Simulations Of The Indo-pacific Warm Pool By Ipcc Models

The importance of the Indo-Pacific warm-pool in the climate system has been widely recognized. The warm pool has been referred to as the furnace of the Earth's climate system. Meanwhile the huge heat content of the Indo-Pacific warm-pool has lots of impact on the climate system and disaster events in Asia and tropical region. Previous study has found that the excessive cold tongue is a common bias in the coupled model. These studies, however, examined only a single run of the concerned models. As the observation is a single realization, it is important to examine the spread of the ensemble runs to draw a conclusion with confidence about the biases in the models.Evaluations of the simulations of Indo-Pacific warm pool by 19 no flux adjustment IPCC AR4 models reveals systematic biases. Excessive cold tongue, equatorial confined Western Pacific warm pool and more southwestward spread of Indian Ocean warm pool are found as the common biases in coupled IPCC models. It is found that most of the models have the smaller and warmer warm pool. And most of the models underestimate the expanding and warming trend of the warm pool under the global warming during the last 50 years in the 20th century. Models show big biases in the regulation of the maximum SST; most of the models overestimate the maximum SST over warm pool and overestimate the warming trend of maximum SST over warm pool during the global warming. Such common biases are more distinct in Indian Ocean warm pool because the maximum SST mostly distribute over the Indian Ocean in IPCC models instead of mostly distributing over the Western Pacific warm pool region in observation. IPCC models show less regulation in maximum SST and prefer lower maximum SST distribution in the tropical SST distribution simulation. The simulation of the mean precipitation over warm pool show systematic biases as below: all the 19 no flux adjustment IPCC models overestimate the precipitation over warm pool and near all the IPCC models simulate the decreasing trend on the contrary with the increasing trend in observation. The Double-ITCZ problem is still a common bias in all the coupled IPCC models. Models show weak relationship between the precipitation anomaly and SST anomaly over central and eastern tropical pacific especially on the precipitation anomaly induced by the warmer SST anomaly.Most of the IPCC models overestimate the latent heat released over warm pool; underestimate the net shortwave radiation over warm pool and thus underestimate the net surface heat flux into warm pool. Most of the IPCC models underestimate the increasing trend of the latent heat released over warm pool and thus underestimate the decreasing trend of the net surface heat flux to warm pool. The warmer SST biases over warm pool and the excessive feedback between SST and the latent heat released in the coupled models lead to the excessive latent heat released over warm pool. The warmer warm pool SST biases even conflict with the insufficient feedback between SST and shortwave radiation over Western Pacific warm pool and dominate the insufficient net shortwave radiation over warm pool. Over all, the surface net heat flux is negativly reponsed to the SST over warm pool instead of positivly regulating the SST over warm pool.Most of the IPCC models show common biases in ENSO simulation: models simulated stronger ENSO events and weak or non-existing ENSO asymmetry. Models simulate weak ENSO asymmetry during the whole 20th century and simulate the more and more weak ENSO asymmetry on the contrary with the stronger ENSO asymmetry during the whole 20th century. It is hypothesized that the weak ENSO asymmetry in the IPCC models leading to the weak residual effect of El Ni?o events and the weak regulation of tropical mean SST, thus lead to the smaller and warmer modeled warm pool biases.The sensitivity experiment based on the NCAR PBM model indicate the lack effect as the heat-mixer of the modeled ENSO, which can lead to the excessive cold tongue problem, warmer Western Pacific warm pool and weak warm anomalies in the subsurface temperature. The sensitivity experiment based on the FOAM model indicate that a better warm pool simulation can corresponding to a better ENSO simulation both on the ENSO activity level and the ENSO asymmetry. The radiation-optimized experiment over warm pool can lead to a better warm pool simulation, stronger ENSO events and stronger ENSO asymmetry. But the heat flux forcing over warm pool may cause to the worse simulation of warm pool and ENSO asymmetry in FOAM. How well the warm pool mean state affect the ENSO activity is still need to be further studied.In addition, how to improve the ENSO asymmetry simulation in coupled models is the study pursuing. Other impact to the warm pool biases such as ocean current simulation and the monsoon simulation biases need to be further studied.Moreover, it seems the strong ENSO events corresponding to the larger warm pool size. The relationship between the warm pool meant state and the ENSO activity is still our future work.