Evaluation of a scheme representing cloud inhomogeneous structure in the Australian Community Climate and Earth System Simulator (ACCESS) www.cawcr.gov.au Zhian Sun, Xiaobing Zhou, Yimin Ma, Hongyan Zhu (Bureau), Charmaine Franklin,, Dave Bi, Martine Dix, Tony Hirst, Simon. J. Marsland, Maciej Golebiewski (CSIRO), Cyril Morcrette (Met Office), John Shonk (Reading University)

Outline Introduction to ACCESS coupled climate model Tripleclouds scheme: cloud horizontal inhomogeneity in grid-box Exponential–random overlap scheme: Vertical structure of clouds Experimental results Summary The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

ACCESS component models and systems Puri (2005) project plan OPS Initial priorities: NWP for Bureau operations Coupled climate modelling for IPCC AR5 &CMIP5 NWP Assimilation 4DVAR Dynamic Vegetation /Disturbance Atmosphere UM Assimilation Coupler OASIS Land surface CABLE Atmos. chemistry UKCA Terrestrial C,N,P cycles Ocean GFDL MOM4 Sea ice CICE Oceanic biogeochemistry Assimilation BODAS OBS

MOM4P1: Atmosphere: (1) Horizontal point : 360x300. Longitudinal direction: uniform 1°, Latitudinal direction is 1/3° from 10oS to 10oN. Mercator grid is used in this region with 1 degree at 30oS to 0.25 degree at 78oS. (2) Vertical direction: 50 levels covering 0-6000 m with a 10m-resolution from the surface to 200m. (3) A global tripolar grid point. Atmosphere: HadGEM 2/3 atmospheric models N96 – 1.875 lon x 1.25  lat; 38 levels

Final result for IPCC AR5 Initial result in 2009 Final result for IPCC AR5 SST bias from ACCESS coupled model The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Why original model has cold SST bias? Energy from atmosphere may not be large enough to heat the ocean Surface wind may not be right for driving the ocean surface current The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Net SW flux at surface The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Problem is likely related to cloud, radiation Clouds are very complex in structure and interact strongly with radiation. Hence they are a very important aspect of the climate system and need suitable representation in climate models. However, representation of cloud in climate model is simple due to model resolution and computational limitation. The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

The Cloud Modelling Challenge We make two main approximations when representing clouds in a radiation code. Horizontal structure: optical depth in a gridbox layer is described by a single value of cloud water/ice content. Vertical structure: cloud is aligned vertically according to an overlap assumption. Cloud in a gridbox layer can then be represented by just two quantities: a cloud fraction and a single value of LWC/IWC.

The Cloud Modelling Challenge Assumption of homogeneous cloud distribution overestimates effect of cloud on radiation, leading to cooling at the surface Visible satellite image from 08 November 2010 at 12:00. 10 The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Tasks to improve representation of cloud Cloud fraction We modified cloud scheme to improve cloud amount prediction (not present here) Cloud horizontal inhomogeneous Implement an inhomogeneous cloud scheme developed by Shock at Reading University Vertical overlap Implement vertical exponential-random overlap scheme by Hogan & Illingworth from Reading University

Schematic demonstration of triplecloud Homogeneous cloud Tripleclouds Mean cloud water content Standard deviation of The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

The Tripleclouds method With Tripleclouds, the continuous water content distribution in a gridbox layer is represented with a two-point distribution function. water content Continuous distribution frequency Plane-parallel: one value Tripleclouds: two values standard deviation Fractional standard deviation fw = 0.75

Cloud overlap: random + maximum The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

From Hogan & Illingworth (QJ 2005) max ran Overlap parameter  Using radar observations to work out cloud cover of pairs of levels as function of level separation and values calculated using different overlap assumptions The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Z0 decorrelation distance z is level separation Z0 decorrelation distance Shock analysed radar data in different locations and found Z0 has a latitude dependence The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Net SW radiation at surface EXP1:Inhomo-cloud EXP2:cloud fraction EXP4: exponential-random overlap

SST biases

SST bias from ACCESS coupled model The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Summary SST in ACCESS coupled-model simulation has been significantly improved The Improvement is mainly due to the modifications in the UM model physics 1) Horizontal inhomogeneous representation of triplecloud scheme 2) New vertical exponential-random overlap scheme 3) Modification to the cloud fraction for both water and ice clouds 4) Modification to the surface wind roughness length All these changes apply to ACCESS and have been used in IPCC AR5 & CMIP5 experiments

Thank you Zhian Sun Phone: 96694408 Email: z.sun@bom.gov.au The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Zhian Sun Phone: 96694408 Email: z.sun@bom.gov.au Web: www.cawcr.gov.au Thank you www.cawcr.gov.au