Online supplemental material (OSM) for

Influences of external forcing changes on the summer cooling trend over East Asia

Bian He, Qing Bao, Jiandong Li, Guoxiong Wu, Yimin Liu, Xiaocong Wang, Zhaobo Sun

  1. Introduction to the AGCM

The model used in this study is the Spectral Atmospheric Model of LASG/IAP(known as SAMIL) (Bao et al. 2010), which has the horizontal resolution R42 (2.81° (longitude)×1.66° (latitude)) with 26 vertical layers in–p hybrid coordinates, extending from the surface to 2.19hPa. The mass flux cumulus parameterization of Tiedtke (1989) is used to calculate convective precipitation. The cloud scheme is a diagnostic method parameterized by low-layer static stability and relative humidity (Slingo 1980,1987). A stratocumulus scheme is also employed, based on a statistical cloud scheme (Dai et al. 2004). A nonlocal scheme is employed to calculate the eddy-diffusivity profile and turbulent velocity scale, and the model incorporates nonlocal transport effects for heat and moisture (Holtslag and Boville1993). The radiation scheme employedis an updated Edwards–Slingo scheme (Edwards and Slingo1996;Sun and Rikus 1999), as used in HadCM3 but with some improvement by Sun (2005, 2011).Gas absorption due to O2, O3, and major GHGs (e.g., H2O, CO2, CH4, N2O, CFC11, and CFC12)are included. The optical properties of aerosols are described in Martin et al. (2006),who determined the aerosol optical depth (AOD) by the mass extinction coefficient, the aerosol mass mixing ratio (CMIP5 datasets in the present study), and the specified mass thickness path length, with the direct effects of the aerosolsbeing calculated using SAMIL radiative codes.

SAMIL is coupled with the land model NCAR CLM3(Oleson et al. 2004) in this study. The land model provides the surface albedo (direct beam and diffuse for visible and near-infrared wavebands), upward longwave radiation, sensible heat flux, latent heat flux,water vapor flux, and surface stresses required by SAMIL.

The spectral model SAMIL is commonly used in studies of climatic change over East Asia. For the topic we discuss here,SAMIL can reproduce the basic spatial pattern of the SAT linear trend over East Asia during summer (Fig.S1a), whereas the up-to-date Multi Model Ensembles (MME) from the Coupled Model Intercomparison Project phase 5 (CMIP5) coupled models cannot (Fig.S1b).

The linear regression of MME, calculated based on the 20 CGCMs’ historical runs from 1951 to 2005 (most of the CGCMs only provide outputs up to 2005), shows a uniform warming trend over East Asia that indicates that current state-of-the-art coupled models still lack the ability to capture the basic SAT trend over East Asia during June–August (JJA). The simulation of SAMIL, which is forced by the same condition except for the use of prescribed monthly SST and sea ice, shows a reasonable spatial pattern (Fig.S1a) compared with observations (Fig.1a in main text). The reasonable performance of SAMIL in this regard raises thepossibility of identifying the cause of the cooling trend over East Asia.

Fig. S1. Linear trendsfor the simulated JJA SAT from 1951 to 2005 (unit: °C/55 yrs).

(a) Results ofSAMILusing the same forcings as CGCMs with the exception of historical SST andsea ice (ALL_RUN in this study).

(b) Multi Model Ensemble Results of 20 CGCMs selected from IPCC/CMIP5 historical runs.

Reference

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