Don Melrose School of Physics, University of Sydney MHD-like turbulence in hot collisionless plasmas Wednesday 20th September 14:05-14:55pm, Carslaw Building Room 373. The literature on the evolution of Alfvenic turbulence in astrophysical plasmas has been dominated by treatments (of three-wave interactions) based on incompressible MHD. The plasmas to which the theory is applied include the interstellar medium (ISM), the interplanetary medium (IPM) and the solar corona. However, these plasmas are all compressible, and the neglect of the fast MHD mode is not well justified. There is some literature on the role of the fast MHD mode, but essentially none on the possible role of the slow MHD mode. I will discuss how compressibility affects the theory of Alfvenic turbulence in compressible fluids, emphasizing the role of the fast MHD mode. The application of MHD itself to these plasmas is questionable: the IPM and the solar corona are collisionless plasmas, as is the hot component of the ISM. Although the properties of Alfven waves are essentially the same in MHD and in the theory of hot collisionless plasmas, and the properties of the fast magnetoacoustic mode are similar, there are important differences between the slow MHD mode and the ion acoustic mode of a collisionless plasma. I will discuss the possible importance of the ion acoustic mode in the evolution of Alfvenic turbulence.