Sensitivity of precipitation formation to secondary ice production in winter orographic mixed-phase clouds

Abstract

Abstract. The discrepancy between the observed concentration of ice nucleating particles (INPs) and the ice crystal number concentration (ICNC) remains unresolved and limits our understanding of ice formation and, hence, precipitation amount, location and intensity. Enhanced ice formation through secondary ice production (SIP) could account for this discrepancy. Here, in a region over the eastern Swiss Alps, we perform sensitivity studies of additional simulated SIP processes on precipitation formation and surface precipitation intensity. The SIP processes considered include rime splintering, droplet shattering during freezing and breakup through ice–graupel collisions. We simulated the passage of a cold front at Gotschnagrat, a peak at 2281 m a.s.l. (above sea level), on 7 March 2019 with the Consortium for Small-scale Modeling (COSMO), at a 1 km horizontal grid spacing, as part of the RACLETS (Role of Aerosols and CLouds Enhanced by Topography and Snow) field campaign in the Davos region in Switzerland. The largest simulated difference in the ICNC at the surface originated from the breakup simulations. Indeed, breakup caused a 1 to 3 orders of magnitude increase in the ICNC compared to SIP from rime splintering or without SIP processes in the control simulation. The ICNCs from the collisional breakup simulations at Gotschnagrat were in best agreement with the ICNCs measured on a gondola near the surface. However, these simulations were not able to reproduce the ice crystal habits near the surface. Enhanced ICNCs from collisional breakup reduced localized regions of higher precipitation and, thereby, improved the model performance in terms of surface precipitation over the domain.

Aerosol–cloud–precipitation interactions during a Saharan dust event – A summertime case‐study from the Alps

“…Dedekind et al . (2021) showed similar results where an enhancement in the ice crystal number concentrations significantly reduces cloud liquid, favouring the growth of ice particles by deposition over riming at low cloud temperatures. However, the redistribution of the growth processes lead to insignificant changes in the regional precipitation amount (Glassmeier and Lohmann, 2018).…”

“…Simulations are conducted with the regional weather and climate model COSMO (Steppeler et al ., 2003). COSMO has been used for simulating (orographic) MPCs in previous studies (Lohmann et al ., 2016; Henneberg et al ., 2017; Possner et al ., 2017; Eirund et al ., 2019a; 2019b; Dedekind et al ., 2021). The simulations are performed on a rotated latitude–longitude grid with 0.01° horizontal resolution, which corresponds to approximately 1.1 km at midlatitudes.…”

Heavy snowfall event over the Swiss Alps: Did wind shear impact secondary ice production?

“…Rime splintering has been used extensively in models but has been shown to be inadequate, having ice number concentrations orders of magnitude less than observed, in SIP in wintertime orographic MPCs (Henneberg et al, 2017;Dedekind et al, 2021;Georgakaki et al, 2022). Ice-ice collisions have been more widely used in models in the last decade (Yano and Phillips, 2011;Phillips et al, 2017;Sullivan et al, 2018;Hoarau et al, 2018;Sotiropoulou et al, 2020;Zhao et al, 2021) since they were first studied in laboratory conditions about four decades ago (Vardiman, 1978;Takahashi et al, 1995).…”

“…Ice-ice collisions have been more widely used in models in the last decade (Yano and Phillips, 2011;Phillips et al, 2017;Sullivan et al, 2018;Hoarau et al, 2018;Sotiropoulou et al, 2020;Zhao et al, 2021) since they were first studied in laboratory conditions about four decades ago (Vardiman, 1978;Takahashi et al, 1995). SIP as a result of ice-ice collisions was shown to contribute significantly to the ice crystal number concentrations and thereby explain the discrepancy between models and observations in the Arctic (Sotiropoulou et al, 2020;Zhao et al, 2021), Antarctic (Sotiropoulou et al, 2021b) and mid-latitudes (Sullivan et al, 2018;Dedekind et al, 2021;Georgakaki et al, 2022). The enhancement of smaller ice particles cause an increase in the combined growth rates (riming and deposition) of up to 33% resulting in larger latent heat release and stronger updraft velocities (Dedekind et al, 2021).…”

“…SIP as a result of ice-ice collisions was shown to contribute significantly to the ice crystal number concentrations and thereby explain the discrepancy between models and observations in the Arctic (Sotiropoulou et al, 2020;Zhao et al, 2021), Antarctic (Sotiropoulou et al, 2021b) and mid-latitudes (Sullivan et al, 2018;Dedekind et al, 2021;Georgakaki et al, 2022). The enhancement of smaller ice particles cause an increase in the combined growth rates (riming and deposition) of up to 33% resulting in larger latent heat release and stronger updraft velocities (Dedekind et al, 2021). When ice-ice collisions occur in wintertime orographic MPCs, the general tendency is for riming to decrease.…”