Abstract:Since the industrial revolution,the content of anthropogenic greenhouse gas is increasing.As a result,the global surface air temperature grows rapidly.However,the global surface air temperature has stalled since 1998,despite the greenhouse gas steadily increases.This paper reviewed the latest research progress on this phenomenon,especially the mechanism of the global warming hiatus.There are two main viewpoints on the mechanism,namely,the external forcing and natural variability.The former includes the influence of solar activity,volcanic aerosol particles,man-made aerosol particles and stratospheric water vapor forcing.Scientists in the opinion of natural variability hold the idea that the missing heat produced by human activity has entered the deep ocean,especially the layer below 700 m.They believe that the oceans play a key role in the global warming hiatus.There are two main ideas for that:Pacific Decadal Oscillation(PDO),especially the cooling in the eastern tropical Pacific,and the Atlantic Meridional Overturning Circulation(AMOC).The widely accepted idea on the mechanism of recent global warming hiatus is natural variability.The missing heat has entered the deep ocean.But it still remains controversial which ocean basins gain the missing heat.

Abstract:Climate change impact refers to the responses of social economy and resources environment to climate change.Climate change risk refers to the possible losses of social economy and resources environment caused by climate change.Climate change risk assessment means the qualitative climate change impact and the quantitative climate change risk.Aiming at the principle and technical system of climate change risk assessment method,current research status,hot issues and common approaches are remarked from three aspects,namely the risk index,the risk probability and the vulnerability.Research gaps and priorities are also discussed.

Abstract:Based on aerosol optical depth(AOD) data derived from MODIS sensors onboard the Terra satellite and NCEP/NCAR reanalysis data set from 2000 to 2013,the principal modes,which show the linkage between AOD and near surface downward solar radiation flux(DSRF) in East Asia in summer,have been explored with the singular value decomposition(SVD) method.The principal mode of AOD is further examined in association with East Asian summer monsoon.The distribution of summer AOD averaged from 2000 to 2013 shows that there are two high value regions(>0.9) in East Asia.One is in the conjunction part of Shandong,Henan,and Hebei provinces,and another is in central part of Jiangsu province.However,the values in Fujian,Taiwan provinces and their nearby ocean surface are less than 0.4.The DSRF increases from south to north,just like the AOD distribution.By using SVD method,a positive correlation between AOD and DSRF has been found under the influence of seasonal trends.By calculating the variance contributions,this paper confirms that the seasonal trends are more important than interannual variability in determining the in phase variations of AOD and DSRF.Left time coefficients of the leading SVD mode(SVD1) have been used to conduct correlation analysis.Results suggest that,in June(except 2013),when both AOD and DSRF values are high in eastern China,the convergence and ascending motion will be stronger than normal from the southeast China to the south of Japan.As a result,summer precipitation will increase.This is due to a fact that the location of the western Pacific subtropical high in June extends southward,resulting in less precipitation in northern parts of eastern China eventually.An anomalous warmer area appears in North China due to the more net surface solar radiation flux.In August,when AOD anomalies are negative over the land,DSRF is also less than normal.August precipitation will be less(more) than normal in the south(north) of China,along with an anomalous cold area in North China.These changes imply that when the aerosols are less than normal in the northern part of East Asia,the total cloud amount is more than normal,and rain will increase,resulting in the decrease of DSRF there.All of these results indicate that the seasonal evolution of East Asian summer monsoon plays an important role in regulating the variabilities of AOD and DSRF.

Abstract:The solar radiation in longwave region is usually neglected in climate models.The matrix formulations for the radiative transfer are applied into the general circulation model (BCC_AGCM2.0.1) developed by National Climate Center to test the effect on simulated radiation flux and temperature after adding the calculation of solar radiation in longwave region.Results show that,relative to the ISCCP and CERES radiation data,the simulated downward radiation flux in longwave region in surface in clear sky is reduced 2.05 W/m² by mean error and 1.29 W/m² by root-mean-square error.The upward radiation flux in longwave region at the top of climate model in clear sky is reduced 0.70 W/m² by mean error and 0.21 W/m² by root-mean-square error.The downward radiation flux in longwave region in surface in whole sky is reduced 1.38 W/m² by mean error and 1.03 W/m² by root-mean-square error.The upward radiation flux in longwave region at the top of climate model in whole sky is reduced 0.99 W/m² by mean error and 0.30 W/m² by root-mean-square error.Relative to ECMWF reanalysis data,the method including solar radiation in longwave region can improve the cold bias simulations of temperature in the region between upper troposphere and lower stratosphere over the equatorial region.The tropopause temperature is reduced 0.27 K by mean error and 0.25 K by root-mean-square error.

Abstract:The observed SST data and CMIP5 data are used to analyze climate state and interdecadal variation of sea surface temperature(SST) over Northwest Pacific(20—60°N,120°E—120°W).Results indicate that the selected 22 models can simulate the climate state perfectly.More importantly,the selected models can simulate the annual and interdecadal variations of SST over Northwest Pacific.Total standard deviation of SST simulted by the models is the largest in Kuroshio extension region.The majority of models have an ability to simulate the first EOF mode of SST.The SST over Northwest Pacific has a significant interdecadal oscillation phenomenon.SSTs simulated by the 13/22 models have obvious interdecadal oscillations.Meanwhile,the simulated deviation of SST climate state has a great effect on the periodic oscillation of SST,especially in Kuroshio extension region.

Abstract:Based on the NCEP/NCAR monthly reanalysis data from 1960 to 2010,this paper analyzed the variation characteristics of summer land surface temperature in Eurasian continent and its relationship with atmospheric circulation by using the empirical orthogonal function(EOF) method.Results show that mean square deviation of Eurasian summer land surface temperature in high latitudes is greater than that in low latitudes.The main feature of summer land surface temperature in Eurasian continent is the consistent variation pattern in the whole region.Except for cooling trend on the east side of Tibetan Plateau,warming trend exists in other areas of Eurasian continent,especially in 40—65°N.Secondly,summer land surface temperature shows “-+-” anomalous pattern in high latitudes.Westerly circulation index closely relates to the warming temperature,while the EU index closely relates to the anomalous pattern of summer land surface temperature in middle and high latitudes.Based on the climate features and spatial-temporal features of summer land surface temperature in Eurasian continent,five key areas have been identified.The indices in the five key areas have warming trend,but their change features are different.The different abnormal circulation patterns correspond to the different indices in the five key areas,and the circulation factors which closely relate to land surface temperature in the five key areas are different.

Abstract:Different responses of Northern winter atmospheric circulation to ENSO events are simulated under different surface sea temperature(SST) forcings using NCAR/CCM3 model.Comparison between simulated results and diagnostic results indicates that the model can simulate the response of Northern winter atmospheric circulation to ENSO events under different SST forcings.The simulated results are agree with the diagnostic results.Under SST forcing after the late 1970s,the strengthening action of El Niño events on Aleutian low is more obvious.Mongolian high is slightly weakened by El Niño events before the late 1970s,but it is markedly strengthened after the late 1970s.After the late 1970s,the strength of ENSO events becomes larger,but the abated effect of ENSO on East Asian trough and East Asian winter monsoon is not clear,and PNA pattern is obviously strengthened by El Niño events.

Abstract:A hybrid ensemble square root filter and three-dimensional ensemble-variational(EnSRF-En3DVar) data assimilation system is developed based on WRF model.The EnSRF is used to update ensemble perturbations in this system.Aiming at Typhoon Saomai,two sets of sensitivity experiments are conducted to test this system.One is choosing different weight coefficients of ensemble covariance,the other is assimilating radar radial velocity(V_r) and/or reflectivity(Z).The first set of experiments is to answer how the flow-dependent covariance estimated from the forecast ensemble works best in the hybrid EnSRF-En3DVar system.The results show that the assimilation effects from experiments with 30 ensemble members and ensemble covariance weight coefficients of 0.25,0.5 and 0.75 are better than those from 3DVar experiment.The best(worst) one is from the experiment when weight coefficient of ensemble covariance is 0.75(1.0).The second set of experiments is to examine the impact of assimilating radar V_r and/or Z on the analysis using EnSRF-En3DVar system.The results show that the combined assimilation of V_r and Z can improve the initial analysis of humidity and wind fields,but the only assimilation of V_r can improve the analysis of wind field most.Finally,the methods to generate the ensemble perturbations are compared.The results show that the “perturbed observation” method gives smaller ensemble spread and needs more expensive computational cost than the EnSRF method.

Abstract:Based on the GIMMS/NDVI data,the wavelet transform technique is used to analyze the dynamic variation of normalized difference vegetation index(NDVI) and its relationship with climate factors such as temperature and precipitation from 1982 to 2006 over Northeast China on intra-and inter-annual scales.Results show that the dynamic variation characteristic of vegetation is remarkable,the I_NDV(descripting the mean value of inter-annual scale NDVI) decreases from northeast to southwest over Northeast China,the I_NDVand ΔI_NDV(descripting the variation of intra-annual scale NDVI) of forest are the largest,which are 0.41 and 0.70,respectively,and those of grass land are the smallest.The I_NDV increases 6.21% over grass land,increases a little over arable land,and decreases over forest.The correlation coefficients between temperature,precipitation and NDVI are remarkable with the former larger than the latter,and the intra-annual scale correlation coefficient is larger than the inter-annual one.On inter-annual scale,the correlation coefficient between NDVI and temperature over arable land is the largest,which is 0.60,and the coefficients between NDVI and precipitation over arable land and forest are not significant.On the intra-annual scale,the correlation coefficients between NDVI and temperature,precipitation over forest are the largest,which are 0.90 and 0.75,respectively.The impact of temperature on NDVI decreases with a nearly linear trend when the lag time is extended on the inter-annual scale.The effects of temperature and precipitation on NDVI decrease more and more fast with the extension of lag time on the intra-annual scale.The responses of forest to temperature and precipitation are quick,and that of grass land is slow.The duration of precipitation influencing NDVI is shorter than that of temperature.

Abstract:Based on the NCEP/NCAR daily reanalysis data during 1948—2010,this paper calculates the Atlantic storm track(AST) and the Siberian High(SH) indexes,and studies the variability of AST and its influence on SH.Results show that there are significant relationships between the longitude index(STIX) of AST and those indices describing the latitude,intensity and area of SH.When the STIX is in the positive months,the synoptic transient waves extend from Atlantic to Europe and even to the east of Mount Ural,thus intensify the anticyclone wave breaking(AWB) in Siberian and East Asian.Through the feedback of the transient waves on the monthly mean flow,the westerly is strengthened to the north of 50°N and weakened to the south of 50°N over Eurasia.The meridinal circulation in midlatitudes is strengthened,thus the ridges over the coastal West Europe and the northern Tibetan Plateau and the trough over East Europe are intensified,while the deep trough of East Asia is weakened and moves eastward.More warm air is transported to the north while the cold air from Arctic is inhibited over Siberian area,so it becomes warmer in Siberian and East Asia regions,the area of SH becomes smaller,and the SH moves southward and becomes weaker.When the STIX is in the negative months,the situation is reverse.

Abstract:In order to use the brightness temperature to set up a rainfall nowcasting model,this paper analyzed the brightness temperature data of microwave radiometer TP/WVP-3000 in Taihu area from January to April 2009.It is found that,at 4-hr before rainfall,the brightness temperature data of seven channels have obvious increasing trends.According to the biggest difference and the biggest standard deviation difference in brightness temperature between the rainfall case and the no rainfall case,this paper chooses the observed data from channel 1,5,and 6 as the forecast factor using the discrimination analysis to set up the rainfall nowcasting model.The time points in the discrimination analysis are 15 and 30—330 min(time interval is 30 min) before rainfall.The equation of 90 min before rainfall is decided as the final model function because of the highest self verification.Using the external data to test this model,the probability of detection is equal to 87%,the false alarm ratio is 24%,and the not alarm ratio is 13%.

Abstract:By using the automatic weather station data and the GFS(Global Forecast System) reanalysis data with high spatial(0.5°×0.5°) and temporal resolutions from NCEP,this paper analyzes the causes of precipitation difference between the northwest and northeast Hubei in a torrential rain process during 1—2 July 2008.Results show that:1)The impermanent precipitation in the northwest Hubei severely occurred in the development of upper and lower-level jets,and located in the right front of a later upper-level jet quickly,which goes against continuous rainfall.The precipitation in the northeast occurred in the stationary stage of upper-level jet and the development period of lower-level jet,and the coupled upper-lower jets induced the formation of mesoscale vortex at the lower level,so the rainfall was heavy and sustaining.2)Moisture transport concentrated in a short time in the northwest,so it was finitely offered.In the northeast,the moisture transport concentrated in a long time,so it was abundantly offered.3)The unstable energy was released faster in the northwest.In the northeast,the unstable energy was always released,meanwhile,the synoptic scale system developed violently and inspired gravitational waves,which were conductive to the precipitation.4)The frontogenesis in the northwest located in the frontal zone,which sloped northward with height,and the heavy rainfall ended soon when the cold air moved southward.In the northeast,the frontogenesis located in the warm frontal zone sloping to the south with height,which was also beneficial to the long-time heavy precipitation,when the confrontation between the cold air and the southwest warm moist air outside the subtropical high led to the strong declination term frontogenesis.

Abstract:This paper statistically analyzes the onset time and height of metric,decameter-hectometric(DH) type Ⅱ radio bursts,and solar energetic particle(SEP) events during Solar cycle 23.Results show that the three events occur in sequence after occurrence of solar flares and coronal mass ejections(CMEs),with their onset heights in ascending order.Onset time and height of the type Ⅱ radio bursts has nothing to do with whether SEP happens.However,there is a greater statistical probability of SEP events for CMEs accompanied by metric and DH type Ⅱ radio bursts.

Abstract:The expression of Eliassen-Palm flux(E-P flux) in quasi-geostrophic spherical coordinates and its transformation form weighted by zonal annular total mass,involving its application and skills in graphic analysis,are discussed.Combined some plotting examples with Interim/ECMWF Re-Analysis(ERA-Interim) data,the distinctions and characteristics lying in real cases under different forms of E-P flux are illustrated.

Abstract:In order to understand the effect of lightning on the trace gases in the upper troposphere,this paper studies the spatial and temporal characteristics of NO and O₃ volume fraction in the upper troposphere,the global lightning activity,and their relationships.The lightning data from April 1995 to June 2006 and the trace gases data from October 1991 to November 2005 are obtained from Global Hydrology Resource Center(GHRC) and the Halogen Occultation Experiment(HALOE) boarded on the Upper Atmosphere Research Satellite(UARS),respectively.Results show that global lightning concentrates in Southern Hemisphere from December to next February,and in Northern Hemisphere from June to August.Global lightning activity is in agreement with NO and O₃ volume fraction in seasonal variations.NO volume fraction reaches the maximum at 350 hPa.At this height,NO volume fraction is from 7×10^-12 to 11×10^-12 in Southern Hemisphere,while is from 3×10^-12 to 17×10^-12 in Northern Hemisphere.At the height range from 450 to 300 hPa,O₃ volume fraction in Northern Hemisphere in summer increases obviously,which is about 25% more than the annual average.Comparatively,O₃ volume fraction in Southern Hemisphere in summer is bigger than that in winter,but the difference is not obvious.All the results prove that there are good relationships between the lightning and NO/O₃ in the upper troposphere.It provides powerful evidences on the research of global climate change.

Abstract:Aiming at the disability of receptor model in the source apportionment for secondary organic and inorganic aerosols in PM_2.5,a pollutant Inventory-based Chemical Mass Balance(I-CMB) model for source apportionment of PM_2.5 is established,and the recent actual pollution data in Beijing is put into the model.Results show that the coal is the largest source(accounting for about 28.06%) of PM_2.5 in Beijing,followed by the vehicle(19.73%),dust(17.88%),industry(16.50%),food(3.43%),and plants(3.40%).Compared to conventional CMB(Chemical Mass Balance),application of I-CMB in source apportionment requires less accurate source profile and is more resistant to interference,and the result is more balanced and detailed.The I-CMB model meets the demands of PM_2.5 reduction in China.

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