Remote sensing of plasma motion and turbulence near the Alfvén surface

Abstract:

Despite a rich nearly-century-long history, Thomson scattering has not been fully exploited as a remote-sensing tool in the corona and nascent solar wind. In particular, stable deep-space coronagraphs such as SOHO/LASCO and STEREO/SECCHI enable time-dependent, photometric analyses that transcend basic feature tracking and brightness estimation. These techniques offer direct insight into the plasma conditions in the outer corona. In particular, fluctuations in the outer coronal brightness comprise both the familiar inhomogeneous "blobs" of material first tracked quantitatively with SOHO/LASCO, and also a recently-discovered compressive wave field that permits remote probing of the plasma even though individual wave fronts do not stand out visually. I will discuss recent and current measurements of this wave field in the outer corona as a means to probe outer coronal heating and wind acceleration near the transition from corona to heliosphere (known as the Alfvén surface); and present current results from a study of the transition from mostly smooth to mostly turbulent flow in the nascent solar wind.