Effect of topographical resolution on cirrus clouds using a high-resolution GCM (Seiki et al., JGR, under review) Tatsuya Seiki1, Chihiro Kodama1, Akira T. Noda1, Masaki Satoh1,2, Tempei Hashino3, Yuichiro Hagihara4, Hajime Okamoto3 1.JAMSTEC, 2. The University of Tokyo, 3. Kyushu University, 4. JAXA The 4th International Workshop on Nonhydrostatic Models (NHM2016) November 30 to December 2, 2016

Cirrus Cirrus is a category of “thin” and “high” clouds Cirrus is broadly distributed, hence has strong CRF 27% for longwave (Chen et al., 2001) However, GCMs have large bias in cirrus (IPCC-AR5; Li et al., 2013) Cirrus image from wikipedia Structures in cirrus (according to Sassen et al., 2007) Each cell has structures smaller than 1km Several cells are embedded in meso-scale systems less than 200km  GCMs (dx~100km) have not been capable of capturing these structures GCRMs (dx~10km) was used for capturing meso-scale system <THIS STUDY>

Objectives Resolving effect of orographic gravity wave on cirrus Homogeneously Nucleated Ice Number Concentration [m-3] Typical Gravity Wave from Durran (1986) Vertical velocity w, trigger of cirrus amplitude [ 10 cm s-1 ~ 100 cm s-1 ] Horizontal wave length [10 km ~ 1000km] Cirrus Layer Ice number concentration (NI) strongly depends on w in cirrus layers Joos et al. [2008; 2010] suggested that NI increases over mountain using a gravity wave parameterization  Does an increase in horizontal resolution improves simulated NI ?

Numerical Settings (resolution) NICAM was used (NICAM = Non-hydrostatic ICosahedral Atmospheric Model) Cloud Microphysics: Double-Moment Bulk (Seiki et al., 2014; 2015) Horizontal resolution was different between grid (Δx) and topography (Δx*factor) １）gtopo30 is averaged within a control volume with averaging radius of r0 ２）Smoothing by hyper diffusion r0 Smoothed Topography (NICAM Default) NOT-Smoothed Topography G8 dx = 28km fr0 = 1 G9 dx = 14km G10 dx = 7km G8T dx = 28km fr0 = 3 G9T dx = 14km G10T dx = 7km fr0 = 6

Resolution of topography dx = 7km dx = 28km

Topographical effect on w and NI SMOOTHED Topo NOT-SMOOTHED Topo

Evaluation of NI (compared to CALIPSO+CloudSat) Cloud Optical Depth Cloud Optical Depth Global Global NI [m-3] IWC [kg m-3] Cloud Optical Depth Rockies Andes Maritime Continent NI [m-3] NI [m-3] NI [m-3] Global NI does not improves by changing resolution and topography. ( IWCs from all experiments are in good agreement with obs. ) NI increases by 50-100 % over the mountain, however, the sensitivity differs by regions.

Summary topographical effect on Global NI What’s the response of cirrus to the change in topography ? As topography becomes fine, Cirrus is strongly perturbed by stronger w Cirrus becomes isolated because of finer horizontal wavelength Orographic cirrus does not always develop/broaden NI does not significantly increases in terms of global mean Topographical data has significant impact on NI when dx ≥ 28 km (G8T)