Fabien Dezitter

HAIC - High Altitude Ice Crystals

Commercial aircraft have been experiencing inservice events while flying in the vicinity of deep convective clouds since at least the early 1990s. Heated probes and engines are the areas of aircraft most prone to mixed phase and glaciated icing threat. In anticipation of regulation changes according to mixed phase and glaciated icing conditions, the HAIC project will provide to the European Aeronautical industry Acceptable Means of Compliance (numerical and test capabilities) and appropriate ice particle detection/awareness technologies for use on-board of commercial aircraft in order to enhance safety when an aircraft is flying in such weather conditions. HAIC will achieve high Technology Readiness Level (TRL6) for technologies (radar, detector) and capabilities (numerical models and tools, test facilities) developed as part of the project HAIC is a 4 years integrated project comprising 37 partners representing the European stakeholders of the Aeronautical industry from 14 European countries.HAIC will also develop international cooperation and collaboration thanks to the involvement of key international organizations and companies as partner of the project or through the advisory board. Finally, HAIC will complement the work performed as part of existing international projects and working groups, notably EASA-HighIWC, HIWC, Engine Icing Working Group and Ice Crystals Consortium, and pave the way towards the ACARE 2020 and Flight Path 2050 safety objectives.

Ice Crystal Sizes in High Ice Water Content Clouds. Part II: Statistics of Mass Diameter Percentiles in Tropical Convection Observed during the HAIC/HIWC Project

High ice water content (IWC) regions in Mesoscale Convective Systems (MCS) are a potential threat to commercial aviation as they are suspected to cause in-service engine power-loss events and air data probe malfunctions. To investigate this, the High Altitude Ice Crystals (HAIC) / High Ice Water Content (HIWC) projects set up a first field campaign in Darwin (Australia) in 2014. The airborne instrumentation was selected to provide the most accurate measurements of both the bulk total water content (TWC), using a specially developed isokinetic evaporator, and the individual ice crystals properties using particle imaging probes. This study focuses on determining the size ranges of ice crystals responsible for the mass in high IWC regions, defined here as cloud regions with IWC greater than 1.5gm -3 . It is shown that for high IWC areas in most of the encountered MCS systems, median mass diameters (MMDs) of ice crystals range from 250 to 500μm and decrease with increasing TWC and decreasing temperature. At the same time, the mass contribution of the smallest crystals (below 100μm) remains generally low (below 15%). In contrast, data from two flight missions in a long-lasting quasi-stationary tropical storm reveal that high IWC values can also be associated with MMDs in the range 400-800 μm and peak values of up to 2mm. Ice crystal images suggest a major growth contribution by vapor deposition (columns, capped columns) even for such larger MMDs values.

HAIC/HIWC Field Campaign - Specific Findings on PSD Microphysics in High IWC Regions from In Situ Measurements: Median Mass Diameters, Particle Size Distribution Characteristics and Ice Crystal Shapes

Despite past research programs focusing on tropical convection, the explicit studies of high ice water content (IWC) regions in Mesoscale Convective Systems (MCS) are rare, although high IWC conditions are potentially encountered by commercial aircraft during multiple in-service engine powerloss and airdata probe events. To gather quantitative data in high IWC regions, a multi-year international HAIC/HIWC (High Altitude Ice Crystals / High Ice Water Content) field project has been designed including a first field campaign conducted out of Darwin (Australia) in 2014. The airborne instrumentation included a new reference bulk water content measurement probe and optical array probes (OAP) recording 2D images of encountered ice crystals. The study herein focuses on ice crystal size properties in high IWC regions, analyzing in detail the 2D image data from the particle measuring probes. Various geometrical parameters were extracted from the images in order to calculate particle size distributions (PSDs) and finally deduce median mass diameters with additional information on the ice density. The preliminary analysis of all HAIC/HIWC flights performed during this first flight campaign out of Darwin, demonstrates that various flights include high IWC regions mostly produced by high concentrations of small crystals while other flights with similar peak IWCs indicates that high IWC regions could be nevertheless composed primarily of larger particles. This interesting result indicates that high IWC can be produced and maintained in various environments, preferentially high concentrations of small crystals, however sometimes by smaller concentrations of larger sized crystal populations.

The Measured Relationship between Ice Water Content and Cloud Radar Reflectivity in Tropical Convective clouds.

In this paper we use unprecedented bulk measurements of ice water content (IWC) up to approximately 5 gm-3 and 95 GHz radar reflectivities (Z95) to analyze the statistical relationship between these two quantities and its variability. The unique aspect of this study is that these IWC – Z95 relationships do not use assumptions on cloud microphysics or backscattering calculations. IWCs greater than 2 gm-3 are also included for the first time in such analysis, owing to improved bulk IWC probe technology and a flight program targeting high ice water content. Using a single IWC – Z95 relationship allows for the retrieval of IWC from radar reflectivities with less than 30% bias and 40-70% rms difference. These errors can be reduced further down to 10-20% bias over the whole IWC range using the temperature variability of this relationship. IWC errors largely increase for Z95> 15-16 dBZ, due to the distortion of the IWC – Z95 relationship by non-Rayleigh scattering effects. A non-linear relationship is proposed to reduce these errors down to 20% bias and 20-35% rms differences. This non-linear relationship also outperforms the temperature-dependent IWC – Z95 relationship for convective profiles. The joint frequency distribution of IWC and temperature within and around deep tropical convective cores shows that at the -50°C ± 5°C level – the cruise altitude of many commercial jet aircraft – IWCs greater than 1.5 gm-3 were found exclusively in convective profiles.

Overview of the HAIC “Space-borne Observation and Nowcasting of High Ice Water Content Regions” Sub-Project and Mid-Term Results

The High Altitude Ice Crystals (HAIC) Sub-Project 3 (SP3) focuses on the detection of cloud regions with high ice water content (IWC) from current available remote sensing observations of space-based geostationary and low-orbit missions. The SP3 activities are aimed at supporting operationally the two up-coming HAIC flight campaigns (the first one in May 2015 in Cayenne, French Guyana; the second one in January 2016 in Darwin, Australia) and ultimately provide near real-time cloud monitoring to Air Traffic Management. More in detail the SP3 activities focus on the detection of high IWC from space-borne geostationary Meteosat daytime imagery, explore the synergy of concurrent multi-spectral multiple-technique observations from the low-orbit A-Train mission to identify specific signatures in high IWC cloud regions, and finally develop a satellite-based nowcasting tool to track and monitor convective systems over the Tropical Atlantic. The paper presents the HAIC SP3 objectives and provides an objective status of the sub-project at mid term of the HAIC project.