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5.3 What control occurrence, intensity, type and life-time of the convective systems?

5.3 What control occurrence, intensity, type and life-time of the convective systems?. Central questions What control the occurrence of convection? What control convective type (intensity, lift time, dynamic structure)?. What control occurrence of convection?. Question:

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5.3 What control occurrence, intensity, type and life-time of the convective systems?

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  1. 5.3 What control occurrence, intensity, type and life-time of the convective systems? Central questions What control the occurrence of convection? What control convective type (intensity, lift time, dynamic structure)?

  2. What control occurrence of convection? Question: Why is convection absent when CAPE and CIN conditions suggest the occurrence of convection? What cause occurrence of convection when CIN is large? Why does convection prefer to occur along the fronts?

  3. What cause occurrence of convection when CIN is large? • Elevated convection:Air is lifted above the boundary layer • occurs at night with LLJ • When large-scale low-level convergence occurs

  4. Modification of lapse rate by large scale circulation

  5. Why is convection absent when CAPE and CIN conditions suggest the occurrence of convection? • Dilution of CAPE, strong mixing with dry environment would significantly dilute CAPE • Wind shear influence: • Insufficient CIN removal

  6. What control convective type (intensity, lift time, dynamic structure)? Role of wind shear: A key parameter that determines life time, intensity and type of convective system, Bulk Richardson number (BRN) BRN=CAPE/(U2/2) Where U is the magnitude of vector different between the mean wind of the surface to 6 km and of the surface to 500 m.

  7. Why? • CAPE: control buoyancy and thus vertical velocity and outflow of the convection • U2/2: controls the kinetic energy of inflow relative to convection (convection is also moving) and wind shear which

  8. If BRN is large, i.e., U2/2 is small relative to CAPE, convection tends to be short lived because • Inflow cannot keep up with outflow • Overlap between rainfall and updraft • Gust flow of convection tends to under cut inflow • Overall, wind shear dominates the intensity, life time and type of convection. • 0-6km wind shear <10m/s: single cell convection • 10-20 m/s: multicells convection • >20m/s: supercell convection

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