The convection and moist stratified flow over an idealized three-dimensional mountain: conditional unstable flow.

The properties of orographically induced convection and flow over the three-dimensional mountain within the conditional unstable atmosphere are strongly dependent on the trigger mechanism of convection, and the interaction between orographic flow, convection and gravity wave induced by mountain or convection. In present study, a series numerical experiment to the quasi steady stratified flow over an idealized three-dimensional mountain with an upstream profile of uniform wind speed, constant moist buoyancy frequency and constant relative humidity are undertaken.Based on the moist Froude number, four different flow regimes for the moist stratified flow over an three-dimensional mountain under the conditional unstable atmosphere are identified: (1) an downstream propagating convection mode, (2) an upstream and an downstream propagating convections mode, (3) an over-peak quasi-stationary and an downstream propagating convections mode, (4) an downslope quasi-stationary and an downstream propagating convections mode.There are two different mechanisms for the formation of orographically induced convection: (1) orographic lifting and flow decreasing, and (2) orographic flow forcing, i.e. upstream splitting, lee vortex and gravity wave breaking. In the case of larger Froude number, the convection induced by the orographic forcing could break the upstream and downstream orographic flow structure, but only a litter effect on the gravity wave breaking over the leeside.Initial CAPE have important role not only on the transportation and evolution of convective system, but also on the orographic flow in the moist environment. The sensitive simulation with a initial lower CAPE demonstrates that the decreased initial CAPE makes the flow regime shift back to regimes for lower Froude number.