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Abstract
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 liquid 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 compared to REF. These results underline the influence of MPC processes on the upper-tropospheric circulation and the need for more MPC observations in midlatitudes.
Significance Statement
The diabatic processes occurring in the warm conveyor belt (WCB) of extratropical cyclones impact the jet stream structure at midlatitudes. This study highlights some sensitivity of upper-level dynamics to mixed-phase-cloud-related processes. Comparisons of two different microphysical schemes for mixed-phase clouds shows that the ratio of liquid to solid clouds along the WCB ascents impacts the latent heat release and the radiation. Data from the NAWDEX campaign helps to determine room for improvement for both schemes and point out the need of a better understanding of these processes for an improved prediction of upper-level dynamics.
Abstract
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 liquid 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 compared to REF. These results underline the influence of MPC processes on the upper-tropospheric circulation and the need for more MPC observations in midlatitudes.
Significance Statement
The diabatic processes occurring in the warm conveyor belt (WCB) of extratropical cyclones impact the jet stream structure at midlatitudes. This study highlights some sensitivity of upper-level dynamics to mixed-phase-cloud-related processes. Comparisons of two different microphysical schemes for mixed-phase clouds shows that the ratio of liquid to solid clouds along the WCB ascents impacts the latent heat release and the radiation. Data from the NAWDEX campaign helps to determine room for improvement for both schemes and point out the need of a better understanding of these processes for an improved prediction of upper-level dynamics.
Abstract
This study investigates diabatic processes along the warm conveyor belt (WCB) of a deep extratropical cyclone observed in the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX). The aim is to investigate the effect of two different microphysics schemes, the one-moment scheme ICE3 and the quasi two-moment scheme LIMA, on the WCB and the ridge building downstream. ICE3 and LIMA also differ in the processes of vapor deposition on hydrometeors in cold and mixed-phase clouds. Latent heating in ICE3 is found to be dominated by deposition on ice while the heating in LIMA is distributed among depositions on ice, snow, and graupel. ICE3 is the scheme leading to the largest number of WCB trajectories (30% more than LIMA) due to greater heating rates over larger areas. The consequence is that the size of the upper-level ridge grows more rapidly in ICE3 than LIMA, albeit with some exceptions in localized regions of the cyclonic branch of the WCB. A comparison with various observations (airborne remote sensing measurements, dropsondes, and satellite data) is then performed. Below the melting layer, the observed reflectivity is rather well reproduced by the model. Above the melting layer, in the middle of the troposphere, the reflectivity and retrieved ice water content are largely underestimated by both schemes while at upper levels, the ICE3 scheme performs much better than LIMA in agreement with a closer representation of the observed winds by ICE3. These results underline the strong sensitivity of upper-level dynamics to ice-related processes.
Abstract
This study investigates diabatic processes along the warm conveyor belt (WCB) of a deep extratropical cyclone observed in the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX). The aim is to investigate the effect of two different microphysics schemes, the one-moment scheme ICE3 and the quasi two-moment scheme LIMA, on the WCB and the ridge building downstream. ICE3 and LIMA also differ in the processes of vapor deposition on hydrometeors in cold and mixed-phase clouds. Latent heating in ICE3 is found to be dominated by deposition on ice while the heating in LIMA is distributed among depositions on ice, snow, and graupel. ICE3 is the scheme leading to the largest number of WCB trajectories (30% more than LIMA) due to greater heating rates over larger areas. The consequence is that the size of the upper-level ridge grows more rapidly in ICE3 than LIMA, albeit with some exceptions in localized regions of the cyclonic branch of the WCB. A comparison with various observations (airborne remote sensing measurements, dropsondes, and satellite data) is then performed. Below the melting layer, the observed reflectivity is rather well reproduced by the model. Above the melting layer, in the middle of the troposphere, the reflectivity and retrieved ice water content are largely underestimated by both schemes while at upper levels, the ICE3 scheme performs much better than LIMA in agreement with a closer representation of the observed winds by ICE3. These results underline the strong sensitivity of upper-level dynamics to ice-related processes.
