1D histograms of solar wind properties over time. Each 1D histogram represents three consecutive Carrington rotations. $n_{{\text{O}}^{7+}}/n_{{\text{O}}^{6+}}$ in the top left (panels (a)–(d)), ${\stackrel{\sim }{q}}_{\text{Fe}}$ in the top right (panels (e)–(h)), v_p in the bottom left (panels (i)–(l)), T_p in the bottom right (panels (m)–(p)). In each panel, each column is normalized to its own maximum. In each panel, the red line indicates the respective median for all solar wind observations, and a red shading estimates the range of all solar wind observations in each Carrington rotation from the 5th to 95th percentile. Each panel shows the respective histograms for each of the four coronal hole wind types of interest. From top to bottom: Zhao et al. (2009) coronal hole, Xu & Borovsky (2015) coronal hole, 7-means CH1, and 7-means CH2. In panels (a)–(d), the decision threshold from Zhao et al. (2009) is indicated with a dashed horizontal cyan line. Green shading in all panels highlights 2009.