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

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 degrees to 127 degrees. 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 degrees, 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.