Dynamical and Microphysical Composite around Tropical Convective Cores as derived from HIWC Aircraft Observations and a Satellite Product

A susceptibility of jet engines to engine power loss and damage events in the vicinity of deep convection has been recently identified, mostly along the Tropical belt. Recent studies concluded that these engine power loss events were likely due to the ingestion of large concentrations of small ice particles, a previously not well recognized form of engine icing, now referred to as "ice crystal icing". This threat is not detected by the pilot radars, because the radar is much more sensitive to ice crystal size than it is to concentration. The conditions of formation and maintenance of these High Ice Water Content (HIWC) regions is not well understood, although hypotheses involving either secondary ice production or homogeneous nucleation of droplets lifted by substantial convective updrafts have been put forth. Safety concerns related to threat and high costs associated with engine repairs led the international regulation authorities and scientific community to organize two field experiments in Darwin, Australia (2014) and Cayenne, French Guiana (2015) where airborne cloud radar and in-situ microphysical measurements were collected within and around deep convective cores. These observations have now all been post-processed and are available for process studies. In this talk, we will present a synthesis of the dynamical (convective vertical velocity, analysis of main upper-level outflows) and microphysical (ice water content, median mass diameter, concentration of ice crystals) properties derived from the aircraft observations, composited using satellite imagery providing the location of the main convective core closest to each aircraft observation and upper-level horizontal winds derived from the airborne cloud radar observations.

Figure: Spatial distribution of selected percentiles of IWC, size, and concentration of ice crystals as a function of distance to nearest convective core, highlighting two main HIWC regions: within 25 km of the convective core and at temperatures ranging from -55°C to 0°C; and 30 to 60 km away from the convective cores, for temperatures > -30°C.