Influence of Secondary Ice Production on cloud and rain properties: Analysis of the HYMEX IOP7a Heavy Precipitation Event

Abstract. A significant part of precipitation originates from ice crystals while the representation of the cloud mixed phase by atmospheric models remains a challenging task. One of the well-known problem is the discrepancy between the concentration of ice nucleating particles (INPs) and the ice crystal number concentration. This study explores the effect of secondary ice production (SIP) on the properties of the intense precipitation event IOP7a observed during the HYMEX campaign. The effect of SIP on cloud and rain properties is assessed by turning on or off SIP mechanisms in the 3D bin microphysics scheme DESCAM. Our results indicate that including SIP gives better agreement with in situ aircraft observations in terms of ice crystal number concentration and supercooled drop number fraction. During the mature cloud stage, and for temperatures warmer than -30 °C, 59 % of ice crystals are produced by fragmentation due to ice-ice collisions, 38 % by Hallet-Mossop process, 2 % by fragmentation of freezing drops and only 1 % by heterogeneous ice nucleation. Furthermore, ours results shows that the production of small ice crystals by SIP induces a redistribution of the condensed water mass toward particles smaller than 3 mm rather than larger ones. As ice crystals melt, this effect is also visible in the precipitating liquid phase. The shift toward smaller particles results in a reduced precipitation flux of both ice crystals and drops. Consequently, SIP induces a decrease of the accumulated precipitation at the surface by 8 % and reduces heavy rainfall exceeding 40 mm by 20 %.