The Error Evaluation Of TraCE-21ka And Improvement Of Its Simulation On East Asian Summer Monsoon Evolution

Geological proxy data analysis and model simulation are the two ways to study paleoclimate,and their combination can enhance our understanding about the paleoclimate effectively.TraCE-21ka is the first transient simulation about the climatic evolution over the last twenty-one thousand years using fully coupled climate model.It can well reproduce the geological date reconstructed climate changes in some regions and further explain their mechanisms.However,the TraCE-21ka simulated climate changes in East Asia are usually inconsistent with the geological proxy data,restricting its application.This paper utilizes the Present Day(PD)observational data and the reconstructed permafrost data during Last Glacial Maximum(LGM)and Holocene Optimum(HO)to evaluate the error of TraCE-21ka and make a revision about TraCE-21ka to improve its ability to reproduce the East Asian summer monsoon evolution.The main results are as follow:(1)TraCE-21ka can well simulate the spatial pattern of large-scale circulation and precipitation during PD.For East Asia,its simulation is satisfactory in winter while deficient in summer.The TraCE-21ka simulated North Hemispheric(NH)temperature during PD is about 3-4? colder than observation.The ratio of PD temperature error and the temperature change from LGM to PD of TraCE-21ka is significant in East Asia,implying the reliability of the simulated evolution of the East Asian monsoon is low.For historical periods,the permafrost data indicate that the TraCE-21ka simulated Eurasia is warmer(colder)than reality during LGM(HO).With the annual mean surface temperature of continuous permafrost boundary is about-7?,the mid-latitude Eurasian warming amplitude of TraCE-21ka from LGM to PD can be quantitatively evaluated as 38%of the real world.(2)The analysis about the PD temperature error of TraCE-21ka show the sea surface temperature(SST)accounts for 50%-60%total NH error,with ambiguous seasonality.The sea ice and vegetation significantly influence NH temperature during winter and summer respectively,and the annual mean contribution of them are both about 16%.The NH PD cold error of TraCE-21ka is mainly attributed to the lower warming amplitude from LGM to PD.The lower warming amplitude results from lower transient climate sensitivity of TraCE-21ka,which leads to climate change error that accumulates in integration.(3)The comparison between TraCE-21ka simulated north boundaries of East Asian summer monsoon and reconstructed arid/semi-arid boarders suggests that TraCE-21ka correctly simulates the change direction of East Asian monsoon on orbital timescale,but underestimates the change amplitude.We revise the atmospheric data of TraCE-21ka with modern observational data and reconstructed continuous permafrost boundaries.The revision takes both PD error and the climate change from historical periods to PD of TraCE-21ka into account,and the annual mean surface temperature of continuous permafrost boundary equal to-7? is taken as the criterion.The revision increases the amplitude of climate change and improves the simulation of East Asian summer monsoon evolution.(4)Vegetation feedback can increase the amplitude of climate change.In PMIP3,the models with more real vegetation treatment simulate larger Eurasian cold anomalies in LGM comparing to pre-industry period.For East Asian summer monsoon,vegetation feedback decrease(increase)the precipitation in Northern China and increase(decrease)the precipitation in Southern China during LGM(Mid Holocene,MH),suggesting the vegetation feedback can increase the amplitude of East Asian precipitation change on orbital timescale.(5)Based on the comprehension of the effect of vegetation feedback,we revise the vegetation of TraCE-21ka by the preliminary revised temperature and precipitation,then use the revised vegetation as the underlying surface of atmospheric model to make a second revision about TraCE-21ka during LGM and MH.The second revision makes the annual mean surface temperature of reconstructed continuous permafrost boundaries closer to-7?and improves the simulation of East Asian summer monsoon during LGM.The first and second revised data of TraCE-21ka can be used to compare with geological data and therefore they have potential value in use.