Abstract:The differences in the seasonal evolution features of Indian Ocean Dipole(IOD) accompanied with two-type El Nino have been investigated based on the observed dataset from 1951 to 2012.Here, this paper focuses on the ocean-atmosphere coupled processes over the tropical Indian Ocean during the evolution of IOD.Results show that, when IOD peaks, the intensity and location of the warming SST anomalies(SSTAs) are different between the IOD co-occurred with EP and CP El Nino.When IOD peaks during EP El Nino, tropical northwestern Indian Ocean warms up and the equatorial southeastern Indian Ocean cools off with a similar intensity, associated with a strong anomalous Walker circulation rising over the western Indian Ocean and sinking over the Maritime Continent.But the warm SSTA locates southward over the central Indian Ocean at the peak of the IOD during CP El Nino, associated with weaker anomalous rising over central Indian Ocean.As to the seasonal evolution of the IOD co-occurred with EP El Nino, the warm and cool SSTAs develop intensely in summer then peak in autumn, which is resulted from the weak southwest summer monsoon over western Indian Ocean and the strong anomalous easterly over eastern Indian Ocean.By comparison, the evolution of IOD during CP El Nino is associated with the strong anomalous easterly over eastern Indian Ocean and anomalous negative vorticity winds in the low troposphere over the central Indian Ocean.The dipole SSTA develops when the west pole of the triple pattern SSTA decays, which is different from the IOD co-occurred with EP El Nino.

Abstract:This paper quantitatively evaluates the simulated present-day global sea surface temperature(SST) and mixed layer depth(MLD) in BCC_CSM developed by Beijing Climate Center(BCC) in order to provide suggestions for BCC_CSM's development and improvement.The simulated SST and MLD from BCC_CSM as well as from other 15 CMIP5 models are analyzed and compared with the observed SST and MLD from World Ocean Atlas 2009(WOA09).This paper also investigates some possible reasons for the biases in these models.According to the analysis, SST in mid-high latitudes of the Northern Hemisphere in BCC_CSM have relatively large biases, while the biases are rather small in other latitudes.This paper finds that the SST biases are mainly caused by biased ocean circulation.There are large biases for simulated maximum MLD in BCC_CSM in mid-high latitudes of the Northern Hemisphere and high latitudes of the Southern Hemisphere, where many CMIP5 models have the same problem.There are also large biases for minimum MLD in mid-high latitudes of the Southern Hemisphere.In winter, the southward shift of the site where the Atlantic Meridional Overturning Circulation(AMOC) sinks leads to a cold bias of SST in high latitudes of the Northern Hemisphere.These results suggest that, in high latitudes of both the Northern and Southern Hemispheres where deep convections occur, many physical processes need to be better represented in the coupled ocean-atmosphere models including BCC_CSM, to enhance their reliability in climate prediction.

Abstract:Based on OISST, ERSST and NCEP2 monthly surface wind data, the structure characteristics and formation of Southern Indian Ocean Dipole(SIOD) and its correlation with ENSO are investigated.Results show that SIOD develops from October to December, peaks in following February, and decays from April to June.Wind, latent heat flux and shortwave radiation fluxes play an important role in the formation of SIOD.The change of the mixed layer depth also contributes to the formation of SIOD.In recent three decades, SIOD are phase-locked to the austral summer season, preceding the ENSO signal by nine-to-ten months.Furthermore, the relationship between SIOD and ENSO is enhanced after interdecadal abrupt climate change in the mid-1970s.El Niño events usually occur after positive SIOD and La Niña events occur after negative SIOD.

Abstract:The abnormal activities of the western Pacific subtropical high(WPSH) are closely associated with other members of the Asian summer monsoon(ASM) system.By using the time-delayed correlation analysis method, the basic fact and physical characteristics how key members of the ASM system influence on the morphology and variation of WPSH are analyzed.And figures of the basic association structure and evolution are drawn.Results show that different subsystems of ASM system play different roles on WPSH:the abnormal intensity and position of WPSH are influenced by five key members of the Indian summer monsoon subsystem, while the abnormal west ridge point of WPSH is mainly caused by the five members of the East Asian summer monsoon subsystem.The results reveal the time-delayed characteristics and statistical correlation between WPSH and the key members of ASM system, which supply the basic fact for the future mechanism study.

Abstract:Based on NOAA daily sea surface temperature(SST) data, NCEP/NCAR daily wind and specific humidity field data, and the daily rainfall data from National Meteorological Information Center of China, the low frequency cycle of climatological SST over the northwest Pacific is discussed, and the relationship between ISO(intraseasonal oscillation) SST over the northwest Pacific and ISO rainfall anomaly in eastern China in summer is also investigated.Results show that the most significant regions of ISO precipitation anomaly in eastern China affected by ISO SST anomaly over the northwest Pacific in summer are the middle reach of Yangtze River and the coastal areas of South China, the Yangtze-Huaihe regions, and most of North China.The wave train with the structure of cyclone-anticyclone-cyclone(anticyclone-cyclone-anticyclone) from south to north along East Asia coast is caused by the interaction between ISO SST over the northwest Pacific and 850 hPa circulation field, which leads to vapor convergence or divergence over East Asia coast and induces the summer ISO rain belt advancing from Yangtze-Huaihe regions to North China(retreating from North China to the middle reach of Yangtze River and the coastal areas of South China).

Abstract:Simultaneous ensemble mean equations for the Lorenz model(LEMEs) are obtained, enabling us to analyze the properties of the ensemble mean from a dynamical point of view.The qualitative analysis for the two-sample and N-sample LEMEs shows that the locations and number of stable points are different from the Lorenz equations(LEs), and the results are validated by numerical experiments.The analysis for the eigenmatrix of stable points of LEMEs indicates that the stability of these stable points is similar to the Les'.The eigenmatrix for non-stable points can be obtained too, but the eigenvalues depend not only on the value of the mean variable but also the other N-1 sample equation's variable, and thus for these points there may be different stabilities compared to the LEs'.The divergence of the LEMEs' flow has a negative value, which is the same as the LEs', and thus the trajectory in phase space approaches zero and the trajectory will be attracted to a low-level dimensional curved surface, i.e., the LEMEs have the attractor property, but the structure of the attractor is not the same as the LEs'.The emsemble mean method only keeps part of the original equations' properties, and thus whether the method is effective depends on the objective problem and other external restrictive conditions.

Abstract:The ensemble members of WRFDA/Hybrid assimilation system come from ETKF(Ensemble Transform Kalman Filter) ensemble forecast system.Sensitivity analysis shows that the ETKF scheme often crashes in cycle assimilation because of oscillation of the covariance inflation factors, which is caused by large variation of observation in cycle assimilation.In order to design a simple and stable hybrid data assimilation system, a new hybrid assimilation method, with physical control variable perturbation and multi-physical parameterization(RCV-Hybrid), was proposed.In RCV-Hybrid, the initial state of ensemble forecast come from hybrid analysis perturbed by physical control variables.Meanwhile, different microphysics and cumulus parameterization schemes were used in ensemble forecast to represent model error.Results of 10 days cycle assimilation and forecast show that the RCV-Hybrid method performs better than 3DVar and is similar to ETKF.In addition, the RCV-Hybrid method can be easily operated without perturbing observation.Thus, it is a new option for hybrid data assimilation.

Abstract:Based on Bayesian theory, a basic model of the probabilistic forecast was established out of the deterministic forecast.The probability forecast was evaluated and put into use by using European Centre for Medium-Range Weather Forecast(ECMWF) ensemble forecast of 2 m temperature taken from the TIGGE data and the observed data.The results show that the probability forecast can provide a plenty of forecast products as well as better forecast average value than the original deterministic forecast.The Bayesian model averaging(BMA) approach was applied to conduct the multimodel ensemble probabilistic forecast by using China Meteorological Administration(CMA), US National Centers for Environmental Prediction(NCEP) and ECMWF ensemble forecast data.More reasonable probability distribution was acquired from the BMA forecast, the distribution average value can be used as the model forecast, and the standard deviation and the confidence interval reflect the variable range of the forecast.Therefore, the probabilistic forecast based on the Bayesian forecast model is able to provide more accurate forecast as well as more comprehensive forecast information.The BMA ensemble forecast is superior to the ensemble mean forecast in terms of its forecast accuracy, and it can quantitatively provide the uncertainty of the forecast as well.The BMA probabilistic forecast experiment was carried out by using 51 members of the ECMWF ensemble forecasts.The results show that the BMA forecast merges the description of uncertainty of each ensemble member, and it adjusts the average value of probabilistic forecast in order to make it closer to the observed value.The probability density distribution(PDF) of BMA forecast can better reflect the realistic distribution of atmosphere.

Abstract:The adaptive observation system based on ETKF(Ensemble Transform Kalman Filter) has been applied to identify sensitive observation area in Jianghuai heavy rain, typhoon, freezing rain disaster and etc.This paper considers the function of humidity factor, increases the information of atmosphere in low troposphere, and develops an optimization scheme to make the system more suitable for high impact weather in China.Selecting summer heavy rain and winter snow around Beijing as high impact weather examples, four groups of test schemes are designed for identifying observation sensitive area.This paper investigates the quality of observation sensitive area and evaluates the results of analysis and forecast.Results show that the optimized adaptive observation system is the best scheme, which has significantly improved the quality of observation sensitive region.The humidity factor can make the strongest observation sensitive area more concentrative, which is more obvious in the heavy rain than in the snow.The information of low-level atmosphere is helpful in identification of the strongest observation sensitive area.Target observations in the sensitive area have positive contribution for the quality of analysis and short-term forecast.

Abstract:Based on the monthly NCEP/NCAR reanalysis data during 1978—2012, this paper studies the precursor of the summertime anomalous circulation to the south of Lake Baikal.Results show that the convection from Indonesia to western Pacific in the preceding winter, consistent with the summertime anomalous anticyclonic circulation to the south of Lake Baikal, is one of the precursors to predict the summertime anomalous circulation to the south of Lake Baikal.When the convection is stronger from Indonesia to western Pacific in the preceding winter, the convection moves northward to the western flank of Tibetan Plateau in summer, which is beneficial to the occurrence and maintenance of the anomalous anticyclonic circulation to the south of Lake Baikal.However, when the convection is stronger in the western Indian Ocean in summer, the convection from Indonesia to western Pacific in the preceding winter is not consistent with that in the western Tibetan Plateau in summer.The stronger convection in the western Indian Ocean weakens the impact of the upward motion in Tibetan Plateau and its western part on the circulation in Lake Baikal, which is against the formation of anomalous anticyclonic circulation to the south of Lake Baikal.Therefore, when the convection is weaker in the western Indian Ocean in summer, the convection from Indonesia to western Pacific in the preceding winter corresponds well with the summertime anomalous circulation to the south of Lake Baikal.When the convection is stronger in the western Indian Ocean in summer, the above relationship will be changed.

Abstract:Aiming at the faults of seawater transparency empirical formulas having no universality based on the assumption of homogeneous water transparency, seawater is divided into several homogeneous layers with similar optical property in vertical direction, and non-uniform water contrast transfer equation is deduced.Based on the contrast transfer equation, the calculation model of seawater transparency is established.The calculation model is used to do numerical experiment and effect analysis using the inherent optical seawater data observed by BROKE_WEST_ACS and the data from transparency plate.Results show that the average relative error between the model calculation values in the paper and the observed values from transparency plate is 9.1%.The model not only overcomes the disadvantages of observations from transparency plate, which are easily influenced by weather conditions and human differences, but also breaks through the limitation of uniform water transparency calculation method.

Abstract:Due to the unresolved conflict in the current IPCC assessment reports about carbon fluxes between the surface and deep ocean, an upwelling-diffusion(UD) global carbon cycle model was developed to investigate the oceanic carbon cycle.Except model structure, the control formulations for δ¹³C of oceanic dissolved inorganic carbon(DIC) were also established.Different from present UD models, the global sediment trap observations were directly used to calculate the in situ regeneration flux without incorporating the well-used depth parameters.The two dynamic parameters, namely, the vertical eddy diffusivity(k) of 3 000 m²/a and the upwelling velocity(w) of 3.5 m/a, were calibrated to match the GEOSECS phosphate distribution and to get a thermocline depth scale at 860 m.These parameters were all between direct observations and model calibrations.By comparing the DIC profiles from model estimate in steady state with those from GEOSECS, we got an oceanic uptake of 78 GtC(Gigatonnes Carbon, 1 Gt=1×10¹⁵ g)from the Industrial Revolution until mid-1970s.This result was considerably supported by other models and data-based estimates.Model estimated the flux from deep ocean to the mixed layer to be 46 GtC/a, which is consistent with that from the IPCC's third assessment report (42 GtC/a) but far less that from the fourth one (101 GtC/a), but still less than the range of δ¹³C budget technique(60—80 GtC/a).

Abstract:The potential energy anomaly and surface layer stratification in large shallow lakes have an important influence on the local weather and climate systems and aquatic ecological environment evolution.Based on the meteorological data and water temperature profiles during 17—28 March and 11—22 August 2009, the variation law and mechanism of potential energy anomaly and surface mixed layer depth in Lake Taihu were studied.Results show that there is a significant diurnal variation for the potential energy anomaly and water stratification in Lake Taihu.The potential energy anomaly is gradually destroyed in nighttime and strengthened in daytime, respectively.The net heat flux between water and air is the key factor influencing on the potential energy anomaly and water stratification in Lake Taihu.The potential energy anomaly in summer is stronger than that in spring, which is resulted from the weak mixing effect originated from wind and the strong strengthening effect caused by the net heat flux on the potential energy anomaly in summer.There is a significant exponential relationship between the potential energy anomaly and the surface mixed layer depth.

Abstract:Baed on the characteristic that there are close relations between the wave, convergence and divergence of wind field and the strong precipitation of landing typhoon, with the high-resolution simulation data, using two dynamic parameters:potential divergence wave action density and divergence vertical flux(they represent the wave features and the convergence and divergence features of strong precipitation area, respectively), this paper carried out a diagnostic analysis on the strong precipitation of landing typhoon "Fung-Wong".Combining the wave disturbance features and the convergence and divergence features, a new physical quantity:thermal shear divergence parameter is defined.Based on the parameter, a further diagnostic analysis is carried out on the strong precipitation of "Fung-Wong".Results show that the rainfall area is always covered by the abnormal value area of thermal shear divergence parameter, and they have the similar spatial distribution and time evolution trend.The dynamic interpretation analysis of GFS(Global Forecast System) forecast products shows that the strong signals of thermal shear divergence parameter locates in the rainfall area and the weak ones in the non-rainfall area, which has a good indicative meaning for forecasting strong precipitation area.

Abstract:A well-structured land surface model NCAR_CLM4.5(Community Land Model 4.5) is evaluated using the observations at a degraded grassland station(Tongyu station) in semi-arid area in China during the Coordinated Enhanced Observing Period(CEOP).Results indicate that CLM4.5 can reproduce the spatial distribution and temporal variation of the radiation flux, water-heat flux, soil moisture and temperature very well.However, the model underestimates (overestimates) the surface absorbed radiation and soil moisture(diurnal variations of the surface absorbed radiation and soil temperature).Under some special atmospheric conditions, for example at the end of August, the model produces large biases.In addition, the simulations(including radiation flux, water-heat flux, soil moisture and temperature) departe largely from the observations in winter, which shows that the parameterization schemes of surface physical processes of CLM4.5 need to be further improved in winter.

Abstract:A thunderstorm happened in Tai Lake region in August 2010, which is used to test the impact of two different land surface models(Noah and RUC schemes) coupled with the weather research forecasting(WRF) model on simulation of the thunderstorm.The short-range weather simulation is performed for 48 h.The simulated results are compared with the observed rainfall, surface temperature and wind speed at Yixing and Wuxian stations.Results show that Noah scheme has a fairly better performance than RUC scheme, and the simulated thunderstorm is sensitive to the chosen land surface model(LSM).The different LSMs can lead to the differences of location, time and intensity of thunderstorm, and the maximum of daily precipitation difference between the two schemes can be above 40 mm.Comparison of the simulated results shows that the convection development delays for 2 h in RUC experiment relative to Noah experiment, which indicates that the land surface representation has a prominent feedback on the mesoscale convection of thunderstorm.Different land surface models can lead to different thermal and dynamic effects, which influence the development of thunderstorm and result in differences of convection initialization, development and maintenance between the two WRF runs with different LSMs.Due to parameterization difference of vegetation properties for different land use categories in the two land surface models, Noah scheme describes the characteristics of underlying surface reasonably better than RUC scheme, especially the urban land use category, which can improve the ability of WRF run with Noah LSM to simulate the thunderstorm.

Abstract:Pentad often appears in sci-tech papers as the unit of time, but the expression of pentad is not normative.This paper discusses the standard expression of pentad based on GB 3101—1993 and GB/T 7408—1994.As the unit of time, pentad is same as day(d).The heading shoud be "time/pentad" or "t/pentad" in chart.Pentad may refer to the year or month for use as the date.The heading shoud be "pentad ordinal".When the pentad appears in the first time, the date range of pentad shoud be explained.