Authors: Xiangrong Fu (New Mexico Consortium)

Enhanced density fluctuations are reported by in-situ and remote sensing observations in the solar wind near the Sun, indicating the importance of compressible fluctuations.   One generation mechanism is the parametric decay instability (PDI), where density fluctuations are associated with the slow mode excited by the decay of a large amplitude Alfven wave in a low-beta environment. In this study, we use 3D MHD simulations to study the generation of density fluctuations in an expanding solar wind. Different types of driving are applied near the solar surface, including incompressible and compressible, coherent and turbulent, magnetic and velocity forces. We compare these density fluctuations with PSP observations near the Sun.