In response to the ice crystal icing hazard identified twenty years ago, aviation industry, regulation authorities, and research centers joined forces into the HAIC-HIWC international collaboration launched in 2012. Two flight campaigns were conducted in the high ice water content areas of tropical mesoscale convective systems in order to characterize this environment conducive to ice crystal icing. Statistics on cloud microphysical properties, such as Ice Water Content (IWC) or Mass Median Diameter (MMD), derived from the dataset of in situ measurements are now being used to support icing certification rulemaking and anti-icing systems design (engine and air data probe) activities. This technical paper focuses on methodological aspects of the derivation of MMD. MMD are estimated from PSD and IWC using a multistep process in which the mass retrieval method is a critical step. Complementary to previous studies reporting on MMD values calculated from the HAIC-HIWC dataset, this paper deals with the uncertainty in MMD by comparing two different approaches for the retrieval of the mass-size (m-D) relationship. The analysis encompasses the data collected in the high IWC areas (IWC > 1g.m-3) sampled during the two HAIC-HIWC field campaigns. MMD series are computed using three different mass-size relationships and statistical values are compared. Overall, MMD values are in good agreement, at least for two methods although they imply quite different assumptions. On the variability in MMD values at a given temperature level, results show that MMD may vary significantly from one flight to the other, even though MMD series produced with the different mass retrieval methods follow a similar pattern. A strong temperature dependence is observed regardless the assumption on the m-D relationship, making MMD to increase by more than a factor of 2 as temperature increases from -50°C to -10°C. Finally, the influence on calculated MMD of two different definitions for particle size (Deq and Dmax) is demonstrated. Generally, MMD computed with Dmax are a few percent larger as compared to MMD calculated from Deq definition, supporting the conclusions from previous studies.
