Rear flank downdraft

The rear flank downdraft can arise owing to negative buoyancy, which can be generated by cold anomalies produced at the rear of the supercell thunderstorm by evaporative cooling of precipitation or hail melting, or injection of dry and cooler air in the cloud, and by vertical perturbation pressure gradients that can arise from vertical gradients of vertical vorticity, stagnation of environmental flow at an updraft, and pressure perturbations due to vertical buoyancy variations (which are partially due to hydrostatic effects). Some findings showed that within the RFDs equivalent potential temperature (θe) is cold with respect to the inflow. Moreover, the lowest wet-bulb potential temperature (θw) values observed at the surface were within the RFD. There are, however, also observations of warm, high-θe air within RFDs. Difference from forward flank downdraft Compared to the forward flank downdraft (FFD) the rear flank downdraft (RFD) consists of warm and dry air. This is because the RFD is forced down from the mid-levels of the atmosphere, resulting in compressional heating of downward moving parcels. The FFD, in contrast, is driven by precipitation loading and evaporative cooling in the precipitation core of a supercell thunderstorm, making the FFD relatively cold and wet. Both are thought to be significant in tornado formation. == Role in tornadogenesis ==

. Association with hook echo Rear-flank downdrafts have a well-established association with hook echoes. Firstly, the initial rear flank downdraft is air from aloft transported down to the surface by colliding and mixing with the storm. • tilts horizontal vorticity to produce vertical vorticity • transports air containing vertical vorticity from mid-level to the surface • enhances the near-ground vorticity convergence beneath the updraft tremendously by entering the updraft and stretching vertically ==See also==