WW2010
University of Illinois

WW2010
 
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Online Guides
 
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Meteorology
 
  introduction
 
  air masses, fronts
 
  clouds, precipitation
 
  el nino
 
  forces, winds
 
  hurricanes
 
  hydrologic cycle
 
  light, optics
 
> midlatitude cyclones
 
  severe storms
 
  weather forecasting

Midlatitude Cyclones
 
  introduction
 
  definition
 
  associated winds
 
  air masses
 
  on satellite images
 
> upper air features

Upper Air Features
 
  geopotential height
 
  troughs
 
  ridges
 
  wave amplification
 
  rising motion
 
  steering level
 
  jet stream
 
> jet streaks
 
  vertical motions
 
  mid-level moisture
 
  wind vectors

User Interface
 
  graphics
> text

NOTE: We've guessed that you're not using a client that supports colored tables and have tried to compensate. Low graphics mode looks much better on clients that do... we recommend switching to Netscape 3.0 or Microsoft Internet Explorer.
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Jet Streaks
wind speed maxima within the jet stream

Jet streaks are localized regions of very fast winds embedded within the jet stream. Sometimes these local wind maxima reach speeds in excess of 160 knots. Below is an ETA Model forecast panel for 300 mb winds and geopotential heights (white contours). The color filled regions indicate wind speed in knots and is color coded according to the legend at the bottom of the image. The shades of blue indicate winds less than 60 knots, while winds greater than 120 knots are given in shades of red.

[Image: jet streak example (21K)]

The yellow, green and red ribbon on the image above represent the jet stream, and along the East Coast, the region of strongest winds (shaded in red) is a jet streak.

As air enters a jet streak, it speeds up. When it leaves a jet streak, it slows down. These accelerations and decelerations, coupled with the curvature of the jet stream and strong wind shears, cause air to pile up in some areas (convergence) and spread out (divergence) in others. These regions of divergence and convergence have a significant influence on surface pressure features.

Intensifying Surface Cyclone:

For example, if a region of diverging winds at upper levels is stronger than the converging winds of a suface low pressure center below it, the low will deepen (intensify). This is because more air is being removed from the vertical column of air above the low than flowing into it, causing the pressure at the surface to decrease. A drop in pressure means an intensification of the low pressure center.


Weakening Surface Cyclone:

In contrast, if a region of diverging winds at upper levels is weaker than the converging winds of a suface low pressure center below it, the low begins to fill (weaken). This is because more air is flowing into the vertical column of air above the low than flowing out of it, causing the pressure at the surface to increase. An increase in pressure means a weakening of the low pressure center.



jet stream
Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

vertical motions