Dynamics and Microphysics of Narrow Cold-Frontal Rainbands as Investigated with a Three-Dimensional Cloud Model

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9633424 Wang The narrow cold frontal rainband (NCFR) is one of several types of mesoscale rainbands observed in mid-latitude cyclones. Previous studies have shown that NCFRs have the potential to produce very heavy rains and high winds. The Principal Investigators will utilize an advanced numerical mesoscale weather model to simulate the dynamics and microphysics of NCFR. Imbedded along the synoptic-scale parent front, NCFR's are dominated by well-marked mesoscale to microscale structure with quasi-periodically spaced precipitation cores separated by gaps containing little or no rain. Previous NCFR studies have shown that riming of snow crystals is highly important to graupel growth aloft and thus to surface rainfall. The numerical model is configured to simulate line convection and includes a three-class ice microphysics parameterization. Initial parameters of main interest will be mid- to upper-level environmental wind shear and the length of mesoscale waves perturbing the leading edge of the cold air. The choice of these two parameters is motivated by recent observational evidence that upper wind shear affects graupel growth in postfrontal snowbands and that strong positive correlations exist among the depth of NCFR precipitation cores, their radar reflectivity and the separation between them. If successful, this research will increase our understanding of the fundamental physics of these systems which are capable of producing severe weather. This may eventually lead to better predictions. ***