Out‐of‐ecliptic tests of the inverse correlation between solar wind speed and coronal expansion factor

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Abstract
In this paper we address the question of whether out‐of‐ecliptic measurements satisfy the inverse correlation between wind speed at 1 AU and flux tube divergence in the corona, already found from measurements in the ecliptic. Using the in‐ecliptic calibration, we derive out‐of‐ecliptic speeds from coronal expansion factors determined from global observations of photospheric field and their current‐free coronal extension. These derived speeds are compared with speeds inferred from interplanetary scintillation measurements during 1972–1988 and with in situ speeds measured by the Pioneer 11 spacecraft at 16°N latitude during 1984–1988. These three sets of wind speed show the same overall variation with latitude and time during the sunspot cycle, with higher latitudes having more years of fast wind than lower latitudes and all latitudes having slow wind at sunspot maximum. Although some detailed discrepancies are also present, the overall agreement is comparable to that achieved in the ecliptic plane.