems are regions in the atmosphere where the air is rising, while high pressure systems are regions in the atmosphere where the air is descending.
The word pressure system is a common term in meteorological reports, and in the news and often indicates that 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.
CONTENTS
1. Overview and Key Difference
2. What are Low Pressure Systems
3. What are High Pressure Systems
4. Side by Side Comparison – Low vs High Pressure Systems in Tabular Form
6. Summary
What are Low Pressure Systems?
A low pressure system is a region in the atmosphere where the air is rising. We also call these systems as lows, depressions, or cyclones. A low pressure system develops 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 vapour makes the air 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.
Figure 01: A Low Pressure System
At the sections closer to the ground, the air of the cyclone tends to spiral inwards, with the help of 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 storms that originate from low pressure systems.
What are High Pressure Systems?
A high pressure system is a region in the atmosphere where the air is sinking. The other names for these systems include highs or anticyclones. Anticyclones are descending air after getting cooled in the upper atmosphere. The temperature of the gas increases as the relative humidity decreases. As a result, the water in the air mass vaporizes, creating dry weather conditions. High pressure regions create calm and unchanging weather. High frequency systems are more frequent than low pressure systems and cover a greater area of the atmosphere. Also, they have a longer lifetime compared to low pressure systems.
Figure 02: A High Pressure System
The sinking air stops the warm air from rising and stabilizes the atmosphere. Also, it stops the cloud formation and cyclone formation. Anticyclones are larger than cyclones and have the ability to block the movement of the depressions. Therefore, high pressure zones help fair, calm weather to prevail for days, sometimes even for weeks. However, in the summertime, 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 Low and High Pressure Systems?
A low pressure system is known as a cyclone and a high pressure system as an anti-cyclone. The key difference between low and high pressure systems is that low pressure systems are zones where the air is rising while high pressure systems are zones where the air is sinking. More importantly, low pressure systems create moist weather, cloudy conditions, and changing weather, whereas high pressure systems support low humidity, dry and warm, fair weather. So, this is another difference between low and high pressure systems.
Furthermore, high pressure systems are larger than low pressure systems and more frequent; hence, they cover a greater area than low pressure systems. Besides, high pressure systems have a longer atmospheric lifetime compared to low pressure systems.
Summary – Low and vs Pressure Systems
The key difference between low and high pressure systems is that low pressure systems are zones where the air is rising, while high pressure systems are zones where the air is sinking. Moreover, low pressure systems create moist weather, cloudy conditions, and changing weather, whereas high pressure systems support low humidity, dry and warm, fair weather.
Reference:
1. Means, Tiffany. “What is a Low Pressure Area in Meteorology?” ThoughtCo, Jun. 22, 2018, Available here.
Image Courtesy:
1. “Southern hemisphere extratropical cyclone” By NASA, MODIS Rapid Response System – (Public Domain) via Commons Wikimedia
2. “High pressure Area Sep 08 2012” By NASA, MODIS Rapid Response System – (Public Domain) via Commons Wikimedia