Xiao et al. (2005) assimilated radial velocities from a single
Doppler radar into MM5 using the 3DVAR scheme for
a heavy rainfall event. The vertical velocity increments were
included via Richardson’s balance equation, and an observation
operator for radial velocity was developed. The results
suggested that the scheme for the radial velocity assimilation
is stable and robust in a cycling mode using high-frequency
radar data. Moreover, continuous assimilation with 3 h update
cycles was important for improving heavy rainfall.