Glossary of Terms: J

Jet Stream

Relatively fast uniform winds concentrated within the upper atmosphere in a narrow band. A number of jet streams have been identified in the atmosphere. The polar jet stream exists in the mid-latitudes at an altitude of approximately 10 kilometers. This jet stream flows from west to east at average speeds, depending on the time of year, between 110 to 185 kilometers per hour. Another strong jet stream occurs above the sub-tropical highs at an altitude of 13 kilometers. This jet stream is commonly called the subtropical jet stream. The subtropical jet stream's winds are not as strong as the polar jet stream.

 

Joint

A fracture in a rock where no movement has taken place or where no movement has taken place perpendicular to the surface of the fracture. Important in rock weathering because it increases the exposed surface area.

 

Joule

Unit for measuring energy. One joule is the energy used by a force of one Newton in moving its point of application in the direction of the force one meter.

 

June Solstice

Date during the year when the declination of the Sun is at 23.5° North of the equator. During the June solstice, locations in the Northern Hemisphere experience their longest day. The June solstice is also the first day of summer in the Northern Hemisphere. Locations in the Southern Hemisphere have their shortest day on the June solstice. This date also marks the first day of winter in the Southern Hemisphere.

 

Jurassic

Geologic period that occurred roughly 144 to 208 million years ago. During this period, the first birds and mammals appear and large areas of the continents are covered by shallow seas.

 

 

Citation: Pidwirny, M. (2006). "Glossary of Terms: J". Fundamentals of Physical Geography, 2nd Edition. Date Viewed. http://www.physicalgeography.net/physgeoglos/j.html