IA/DA waves and polar mesospheric summer echoes

Excitation of ion-acoustic (IA) and dust-acoustic (DA) waves in the Earth's mesosphere, at altitudes of similar to 85 km, is considered as a possible cause of polar mesospheric summer echoes (PMSE). Although electric fields of a few tens of mV/m appear to be capable of producing IA waves, these fields are too small for exciting DA waves. Since some of the observed features of PMSE conform to the expected properties of DA waves, alternative mechanisms for DA wave excitation should be considered, such as excitation by velocity shear. (C) 2005 Elsevier B.V, All rights reserved.