I often see references to 'sporadic E' in the meteor literature. What is the cause of this phenomenon and why is it of concern to radio observers? I can appreciate that it's an upper atmospheric effect and is undesirable to such observers. Thanks for help offered! Richard. To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at: http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html