is the jet stream always present and what is the main force in determining its fluctuations?

Answer 1

Yes, and it is influenced by temperature and the rotation of the ionosphere.

Answer 2

There are actually several upper atmospheric jet streams, the polar jet of high latitudes and the sub-tropical jet of lower mid-latitudes. The polar jet results from the Coriolis force acting on the air that is warmed near the equator, rises and begins to flow toward the poles. As it flows north in the so called Hadley circulation, it gains speed due to the conservation of angular momentum (as it moves north it is closer to the axis of rotation and like a skater who pulls in their arms, rotates faster) and turns eastward as a result of the Coriolis force.

Answer 3

When you say "the jet stream" you're really being incorrect in weather terminology.

There are several jet streams.

There is the subtropical jet stream that forms poleward of the subtropical ridge due to conservation of angular momentum in the transportation of heat out of the tropics. It's often found across northern Mexico and the southwest US/Gulf of Mexico.

The Polar Front jet separates hot/warm tropical air masses from cool/cold polar air masses. In the summer it's well up over central Canada and dips are far south as the Gulf Coast in the winter. Severe, springtime weather outbreaks are often associated with the Polar Front boundary. The Polar Front Jet is normally about 35,000 feet and can be distinguished by the temperature at it's core which should be about -55 degrees.

The Arctic Front Jet separates cold/cool polar air masses from frigid arctic air. It's lower in height, about 30,000 feet and colder at it's core at about -60.

Arctic outbreaks (when this jet dips south) can bring freezing temperatures into south Florida and absolutely brutal temperatures as far south as the Missouri and Ohio River Valleys.

There's one more jet. The Tropical Easterly Jet forms during the summer time over Indo-China and flows over the Bay of Bengal, India and the Indian Ocean into west Africa.

Like the name indicates, this one flows from east to west. It's associated with the southwest (wet) monsoon and the strong thermal lows that setup along the Tibetian Plateau.

One more thing. Jet streams rotate cyclonically. That's one reason why you have instibility on the equatorward side of jets and this is the reason for the sharp line of cirrus that often marks the equatorward side.

Answer 4

Yet it does, it is influenced by the spinning of the earth and the temperature difference of the world, such as the N & S Poles and the deserts. It is also influnced by the Ocean temperatures.

Answer 5

it is present and based mainly the temp pressure of stream and indeed earths revolution ( spinng u can call) mostly depends on area if below sea or surface