Polarimetric localization: A new tool for calculating the CME speed and direction of propagation in near‐real time

[1] The polarimetric localization technique uses the percent polarization observed by a single coronagraph to obtain a three-dimensional reconstruction of a coronal mass ejection (CME). We use this technique to analyze STEREO/SECCHI/COR2 beacon data for 12 different events at spacecraft separations ranging from 9° to 127°. To determine if the technique is efficacious, we compare the three-dimensional location and velocity, including speed and direction, computed by polarimetric localization to the same quantities computed by geometric localization. The geometric localization technique utilizes a series of lines of sight from two space-based coronagraphs to determine gross propagation characteristics of CMEs in three-dimensional space. In particular, we present a detailed comparison of the techniques for two events: the first example is from very early on in the mission, on 23 May 2007, when the spacecraft separation was only 9.2°, and the second event is from 12 December 2008, when the spacecraft were almost in quadrature. We find that the two techniques yield comparable CME velocities; furthermore, both are straightforward to apply and they can be used in near-real time. In conclusion, we believe that these techniques promise a substantial improvement in our capability to locate and characterize CMEs for forecasting, as well as research purposes.