1. 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

2. 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>

3. 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 ?

4. 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

5. Resolution of topography
dx = 7km
dx = 28km

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

7. 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 % over the mountain, however, the sensitivity differs by regions.

8. 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)