"The Influential Jet Stream"

  By JosÚ Reyes                                                                            

                  A "Jet Stream" is an amazing phenomenon of wind current which twirls around our planet, capturing and changing anything in its path. These giant, so-called "river" of winds can be several hundred miles wide, 1 to 2 miles in depth and can be found from as low as 12,000 to as high as 80,000 feet above the surface of the Earth and can reach the speed of 400 miles an hour. This picture provided by NASA (Right) shows that a jet stream is visible to the eye when carrying clouds. There are basically 5 major jet streams, the Polar jet streams (North and South) of the Equator, the Sub-Tropical jet streams, (North/South) of the equator and the Equatorial Jet Stream, just North of the equator. There are other significant jet streams that form on certain times of the year when the weather pattern is favorable and can bring on very powerful weather events. The Polar jet streams are the most prominent and are year round events while the  Sub-Tropical jet streams and the Tropical jet Stream are more prominent when it is summer in the Northern hemisphere. The Earth's rotation is the principle the reason why the jet streams flow from West to East in the Northern Hemisphere and also in the Southern Hemisphere except for the Equatorial Jet Stream, it is an easterly wind (East to West) but travels very little and at a certain time of the year. These amazing winds are steered and directed North and South by warm and cold air and by the by the Coriolis Effect. Jet Streams change in form almost everyday, sometimes very slightly and other times very drastically. Remember, a stream of air must be over 56 miles an hour to be considered, a "Jet Stream". Jet Streams are independent but they can create or aid and become part of a minor or major weather pattern or event. Checkout these animated maps:Virga.SFSU.Edu  WeatherBank.com                                                                                       

                         Major Jet Streams and other Minor Jet Streams 

Links to better understand these Jet Streams:The Atmosphere of the Earth 

                                                                              Map of Latitudes and Longitudes

                                                           

The Polar Jet Streams: These Jet Streams are located 50░-60░ North/South of the equator and at 35,000 Feet (About 6.6 Miles), is a powerful, current of wind that acts as a boundary line, separating the extremely cold polar air (North) from the warm sub-tropical air (South). The Speed of the Polar Jet Stream varies depending on the time of the year. When it is winter in the Northern hemisphere it can reach up to 300 miles an hour but it has been measured at a speed of 400 miles an hour in southwest Scotland.

The Subtropical Jet Stream: These strong jet streams are located at about 30░ North/South of the equator at a height of about 41,000 feet (About 8.1 Miles) and along with the Polar Jet Stream is responsible for many types of weather patterns, depending on the time of the year.

The Equatorial Jet Stream: The equatorial Jet Stream is located 7░ to 10░ North of the Equator at an altitude of 50,000 Feet (About 9.5 Miles). This stream only travels from Asia to Africa and is the strongest during the summer months of July and August. This Stream travels in an easterly direction and is formed when there is a great temperature change with the coldest air nearest the equator.

The African Easterly Jet Stream: The African Easterly Jet Stream forms at an altitude of 12,000 to 15,000 Feet and is sometimes present during the summer months of July and August. This jet stream is located right under the Equatorial Jet Stream at (About 2.2 to 2.9 Miles) high. 

The Polar-Night Jet Stream: This jet stream is only active during the winter months of the Northern Hemisphere and is located at 60░ North only, at a height of about 80,000 feet (About 15.2 Miles).    

                                                          Global Air Circulations

           Global air circulation and the Coriolis Effect is responsible for the positioning of the Jet Streams, that is why these currents are located between 50░-60░ North/South (Polar Jet Streams) 30░ North/South (Sub-Tropical Jet Streams) and so on with the other Jet Streams. The Heat of the Sun  on water, Friction, the Earth's  rotation and the tilt of the planet generate the global air circulations and 3 large air circulations (Cells) develop.

Atmospheric Pressure Air pressure is the force of air upon the Earth's surface. The closer to the Earth's surface, particularly on sea level, the higher the air pressure. If you are standing on top of a high mountain peek then the air pressure below you, let's say in a valley, would be higher than the air pressure around you, where you are standing. Very important to remember this, when the temperature of the air cools down, air pressure will increase and will drop directly to the Earth's surface, this will push warmer air and force it away from the Earth's surface and upwards towards the sky. This creates a mass movement of air which is known to everyone as wind.

Barometer: Evangelista Torricceli constructed the first Mercury Barometer in 1643-1644. One could say this discovery was the beginning of the science of Meteorology and prediction of weather could now be achieved. The barometer is a device filed with mercury that measures atmospheric pressure. The  (US) standard measurement of atmospheric pressure at sea level is 760 mm (760Torr),  converting to inches, 1 meter equals 39.37 inches, so 760 mm equals 76 cm equals 29.92 inches of mercury. Mercury Barometers are not used any more by the major weather predicting organizations, they are using Aneroid Barographs now.

How Mercury Barometers and Aneroid Barographs work

How a Barometer Measures Air Pressure:

Read about the Invention of the Barometer 

The Hadley Cell: Three-dimensional atmospheric circulation cell located at roughly 0 to 30░ North and South of the equator. The Hadley cell consists of rising air (inter-tropical convergence zone) at the equator and descending air (subtropical highs) at 30░ North and South. 

The Ferrell Cell: Three-dimensional atmospheric circulation cell located at roughly 30 to 60░ North and South of the equator.

The Polar Cell: Three-dimensional atmospheric circulation cell located at roughly 60 to 90░ North and South of the equator. Vertical air flow in the Polar cell consists of rising air at the polar font and descending air at the polar vortex.

Definitions for Cells from:

More complete explanation of Global Air Circulation: PhysicalGeography.Net 

 

                    The "Coriolis Effect", Pressure Gradient Force and Friction  

Coriolis Effect: The Coriolis Effect named after Gustave-Gaspard Coriolis, a French scientist, who in 1835, explained how the rotation of the Earth propelled the earth's wind to move horizontally, in a wave-like manner from West to East (Except the the Tropical Jet Stream during July and August). The tilt of the earth towards the Sun and water are also very important components of this natural phenomenon. 

                      No Coriolis Effect   Coriolis Effect                                                Images Courtesy of  NOOA 

           The main effect the "Coriolis Effect" has on the Jet Streams is the constant feeding of air but the major force factor and real power supply is when the Pressure Gradient Force is extended in long distances. This will create giant rivers of winds, directing and shifting North and South and West to East. Pressure gradient force has a great deal to do with the Jet Streams and also with the fierce turning and twisting of Hurricanes and Tornadoes. It would also be important to understand a little about "Friction" and exactly how it works to create wind energy.

Great Animations of "Coriolis Effect": Oregon State, Physics Department 

Pressure Gradient Force (PGF): A packet of air from high atmospheric pressure moving to low atmospheric pressure is accelerated by pressure gradient force, thus we have wind. The pressure gradient force is responsible for triggering the initial movement of air. The pressure gradient force acts at right angles to isobars. The greater the pressure difference over a given horizontal distance, the greater the force and the stronger the wind. Pressure Gradient Force is measured with Isobar Maps.

Isobar Maps: An Isobar is a (line of wind) when plotting barometer readings throughout an Isobar Map. Here's more: Illustrated Description   

Friction: The Earth's surface exerts a frictional drag that can speed up or slow down wind. On the surface of a body of water (Ocean, Lakes, etc) friction is not so major but when rushing up a mountain and rubbing against its corners and crevices, winds can pick up and effectively change the air stream patterns throughout its surroundings.        

                                             Types of Winds 

             Now that we know about Atmospheric Pressure, how it works and how it is measured, we can learn about other types of winds. These winds created by changing air pressure are: Geostrophic Wind, Gradient Wind, Boundary Layer Wind, Sea Breezes and Land Breezes. These winds are important to know because they help contribute to creating and shaping  up massive air movements like Jet Streams, Hurricanes, and Tornadoes, they are all interconnected throughout our planet. 

                             (Courtesy WW2010 University of Illinois)

Geostrophic Wind: This wind is created by a combination Coriolis Force and Pressure Gradient Force.

Read about Geostrophic Wind and Watch Movie


Gradient Wind: This is the wind created solely by Pressure Gradient Force.

Read about Gradient Wind and Watch Movie


Boundary Layer Wind: This is wind created when friction prevents Geostrphic Wind from occurring.

Read about Boundary Layer Wind and Watch Movie:


Sea Breezes: This wind is created when there is a change of temperature between a body of water and a land mass and the wind blows from towards the shore.

Read about Sea Breezes and Watch Movie:


Land Breezes:  This wind is created when there is a change of temperature between a body of water and a land mass and the wind blows towards the sea, away from land.

Read about Land Breezes and Watch Movie:  

                                  The Jet Streaks Influence on Weather 

Jet Streak (Definition from NOOA.Gov): A concentrated region within the jet stream where the wind speeds are the strongest. It sets up unique wind currents in its vicinity which either enhance or diminish the likelihood of clouds and precipitation. It will propagate downstream along the jet stream axis. 

More Information: 1.http://www.weathernotebook.org/transcripts/2000/01/26.html

                                 2.http://www.usatoday.com/weather/tg/wjstream/wjstrea1.htm

                                 3.http://www.theweatherprediction.com/habyhints/256/   

                                 4. http://www.atmos.albany.edu/student/cunning/jet_streak.html      

         

                          The Advantages and Dangers of the Jet Stream

Advantages: 

-Commercial and Private airplane pilots study the Jet Streams and use them to their advantage so they can hitch a ride on them to cut down on travel time and in turn, save fuel.

-Meteorologist can predict the severity of storms that are near Jet Streams or are influenced by them. Jet Streams and of course, Jet Streaks are very important when predicting weather.

-Balloonists rely on the Jet streams for when they are traveling on their long voyages. This will cut traveling time down and keep them airborne for much longer.

Dangers: 

-Japanese fighter pilots during WWII learned of Jet Streams and before the United States and used it to conduct an unusual balloon attacks from late 1942 to early 1945 in a destructive line of attack, as they launched 9,000 of these lethal weapons up so they could be picked up by jet streams heading towards the western world.

Newspaper Reports: http://www.stelzriede.com/ms/html/mshwfug4.htm 

More Detail on the Balloon Raids: http://www.axishistory.com/index.php?id=932 

 

                                                 Links of Interest  

1.Live Weather Images: http://www.weatherimages.org/index.html#aviation

2.BBC Weather A-Z: http://www.bbc.co.uk/weather/

3.Ask Weatheroutlook: http://www.theweatheroutlook.com/othyourquestions.asp     

4.Jet Stream images: http://virga.sfsu.edu/crws/jetstream.html

5.Ocean Currents: Ocean Currents "The Distribution of Life". (Science Simple)

6.Aviation and Jet Streams: http://www.avsim.com/avwx/avsim_wxus_jetstream.html

7.Earth's Observatory (NASA): http://earthobservatory.nasa.gov/