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Are Upper Winds Faster in the Winter or Summer?

Other variables aside, upper-level winds are generally faster in the winter than in the summer. This holds true for both hemispheres. The seasonal difference in wind speeds has significant impacts on weather patterns and air traffic and can even affect the dispersal of pollutants or ash from volcanic eruptions. Knowing the basics about upper-level winds, including how, why and where they occur, can help in understanding the reasons why they blow faster in the winter than in the summer.

Upper Winds Description
- Globally, the flow of air -- wind -- is greatest away from the Earth̵7;s surface, in the upper levels, or higher altitudes, of the atmosphere. High-altitude wind speeds vary on a daily basis, and also change with height. Additionally, they reverse direction according to latitude. In the tropics and near the poles, upper winds tend to blow from east to west; in the middle latitudes, winds tend to blow from west to east.
Formation of Upper Winds
- At the most basic level, the forces that generate wind are initiated by the sun heating the Earth̵7;s surface unevenly. Unequal heating encourages the formation of rotating high and low pressure systems. The differences, or gradients, between areas of high and low pressure cause air to flow from one region to another, producing upper-level winds. The greater the pressure gradient, the stronger the winds.
Imperative Influence of Latitude
- Overall, solar heating is highest near the equator and lowest at the poles. The poles also experience the greatest variation in solar heating between summer and winter. This is because the planet tilts on its axis, exposing the poles to constant sunshine during summer and constant darkness during winter, whereas equatorial regions are exposed to relatively uniform solar radiation year-round. The heating differential between the poles and the tropics is most pronounced in whichever hemisphere is experiencing winter. Thus, strong high and low pressure systems don̵7;t typically develop over high latitudes during the summer. Conversely, very strong highs and lows -- such as the Siberian High and Aleutian Low ̵1; regularly develop over high latitudes during the winter months. Hence, because the sharpest temperatures and therefore pressure gradients occur during winter, so do the strongest upper-level winds.
Where the Winds are Fastest
- This seasonal variability of winds is most notable in the stratosphere, the layer of the atmosphere that begins around 10 kilometers (6 miles) above the Earth̵7;s surface and reaches upward to 50 kilometers (31 miles). Here, wind speeds can be up 160 kilometers per hour (100 miles per hour) faster in winter than in summer. Additionally, the strongest upper winds tend to occur at around 60 degrees latitude and extend up to 20 degrees north and south.

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