Authors: Catherine Ballard (University of Michigan), Liang Zhao (University of Michigan), Jim Raines (University of Michigan), Ryan Dewey (University of Michigan), Daniella Ranario (University of Michigan), and Yusuf Shwket (University of Michigan)

Solar wind is the primary driver of space weather effects that negatively impact technology on Earth and in space. Understanding the driving forces of the solar wind and how it varies over time is important so we can improve our models for space weather predictions. Among the various characters and patterns in the in-situ solar wind observations, some intervals have been found where the solar wind has minimal proton density.. For example, previous research has identified one primary disappearance event in 1999 (Balasubramanian, 2003). In this study, we are using Advanced Composition Explorer (ACE) and Solar Orbiter observations to identify disappearance events that occurred between 1998 and 2024, how frequently they occur, and if there are any similarities between the events outside of the lower speeds and densities. Solar wind disappearance events are defined when both the speed and density of the solar wind are low concurrently (speeds below 350 km/s and densities below 1 cm^-3). Categorizing these events allows us to work toward determining their other in-situ properties and the acceleration processes in the corona to produce these winds, along with the driving forces behind them. In our research, we have identified over fifty solar wind disappearance events using data from ACE and Solar Orbiter. The identified disappearance events have been compared for similarities and differences in their durations, heavy ion charge states, magnetic fields, and mass fluxes. Our next steps will be to investigate their potential coronal sources from the sun to further understand the physical mechanisms of how the plasma is accelerated in the inner corona.