STEREO-Wind Radio Positioning of an Unusually Slow Drifting Event

On 13 March 2010 an unusually long-duration event was observed by radio spectrographs onboard the STEREO-B and Wind spacecraft. The event started at about 13:00 UT and ended at approximately 06:00 UT on 14 March. The event presents itself as slow drifting, quasi-continuous emission in a very narrow frequency interval, with an apparent frequency drift from about 625 kHz to approximately 425 kHz. Using the Leblanc, Dulk, and Bougeret (Solar Phys.183, 165, 1998) interplanetary density model, we determined that the drift velocities of the radio source are ≈ 33 km s⁻¹ and ≈ 52 km s⁻¹ for 0.2 and 0.5 times the densities of Leblanc model, respectively, with a normalization density of 7.2 cm⁻³ at 1 AU and assuming harmonic emission. A joint analysis of the radio direction-finding data, coronograph white-light observations and modeling revealed that the radio sources appear to be located in interaction regions with relatively high density and slow solar wind speed.