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Drylines and Convection



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Drylines and Convection Andy Rye and Jeff Duda Introduction Characteristics Formation Movement Role in initiating convection Large scale along dryline variability Small scale along dryline variability Characteristics Dewpoint difference Change of 3 C at rate of 5 C per hour up to 18 C Wind shift Sharp wind shift on west with weak winds to the east The zone between two air masses or boundary layers Depth of boundary layers oscillate Characteristics Doppler velocity used to study Low level convergence and upper level divergence Hot air from west overflowed to east Secondary circulation with descent to the east Driven by vertical potential temperature gradient Westward tilt with height of vertical vorticity Formation Negatively tilted longwave trough at 500 mb over western U S Weak jet at 500 mb across southern CO 850 mb southerly winds over Texas from Gulf Appearance of strong inversion at 1200Z Terrain slope heat fluxes and soil moisture affect formation and movement Movement Warm dry air on west side overruns and forms cap Dry air creates higher PBL Moves by mixing and lowering dewpoint Can retrograde at night Movement Move smoothly in morning and jump in afternoon Bulges can form Evidence of other boundaries forming near dryline with similar characteristics Double dryline possible Convective Initiation Large scale along dryline variability Soil Moisture Pressure Gradient Force Cloud Streets Small scale along dryline variability Horizontal Convective Rolls HCRs Misocyclones Air Parcels Horizontal Convective Rolls HCRs Tubes of horizontal vorticity Generated by convective instability and wind shear Aligned with boundary layer shear vector Cloud streets reflectivity fine lines Near Surface Moisture Convergence modeled Enhanced surface convergence enhanced upward motion HCR Conceptual Model From Xue and Martin 2006 HCRs on Radar HCRs on Radar cont HCRs on Satellite Cloud Streets A Closer Look Near Surface Moisture Convergence Misocyclones Vertical vorticity tubes 4km



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