On the penumbral jetlike features and chromospheric bow shocks

We present observations of sunspot penumbrae obtained during the disk passage of AR 10923 (2006 November 10-20) with the SOT instrument on Hinode in 4305 Å G band and Ca II λ3968 H line. Along with recently discovered jetlike features (Katsukawa et al. 2007), we find other kinds of bright elongated transients abundantly pervading the entire penumbra and drifting as a whole in a direction almost perpendicular to their long axes. Their measured velocities strongly depend on their orientation with respect to the line of sight and range from ≃1 to ≃20 km s^-1. We present quantitative analysis of these features and interpret them relative to our recent penumbral model (Ryutova et al. 2008) to show that they are produced by shocks resulting from a slingshot effect associated with the ongoing reconnection processes in neighboring penumbral filaments. Due to sharp stratification of the low atmosphere, postreconnection flux tubes moving upward quickly accelerate. At transonic velocities a bow (detached) shock is formed in front of the flux tube, as usually occurs in cases of blunt bodies moving with supersonic velocities. Observed parameters of transients are in good agreement with calculated parameters of bow shocks. On some, much more rare occasions compared to "drifting" bow-shock-type transients, there appear compact bright transients moving in the radial direction, along their long axis, and having velocities of 20-50 km s^-1. We relate these features to a category of true microjets.