Abstract:Anthropogenic heat (AH) was considered in the Weather Research and Forecasting (WRF) model that is coupled with the urban canopy model (UCM) to investigate its effects on model simulations of the atmospheric condition in Beijing. Results indicated that:1) The consideration of AH can significantly improve the simulation of meteorological variables, especially in the simulation of the boundary layer height, which is a key factor that determines the vertical dispersion of pollutants in air quality models; 2) The model can better reproduce the spatial patterns of wind and temperature fields with the consideration of AH; 3) The vertical distribution of pollutants in the model simulation is also improved with the consideration of AH.

Abstract:The lagrangian particle dispersion models require an accurate source term as input to obtain better simulation results. In this paper, two different ¹³⁷Cs source terms of Fukushima accident from Terada and Stohl were utilized. The FLEXPART (FLEXible PARTicle dispersion mode) was used to simulate global atmospheric dispersion and transport of radionuclides released from the Fukushima Daiichi nuclear accident. The atmospheric radiation monitoring data enable us to assess the spatial-temporal distribution of the two radioactive plumes and explore the uncertainty in results due to the different source terms. The results showed that despite the differences in the total emission, emission rate, and height of emission between the source terms of Terada and Stohl, the two source terms were alike in the whole developing trend. Thereby the two radioactive plumes had similar diffusion processes and reached similar regions. Under the influence of mid-latitude westerlies, the two radioactive plumes moved eastward across the Pacific Ocean, the American continent and Continental Europe, and eventually spread over the entire Northern Hemisphere. For short-range stations in the Asia-Pacific and North American regions, the simulated time of first detection of radioactive plume arriving at these stations with the two source terms both agreed well with the observed time. For long-range stations, the simulated time of first detection of the radioactive plume at these stations agreed better with the observed time when using the Stohl source term as input compared to that using the Terada source term as input. Second, using the two different source terms as input respectively, FLEXPART was applied to simulate global atmospheric dispersion of radionuclides. Results indicated that the simulated radioactivity concentrations were more accurate at the short-range stations than at the long-range stations. In addition, the simulated radioactivity concentrations were more accurate with Stohl's source term as input than that with Terada's source term as input. Terada's source term appeared to be lower than observations. Finally, the influence of the number of particles in the global model simulation was evaluated. It was found that differences in the number of particles could affect the statistical indexes of long-range transport of pollutants and the density of the diffusive radioactive plume in its late stage.

Abstract:Three statistical forecasting methods, i.e. ARIMA (Auto-Regressive Integrated Moving Average) model prediction, EMD (Empirical Mode Decomposition) decomposition prediction, and isolated prediction of frequency and amplitude based on Hilbert transformation, are designed and employed to make extra-seasonal prediction tests on the precipitation over Nanjing in 1998. Results show that the ARIMA model exhibits severe system errors and is hard to reproduce the abrupt variation of precipitation. Although the EMD decomposition prediction makes an obvious improvement in the evolution trend of precipitation, it still fails in the depiction of precipitation catastrophes in the summer due to its incapability of predicting high frequency modes. The isolated prediction method improves the prediction of high frequency modes since it can separately predict the frequency and amplitude of each mode and their interactions are avoided. Thereby the isolated prediction method gives a pretty good final prediction with the highest trend correlation and the smallest deviation. The two precipitation catastrophes in the summer of 1998 are realistically predicted. Additionally, a further verification of the precipitation prediction for 2003 also indicates that the isolated prediction method performs best among the three methods proposed in this study. The above results suggest that the isolated prediction method may provide a new idea for the technological improvement on extra-seasonal short-term climate prediction.

Abstract:The data collected on the transmission lines of Central China Power Grid from 2009 to 2013 in Hubei Province, the MICAPS meteorological data, the atmospheric soundings, and the NCEP reanalysis data are analyzed to investigate the synoptic situation, the duration of the wire icing, and the inversion layer during the wire icing. Results show that the upper-level circulation during the wire icing process can be divided into three types:Small transverse trough development-oriented type, transverse trough type, and eastward-moving low trough type. The occurrence frequency of each type is 43.8%, 31.2%, and 25%, respectively. Wire icing mainly occurs in January, February, November, and December and the average monthly icing hours in each individual month are 65 h, 42 h, 11 h, and 9 h. The icing processes can be divided into two types:Precipitation icing and foggy icing. A shear of wind direction from north to south could be found in the layer between 900 hPa and 700 hPa when precipitation icing occurs. A far more thick inversion layer could be developed, which is favorable for the maintenance and development of the icing process.

Abstract:Effective and objective assessment of the high-resolution numerical model ability to forecast gridded precipitation is not only the basis for the development of the model, but also directly related to the main objective of China Meteorological Administration to improve gridded weather forecast. Based on the ECMWF (European Centre for Medium-Range Weather Forecasts) forecast of high resolution gridded precipitation data, CMORPH (NOAA Climate Prediction Center Morphing Method) satellite data, and the fusion of hourly precipitation data collected at 30000 automatic weather stations in China, 55 precipitation cases of high resolution gridded precipitation forecast from June 2015 to August 2015 were selected for verification. Advantages and disadvantages of the traditional method were compared to that of the object-oriented MODE (Method for Object-based Diagnostic Evaluation) method and the neighborhood method to provide references for the evaluation of high-resolution gridded precipitation forecasting. The main results are:(1) Although the traditional point to point method has some limitations in verifying high-resolution gridded precipitation forecast, the traditional method can reveal regional differences in high-resolution gridded precipitation forecast skill, and depict the overall temporal performance of the model forecast. Thereby it still has important practical value for performance evaluation of high resolution gridded forecasts. (2) one significant advantage of the neighborhood method is that it can obtain traditional forecasting techniques on different spatial scales by varying the neighborhood window. On the other hand, the unique skill of this method to obtain the FSS (Fractions Skill Score) score can provide the ratio of the number of points with precipitation between observed and predicted precipitation. Combining the traditional techniques with neighborhood FSS scores on different neighborhood windows, the spatial scale on which the model has a better performance of forecast can be determined. (3) In the MODE precipitation verification method, an object is extracted on the basis of conversion convolution radius. Such objects can not only provide information similar to that obtained by the traditional techniques such as forecast skill scores and scale-depending forecast performance, but also show the centroid distance between precipitation objects, the axis angle, size, strength, comprehensive income, displacement distance, etc. These attributes can provide information of the model forecast performance from multiple perspectives and quantify errors of the weather system development speed, strength and other forecast variables. Thereby this method has unique advantages. However, there still exist some difficulties regarding how to improve the practical forecasting capability using these object attributes.

Abstract:In order to overcome the quality control problem over areas where the station density is low, or for some stations that have no adjacent stations and lack effective internal reference data, for example those newly deployed stations and special single factor stations, a new quality control method for surface temperature observations based on the ensemble learning algorithm of Phase Space Reconstruction (PSR) and Extreme Learning Machine (ELM) that was improved by Particle Swarm Optimization (PSO) was introduced in detail in this paper. This method considers the chaotic characteristics of the time series of temperature. In order to assess the feasibility and applicability of the proposed method, it was applied to hourly temperature observations from 2007 to 2009 in eight cities of Jiangsu Province. Results were examined and compared against that of conventional single-station quality control method and Tshebyshev Polynomial Interpolation (TPI) method. It was found that the method introduced in this study can flag suspicious data more effectively, and it also has the advantages of high identification accuracy and good adaptability and controllability over different regions with various climate backgrounds.

Abstract:High-performance parallel computing has always been an important scientific issue in the study on climate system models. However, with the development of computer technology, computer architecture is becoming more and more complicated while the complexity of the climate system has made it a challenge to develop high-performance climate system models. This paper adopted a completely new parallel programming method. Based on the programming framework J-Earth, a high-performance parallel general circulation model, H-GAMIL, was developed. With detailed analysis and deconstruction of the original GAMIL model, the characteristics of J-Earth was combined with GAMIL to reconstruct the H-GAMIL in this paper by using the object-oriented programming method. The reconstructed H-GAMIL possesses the features of standardization and modularization of modern software and also has new functions of automatic 2D subdivision, hybrid parallel implementation of MPI (Message Passing Interface) and OpenMP (Open MultiProcessing), as well as parallel output, thus solving the problem that the one-dimensional subdivision of the original model was subjected to the restriction of the processor and the serial IO problem in the original model. Based on the above work, in the present study we conducted a parallel efficiency test on the H-GAMIL. The result shows that when the model's horizontal resolution was 1°×1°, hundreds of processors could be used and the parallel efficiency could reach above 40%, and the load balance totaled more than 70%. The test result suggests that the H-GAMIL possesses a relatively high parallel efficiency and scalability. Meanwhile, a comparative analysis of the simulation performance of H-GAMIL was conducted in this study. The result shows that the H-GAMIL maintains the conservativeness of the original model and has the same simulation performance as the original one. Thus it meets the computing requirements for climate study and can be applied for practical use.

Abstract:Based on rainfall datasets obtained from meteorological stations in China and the NCEP/NCAR reanalysis data, the simultaneous relationship between the Scandinavian teleconnection pattern (SCA) and late autumn precipitation over the western region of Southwest China (WSWC) during 1961-2012 is investigated. Results show that there is a significant negative correlation between the SCA index and the rainfall over WSWC. The negative correlation is asymmetric. During the positive SCA years, the rainfall in WSWC is less than that in normal years. However, during the negative SCA years, the relationship between the SCA index and the rainfall over WSWC is not significant. The negative rainfall anomaly over WSWC during positive SCA years is consistent with local anomalous descending motion in the lower and middle troposphere. The diagnostic analysis of the vertical motion equation indicates that the local descending motion is primarily maintained by anomalous cold temperature advection. The advection of anomalous temperature by mean westerlies contributes most to the anomalous cold temperature advection in WSWC. The downstream Rossby wave propagation triggered by the positive SCA pattern weakens the East Asian trough. Consequently, the eastern part of Southwest China becomes warmer. The climatological westerly wind brings anomalously cold air into the WSWC area, resulting in local descending motion and drought.

Abstract:A two-dimensional fractional Brown motion (fBm) model was used to describe the irregular terrain, and the Longmire-Scott soil-parameter frequency dependent model was applied to investigate the propagation effect of soil moisture on the lightning vertical electric field over irregular terrains. Main results are as follows:(1) The surface irregularity can lead to the attenuation of the magnitude of the vertical electric field and lags of the rise time of the field waveform. With the increase in the surface irregularity, the attenuation of the vertical electric field intensifies and the rise time of the field waveform increases. (2) Regardless of the degree of surface irregularity, increases in the soil moisture will reduce the attenuation of the vertical electric field. (3) Generally, increases in the surface irregularity and decreases in the soil moisture can result in stronger attenuation of the vertical electric field and longer rise time of the field waveform.

Abstract:This paper analyzes the relationship between regional large-scale wind power ramp and large-scale weather system based on real-time 15-min power outputs of 24 wind farms in Shandong Province in 2013 and related WRF (Weather Research and Forecasting) forecasting data and the FNL (Final Operational Global Analysis) re-analysis data. Results indicate that large-scale weather systems, especially the blocking high, are the important reason that induces the large-scale wind power ramp in Shandong Province. Using the swinging door algorithm, the wind power ramp events are re-defined and recognized first. The characteristics and predictability of wind power ramp events are then analyzed. It is found that the wind power report-check regulation should seriously consider the forecasting accuracy during the ramp events for the purpose to improve the stability of grid operation.

Abstract:Cavity attenuated phase shift spectroscopy (CAPS) technique has many advantages such as the impressive detection sensitivity and the high performance-price ratio of light source. It is also easy to control and has a longer effective absorption optical path. Based on the above prominent advantages, a continuous measurement system of atmospheric aerosol extinction coefficient using the CAPS is developed. The cavity reflectivity of the system is about 0.9999, and the corresponding effective optical path of 4.4 km is calculated. Based on the analysis of Allan variance, the best integration time of the system is 80 s, and the corresponding extreme value of extinction coefficient detection is 0.06 Mm^-1. The CAPS system is applied to the 12 cycles and 48-hour continuous monitoring for atmospheric aerosol extinction coefficient. The result shows that the empty cavity phase shift is basically stable, the cavity attenuated phase shift of the sample measurement is evident, and the retrieved atmospheric visibility is reliable. The above results suggest that the continuous measurement system of atmospheric aerosol extinction coefficient based on the CAPS can be used for practical atmospheric aerosol measurement.