Simulation Performance Evaluation And Correction Of Climate In The Northern Hemisphere By CMIP5 Model

Based on the correction method of climatic drift and multiple linear regression,this paper evalued the monthly mean precipitation,temperature,sea level pressure and water vapor flux in the northern hemisphere historical period(1956~2005)for the 26 modes of the Coupled Model Intercomparison Project 5(CMIP5).These fields in future scenarios(2006~2055)are revised and estimated.In the study,we used the monthly average precipitation and temperature observations of CRU(Climatic Research Unit)provided by the University of East Anglia were selected,the NCEP sea level pressure data set of the NOAA Center in the United States,and the CERA20 C wind field of the short-term climate prediction of the European Center as observations.The surface pressure and the specific moisture fields are used in evaluations.In the study,we revised histotical precipitation,temperature,sea level pressure and water vapor flux,and analysied the differences between raw and revised distribution,especially for the changes in their time series.The regression equations established in the historical period were used for 3 representative concentration pathway(RCP 2.6,RCP4.5,RCP8.5)to estimate the changes and trends in the next 50 years.The main conclusions are as follows:(1)(1)In the historical period,the CMIP5 multi-mode ensembles in the northern hemisphere have the best capabilities to simulate the spatial distribution of temperature,followed by the precipitation and the sea level pressure,while the simulation capability for water vapor transport is the worst.As for north hemisphere mean time series,temperature is the best,followed by the water vapor transport,precipitation and sea level pressure in sequence.Besides that,the faster increasing of temperaturn can be captured by the CMIP5 models.(2)Through the spatial distribution of Northern Hemisphere,deviations between the model and the reference are found,especially over Indian Ocean at low latitudes,North Pacific and North Atlantic.Models have weak bias for the zonal water vapor transport over the Indian Ocean at low latitudes,strong bias for the westward meridional transport over the North Pacific,and strong bias for the northward meridional water vapor transport over the North Atlantic.On the plateau terrain,the model precipitation forecast is on the big bias,the temperature forecast is on the small bias,and the sea level pressure value is on the big bias and the low pressure center intensity forecast is on the big bias.The time series variations of precipitation,water vapor transport and sea level pressure show that the fluctuation amplitude of increase and decrease in the three latitudes simulated by the model is weak,especially in the mid-latitude zone,there is a large deviation from the reference field.(3)At low latitudes,the meridional water vapor transport value simulated by the model is generally higher.At the center of the high value of water vapor transport,the predicted precipitation by the model is smaller,while in the south of the Sahara Desert,the predicted precipitation by the model is higher,while in the north-upper latitudinal water vapor transport in the Asian monsoon region,the predicted precipitation is weaker,the simulated precipitation is lower,and the sea level is lower.In the mid-latitude zone,the northward and upper latitudinal water vapor transport over the ocean is strongly simulated,as well as the precipitation and temperature forecasts on the east coast of Asia and the west coast of North America are also strong,while the Aleutian low center value in the region is strongly predicted and its range is large,and the prediction of water vapor meridional transport on the west coast of Asia-Europe continent is biased.In the high latitudes,the model predicts the precipitation and temperature of Greenland Island on the low bias,and in the low pressure center of southern Greenland Island on the strong bias.(4)in the future forecast stage,the forecast trend under different carbon emissions scenarios is not the same.In the water vapor transport,sea level pressure and precipitation,the revised RCP8.5 carbon emission scenario has a better prediction effect,followed by RCP4.5 and RCP2.6,but the future cold season prediction in precipitation is better under the revised RCP4.5 carbon emission scenario,while in temperature,the revised RCP8.5 carbon emission scenario is better after based on simple climate drift.(5)After the correction,the strength of the low-pressure system in the northern hemisphere sea level pressure field is enhanced,and the high-pressure center has a slightly increasing trend.In the future precipitation field after correction,the average precipitation in the northern hemisphere will show a decreasing trend in the complex topographic areas of the middle and high latitudes,while the precipitation in the large topographic areas of the low latitude plateau will show an increasing trend.The obvious change of the water vapor transport field in the future prediction stage is that the intensity of the northward warming current of the North Pacific sample will be weakened.In the next 50 years,the linear increasing trend is estimated to be slower than before.