Understanding Upper Air Circulation

Understanding Upper Air Circulation

Upper air circulation refers to the large-scale movement of air in the Earth's atmosphere, encompassing the stratosphere and troposphere. This dynamic system is responsible for redistributing heat and moisture to sustain our weather and climate patterns.

Key Features and Patterns

1. Thermally direct cells: The Hadley cells, located near the equator, and polar cells, near the poles, are the two strongest thermally direct cells. Air rises at the equator, ascending from the surface to the stratosphere, and descends at the poles, forming weather patterns at these latitudes.
2. Thermally indirect cell: The Ferrel cell, located in midlatitudes, is a weak thermally indirect cell. It is primarily responsible for transferring air mass from the subtropics toward the polar regions.
3. Meridional circulation: The mean meridional circulation (MMC) is the north-south movement of air, which is driven by the Earth's rotation. As air moves poleward, it must conserve its angular momentum, leading to the formation of westerly winds in the upper troposphere.

Influences and Variation

1. Solar radiation: Solar radiation absorbed by Earth's surfaces drives air temperature differences, which create air pressure gradients that drive the movement of air masses.
2. Human influence: Anthropogenic changes, such as increased greenhouse gas emissions, have altered atmospheric circulation patterns over the past century. The Arctic is particularly sensitive to overall warming, which has reduced the temperature gradient and increased the waviness of the north polar jet stream.
3. Natural forcings: Changes in the Earth's orbit around the Sun and volcanic eruptions can also affect atmospheric circulation.

Measurements and Modeling

1. GRUAN: The Global Climate Observing System's Reference Upper-Air Network (GRUAN) has established a global network of reference-quality upper-air observing stations, providing essential climate variables to monitor and research climate change.
2. General circulation models: Numerical models like the ICON general circulation model (ICON) help us understand how the upper atmosphere contributes to and interacts with the circulation of the middle and lower atmosphere.

Understanding upper air circulation is crucial to predicting weather and climate change. This knowledge allows scientists to make accurate forecasts, develop climate models, and monitor changes in the Earth's atmosphere.