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The Mesoscale and Microscale Structure and Organization of Clouds and Precipitation in Midlatitude Cyclones. XII: A Diagnostic Modeling Study of Precipitation Development in Narrow Cold-Frontal Rainbands
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1984
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Midlatitude CyclonesPrecipitation DevelopmentEngineeringMicroscale StructureEarth SciencePrecipitationPrecipitation ProcessesMicrometeorologyAtmospheric ScienceModel ResultsMeteorological MeasurementHydrometeorologyMeteorologyUpdraft RegionMesoscale MeteorologyAtmospheric IcingCloud DynamicGeographyCryosphereCloud PhysicHydrologyClimate DynamicsClimatologyMeteorological ForcingDiagnostic Cloud Model
The highest precipitation rates in midlatitude cyclones are often associated with the narrow cold‑frontal rainband. The study analyzes the formation of precipitation in this rainband using a diagnostic cloud model and field measurements. The model shows that graupel forms when ice particles from the stratiform cloud rim in the rainband’s strong updraft, and when such particles are absent, graupel still forms from rimed frozen drops originating from autoconverted cloud water and frozen by collisions with ice crystals; sensitivity studies explore model inputs and parameters. Model results indicate that high precipitation rates in narrow cold‑frontal rainbands are driven by graupel, and even without the primary ice source precipitation remains mainly graupel‑based, with the model agreeing reasonably well with field observations.
The highest precipitation rates in midlatitude cyclones are often associated with the narrow cold-frontal rainband. In this paper the formation of precipitation in this type of rainband is analyzed with the aid of a diagnostic cloud model and field measurements. Model results indicate that the high precipitation rates in narrow cold-frontal rainbands are associated with graupel. The graupel forms when ice particles, which originate in the stratiform cloud ahead of the rainband, grow rapidly by riming after entering the strong updraft (and hence a region of high liquid water content) associated with the rainband. When this source of input ice particles is not present the precipitation is somewhat weaker, but still mainly associated with graupel. In this case, the graupel forms as small, frozen drops grow by riming. The drops form in the updraft region due to the autoconversion of cloud water and they are frozen by collisions with small ice crystals. A series of sensitivity studies dealing with various model inputs and parameters are discussed. The model results agree reasonably well with field measurements.