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Strong-field ionization of polar molecules contains rich dynamical processes such as tunneling, excitation, and Stark shift. These processes occur on a sub-cycle time scale and are difficult to distinguish in ultrafast measurements. Here, with a developed strong-field model considering effects of both Coulomb and permanent dipole, we show that photoelectron momentum distributions (PMDs) in orthogonal two-color laser fields can be utilized to resolve these processes with attosecond-scale resolution. A feature quantity related to the asymmetry in PMDs is obtained, with which the complex electron dynamics of polar molecules in each half laser cycle is characterized and the subtle time difference when electrons escaping from different sides of the polar molecule is identified., Comment: 6 pages, 4 figures

The slow solar wind, or at least a significant part of it, originates from the region bordering streamer helmets, where the flow tube geometry is distinct from flow tubes rooted in the center of coronal holes. We examine whether this particular tube geometry leads to standing shocks in the inner slow wind in this region. To isolate the influence of tube geometry, a simple isothermal wind model is employed and is solved in terms of the Lambert W function. In addition to a continuous solution, the model may also admit solutions with shocks, readily constructed with a graphical approach. When allowed, the shock solutions appear in pairs, one with a shock located in the streamer stalk, the other with a shock below the cusp along the streamer border. We show that solutions with standing shocks exist in a broad area in the parameter space characterizing the wind temperature and flow tube. In particular, streamers with cusps located at a heliocentric distance $\gtrsim 3.2 R_\odot$ can readily support discontinuous slow winds with temperatures barely higher than 1 MK., Comment: 4 pages, 3 figures, accepted by Chinese Physics Letters, volume 28, number 5, id 059601