Impact of Mixed-Phase Cloud Parameterization on Warm Conveyor Belts and Upper-Tropospheric Dynamics

This study investigates mixed-phase cloud (MPC) processes along the warm conveyor belts (WCBs) of two extratropical cyclones observed during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX). The aim is to investigate the effect of two radically distinct parameterizations for MPCs on the WCB and the ridge building downstream: the first one (REF) drastically limits the formation of liquid clouds, while the second one (T40) forces the liq-uid clouds to exist. REF exhibits a stronger heating below 6-km height and a more important cooling above 6-km height than T40. The stronger heating at lower levels is due to more important water vapor depositional processes while the larger cooling at upper levels is due to differences in radiative cooling. The consequence is a more efficient potential vorticity destruction in the WCB outflow region and a more rapid ridge building in REF than T40. A comparison with airborne remote sensing measurements is performed. REF does not form any MPCs whereas T40 does, in particular in regions detected by the radar-lidar platform like below the dry intrusion. Comparison of both ice water content and reflectivity shows there may be too much pristine ice and not enough snow in REF and not enough cold hydrometeors in general in T40. The lower ice-to-snow ratio in T40 likely explains its better distribution of hydrometeors with respect to height com-pared to REF. These results underline the influence of MPC processes on the upper-tropospheric circulation and the need for more MPC observations in midlatitudes.