  Ridge formation in near-side correlation in heavy-ion collisions is studied
in the framework of a phenomenological model, called Correlated Emission Model
(CEM). Successive soft emissions due to jet-medium interaction lead to the
enhancement of thermal partons which follow the local flow directions. The
correlation between the flow direction and the semihard parton direction is the
major factor that causes the ridge formation to depend on the trigger direction
relative to the reaction plane. With the use of a few parameters we have been
able to reproduce the data on the ridge yields as functions of the trigger
azimuthal angle for different centralities. An inside-outside asymmetry
function is proposed to further probe the characteristics of the azimuthal
correlation function. Insights are provided for the understanding of some
detailed aspects of the centrality dependence.
