Interplanetary scintillation (IPS) observations of polar solar wind streams are discussed. The IPS observed several streams which show low speeds (≤400 km/s) inside of 0.3 AU and high speeds (≥700 km/s) outside of 0.3 AU. The foot points of these streams were located in the HeI coronal holes or at their boundaries. Since the IPS measurements are indirect measurements of the solar wind speed, the derived speeds might be biased by one or several mechanisms. We investigate whether the discrepancy between the observations inside and outside of 0.3 AU can be explained by the geometry of low and high speed regions along the line of sight. We also investigate the effect of changing the turbulence level of the electron density, and finally, by comparing observations from different antenna systems, we discuss the effect of the transition from the weak to strong scattering region.
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