The role of heating and cooling associated with ice processes on tropical cyclogenesis and intensification: Tropical Cyclogenesis

The article of record as published may be found at http://dx.doi.org/10.1002/qj.3187A recent idealized numerical study of tropical cyclogenesis and subsequent intensification using warm-rain-only microphysics is extended to examine the modifications brought about by a representation of ice processes. It is found that the time taken to reach cyclogenesis is more than twice that in the equivalent warm-rain-only simulation. The subtle reasons for the difference in the length of the gestation period are discussed. A mid-level vortex forms during the early gestation period when ice processes are present, but not when warm-rain- only processes are present. Axisymmetric balance calculations show that the spin-up of this mid-level vortex is related to the different spatial distribution of diabatic heating rate in the presence of ice, which leads to a system-scale radial influx of absolute vorticity in the middle troposphere. The tropical-cyclone vortex that forms in the simulation with ice is similar to that in the warm-rain-only simulation, with the strengthening frictional boundary layer exerting a progressively important role in focusing inner-core deep convection. This vortex develops in situ on a much smaller scale than the mid-level vortex and there is no evidence that it is a result of the mid-level vortex being somehow carried downwards, as has been suggested previously by some researchers. Some implications of the results in relation to previous theories of tropical cyclogenesis are discussed.GK and RKS acknowledge support for tropical cyclone research from the German Research Council (Deutsche Forschungsge- meinschaft) under grants SM30/23-3 and SM30/23-4 and the Office of Naval Research Global under Grant No. N62909- 15-1-N021. MTM acknowledges the support of NSF grant AGS-1313948, NOAA HFIP grant N0017315WR00048, NASA grant NNG11PK021 and the US Naval Postgraduate School.GK and RKS acknowledge support for tropical cyclone research from the German Research Council (Deutsche Forschungsge- meinschaft) under grants SM30/23-3 and SM30/23-4 and the Office of Naval Research Global under Grant No. N62909- 15-1-N021. MTM acknowledges the support of NSF grant AGS-1313948, NOAA HFIP grant N0017315WR00048, NASA grant NNG11PK021 and the US Naval Postgraduate School