Abstract : J.4
The role of aerosol particles on precipitation and ice phase processes: numerical studies with a high resolved 3D cloud model using detailed (bin) microphysics

Delphine Leroy, Wolfram Wobrock, Andrea Flossmann
Laboratoire de Météorologie Physique (LaMP)

A 3D cloud model with detailed microphysics for ice, water and aerosol particles (AP) is used to study the role of AP on the ice phase processes and precipitation formation in mixed clouds. The model couples the dynamics of the NCAR Clark-Hall cloud scale model (Clark et al., 1996) with the detailed scavenging model (DESCAM) of Flossmann and Pruppacher (1988) and the ice phase module of Leroy et al. (2007). The microphysics follows the evolution of AP, drop, and ice crystal spectra each with 39 bins. Aerosol mass in drops and ice crystals is also predicted by two distribution functions to close the aerosol budget.

The first simulated case is a deep convective cloud with a large anvil, sampled during CRYSTAL-FACE campaign on July 2002 18th (Heymsfield et al., 2005). Using a 3D grid resolution of 250 m, our model, called DESCAM-3D, is able to simulate a Cb with anvil in very good agreement with the measured temperature and vertical wind at 10 km and with the microphysical observations. Concerning the role of AP on the cloud evolution and structure, our findings significantly differ from those of Fridlind et al. (2004) who investigated the same case. They estimate that AP between 6 and 10 km account for about two-third of the anvil nuclei. The same work with DESCAM-3D leads to quite different conclusions.

The second case is a medium convective case over the Cévennes’ foothills in fall 2004 that produces a total rain accumulation over 24h larger than 100 mm in Alès (Chapon, 2006). Continuous observations with a volumetric C band radar at Bollène as well rain gauge and disdrometer measurements are also available. Once again, DESCAM-3D simulates a realistic cloud field with radar reflectivities, rain accumulation and spectra in agreement with the observations. The role of the ice phase for this event has been studied by turning off the cold microphysical package in a second simulation. The impact of pollution in terms of the initial AP number has also been investigated.