What is the fine-grained topic of the following text: We propose that the dynamic evolution of non-thermal broadening is the result of the growth of Alfvén wave amplitudes in the magnetically open rarefied dimming region, compared to the dense closed corona prior to the CME. Only return the topic.
Alfvén wave amplitudes' growth in magnetically open rarefied dimming region due to dynamic evolution of non-thermal broadening.