Impact of the vertical resolution on Climate Simulation using CESM Speaker: Tzu-Ling Lai Wei-Liang Lee, Huang-Hsiung Hsu

Objective: Investigating the impact of the increasing model vertical resolution → A case of dust simulation in Africa → A quick comparison between the coupled and non-coupled model run

Data Model: Community Atmosphere Model 5 (CAM5), SST= Prescribe 1850 Horizontal resolution: (lat=192,lon=288) Vertical resolutions: 30 layers (L30) and 60 layers (L60). Vertical resolutions are shown in Table Average the last 10-years model simulation (focus on JJA) 30 layers 60 layers

Aerosol optical depth L60 L30 Dif. (L60-L30) Aerosol optical depth from dust L60 L30 Dif. (L60-L30) The differences showed that the L60-model had less aerosol optical depth over the Africa.

Dust distribution L60 L30 The results showed that vertical transport of dust in L60 was lower than in L30. Both horizontal and vertical profile showed less dust in L60 Average: 30W~60E, scaled: 1e08 Dif.(L60-L30)

Meteorological conditions: surface 10m wind speed Surface temperature RH( ref. height) Total precipitation rate Weaker 10-m wind speeds; Lower relative humidity at reference height; The temperature dropped 0.5 to 3 degree in most areas of Africa. Total precipitation rates were enhanced around the equator and south of the equator.

Meteorological conditions: sea level pressure, 850mb vector The easterly anomalies reflected the weakened westerly flow in the southern flank of cyclonic circulation. L60-model simulated: a weaker cyclonic circulation in northeastern Africa, wider areas influenced by the anti-cyclonic circulation in Africa and Middle East.

Meteorological conditions: vertical L60-model showed smaller wind speeds near the surface and weaker vertical motion in this region. In addition, more stable condition in the low boundary layer were observed, as indicated in both dry and moist static energy profiles

Case Summary 1. The higher vertical resolution resulted in weaker cyclonic circulation in northern Africa and Middle East during boreal summer. The vertical velocity and the precipitation patterns indicated the southward shift of the inter-tropical convergence zone (ITCZ) and the local Hadley circulation. 2. The more stable boundary layer in the lower troposphere and the weaker vertical velocity occurred in the main dust sources regions. 3. The weaker 10-m wind speeds seem to be the main cause of the less dust production in northern Africa in the L60 model.

Case of coupled model (E1850) Less AOD and Dust Weaker surface wind

Annual Cycle Global Mean Climatology Take the Non-coupled run as the example: PBL high cloud Both coupled and non-coupled model showed the similar results: Lower PBL in L60-run; Less low-cloud; More mid- and high- cloud mid cloud Low cloud

Annual Cycle Plots of Zonal Mean Non-coupled Coupled The different results on couple and non-coupled after changing vertical resolution: Precipitable water

Annual Cycle Plots of Zonal Mean Non-coupled Coupled The different results on couple and non-coupled after changing vertical resolution: Precipitation rate

Summary Both coupled and non-coupled model showed the similar results: lower PBL in L60-run; reduced global cloud amount, also low-cloud; increased mid- and high- cloud; weakened surface wind; less AOD and Dust Non-coupled model showed less precipitable water between 30S~30N; especially in the months of JJASO. The coupled model presented more precipitable water in the annual cycle

Thanks

Meteorological conditions: vertical U Omega Westerly wind appeared around 10oN in the lower troposphere in L30-model. After increasing the vertical resolution, the westerly wind had become weakening. In the region north of 20N, the areas of easterly and westerly wind were relatively weak in L60-model. The omega profiles indicated that the upward and downward motion were around 10oN-20oN and 30oN, respectively. After increasing the vertical resolutions, the upward-motion area shifted southward toward the equator, while the downward motion tended to dominate in more areas of northern Africa. This southward shift of local Hadley circulation might have a notable effect on the weakening of near-surface wind.

Future Work Using the different type of high vertical resolution Further analysis………….