When the height contours bend strongly to the north (as in the diagram below), this is known as a RIDGE. Strong ridges are accompanied by warm and dry weather conditions at the surface. Below is an example of a ridge in an upper-level height field (red contours). The purple line denotes the ridge axis.

The image below depicts geopotential height (solid white contours) and temperatures (colored regions) at 500 mb. Temperatures decrease with color from light blue to purple. A ridge is located from Texas into Montana and is indicated by the bulge in the geopotential height field. This is the upper level extension of a surface high pressure center, which is why ridges are also called upper level highs.

Notice the relatively warm temperatures associated with the ridge. This is caused by the northward transport of warmer air in the lower troposphere. The ridge will intensify (bulge further northward) if warm air continues to move northward at low levels in the troposphere.

troughs

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.

wave amplification