Abstract:The influence of round-off error on summer climate simulation in the northwestern Pacific and East Asia has been investigated by using AGCM(atmospheric general circulation model) which is compiled by single precision and double precision. It is found that double precision computation has better skill than single precision one when simulating zonal wind at 850 hPa in the region. And the reason is also investigated, and the simulating results of 850 hPa zonal wind are mainly studied. The first empirical orthogonal function(EOF) mode of 850 hPa zonal wind simulated by double precision computation is better than that by single precision one, and the second mode time series of the double precision computations has a higher correlation coefficient with the second EOF mode time series of observations. Results show that the round-off error may result in higher atmospheric internal noise in the northwestern Pacific and East Asia, which can weaken the model simulation skill, therefore the double precision computation can better simulate climate than single precision one in this region.

Abstract:In this paper, El Nino events are classified into three categories:eastern pattern, western pattern and stationary wave pattern according to the region El Nino initially occurs and the propagation features of the positive sea surface temperature anomaly(hereafter referred as SSTA) of El Nino. In order to study the differences of the physical mechanisms of El Nino events, our prime task is to simulate the development process of these various types of El Nino. OPA9, a global oceanic general circulation model with high resolution, is applied to simulate the three categories of El Nino events. Global sea surface temperature changes from 1950-2005 are simulated in this model forced by monthly sea surface wind stress and heat flux. Analysis of the simulation results for the 56 years shows that, the model simulates oceans' climatology very well;in addition, the region El Nino initially occurs and the propagation features of SSTA of El Nino are properly simulated by the model. That is to say, the model simulates the warm events of the three categories successfully.

Abstract:This article gives a brief introduction of using multiple precision(MP) computing and interval analysis(IA) in the study of science computation. First it reveals the sensitive dependency of floating point computational results on computation precision and step-size and its indeterminacy in the computation of the Lorenz nonlinear equations by applying a MP method, and then studies the method for obtaining a real numerical solution. The paper also discusses a new multiple-precision-based scheme to identify the maximum effective computation time(MECT) and optimal step-size(OS). Moreover, the concept of interval analysis is shown and the application of interval analysis in the proof of the existence of chaotic attractor for Lorenz equation is demonstrated. These advanced numerical computation concepts and tools are valuable for the research of fluid mechanics, atmospheric sciences and nonlinear dynamical systems.

Abstract:In this paper, climatology and interannual variation in the intensity, track and landfalling location of tropical cyclones(TCs) landfalling in China over the Northwest Pacific(NWP) are systematically examined, using the about 30 years(1979-2006) TC dataset from the Joint Typhoon Warming Center. The results indicate that a large proportion of landfalling TCs originates in the western part of the NWP and the mid-north part of the South China Sea. The landfalling TCs forming in the southwest part of the NWP are characterized by northwestward tracks, while those forming in the northwest of the NWP and the South China Sea mainly have meandering and recurving tracks. The intensity of landfalling TCs has a tendency to increase. The landfalling locations of TCs display a trend of northeastward shift, which leads to the increase in landfalling TCs north of Xiamen and the decrease south of Xiamen, thus showing the interdecadal variation in TC tracks over the NWP.

Abstract:Eight brightness temperature ratios are calculated by using 2005 and 2006 AMSR-E(advanced microwave scanning radiometer-earth observing system) data to be the candidate drought indexes(DI). Under the assumption that the retrieved AMSR-E Land3 soil moisture(AMSR-E Land3 SM) data could reproduce the extent of the soil drought, the best candidate DI is selected according to the correlation coefficients between candidate DI and SM data, then annual variation of the best DI is analyzed for 3 stations in Hebei province, and the spatial distribution of the DI in March 2006 is compared to that of precipitation abnormity percentage derived from 136 stations data in the same period. Results indicate that the DI is available.

Abstract:The advanced regional E-grid η-coordinates model(AREM) is used to simulate the persistent heavy rain in South China during the period of June 20 to 22, 2005, which caused a historical flood, and the AREM-simulated precipitation sensitivities to initial and boundary fields are tested. Results show that there are obvious differences between initial and boundary conditions' impact on simulated precipitation in the different time periods of simulation. The larger the initial disturbance error is, the larger is the model error. The experiments also reveal that forecast error firstly rapidly grows in the meso-and small scale systems accompanied with unstable moist convection process, then propagates to large scale ones. Because of the gradual release of convective available potential energy, the atmospheric instability reduces, and the error grows slowly in the large scale system. However, in the case that the initial and boundary fields are of the same precision, it is better to add the boundary mesoscale information, especially below 400 km, rather than to add the initial mesoscale information for effectively suppressing the growth of errors.

Abstract:Experiments of 15 ensemble members are performed by using AREM, MM5 and WRF models with different model physical process parameterization schemes and identical initial values for rainy season in July 2003, and multi-model short-range ensemble precipitation probability forecasts are made by means of "Average", "Correlation" and "Rank". Results indicate that the ensemble precipitation probability forecasts made by the three methods above-mentioned all can give accurate estimation of center and region of the precipitation, and the "Rank" is superior to the "Average" and "Correlation" for performing better in forecasting the areas, intensity and boundary of precipitation but the other two expand improper areas. Evaluation results of ranked probability score(RPS), Brier score(BS) and relative operating characteristic(ROC) show there is little difference in a certain critical grade precipitation of the "Rank" results and that of the other two, but for synthetic effect of someday in the rainy season the "Rank" surpasses the "Average" method and "Correlation" method obviously. The higher score of RPS and every grade BS for the heavier and wider precipitation case means that multi-model short-range ensemble precipitation probability forecasts are a challenge.

Abstract:The fundamental goal of ensemble forecasting(EF) is to estimate a forecast probability density function(PDF) of possible future states of the atmosphere from which the true state is consistently a random sample. The skills of EF is superior to the deterministic-style NWP(numerical weather prediction) where a single run is considered in long-/meso-range. However, the skills of EF in the storm-scale is inscient. So an ideal storm case is simulated by the WRF(weather research and forecasting) model V2.2 on the supercell severe local storm, occurred in central Oklahoma on 20 May 1977 to study the feasibility whether EF can be applied to the forecast for the storm-scale system. Simultaneously the influence of the different ensemble sizes on the skills of the ensemble is explored through experiments with the addition of the random initial errors to different areas. It is found that the ensemble average can work in gaining higher forecast skills and protracting the effective forecasting. Although it enhances with the increase of ensemble sizes as a whole, the improvement is saturated when the ensemble sizes comes to 5-13.

Abstract:Based on Terra MODIS(moderate resolution imaging spectraradiometer) data in 500 m resolution in 2004, this paper retrieves the albedo over the Qinghai-Tibet Plateau by using the linear RossThick-LiTransit kernel-driven BRDF(bidirectional reflectance distribution function) model. Given mean aerosol optical depth as 0.11, the actual albedo at 1200 BST is calculated. The retrieved albedo distribution is well consistent with local land cover types and terrain characteristic from DEM(the digital elevation model). In addition, comparisons of retrievals and ground-based albedo observations from four radiation stations located in the northern Tibetan Plateau reveal that the accuracy of retrievals in 500 m resolution not only can meet requirement of albedo in climate model and land surface process model, but also is better than that of retrievals from the U. S. BRDF/albedo products in 1 km resolution.

Abstract:In this paper, the influence of different interpolation methods on the stability of climate system model NCAR CCSM2 has been studied. The results of idealized experiment show that the stability of the conservative interpolation method is better than that of the bilinear one. While the air-sea interface flux calculated by two kinds of interpolation methods is far less than that obtained by the idealized experiment because of the complicated air-sea interaction. The long-term numerical integration experiments point out that the conservative interpolation method is in favor of the conservation of the physical quantities for the first ten-year, but the differences between these two interpolation methods are not remarkable with the increment of integration time.

Abstract:Based on the NCEP/NCAR reanalysis data, the sea level pressures(SLPs) in Northern Hemisphere in summer of 1948-2005 are studied, indicating that they have an obvious interdecadal variation, especially in East Asian, North Africa and northern polar area. There are two abrupt processes for summer SLPs in the mid-late 1960's and 1970's. In terms of the interdecadal variation of the summer SLPs in Northern Hemisphere, the SLP anomalies firstly change in North European at the end of 1960's, then gradually moving southeastward. The positive anomalies of SLPs appear around area of Baikal Lake in the early of 1970's, then moving southward, in such a way that the positive center of SLP anomalies appears in East Asian in the middle of 1970's. Furthermore, SLP anomalies also change in Northwest Atlantic in the middle of 1960's, then moving gradually northward and southward, respectively. The positive anomalies strengthen the interdecadal variation intensity of SLPs in North European in the early of 1970's, meanwhile the SLP anomalies start to change in North Africa.

Abstract:The stratospheric sudden warmings(SSW) in 2002/2003 and 2003/2004 winters are analyzed using the daily four times ECMWF data. The differences of the average temperature and zonal wind are compared between these two winters, with calculating EP flux and the residual mean circulation. The results show that there are several times warming during 2002/2003 winter and a long time persistent warming in 2003/2004. The high level pole vortex recovers quickly and the lower one slowly after breakdown in 2003/2004, whereas both the high and lower level ones recovering slowly in 2002/2003. The persistent easterlies, induced by EP flux convergence in the pole, prevent the propagating upward of planetary wave in 2003/2004, whereas many times propagation upward taking place in 2002/2003. Besides, the residual mean circulation indicates that the circulation is the downwelling in the high latitude while SSW taking place, with no circulation circle forming in 2002/2003. The reverse circulation circle after SSW in 2002/2003 is lower than that in 2003/2004.

Abstract:Based on the observed monthly surface temperature and daily precipitation of 550 stations in China from 1961 to 2000, and the surface temperature and precipitation simulated by 13 IPCC AR4(the fourth assessment report of the intergovernmental panel on climate change) models and their multi-model ensemble(MME) mean, the simulation abilities of the 13 models are evaluated. Results show that the IPCC AR4 models certainly have a capability of modeling the surface temperature and precipitation changes in China. The annual variation and spatial distribution of surface temperature are well simulated, but the simulations are systematically smaller than the observations in the simulated region with the well simulation in the eastern China than that in the midwestern China. The annual variation and spatial distribution of China precipitation can be well simulated by the most models, but the simulations have the large differences among the different simulated regions. The most models can well simulate the northward process of summer monsoon rain belt in eastern China, but the simulated rain belt lies poleward of its observed position. The updated IPCC AR4 models can simulate the linear trend of surface temperature, but they have poor performances in simulating the interannual variability of surface temperature and precipitation. Comparisons of many evaluation indexes indicate that the surface temperature simulation of the multi-model ensemble(MME) is the best, while the precipitation simulated by UKMO-HadCM3 is the best among the 13 models and MME.

Abstract:A comprehensive fog observation was carried out in Nanjing between 24 and 27 December, 2006 to investigate development processes and microstructure of fogs, using the Vaisala DigiCORA Tethersonde system, automatic weather station, fog particle spectrometer(FM100) and other instruments. Results show that the development and dissipation of the relatively typical advection fog were dominated by warm and cool airflow, respectively. The averaged number concentration, diameter, liquid water content and maximum diameter in different stages of the fog process were in the ranges of 123.58-661.24 cm^-3, 3.12-7.33 μm, 0.016-0.137 g·m^-3, and 20.28-50.00 μm, respectively. During the formation and development stage, the droplet size distributions broadened gradually, mean while the spectrum pattern turned from the unimodal pattern peaked at 2 μm to the bimodal one peaked at 2 μm and 16 μm and the trimodal one peaked at 2 μm, 16 μm and 23 μm, respectively. During the maintenance stage, fog droplet spectra varied in 2 h or 4 h periodic oscillation, and the evolution of spectra had an obvious characteristic of diurnal variation. In the initial period of dissipation stage, drizzlies appeared with the great variation of fog droplet spectrum pattern due to the weak cool airflow. The fog had a short-lived development after the sunrise, thereafter dissipated as the result of a intensive outburst of cool airflow.

Abstract:A simulation experiment is conducted using the WRF model and the track and 24 h accumulative rainfall is successfully modeled, but the simulated central pressure of Saomai is much higher than that of the real situation. To study the orographic uplifting effect upon the rainstorm and the structure of typhoon Saomai(0608) during the landfall, a set of orographic sensitive experiments are further carried out by changing the terrain altitude within the selected area. It is concluded that during the landfall of Saomai, the orographic uplifting is able to enlarge the rainfall of the typhoon, and also to enhance the centre potential vorticity, vertical velocity as well as the convergence of moisture flux obviously. Meanwhile, the orographic uplifting peaks at the moment of typhoon Saomai's landfall.

Abstract:By utilizing the WRF(weather research and forecasting) model V2.2, a heavy rainfall process during 0000 UTC 30 June-1200 UTC 1 July 2006 in the region of Baoying located north of Jiangsu province was simulated;based on the extracted data of environmental wind field and mesoscale disturbance wind field from the model output, the spatial-temporal structures of the rainstorm, especially the perpendicular shear of wind field and nonlinear subcritical symmetric instability were analyzed. The results show that after the direction turning of vertically averaged wind shear from WNW to WSW, the maximum of south wind component indicates the precipitation peak which emerges after 5-4 hours as well as the peak of absolute horizontal helicity. The first emergence of strong updrafts though the total column of the atmosphere indicates the torrential rain 3 hours later. The π/2 phase difference between divergence and vorticity at 200 hPa in 9 h before the rainstorm, corresponding to intensely non-geostrophic gravity waves, propagates downward to 800 hPa within 3 hours before the rainstorm. The increase of mesoscale disturbance wind field was closely related to the increase of the precipitation. Nonlinear subcritical symmetric instability appears in 2-1 h before the rainstorm and simulates the heavy rainfall, which has the indicative meaning to the rainstorm.

Abstract:Based on the NCEP/NCAR wind field, height field, sea-level pressure and surface temperature reanalysis data from 1948 to 2006, the linear correlation analysis, composite analysis and regression analysis are used to study the interannual variations of the cross-equatorial flows(CEFs) in the lower troposphere of Eastern Hemisphere in summer and the correlations between the cross-equatorial flow intensity and circulation system, and the preceding sea-land thermal difference. Results show that there are close relationships between the interannual intensity changes of the cross-equatorial flows and the low-latitude circulations in Southern and Northern Hemispheres, especially the Asia-Australia pressure difference. Besides, Somali jet(SMJ) and Bay of Bengal CEF are significantly influenced by the sea-land thermal difference, while Eastern Asian CEF is remarkably affected by the sea surface temperature.

Abstract:The activity of cold-dry air and its impact on a heavy rain-snow storm in late winter in North China is studied by using FY-2 meteorological satellite data, Doppler radar data, normal observations and 1°×1° NCEP/NCAR reanalysis data, and the water vapor source is analyzed with black body temperature(T_BB), isentropic potential vorticity(I_PV), water vapor flux, relativity humidity and wind fields. Results show that the east and south airflow of the Jianghuai cyclone provided abundant water vapor for the heavy rain-snow storm, meanwhile, cold-dry air played different roles at different heights and paths:1)in the lower troposphere, cold-dry air acted as a cold cushion that wedged into the bottom of warm wet air flow, resulting in frontogenesis, elevation of warm-wet air and condensation. 2)in the upper troposphere, cold-dry air with high potential vorticity moved downward from high latitude along 320 K isentropic surface which offered the dynamical and thermal conditions for Jianghuai cyclone's triggering, strengthening and maintaining. The area with high positive potential vorticity(I_PV ≥ 10^-6m²·s^-1·K·kg^-1) and the dry zone with a relative humidity ≤ 45% on the isentropic surface correspond well to the dark zone of T_BB ≥ -32℃ on the infrared cloud image, suggesting means that it is feasible to trace the high positive potential vorticity track by satellite data. 3)The intrusion into the storm and overlay on the warm/wet air flow of the cold-dry air from the sub-cold transfer belt at the head of spiral cloud at the height 2-3 km was beneficial to the formation of unstable straification and the release of unstable energy, therefor, it is one the important factor for the local heavy and violent snow in the western coastal of Bohai Bay.

Abstract:Based on the output data of model RegCM3 during the heating period of 2005 and 2006, and the daily monitoring data of Zhengzhou Municipal Environmental Monitoring Center, a prognostic equation is constructed to forecast the mass concentrations of air pollutants PM₁₀, SO₂ and NO₂ by using the stepwise regression method. But the application of the method to forecasting tests of the pollutants' mass concentrations in the heating period of 2007 is not satisfactory, and the forecasting accuracy is significantly lower than the historical fitting rate. In order to improve the forecasting accuracy, according to deficiency of the statistical method(the correlations among forecasting factors are not considered when selecting them, so the nonorthogonalities among them result in regression instability and more errors), a new forecasting model is proposed by using the empirical orthogonal function(EOF) combined with the multiple linear regression analysis, and the daily mean mass concentrations of pollutants are chosen as the forecasting object during the heating period. Results show that the new method can improve the forecasting accuracy of air quality in a certain degree.

Abstract:Based on the NCEP/NCAR 1°×1° daily reanalysis data and TBB(temperature of black body) data of FY2 satellite, the multiscale circulation features of heavy rain over Huaihe River Basin in rainy season in 2007 are studied. Results show that the main rainband is located in Huaihe River Basin in the rainy season. Specially, the heavy rain and rainstorm successively occurr in Huaihe River Basin from 30 June to 8 July, and the concentration degree and intensity of precipitation are stronger than those in 2003, which cause the greatest flood over Huaihe River Basin since 1954. During the rainy season, the Ural blocking high frequently emerges, and the west Pacific subtropical high is stronger than the normal with a stable location. When strong monsoon surge meets with dry cold air from middle and high latitudes, there will be heavy rain in Huiahe River Basin. The favorable relationships of the strong and stable west Pacific subtropical high, strong monsoon surge, dry cold air from middle-high latitudes and propagating eastward convection disturbance over the Tibetan Plateau lead to the heavy rain over Huaihe River Basin in 2007.

Abstract:The present national standard and method of haze judgment are summarized, and the essence of haze is described. Based on the water vapor congealment theory, the relationships of the relative humidity, the visibility, the haze and the mist(or fog) are studied, and a humidity-visibility index method is proposed to judge the haze and the mist(or fog). Using the transmitted light weakening theory and the visibility definition, the mathematical model of humidity-visibility index is gotten. On the basis of the strict implementation of Surface Weather Observation Standard, combined with the observation records and considered the continuity of historical data in most of China, the mathematical formula of haze judgment is established.

Abstract:Based on the data collected from the area of 300 km×300 km(it covers 44 cities or counties) around the Dafan Nuclear Power Plant in Tongshan county, Hubei province from 1956 to 2000 through many ways, such as the record at meteorological stations, the collection of disaster events, the reports of climate impact assessment, etc. , the relationships between main parameters that describe the characteristics of a tornado are calculated according to Collections of National Standard for the Safety of Nuclear Power Plant. Finnally, the design basis standard parameters of tornadoes for the plant are given:maximum wind speed is 70 m/s(the corresponding probability is 1×10^-8), the horizontal moving speed of tornadoes is 13.5 m/s, the rotating radius is 206 m, the maximum air pressure drop is 9.9 hPa, the design basis standard wind speed category is F3(Fujita tornado scale). And the above results have been used by the associated planning and designing departments.