Time Evolution of Coronal Holes and Their Impact on the Solar Wind

Coronal holes, which can be defined as open magnetic field regions on the Sun, are the source of high-speed streams and possibly slow wind and thus play an important role in nature and structure of the solar wind/heliosphere. Over the last decade, significant progress has been made in our ability to predict ambient solar wind conditions days in advance using a number of different models that vary widely in their sophistication (e.g., MHD and Potential Magnetic Field Source Surface Models) but all of which are driven by observations of the photospheric magnetic field in the form of synoptic maps. These ambient solar models based on extrapolation from photospheric magnetic fields are limited and cannot duplicate the complexity of the solar wind during periods of transient wind. However, a very recent comprehensive study by Arge et al. has shown that significant discrepancies often occur between model predictions and observations after transient wind has completed its passage past Earth and the observed solar wind has returned to ambient/background conditions (i.e., when the model is expected to resume performing well). Such discrepancies can persist for 2 to 3 days after the passage of the transient. To understand the origin of these differences, we will use coronal observations at time of CMEs to study variations in the pattern of coronal holes at the Sun. Our goal is to investigate if changes in coronal holes (probably not visible in photospheric field synoptic maps) can be responsible for the changes seen at 1AU.