Convective initiation on 19 June 2002 during IHOP: High‐resolution simulations and analysis of the mesoscale structures and convection initiation

Abstract

The 19 June 2002 convective initiation (CI) case from the International H2O Project (IHOP) is simulated using the ARPS at 1 km grid spacing. It involves three distinct CI groups, CI‐A, CI‐B, and CI‐C, associated with a cold front‐dryline system. Initial condition at 1800 UTC, 19 June 2002 was created using the ARPS 3DVAR, including standard as well as special observations. The simulation captured the three groups of CIs rather well, with small timing and spatial errors. CI‐A is most typical of dryline initiation. Vertical cross sections through the initiation locations show typical dryline structures with an upward moisture bulge forced by lifting along the dryline convergence. For CI‐B, the model‐predicted mesoscale structures agree with special IHOP aircraft dropsonde observations closely. Strong low‐level convergence from opposing cold front and dryline circulations produces deep symmetric upwelling of moist air, and the convection is initiated at the crest of the moisture bulge. CI‐C is more typical of frontal convection where deep convection is first initiated at the front edge of the cold air. For CI‐B and CI‐C, north‐south moisture bands that have dryline characteristics (and can be considered multiple drylines) and contain enhanced vertical motion and upward moisture bulges intercept the dryline and cold front, respectively, providing the most favored locations on the dryline or cold front for initiation. Furthermore, the air parcels feeding the initial cells at CI‐B and CI‐C have trajectories along the moisture bands and have already experienced uplifting when they reach the dryline and cold front locations.