Flexible Global Ocean Atmosphere Land Research Articles

Sensitivities of simulated global aerosol optical depth and aerosol-radiation interactions to different horizontal resolutions in CAS-FGOALS-f3

The variations of horizontal grid spacing in aerosol climate models lead to discrepancies in simulated aerosol optical properties and radiation effects. To quantitatively investigate the effects of model horizontal resolution on global atmospheric aerosol simulation, the aerosol optical depths (AODs) and aerosol-radiation interactions (ARIs) for 10 years (2005–2014) are simulated by the Chinese Academy of Sciences Flexible Global Ocean Atmosphere Land System (CAS-FGOALS-f3) with a high resolution (HRM, ∼25 km) and a low resolution (LRM, ∼100 km). The experiments are performed with the same model parameterizations except the time step in HRM and LRM to maintain the stability of the dynamical core. The results show that the AODs simulated in HRM are more comparable to the multi-satellites and ground-based retrievals than those in LRM. Upon investigating the aerosol components, the differences in the carbonaceous and sulfate AODs between the HRM and LRM are more than 30%. The resolution sensitivities of hygroscopic aerosol simulations are mainly attributed to the simulated relative humidity (RH) and aerosol wet scavenging. The aerosol transports by wind fields alter the distributions of aerosol. The more reasonable simulations of the meteorological fields in the CAS-FGOALS-f3 with high resolution are favorable for aerosol simulations. The HRM-simulated ARI (−2.35 W m−2) is generally lower than the LRM-simulated one (−3.40 W m−2) at top of the atmosphere, and the relative difference is about 30%, which is similar to the relative difference of AOD.

Modelling study on the source contribution to aerosol over the Tibetan Plateau

AbstractUnderstanding the source of atmospheric aerosol is an essential step in determining the aerosol radiative effect over the Tibetan Plateau (TP). This study aims to clarify the contributions of anthropogenic and natural emission to the aerosols (carbonaceous and sulphate) characteristics inside the TP. An aerosol model named Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) recently coupled to the climate model named Chinese Academy of Sciences Flexible Global Ocean Atmosphere Land System (CAS‐FGOALS‐f3‐L) is used to simulate meteorological conditions and aerosols from 1985 to 2013, given emissions from the sixth phase of the Coupled Models Intercomparison Project (CMIP6). Comparisons between the simulations and ERA5 reanalysis data present that the model can capture the key spatial and temporal features of meteorological elements (2‐m temperature, relative humidity, and wind field at 500 hPa) over the Asia. Subsequently, we conduct six sensitivity studies to quantify the contributions of sources to aerosol surface concentration, burden and aerosol optical depth (AOD) over the TP. Our results illustrate that the outside and local anthropogenic sources contribute about 75.2% (78.9% in summer and 66.6% in winter) and 13.5% (7.4% in summer and 24.0% in winter) to the annual mean aerosols surface concentrations over the TP. The outside anthropogenic sources contribute to AODs in TP up to 87.3% (93.9% in autumn and 80.6% in winter). The ascending air over the TP is conducive to the transportation of the outsource pollutions to the TP. The outside natural sources (refer to biomass burning sources) contribute about 10% to aerosols over TP, and the inside natural sources play minor roles. The black carbon, organic carbon and sulphate (BOCS) induce average radiative forcing of −0.7 W m−2 at the near surface over the TP.

Statistical Downscaling of FGOALS-s2 Projected Precipitation in Eastern China

AbstractA statistical regression downscaling method was used to project future changes in precipitation over eastern China based on Phase 5 of the Coupled Model Intercomparison Project (CMIP5) the Representative Concentration Pathway (RCP) scenarios simulated by the second spectral version of the Flexible Global Ocean- Atmosphere-Land System (FGOALS-s2) model. Our validation results show that the downscaled time series agree well with the present observed precipitation in terms of both the annual mean and the seasonal cycle. The regression models built from the historical data are then used to generate future projections. The results show that the enhanced land-sea thermal contrast strengthens both the subtropical anticyclone over the western Pacific and the east Asian summer monsoon flow under both RCPs. However, the trend of precipitation in response to warming over the 21st century are different across eastern China under different RCPs. The area to the north of 32°N is likely to experience an increase...

Historical evolution of global and regional surface air temperature simulated by FGOALS-s2 and FGOALS-g2: How reliable are the model results?

In order to assess the performance of two versions of the IAP/LASG Flexible Global Ocean-AtmosphereLand System (FGOALS) model, simulated changes in surface air temperature (SAT), from natural and anthropogenic forcings, were compared to observations for the period 1850–2005 at global, hemispheric, continental and regional scales. The global and hemispheric averages of SAT and their land and ocean components during 1850–2005 were well reproduced by FGOALS-g2, as evidenced by significant correlation coefficients and small RMSEs. The significant positive correlations were firstly determined by the warming trends, and secondly by interdecadal fluctuations. The abilities of the models to reproduce interdecadal SAT variations were demonstrated by both wavelet analysis and significant positive correlations for detrended data. The observed land–sea thermal contrast change was poorly simulated. The major weakness of FGOALS-s2 was an exaggerated warming response to anthropogenic forcing, with the simulation showing results that were far removed from observations prior to the 1950s. The observations featured warming trends (1906–2005) of 0.71, 0.68 and 0.79 ◦ C (100 yr) −1 for global, Northern and Southern Hemispheric averages, which were overestimated by FGOALS-s2 [1.42, 1.52 and 1.13 ◦ C (100 yr) −1 ] but underestimated by FGOALS-g2 [0.69, 0.68 and 0.73 ◦ C (100 yr) −1 ]. The polar amplification of the warming trend was exaggerated in FGOALSs2 but weakly reproduced in FGOALS-g2. The stronger response of FGOALS-s2 to anthropogenic forcing was caused by strong sea-ice albedo feedback and water vapor feedback. Examination of model results in 15 selected subcontinental-scale regions showed reasonable performance for FGOALS-g2 over most regions. However, the observed warming trends were overestimated by FGOALS-s2 in most regions. Over East Asia, the meridional gradient of the warming trend simulated by FGOALS-s2 (FGOALS-g2) was stronger (weaker) than observed.

Analysis of Decadal Climate Variability in the Tropical Pacific by Coupled GCM

This study presents the spatial and temporal structures of the decadal variability of the Pacific from an extended control run of a coupled global climate model (GCM). The GCM used was version g2.0 of the Flexible Global Ocean Atmosphere Land System (FGOALS-g2.0) developed at LASG/IAP. The GCM FGOALS-g2.0 reproduces similar spatial-temporal structures of sea surface temperature (SST) as observed in the Pacific decadal oscillation (PDO) with a significant period of approximately 14 years. Correspondingly, the PDO signals were closely related to the decadal change both in the upper-ocean temperature anomalies and in the atmospheric circulation. The present results suggest that warm SST anomalies along the equator relax the trade winds, causing the SSTs to warm even more in the eastern equatorial Pacific, which is a positive feedback. Meanwhile, warm SST anomalies along the equator force characteristic off-equatorial wind stress curl anomalies, inducing much more poleward transport of heat, which is a negative feedback. The upper-ocean meridional heat transport, which is associated with the PDO phase transition, links the equatorial to the off-equatorial Pacific Ocean, acting as a major mechanism responsible for the tropical Pacific decadal variations. Therefore, the positive and negative feedbacks working together eventually result in the decadal oscillation in the Pacific.

A fast version of LASG/IAP climate system model and its 1000-year control integration

A fast version of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG)/Institute of Atmospheric Physics (IAP) climate system model is briefly documented. The fast coupled model employs a low resolution version of the atmospheric component Grid Atmospheric Model of IAP/LASG (GAMIL), with the other parts of the model, namely an oceanic component LASG/IAP Climate Ocean Model (LICOM), land component Common Land Model (CLM), and sea ice component from National Center for Atmospheric Research Community Climate System Model (NCAR CCSM2), as the same as in the standard version of LASG/IAP Flexible Global Ocean Atmosphere Land System model (FGOALS g). The parameterizations of physical and dynamical processes of the atmospheric component in the fast version are identical to the standard version, although some parameter values are different. However, by virtue of reduced horizontal resolution and increased time-step of the most time-consuming atmospheric component, it runs faster by a factor of 3 and can serve as a useful tool for longterm and large-ensemble integrations. A 1000-year control simulation of the present-day climate has been completed without flux adjustments. The final 600 years of this simulation has virtually no trends in global mean sea surface temperatures and is recommended for internal variability studies. Several aspects of the control simulation’s mean climate and variability are evaluated against the observational or reanalysis data. The strengths and weaknesses of the control simulation are evaluated. The mean atmospheric circulation is well simulated, except in high latitudes. The Asian-Australian monsoonal meridional cell shows realistic features, however, an artificial rainfall center is located to the eastern periphery of the Tibetan Plateau persists throughout the year. The mean bias of SST resembles that of the standard version, appearing as a “double ITCZ” (Inter-Tropical Convergence Zone) associated with a westward extension of the equatorial eastern Pacific cold tongue. The sea ice extent is acceptable but has a higher concentration. The strength of Atlantic meridional overturning is 27.5 Sv. Evidence from the 600-year simulation suggests a modulation of internal variability on ENSO frequency, since both regular and irregular oscillations of ENSO are found during the different time periods of the long-term simulation.