1. 
   sub-refraction
   refraction for which the refractivity vertical gradient is greater than the standard refractivity gradient
   Found op http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=705-05-20
   
   
2. 
   SUBREFRACTION
   Less than normal bending of light or a radar beam as it passes through a zone of contrasting properties, such as atmospheric density, water vapor, or temperature. Related term: superrefraction
   Found op http://www.weather.com/glossary/s.html
   
   

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