"Broadband" plasma waves in the boundary layers

Boundary layers are commonly encountered in space and astrophysical plasmas . For example, interaction of solar wind plasma with the planets and comets produces magnetopause and cometopause boundary layers, respectively. Gener ally, the boundary layers are formed when plasmas with different characteri stics interact with each other. The plasma sheet boundary layer in the Eart h's magnetotail is formed owing to the interaction of hot dense plasma in t he plasma sheet region with the rarefied plasma of the lobe region. Boundar y layers are the site where energy and momentum are exchanged between two d istinct plasmas. Boundary layers occurring in space plasmas can support a w ide spectrum of plasma waves spanning a frequency range of a few mHz to 100 kHz and beyond. The purpose of this review is to describe the main charact eristics and the possible generation mechanisms of the broadband plasma wav es (with frequencies of > 1 Hz) observed in the Earth's magnetopause bounda ry layer, the Jovian magnetopause boundary layer, the plasma sheet boundary layer, and the Earth's polar cap boundary layer. The rapid pitch angle sca ttering of energetic particles via cyclotron resonant interactions with the waves can provide sufficient precipitated energy flux to the ionosphere to create the dayside aurora at Earth and a weak high-latitude auroral ring a t Jupiter. In general, the broadband plasma waves may play an important par t in the processes of local heating/acceleration of the boundary layer plas ma. Recent exciting high time resolution results on the broadband plasma wa ves coming from Geotail, Polar, and FAST will be discussed.