1. SHEBA model intercomparison of weakly-forced Arctic mixed-phase stratus Hugh Morrison National Center for Atmospheric Research Thanks to Paquita Zuidema (Univ. Miami)

2. Overview Case study is derived from measurements during Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment (1997-98 over the central Arctic Ocean) Long-lived low-level mixed-phase stratus were observed during early May, focus is on May 7, 1998 Several key differences from MPACE cases: o Colder temperatures (~ -22 C vs. -15 C) o Much smaller surface turbulent heat fluxes (ice-covered vs. open ocean) o More polluted aerosol o Much smaller amounts of cloud liquid water

3. Goals Document ability of models to simulate thin mixed- phase clouds for conditions much different than MPACE Specifically, we want to focus on: o Longevity of mixed-phase clouds in simulations o Sensitivity to concentration of ice nuclei or ice crystals, and how this differs between LES, CRM, and SCM

4. LWP (black), IWP (red) Radar reflectivity

5. Radar reflectivity, aircraft track Sonde T LWP

6. Aircraft LWC

7. Aircraft particle concentrations

8. Large-scale horizontal and vertical advection from constrained ECMWF analyses (Morrison and Pinto 2004), modified above BL so that T and qv profiles are approximately constant in time. Initial profiles:

9. Intercomparison is being conducted jointly with 2008 WMO Cloud Modeling Workshop in Cozumel, Mexico, July 2008 Details of the model specification and protocol and model forcing dataset are given in the case study documentation, available at: http://www.rap.ucar.edu/%7Egthompsn/workshop2008/ (Scroll down to “Arctic mixed-phase stratiform clouds (case #2)”)

10. Example of results using ARCSCM

11. Timeline Discussion of results in breakout session at WMO Cloud Modeling Workshop in July 2008 Submission of results by fall 2008 (no deadline set yet) If interested, send an e-mail to morrison@ucar.edu morrison@ucar.edu