Jet Stream

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Introduction

A jet stream is a narrow band of very strong winds. In the upper air in middle latitudes a jet can be thousands of kilometers long and concentrated into bands a few hundred kilometers wide and a few kilometers thick. Winds can exceed 100 knots and sometimes 200 knots. They are typically between 10 and 14 kilometers above sea level in the vicinity of the tropopause. Often, especially in the winter, there are two jets: a lower northern polar jet and a higher one farther south referred to as the subtropical jet.

Although we will focus on the middle latitude jet streams discussed above in this activity, there are also other jets. One that we will discuss in a later Unit is the low-level jet that can form near the surface in the Central Plains. During the summer this can contribute to the formation of nighttime thunderstorms. 

Objectives

Understand some characteristics of the jet stream
Recognize the relationship between the jet stream and other common weather products

References

Chapter 7 in your text.

Instruction & Web Examples

We'll use the web to study some general features of the jet stream by taking a tour of the current jet stream analysis and the atmosphere that produced it. Link to the following weather products and study the features discussed for each.

Jet Stream Analysis (You will probably find it helpful to print a copy for reference.)
What is the valid time? You will want the same valid time for all of the maps.
How many jets are there? The northernmost is normally referred to as the polar jet and the one farther south as the subtropical jet.
Many of the comments below will apply best for the polar jet under typical winter conditions.
Note that the jet is a fast-moving current of air with a wavy west-to-east orientation.
Upper-air Maps at OSU (select Upper Air, Analysis, U.S. Height/Temperature, Level)
Look at a 500-mb map and compare the positions of the troughs with the dips in the polar jet. In general they will correspond.
Notice that underneath the jet, the 500-mb winds are stronger and the contours are closer together than at places far away from the jet.
Surface Isotherms
The coldest air is north of the jet and the warmest air to the south.
The pattern of troughs and ridges that you see in the jet and in the 500-mb map is generally also present in the surface isotherms.
1000-500 mb Thickness
The same wavy pattern of troughs and ridges that you saw in the previous three maps is evident again.
Where the contour values are their lowest to the north is where the coldest air from 1000-500 mb is located.
Surface Map
The surface fronts in the eastern one half of the United States may lie parallel and very close to the polar jet
Sounding (select GIF, Stuve, sounding time, and station identifier)
Recall that on this form of sounding
the winds are plotted along the right hand side (rhs)
the tropopause level in mb may be given as "TP:  " on the rhs
the tropopause can normally also be identified from the temperature graph
Use the clickable sounding map to inspect the soundings at several locations along each of the jets and note the following:
The level of maximum winds on each sounding is near the tropopause
Above the level of maximum winds, the wind speed decreases
The maximum wind direction is the same as on the jet stream analysis
The subtropical jet is located at a higher altitude than the polar jet

Practice Questions

Link to the Jet Practice page.

 

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Revised 06/16/04