WW2010
University of Illinois

WW2010
 
  welcome
 
> online guides
 
  archives
 
  educational cd-rom
 
  current weather
 
  about ww2010
 
  index

Online Guides
 
  introduction
 
> meteorology
 
  remote sensing
 
  reading maps
 
  projects, activities

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

Forces, Winds
 
  introduction
 
> pressure
 
  pressure gradient
 
  coriolis force
 
  geostrophic wind
 
  gradient wind
 
  friction
 
  boundary layer wind
 
  sea breezes
 
  land breezes

Pressure
 
  definition
 
  variation with height
 
> isobars
 
  pressure surfaces
 
  variation with temps
 
  high pressure center
 
  low pressure center

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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Isobars
lines of constant pressure

A line drawn on a weather map connecting points of equal pressure is called an "isobar". Isobars are generated from mean sea-level pressure reports and are given in millibars.

The diagram below depicts a pair of sample isobars. At every point along the top isobar, the pressure is 996 mb while at every point along the bottom isobar, the pressure is 1000 mb. Points above the 1000 mb isobar have a lower pressure and points below that isobar have a higher pressure.

Any point lying in between these two isobars must have a pressure somewhere between 996 mb and 1000 mb. Point A, for example, has a pressure of 998 mb and is therefore located between the 996 mb isobar and the 1000 mb isobar.

Sea-level pressure reports are available every hour, which means that isobar maps are likewise available every hour. The solid blue contours (in the map below) represent isobars and the numbers along selected contours indicate the pressure value of that particular isobar.

Such maps are useful for locating areas of high and low pressure, which correspond to the positions of surface cyclones and anticyclones. A map of isobars is also useful for locating strong pressure gradients, which are identifiable by a tight packing of the isobars. Stronger winds are associated with stronger pressure gradients.



variation with height
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.

pressure surfaces