应用气象学报

Simulation of the Precipitation and Its Variation During the 20th Century Using the BCC Climate Model (BCC_CSM1.0)

Dong Min, Wu Tongwen, Wang Zaizhi, Xin Xiaoge, Zhang Fang

2013, 24(1): 1-11.

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Abstract:
The precipitation of the late 19th and 20th century (1870—2005) is simulated using Beijing Climate Center's Climate System Model (BCC_CSM1.0) under specified external forcing of solar constant, greenhouse gases, sulfate aerosols and volcanic ashes. The simulated precipitation and its variations are validated, showing that the BCC_CSM1.0 can pretty well simulate the basic climate state of global precipitation, the seasonal transition, the intra-seasonal oscillation of tropical precipitation and the inter-annual variation. The simulation shows there is an increasing trend in global land precipitation and in the extreme precipitation events during 1901—2005. The result consists with the CMAP and CRU analysis data which is based on observations in general, but there are still some discrepancies between the simulated and observed precipitation in the spatial distribution and temporal evolution. The simulation ability of the model needs improvement in some aspects. The simulated seasonal transition of the main rain belt in east part of China is faster than the observation. And the simulated precipitation over northeast part of Tibet Plateau and nearby region is heavier than observation especially in summer. The simulated intra-seasonal oscillation of the tropical precipitation is weaker than the observation. The simulated inter-annual variability is larger than the observation, which mainly occurs in the tropical region where the precipitation is large. The mean precipitation of global land, Eurasia, Asia, east part of China, the south part of the Yangtze River and North China during 1901—2005 from BCC_CSM1.0 is consistent with corresponding CRU data. In most of the above regions the simulated precipitation is lower than the observation. The simulated precipitation trend of global land, east part of China, the south part of the Yangtze and North China from BCC_CSM1.0 is consistent with that from CRU data. The simulated precipitation of global land for 1901—2005 has obvious increasing trend which is more significant than that from CRU data. But for the other regions mentioned, the precipitation trend simulation result is unsatisfactory and needs further improvement.

Inter-decadal Variations of Summer Water Budgets in the Monsoon Wetness Region of Eastern China

Liao Rongwei, Zhao Ping

2013, 24(1): 12-22.

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Abstract:
Using monthly means of NCAR/ NCEP reanalysis datasets and rainfall data from 660 surface stations in China, a water budgets time series over the monsoon wetness region in Eastern China is calculated by a water vapor transport method for the period from 1983 to 2002, referring to changes in inter-decadal variability of water budgets associated with the anomalous atmospheric circulations and precipitation in the monsoon wetness region of Eastern China. Relationships between the water budget index and the variability of the atmospheric circulation and rainfall in China are examined. The results show that the summer water budget time series displays the variability on the inter-decadal scale from the 1980s to the 1990s in the region. The correlation coefficient is 0.71 between the water budgets and regional average precipitation and decreases to 0.55 after removing the trends. The index reflects the variations of the meridional winds anomalies and indicates an intensity of summer monsoon and an anomaly of rainfall along the valleys in the monsoon wetness region of Eastern China. The anomalous water vapor transport is affected by four anomalous circulations: The anomalous cyclonic circulation between 20°N and 30°N over the Eastern China, and the anomalous anti-cyclonic circulations between 40°N and 60°N over East Asian continent, between 18°N and 30°N over the west Pacific, and between 5°N and 20°N over the Bay of Bengal. Anomalous moisture flux convergence appears in the south of the Yangtze. Corresponding to the higher-index value decades, the low pressure centering in Mongolia is weaker and the surface temperature, sea surface temperature, the convergence in lower troposphere and divergence in upper troposphere are generally stronger in East Asia and the western north Pacific. Meanwhile, the southerly wind anomalies are prevailing in the eastern coast of China. This anomaly intensifies upward motion over the south mainland of China and drives the water vapor transport from South China Sea, and increases the water budgets and precipitation, with the difference of rainfall above 100 mm in the southern China. The water budgets are net surplus though uneven from 1983 to 2002. Vapor income in the low value year is about 24.3% less than in the high value year, and the precipitation is less by 18%. The anomalous meridional water budget is larger than zonal one, accounting for 71.3% of net budget. The anomalous water budget of low-index value decades accounts for 7% in latitude and 24% in longitude relative to the high-index value decades. The variation of the meridional water budget is larger than zonal one and is greater in magnitude. Therefore, the net water budget is quite different between high and low value decades of water budget and the anomalous precipitation is also significantly different.

Continuous Spring and Meiyu Rainfall in the Mid-lower Reaches of the Yangtze During the Past 50 Years

Deng Hanqing, Luo Yong

2013, 24(1): 23-31.

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Abstract:
Using the daily precipitation data from 52 meteorological stations in the mid-lower reaches of the Yangtze and NCEP/NCAR reanalysis data from 1961 to 2009, the characteristics of spring and Meiyu precipitation are analyzed. It shows that spring precipitation takes on significant inter-annual and inter-decadal variations while Meiyu precipitation doesn't. Based on the annual spring and Meiyu precipitation characteristics, it is divided into four classes: Flood-flood, flood-drought, drought-drought and drought-flood. Generally, drought-drought and flood-flood events take place frequently. The variation of circulation features affects the precipitation anomaly too. The mechanism of different type is also discussed, finding the correlation coefficient between previous winter Niño3 index and spring, Meiyu precipitation to be 0.42 and 0.30, which reach 0.01 and 0.05 levels, respectively. The previous winter snow of Tibetan Plateau and western Pacific summer monsoon index are shown both significantly correlated with Meiyu precipitation. The abundant water vapor is carried by the anomalous southerly from the South China Sea and the western Pacific, the western Pacific subtropical anticyclone strengthens, and its position leans westward in June. That would make a successive flood event. When water vapor over the reaches is abundant but insufficient in source region, position of the western Pacific subtropical anticyclone appears from west to east anomaly in spring and Meiyu periods, and that would cause the flood-drought events. When water vapor is insufficient in both areas, drought event occurs. In 2011, a sudden turn of drought and flood takes place in the mid-lower reaches of the Yangtze, leading to big economic losses of agriculture. The factors which may cause the sudden turn of drought and flood events are analyzed. The sea surface temperature anomaly of the equatorial eastern Pacific happens in precious winter and less water vapor cause spring drought, and with Meiyu occuring, the western Pacific subtropical anticyclone moving westward and precipitation increasing greatly. On the basis of preliminary analysis of related impact factors, numerical experiments are needed to evaluate the result further.

The Low Frequency Oscillation and Circulation Characteristics of Cold Rainy Weather in Guangdong

Ji Zhongping, Gao Xiaorong, Gu Dejun, Wu Xiulan, Shu Fengmin

2013, 24(1): 32-42.

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Abstract:
In order to predict cold rainy weather on medium-term and extended range during February—March in Guangdong, the relationship between annual prospect of cold rainy weather during 1953—2011 in Guangdong and that in Guangzhou, and the relationship between low-frequency oscillation of Guangzhou daily temperature and cold rainy weather are analyzed from December to next April with wavelet transform and correlation analysis. The result shows that the similar ratio between the annual prospect of Guangzhou cold rainy weather and that of Guangdong is 94.9%(56/59). In mild year of cold rainy weather, Guangzhou daily temperature exhibits quasi-periodic oscillations of 8.0—18.3 days, 10.1—28.4 days and 30—89.6 days for middle and severe year, respectively.The long cold rainy weather during February—March has mainly close relationship with the intraseasonal oscillation with period more than 18 days, especially with the oscillation intensity more than 45 days. The weather concept model of long cold rainy weather with intraseasonal oscillation of 30—64 days is set up based on composite analysis of typical cases.They reflect the evolution characteristics of atmospheric circulation of warmer—cooling—starting—maintenance—ending period of long cold rainy weather. During warmer—cooling—starting period, the blocking high in Ural Maintain and west of Baikal Lake at 500 hPa geopotential height field is maintained, the South China is controlled by straight and fluctuant westerly from weak ridge at warmer period and obvious negative anomalies of height field, the Mongolian High gradually enhances and moves southward in ground, and the South China is controlled by enormous cold pressure ridge from weak trough.The stronger cold air moves southwards and weak cold air continuously supplements. All of the above lead to strong temperature drop and the start of cold rainy weather. When the blocking high in Ural Mountain—west of Baikal Lake is weakened, an obvious ridge maintains, the South China is still controlled by straight and fluctuant westerly, the weak cold air is continuously supplement, the cold rainy weather maintained. When Ural Mountain—north of Baikal Lake controls by weak trough, the South China is controlled by weak ridges at 500 hPa and surface which moving eastwards, the cold rainy weather ends. So the blocking high in Ural Mountain—west of Baikal Lake can be regarded as 500 hPa precursor of cold rainy weather in Guangdong. When this precursor stably maintains, the straight and fluctuation westerly influences the South China, Mongolian High gradually intensifies and move southwards at surface, the long cold rainy weather in Guangdong can be predicted.

Causes and Dynamic-statistical Forecast of the Summer Rainfall Anomaly over China in 2011

Zhao Junhu, Yang Jie, Feng Guolin, Zhang Shixuan

2013, 24(1): 43-54.

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Abstract:
The large-scale rainfall over China in summer of 2011 is reviewed, the prediction results of dynamic-statistical objective quantitative (DSOQ) and dynamic-statistical diagnostic (DSD) methods are evaluated. Compared to the DSOQ, the anomaly correlation coefficient (ACC) and predictive score (PS) of which are 0.12 and 70, the DSD method has obvious advantage in predicting skill by increasing the ACC and PS to 0.25 and 75, respectively. Taking the middle and lower reaches of the Yangtze (MLRY) as an experiment region, the differences in predictive factors of these two methods are compared and the advantages of DSD method are analyzed. The probable causes of summer rainfall anomaly distribution in 2011 and the relevant circulation anomaly characteristics are also discussed, such as the blocking-high (BH) anomaly in middle-high latitudes and the western Pacific subtropical high (WPSH) anomaly in low latitudes. The results indicate that the abundant rainfall in June over the middle and lower reaches of the Yangtze and the uneven distribution of June-July-August (JJA) rainfall are the direct causes for the southerly rainbelt in the summer of 2011. And this is related to the BH activities, the intra-seasonal oscillations (ISO) of WPSH and the monthly different configurations between them. In June, the atmospheric circulations reveal two trough areas and one ridge area at the middle-high latitudes. The intensity and western boundary of the WPSH are normal, while the latitude of the ridge line is northerly. The southward cold air behind the trough converges with the northward warm wet airflow over MLRY, which causes substantial precipitation in this area. Compared with June, the atmospheric circulations in middle-high latitudes change into the two ridge areas and one trough area in July, the WPSH becomes weaker and its western boundary moves eastward, and the ridge line is more northward. These situations lead to stronger cold air than the warm wet airflow, resulting in drought of the whole areas. In August, the strength of the trough and ridge weaken relative comparing to July, which makes the convergence of the southward cold air and the northward warm wet airflow over East China. The situations above lead to a large amount of precipitation in East China. Besides, the variation of the BH and the ISO of WPSH is affected by the interactions among the East Asian circulation systems (EACS), and the external forcing of sea surface temperature (SST) and snow cover. The interactions and configurations among EACS are key effective factors of summer climate. Thus, by predicting the seasonal and monthly key circulation factors (e.g., BH and WPSH, etc.) to revise the summer precipitation prediction would be a feasible way for the improvements of the dynamic-statistical prediction skill.

The Statistical Characteristics of pH Measurement Bias in the Monitoring Data of CMA-ARMN

Tang Jie, Ba Jin

2013, 24(1): 55-64.

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Abstract:
Precipitation pH and conductivity are measured routinely in the nation-wide network with more than 300 stations, known as the Acid Rain Monitoring Network (ARMN), under the infrastructure of China Meteorological Administration (CMA) since early 1990s. Previous studies indicate that a systematic negative bias in the pH measurement, caused by the aging of pH electrode, which has weakened the data quality obviously. Characteristics of the bias are investigated to describe the temporal and spatial features of the negative pH measurement bias (NBpH) and to estimate its magnitude with meticulous statistical approaches, based on the monitoring dataset obtained from CMA-ARMN during 1992—2011. The result indicates that 40% stations of CMA-ARMN suffers from NBpH problem in the early 1990s, while this ratio decreases to 25% during 2010—2011. The proportion of data infected with NBpH problem during 2010—2011 reduces to 2% from 10% in the early 1990s. This improvement of pH measurement mentioned above can be attributed to the renewal of pH meter for all CMA-ARMN stations in 2000, the re-approval of Standard Operation Manual of CMA-ARMN in 2005, and the recent trail measures on the pH electrode aging. Also, statistics shows that NBpH problem seldom occurs in the stations over the Northwest China and Qinghai-Tibet Plateau, but frequently occurs in the stations of other regions over China. On the whole, NBpH problem in southern part of China is more serious than those in the northern part of China. This geographical feature of NBpH is related with the behavior of aged pH electrode which shows bigger negative bias when measuring the solution of low pH and low conductivity. Quasi-quantitative estimation of NBpH based on the K-pH inequality principle shows that the magnitude of NBpH for about 80% data ranges from-0.6 to 0, with a few of extremes lower than-3.0. The lower pH is, the larger NBpH tends to be. To avoid NBpH problem in future, substitution of the now-using normal pH electrode in CMA-ARMN with the pH electrode for low ion strength is suggested, together with the corresponding QA/QC (quality assurance/quality control) procedures. In addition, the possibility and the example of data correction with NBpH are discussed.

Quality Evaluations and Comparisons of Radiation Data at Lin'an and Longfengshan Stations

Song Jianyang, Zheng Xiangdong, Cheng Xinghong, Ma Qianli, Yu Xiangming, Dai Xin, Yu Dajiang

2013, 24(1): 65-74.

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Abstract:
Solar radiation is widely used in the studies of climate change, evaluation of model simulations and assessment of solar radiation energy resources. Therefore, accurate observations of solar radiation data are absolutely needed. An international BSRN method of solar data quality assessment and quality control (QA-QC) is applied to investigate data quality of solar radiation and downward long-wave radiation (DLR) measured from 2005 to 2011 at Lin'an and Longfengshan, two regional background stations in the mainland of China. The method includes 3 steps of testing. They are the sequential limits of physically possible, extremely rare and relevant factor comparison. The results show that percentages of radiation data meeting requirements of the first two test steps of the quality test at both sites are more than 99.5%, but in the third step, the percentage dropped to 97.9% at Lin'an and 95.9% at Longfengshan. The error of the 2AP (2 axis position) in tracking sun-disk is the main cause for those direct and diffuse radiation data failing to meet the conditions of quality test, and the scenario is more frequent at the high SZA (solar zenith angle). Compared to the rate evaluated by the prevalent limit of global radiation error, the BSRN third step makes the rate of validated solar radiation data be reduced by 0.9% and 1.6% at Lin'an and Longfengshan, respectively. The thermal offset of CM21 pyrometer is from-5 W·m^-2 to-2 W·m^-2. With the compensation of thermal offset, the rate of radiation data meeting requirements of the BSRN quality test is obviously improved.It is well known that the most important factor affecting the surface solar radiation includes cloud, water vapor and aerosol. Therefore, variations of solar radiation with changes of SZA are analyzed with removal of cloud effect. It is identified that the global and direct radiation irradiances at Lin'an are obviously lower than those at Longfengshan with the same SZA, while the diffuse radiation is opposite. The cause for these phenomena is due to the lower atmospheric transparency and higher atmospheric turbidity at Lin'an.The annual averages of solar radiation and DLR at the sites are calculated. The annual averaged daily integrated global solar radiation and global solar radiation under clear condition at Lin'an are 12.4±7.2, 16.5±5.0 MJ·m-2, while the coincident average radiations at Longfengshan are 13.5±7.2, 15.5±6.2 MJ·m^-2. Annual average DLR at Lin'an is 363.7±59.3 W·m^-2, obviously higher than that at Longfengshan (274.9±77.6 W·m^-2). There is an obvious decreasing trend of DLR at Lin'an, and global solar radiation takes on an increasing trend at Longfengshan under clear sky.

Assessment of Two Aerosol Modules of CAM5

Li Xin, Liu Yu

2013, 24(1): 75-86.

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Abstract:
The Community Atmosphere Model (CAM) is widely employed in research of climate simulation and climate change. The latest version 5.0, provides two modules to simulate atmosphere aerosol, named MAM3 and MOZART, respectively. Several main atmosphere aerosols are simulated by these two modules, and the simulated surface concentrations of these aerosols are examined by Interagency Monitoring of Protected Visual Environments Program (IMPROVE) and European Monitoring and Evaluation Program (EMEP). The simulated global distributions of aerosol column concentration, as well as aerosol global budgets are compared with median model results on AeroCom website.Both MAM3 and MOZART modules can capture the seasonal distribution of sulfate aerosol; the simulated surface concentrations are in reasonable agreement with observations, although the values in summer are usually high. The correlation coefficients between models and observations for two modules are both around 0.89. Also, both MAM3 and MOZART can capture spatial and temporal distribution of black carbon aerosol. However, these two modules both underestimate surface concentration of black carbon by a factor of 2—3. The correlation coefficients between models and observations for two modules are both around 0.62, which are believed to be caused by smaller emission fluxes and higher rates of wet removal. The two modules have large difference in simulating organic matter, both having a bias by a factor of 2—3. MAM3 overestimates surface concentrations of organic matter with a normalized mean bias of 92.1%, while MOZART makes an underestimation of 58.1%. It's found that both of these biases usually happen in summer and autumn. A separate analysis demonstrates that the primary organic matter simulated by these two modules are very close, while MAM3 and MOZART have serious differences on simulation of the secondary organic carbon (SOC), which primarily contributes to the bias of total organic matter. Sea salt global budgets by MAM3 and MOZART are close, but the total content of sea salt is larger than median model results on AeroCom. The most likely cause is that lower rates of dry removal and wet removal in the CAM5. With similar mechanism but different emission factor, the two modules perform differently in simulating mineral dust; flux of mineral dust emission in MAM3 is nearly three times as large as that in median model results on AeroCom, and thus overestimates the total content, while MOZART underestimates mineral dust burden, because its emission flux is 40% smaller than that in median model results on AeroCom.According to the comparison in global distribution and global budget, it indicates that CAM5 has a weaker intensity of aerosol translation and diffusion, thus, the removal mechanism should be improved.

Cumulus Merging in the Massive Mudslide of Zhouqu Using Meteorological Satellite Data

Huang Yong, Qin Danyu

2013, 24(1): 87-98.

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Abstract:
Heavy rainfall occurs abruptly at Zhouqu, Gansu Province from 7 August to 8 August of 2010, causing massive mudslide and brings about huge casualties. As an observational fact, it is clear that a meso-scale convective system, which is produced by several convective cells merging, brings heavy rain in local field and the massive mudslide at Zhouqu. The phenomenon of cumulus merging is analyzed using meteorological satellite data, such as FY-2D/E, NOAA-18 and FY-1D, to find out its impact on heavy rain.As NOAA-18 satellite image shows, there are several cells around the Zhouqu at 0638 UTC 7 August 2010. One and half hours later, cells are merged and forms a meso-scale system. And the meso-scale system is still developing in FY-1D satellite image.From FY-2D/E satellite images, there are five stages of cumulus merging in the whole process. First, the meso-scale convective system comes out due to the merging of multi-cells from 0700 UTC to 0800 UTC. And it is the developing and maintaining period of meso-scale convective system. The cumulus merges in 3 stages. First, a developing system merges with several nearby new generation cells at about 0930 UTC. Then a systems merges between a mature new generation system and the old convective system from 1000 UTC to 1030 UTC, the new and old systems merge from 1130 UTC to 1200 UTC. Finally, two centers of cloud with cold cloud top temperature are merged as the dissipating of convective system after 1300 UTC. As the centers have been merged, the system develops again and the cold cloud areas have increased.As a result of the merging effect, not only a large and complex convective system is produced and becomes more intensity, but also the lifetime of convective system is greatly enhanced with more convective energy.On the other hand, the mechanisms of merging in five stages could be classified as change of inner dynamical structure and collision with outer force. At the building stage of meso-scale convective system, collision with outer force is the main cause of cumulus merging. But with the development and maintain of system, inner changes of dynamical structure, such as pressure gradient force, convergence and up-down circumfluence, are the primary mechanisms for merging.

The Pre-event Risk Assessment of Beijing Urban Flood

Hu Haibo, Xuan Chunyi, Zhu Lishang

2013, 24(1): 99-108.

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Abstract:
A three-level index system for urban flood risk assessment is put forward, in which higher level indexes of the system can be calculated from lower level indexes following a bottom-to-up deducing rule. The possibility estimation of risk zoning can be conducted in two ways. The first way is based on historical data. 100 extreme storms in study areas are selected from historical storm data, and then the precipitation of these rainstorms in the area are interpolated for 100 times, followed by summing up risk values of these storm events for each grid cell. The second way is based on observation and forecasting precipitation data. Sensitive indexes are determined by evaluating the effects of land surface topography, impervious surface area and river network on flood formation. The sensitive index of topography is obtained by considering land relief and elevation in each grid cell, and the measurement transforms land topographical characteristics into flood risk sensitivity. Impervious surface also plays an important role in flood formation since it greatly reduces water infiltration, quickens stream flow peaks, and increases storm flow. On the other hand, population density and GDP per square kilometer as well as distribution of critical areas for flood controlling are indicators for exposure in the flood risk analysis. As a result, the comprehensive flood risk indexes have been deduced by integrating the estimated second-level indexes (the precipitation index, the sensitive index and the exposure index). The application of the flood risk zoning with the bottom-to-up assessment method indicates that the risk zoning areas can be promptly accomplished by this way, estimating the distribution of actual risk areas properly. Meanwhile, it is found that the flood risk in urban is higher than that of rural and suburb, because the urban is flat in topography with much larger areas with impervious surface, and its population and economic entities are more heavily aggregated, and the rainstorm possibility is greater in urban with the analysis of the rainstorm historical data. Referring to the historical loss data of rainstorm floods occurring from 2004 to 2008 in Beijing, it has also been demonstrated that the result is consistent. Application of the model for risk warning is further validated with a storm event happened on 23 June 2011 in Beijing. In this case, quantity precipitation estimation (QPE) is used to estimate flood risk index, combined with the bottom-to-up assessment framework to estimate potential flood risk. Results of this application suggest that the bottom-to-up quick risk assessment fits the actual risk condition very well. Besides risk zoning and assessing, it can also be used to provide quickly-processed products for flash flood risk warning.

A New MCP Method of Predicting Long-term Wind Speed with Height Error Revision

Liu Yujue, Li Jun, Hu Fei, Zhu Rong

2013, 24(1): 109-116.

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Abstract:
In recent years, modern wind turbine generators have grown rapidly and wind power plants have been established, delivering clean and inexhaustible energy. Therefore, the need for effective methods to evaluate wind power. Based on the fact that wind field has some degree of spatial correlation, measure-correlate-predict (MCP) algorithms can use concurrent data from target sites and a nearby reference site to predict the wind resource at target sites for wind power development. During last 15 years, over a dozen of MCP methods have been established, which differ in terms of overall approach, model definition, use of direction sectors, length of data. There are linear regression model, composite of wind speeds at two-site model, vector regression method, composite of standard deviations of two datasets and so on.But MCP algorithms mentioned above can only predict wind speed of target site with the same altitude. If the target site is higher or lower than the reference site too much, the result will be unreliable. So a new MCP method with height error revision is proposed based on data of two wind measurements, including six-layer wind data in one year. The fitted equations of Weibull parameters k and c as the function of height have been derived. By means of fitted equations, the relationship between winds of high and low altitude can be formulated. So, a method for error reduction is presented.At last, a set of performance comparison are carried out. The coefficient of correlation, the mean speed, the wind distribution and the correct annual energy production are selected as metrics at the target site, and a sample wind turbine power curve is analyzed. The mean and standard deviation of those estimates are used to characterize results. Results indicate that the new MCP method with height error revision work much better than previous ones.

Automatic Identification and Alert of Gust Fronts

Zheng Jiafeng, Zhang Jie, Zhu Keyun, Liu Yanxia, Zhang Tao

2013, 24(1): 117-125.

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Abstract:
Gust fronts often cause serious ground gale and strong wind shear. Therefore, the short-term forecast, nowcasting and civil aviation department pay high attention to the research of gust fronts. Based on the echo characteristics of gust fronts in reflectivity field and velocity field of Doppler radar, an identification algorithm for gust fronts is designed. In the velocity field, the convergence line is identified by finding the consistent decreasing radial velocity and inspected by using a convergence parameter threshold, a grads threshold and a flux threshold. In the reflectivity field, the reflectivity data are classified into different levels. Then, the narrowband is identified by an algorithm called bilateral grads, which is designed by fully using the narrowband geometrical characteristic, the interval between narrowband and echo matrix. The bilateral grads algorithm can effectively filter out the wide range of precipitation echoes and reserve the narrowband in reflectivity image. Meanwhile, in order to filter out the remainder noise, length calculated and image thinning technique are used during above processes. According to the consistency of narrowband and the convergence line in the space, the gust front can be identified. The achievement of alert function uses an image flicker and some physical quantities output to represent the strength of the gust front. Finally, 98 volume-scanning data from 3 radar stations and the automatic weather station data and I_CS are used to evaluate the identification effect. The bilateral grads algorithm can effectively filter out the big range precipitation echo and keep the narrowband signal, it has an important relationship with the distance between the narrowband and maternal storm echo. Combined with the composite reflectivity to contrast all-layer reflectivity, the narrowband or the stronger reflectivity doesn't exist at the higher elevation, therefore, the algorithm simply handles the low elevation, which can improve the identification efficiency. The convergence line can be identified effectively by this method, and at the same time, it can also identify the low-level wind shear. The identification rate evaluated by I_CS from 98 volume-scanning data reaches 68.4%, indicating that the identification algorithm has the capacity of identifying gust fronts.

2013, 24(1): 126-128.

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Abstract:

Vol.24, NO.1, 2013