Normalized profiles of ortho- and para-HO transitions observed by HIFI compared to models with different values of the turbulence velocity and all other parameters kept fixed. The solid red line represents the data, and models with turbulence velocities of 0.5, 0.8 and 1.4 km s^-1 are represented by dotted purple, long-dashed green and short-dashed blue lines, respectively. The adopted value for the υ_LSR of 40.4 km s^-1 was subtracted from the observed lines.