Where are the strongest jet streams located? over high altitudes over land in the lower atmosphere far away from the equator

Jet streams are formed of the boundaries of enormous bodies of air.  

The strongest jet streams are the polar jets. And they are located at high altitudes (30000-39000 ft.) over sea level.

There are northern and southern polar streams.

There are northern streams (present in North America, Europe and Asia) and the Southern  mostly present in Antarctica).  

Jet streams are stronger during winter, because these are fast bodies of  moving air, they can turn into dangerous cyclones and typhoons.  

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