应用气象学报

Long term Total Ozone Comparisons Between Space based and Ground based Observations at 4 Sites in China

Zheng Xiangdong, Wei Xiaoli

2010, 21(1): 1-10.

[FullText HTML] (944) [PDF 2657KB](2454)

Abstract:
The observed total ozone differences between ground based data and available satellite products over Xianghe, Kunming, Waliguan and Longfengshan are analyzed. The absolute differences of total ozone between space based and ground based observations are-5—10 DU. And the relatives differences (RD) is—5%—4%, fitting the normal distribution of 0.05 significance. Compared with the ground based observation, the precision of TOMS (Total Ozone Mapping Spectrophotometer) version total ozone is better than that of DOAS (Differential Optical Absorption Spectroscopy). Total ozone RDs are statistically similar at Xianghe and Longfengshan where total ozone is high, while the similarity of RDs are also detected at low total ozone region Kunming and Waliguan. The regional similarities also indicate in the sensitivity validations of total ozone RDs to the SZA (solar zenith angle) and total ozone references. The integrated total ozone dataset with the ground based and TOMS as well as OMI observations in the 4 proxy sites also reflect the substantial depletion of global total ozone event around 1993. An eventual recover trend emerged in Xianghe, Kunming, and Longfengshan during 1995—1996, but the recover trend in Waliguan doesn't occur until 2001. The inter comparisons also reveal the quality information of ground based total ozone observations. For example, due to Brewer grating scratches in 2000—2006, total ozone observation from Longfengshan intends to be lower at high SZA conditions, which has been reflected in the RDs sensitivity validation to SZA. The increasing total ozone difference between Dobson#075 and OMI or SCIAMACHY products since 2007 needs further investigation.

The Statistical Analysis of Low Vortex During Meiyu Season in the Lower Reaches of the Yangtze

Yang Yinming, Gu Wenlong, Zhao Ruilei3, Liu Jie

2010, 21(1): 11-18.

[FullText HTML] (890) [PDF 2979KB](1790)

Abstract:
Local generated mesoscale vortexes (LMVs) in the lower reaches of the Yangtze is one key factor to improve rainstorm forecast accuracy since they can efficiently trigger and organize mesoscale convective systems (MCSs). There are many case studies focusing on the MCSs caused by LMVs, but in order to improve operational weather forecast ability during Meiyu season, the study about LMVs activities, structures and formative environment are necessary. Based on conventional weather data, satellite cloud images and numerical weather predictive outputs during Meiyu season of 1998—2005, the activities and structures of LMVs related to rainstorms in the lower reaches of the Yangtze are statistically analyzed, including the vortex generation, movement, life cycle, spatial range and related convective activities etc. Large scale environments and physical conditions are also synthetically analyzed. The result shows that LMVs in the lower reaches of Yangtze mainly generated around the Dabie Mountain area in Anhui Province. Typically, their horizontal scale changes from 100 km to 400 km, and most of them vary from 200 km to 300 km. Their vertical developing height usually changes from 1000 hPa to 700 hPa. LMVs moves mainly in two directions, one is northeast to as far as the Yellow Sea through north of Shandong Province, ant the other is southeastward towards the East China Sea through south of Jiangsu Province or north of Zhejiang Province. The life cycle of LMVs is less than 48 hours and it has no clear relations with their spatial scales. About 70% LMVs trigger single MCS or series MCSs and can lead to rainstorms. Rainstorms mainly happen to the south or southeast of LMVs, where there are enough warm and moisture flow. LMVs generated at the bottom of upper level trough of 500 hPa are especially possible to cause rainstorms. Analysis of large scale environments and physical conditions show more than 90% of LMVs develops at the bottom or in front of upper level trough at 500 hPa. The positive vorticity advection in front of upper level trough is necessary to LMVs generation and development. While the other conditions such as low level and upper level jet, middle level turbulence, low level moisture transfer and topographic conditions are all important to LMVs generation and development. Further studies such as mechanisms about LMV generation, development and the mechanisms about LMV trigger and organize MCSs are necessary.

Assimilation Application of AMDAR Data to the Operational NWP System of Beijing

Zhong Jiqin, Chen Min, Fan Shuiyong, Zhang Chaolin

2010, 21(1): 19-28.

[FullText HTML] (886) [PDF 1885KB](1989)

Abstract:
AMDAR data has been widely proved valuable in improving accuracy of numerical weather forecast. But assimilation application of AMDAR data in operational NWP model is seldom accessed in China. BJ RUC, the operational rapid update and cycling NWP system of Beijing Meteorological Bureau, is used to evaluate the impacts of assimilating AMDAR data on forecast performance. Durative experiments with and without AMDAR data are conducted from 15 Jul to 15 Aug, 2007. The average RMSE difference and average precipitation scores difference of AMDAR and NOAMDAR experiments are compared to discuss the impacts of AMDAR on short range numerical weather forecast.Analysis shows that the assimilation of aircraft data has remarkable positive impacts on the first 9 hours forecast especially on upper levels. Forecasts of wind on the levels of 925 hPa to 250 hPa and temperature on the levels of 850 hPa to 400 hPa are improved. The assimilation of AMDAR data contributes more in rapid updated cycle mode than in cold start mode. It has positive impacts on the threshold score of accumulated precipitation forecast of 0—12 hours, 0—24 hours, 12—18 hours, and 18—24 hours. It also improves the overestimating in the NOAMDAR experiments. The increment analysis shows parallel characteristics with the horizontal distribution of AMDAR data and the vertical improvement characteristic of the 3 hours forecast. The comparability indicates the improvement of wind and temperature in first guess field made by assimilating AMDAR data. The relative observation errors of AMDAR against Beijing radiosonde are discussed and proved reliable. It suggests that determining AMDAR observation errors properly in assimilation can help make better use of AMDAR data.Experiments on AMDAR data assimilating application in the operational BJ RUC system show that AMDAR assimilating has important positive impacts on improving the upper temperature, wind and precipitation forecast. Reasonable amendment of observation errors will bring more efficient utilization of AMDAR data, so priority is assigned to adjusting the AMDAR observation errors in BJ RUC.

The Climatic Change Trend and Seasonal Characteristics of Daily Temperature Extremes in China for the Latest 40 Years

Yang Ping, Liu Weidong, Wang Qig uang, Xiong Kaiguo, Hou Wei

2010, 21(1): 29-36.

[FullText HTML] (854) [PDF 1276KB](2771)

Abstract:
Extreme events have heavy negative effects on the society causing great economic loss so they have attracted much attention. Using maximal/minimum daily tempera ture data from 194 stations for the period of 1961—2000 of China and adopting indices of extreme climate, seasonal characteristics and the changes of daily tem perature extremes are analyzed. The indices of temperature extremes are introduc ed concluding absolute and relative definition. Then the annual indices of hot a nd cold extreme events are discussed. In order to compare the differences of the indices among different seasons, the season indices are also researched. The re sults indicate the hot extreme indices and cold extreme indices defined by absol ute threshold show the trend of summer and winter, but the result of absolute an nual indices of temperature extremes is not satisfying because the differences between southern and northern are not considered. Another indices based on the pe rcentage definitions indicate that cold and hot extremes indices are anisomerous. Hot days and cold days are not consistent and the indices in same area between hot days and cold days are not symmetrical. But indices for hot nights and cold nights show good consistency and symmetry. The indices change little for daytim e but change rapidly at night. The indices of seasonal temperature extremes show that the changes of indices in spring and autumn are most indistinctive, while the indices in winter is the most notable. The cold indices of spring, autumn an d winter are decreasing while trends of summer indices are increasing most of th e time.

The Relationship Between the Anomalous Snow Cover on the Qinghai Tibetan Plateau and Atmospheric Anomalous Circulation

Zhong Aihua, Yan Huasheng, Li Yueqing, Xia Lan

2010, 21(1): 37-46.

[FullText HTML] (1092) [PDF 3099KB](2038)

Abstract:
Based on the previous researches, the longer time series about the typically anomalous snow cover years from 1957 to 2003 are confirmed initially. Using NCEP data of global monthly mean geopotential height (144×73) at 100 hPa and 500 hPa, the relationship between anomalous snow cover and atmospheric anomalous circulation at the Qinghai Tibetan Plateau is analyzed from December to next May of 1957 to 2003. And the possible mechanisms in which the atmospheric anomalous circulation affects the anomalous snow cover at the Qinghai Tibetan Plateau are propounded. It is found that the atmospheric circulation affects the weather and climate and lead to the snow cover anomaly first, and the abnormal snow cover affects the atmospheric circulation in slighter extent subsequently. The atmospheric pressure of key tropical areas changes in an opposite phase to that of key areas in the middle and high latitudes of Southern Hemisphere. Meridional circulation of two hemispheres is strengthened by this strong meridional atmospheric pressure gradient. Abnormal Antarctic Oscillation causes anomalous Mascarene high and Australia high by meridional circulation, and then they impact local meridional circulation of East Asia through meridional teleconnection which makes the anomalous climate of winter in East Asia, causing the abnormal snow cover at the Qinghai Tibetan Plateau at last. On the basis of results, a statistical method to discriminate the anomalous years of snow cover at the Qinghai Tibetan Plateau objectively and quantitatively is proposed, applying the 2 discriminant equation of the three factor optimal subset. According to the typical anomalous snow cover years given, the discriminant equation is built and argued time and again. Finally, the abnormal snow cover years from 1957 to 2003 of the Qinghai Tibetan Plateau are distinguished.

The Variation Tendency of Heavy Precipitation Events in Different Grades During Recent 45 Years over Central China

Chen Bo, Shi Ruiqin, Chen Zhenghong

2010, 21(1): 47-54.

[FullText HTML] (776) [PDF 7219KB](1917)

Abstract:
In the context of global climate change, frequencies and intensities of various extreme climate events are also changing. Central China is located at mid lower reaches of the Yangtze River, where rainstorm flooding disaster caused by heavy precipitation almost occurs every year. So it is extremely necessary to research variation characteristics of heavy precipitation events in Central China, which has important effects on improving the forecast of heavy precipitation and reducing the loss in this area. The interdecadal spatial temporal change trend, break and periods characteristics of all grade heavy precipitation events are studied using daily raingauge data of 84 weather stations from 1961 to 2005. These data are analyzed in terms of several modern statistical test methods such as percentile, trend coefficient, Monte Carlo statistical test, Mann Kendall break detector, Morlet wavelet transform etc.The results show that thresholds of heavy precipitation for 10%, 8%, 5% and 2% percentile is 24.7 mm, 28.6 mm, 37.6 mm and 57.8 mm by area averaged, respectively. The mean and standard deviation of heavy precipitation and raining days decrease with the percentile, variation coefficients of those increasements; while the mean, standard deviation and variation coefficient of intensity all rise gradually. As for spatial distribution, the heavy precipitation rises from Henan to Hunan and Jiangxi, the raining days rise from north to south. The intensity is lower in western Henan, northwestern Hubei, some parts of southern Hunan, and higher in the mid lower reaches of the Yangtze River, from eastern Hubei to northern Jiangxi, and some parts of northwestern Hunan. For a fixed grade, the heavy precipitation shows stronger linear trend than raining days, and linear trend of intensity is the weakest. The total heavy precipitation, raining days and intensity by area average show increasing trends in all grades. The total heavy precipitation in Grade Ⅳ and Ⅲ passes the 0.1 level test, and have distinct rising trend. The linear trend coefficients of total heavy precipitation, raining days, and intensity in different weather stations show various characteristics. With the percentiles decreasing, the trend coefficients show a decreasing trend in mid lower reaches of the Yangtze River from Yichang to its east, while opposite trend appears in southern Hunan and southern Jiangxi. For all grades, the total heavy precipitation breaks congruously in 1993, and shows a rising trend. The raining days breaks during the end of 1980s and the beginning of 1990s. The intensity begins to strengthen from 1994, but becomes unobvious after the year of 2000. For all grades, the heavy precipitation, raining days and intensity change regularly at an interdecadal period of 12—14 years and a short term period of 6—9 years.

An Improved BP Algorithm and Its Application to Precipitation Forecast

Min Jingjing, Sun Jingrong, Liu Huanzhu, Wang Shigong, Cao Xiaozhong

2010, 21(1): 55-62.

[FullText HTML] (885) [PDF 1209KB](2042)

Abstract:
Objective forecast of precipitation is difficult because of its complex nonlinear characteristics. In order to enhance the ability of forecasting precipitation, artificial neural network (ANN) method is applied in numerical weather products interpretation. Among different types of ANN, the back propagation (BP) neural network is the most popular and influential one. However, traditional BP algorithm has some limitations such as the difficulties in determining network structure and the learning parameters, poor generalization ability and possibility of misleading to local minimum in learning process, etc. To resolve these problems, an improved algorithm is proposed.Based on T213 numerical forecast products of National Meteorological Center from May to September during 2003—2005, 25 factors are selected in terms of dynamic diagnostic analysis and statistical methods. The precipitation forecasts of operational global models from China National Meteorological Center, Japan Meteorological Agency and German Meteorological Administration are studied. Using the reformative BP algorithm, three grades forecast (≥0.1 mm, ≥10.0 mm, ≥25.0 mm) models are built to forecast 24 hour precipitation of 68 stations over Jiang Huai Basin. During the training process, precipitation samples are randomly divided into two kinds according to a certain proportion, training samples and testing samples. They are used to train the network and to check the error of output respectively so that all parameters are confirmed. By repeating training and learning of network, an optimal network model is obtained. The optimized forecast model is used to forecast precipitation of different grades, times and stations, from May to September during 2006—2007. The forecasting results of improved BP algorithm are compared with those of tradition BP algorithm and numerical models outputs. The average threat score (TS) of improved BP algorithm is the highest; the average false alarm rate (FAR) and missing alarm rate (MAR) of improved BP algorithm are much lower than the others. So the improved BP algorithm is superior and it indicates a potential for more accurate precipitation forecasting.

Icing of Wires with Different Heights and Diameters from Lanzhou to Guanzhong

Wu Suliang, Fan Jianxun, Jiang Chuangye, Li Weilin, He Xiaoai, Cui Wei

2010, 21(1): 63-69.

[FullText HTML] (836) [PDF 1520KB](1925)

Abstract:
Based on the characteristic of the wire icing data of different diameters, diffe rent heights observed from Gansu, Shaanxi and Ningxia, the concept of net diamet er, net thickness are brought forward. The relations between net diameters, net thicknesses, average thickness and mass of wire icing of different diameters at different heights are studied, and the regularities are analyzed. It provides re ference for the calculation of the standard thickness of wire icing on power lin e between Gansu and Shaanxi. The results show that there are remarkable linear r elations between net diameter, net thickness, average thickness and masses of wi re icing. The mass, net diameter, average thickness, and net thickness of 26 mm conductor respectively are 1.3, 0.72, 0.65 and 0.4 times big as those of 4 mm wi re, and are 1.2, 1.037, 1 and 0.8882 times big as those of 18 mm conductor. The linear relations between 26 mm conductor and 18 mm conductor are more obvious th an the relations between 26 mm conductor and 4 mm wire. The net diameters, net t hickness and average thicknesses of ice accretion on the 26 mm conductor respect ively are smaller than that of 4 mm wire. The average power exponent of average thickness of ice accretion with height is 0.40. The power exponent is 0.45 at th e heights of 10 m to 5 m, 0.35 at the heights of 5 m to 2 m, 0.38 at the heights of 10 m to 2 m. By neglecting the sinking speed of water droplets, assuming tha t capture coefficient is a constant, and assuming various physical quantities ar e equilibrium constant, the weight of wire icing is proportional to conductor di ameter, and increases with the height of conductor. In the experiment, the order of ice accretion mass from small to big is 2 m high 18 mm conductor, 2 m high 2 6 mm conductor, 5 m high 18 mm conductor, 5 m high 26 mm conductor, 10 m high 18 mm conductor, 10 m high 26 mm conductor.

A Sampling Technique of Typical Atmospheric Profiles Database in China

Qi Chengi, Liu Hui, Ma Gang, Zhang Peng, Wu Xuebao

2010, 21(1): 70-75.

[FullText HTML] (820) [PDF 1091KB](2680)

Abstract:
Atmospheric profiles are important input parameters in simulation of atmospheric radiative transfer, emulation of new satellite instruments spectral characteristics, development of transmittance model, retrieval of atmospheric parameters and the assimilation of satellite data in numerical weather prediction. It is very necessary that built a sampled atmospheric profiles database to meet many kinds of application requirements. The quantity, covering region, and source of atmospheric profiles affect the efficiency and results of application a lot. A major attempt to sample atmospheric profiles on a global scale has been the constitution of successive versions of the Thermodynamic Initial Guess Retrieval database (TIGR), despite the high dimensionality. Each version groups together hundreds of profiles sampled from mass soundings observations of the atmosphere. There are dozens of atmospheric profiles database currently, but profiles in China region are very deficient. An atmospheric profiles database with samples in China region can enhance the accuracy in calculation of radiative transfer and profiles retrieval. 61308 profiles of year 2002 are collected as a preparatory database that includes 124 radiosond station measurement distributing in China region through Meteorological Data Storage System, and a database is set up comprising 30 atmospheric temperature and humidity profiles and named it CRASD 2 (China Regional Atmospheric Sample Database 2) with topology method. It is classified by surface pressure and divided into 5 groups and their respective surface pressure are 500 hPa, 700 hPa, 850 hPa, 925 hPa, 1000 hPa.The CRASD 2 covers the four seasons of one year and the two radiosond observation time of 00:00 and 12:00, so that it has characteristics of well proportioned time and season range. Considering the vertical height range it contains the samples located in stations with the altitude of several to several thousand meters. Besides, the profiles in this database distribute in large overcast geographical region of China, and the profiles with large discrepancy distribute in north—east, north—west and south region, while samples with relative less difference mostly are located in south of the Yangtze River and Yellow and Huai River region. The diversity between profiles mainly exist in the different height of tropopause, discrepancy in atmospheric temperature and humidity condition of the same pressure level, and the existence of temperature inversion layer. With the independency between profiles and good climate representative, the CRASD 2 database is accord with the principle of a sampled database, so it can support the application of atmosphere samples in research of radiative transfer and remote sensing retrieval. This elementary employment of topology sampling technique in extracting regional profiles database implies it may support sampling database from longer time serial observation data, and adding more profiles variables in sampling method in the future work.

Satellite Remote Sensing Application to Enteromorpha Prolifera Monitoring in the Yellow Sea

Li Sanmei, Li Yajun, Dong Haiy ing, Sun Ling, Liu Cheng, Liu Zheng, Dian Qing, Yan Hua, Zhao Changhai

2010, 21(1): 76-82.

[FullText HTML] (894) [PDF 1645KB](2447)

Abstract:
A method of enteromorpha prolifera monitoring using moderate resolution environm ent satellite data is proposed. Based on the spectral characteristics of enterom orpha prolifera, remote sensing methods and processing procedures are established and then the monitoring results are derived. With the support of GIS technique, the affected range, extent, moving path and coverage of enteromorpha prolifera can be developed and relevant products are produced. During the marine alga catchi ng campaign, enteromorpha prolifera monitoring products are made and provided to the campaigners in time. These products help to find enteromorpha prolifera are a promptly and are highly evaluated.The monitoring results show that enteromorpha prolifera in the Yellow Sea appear s in mid May of 2008 at first, and then the range of enteromorpha prolifera expand grad ually and move northwestward. In mid June, enteromorpha prolifera influence the region of Yellow Sea near Qingdao Olympic regatta sea area and the size reaches up to 800 km². With the progress of a massive algae clearing activity, the ra nge of enteromorpha prolifera decreases rapidly. In mid July of 2008, there is little e nteromorpha prolifera in Qingdao Olympic regatta sea area.The temporal and spatial distribution characteristics of enteromorpha prolifera from 2006 to 2008 are analyzed using multiple observations of EOS/MODIS data and t he result shows that there are no evident phenomena of enteromorpha prolifera in Yellow Sea in the summers of 2006 and 2007.The coverage map of enteromorpha prolifera accumulated from multiple observation shows that high density enteromorpha prolifera appears most frequently in the o ffshore area and the sea area about 100 km south of Qingdao. About more than 200 00 km2 of sea area is influenced by enteromorpha prolifera in different extent in the summer of 2008 altogether.The moving path of enteromorpha prolifera induced from the multiple observation from May to July of 2008 shows that enteromorpha prolifera moves from southeast to northwest. It can also be concluded that enteromorpha prolifera moving path is deeply influenc ed by the wind and ocean current.

A Preliminary Analytical Study on the Spontaneous Emission of Inertia gravity Waves from Vortical Flows

Zhao Nan, Gan Lu, Shen Xinyong

2010, 21(1): 83-88.

[FullText HTML] (852) [PDF 510KB](1781)

Abstract:
The emission of inertia gravity waves from the adjustment of balanced flows (or, basically, vortical flows) is currently regarded as a new mechanism of the pro duction of inertia gravity waves and referred as the spontaneous emission. Base d on f plane barotropic model, a preliminary analytical study on the spontaneou s emission of inertia gravity waves from vortical flows is conducted. First of all, the concept of slow manifold and balanced flow are discussed via this model and vortical property of the balanced flow is emphasized. Then, by assuming tha t the Froude number F and Rossby number satisfy and (implying that vortic al flow approximately balanced flow that includes gradient wind and other ageost rophic contributions), the basic equations are simplified to an inhomogeneous wa ve equation of inertia gravity wave, while the inhomogeneous term is related to the imbalance of the vortical flow. This inhomogeneous term vanishes when vorti cal flow is exactly balanced. So the imbalance of the vortical flow provides a f orcing or source to the inertia gravity wave. The Green function of this equa tion is found to give the inhomogeneous solution standing for the spontaneous em ission. In the field far from the wave "source", this inhomogeneous solution c an be expanded into far field form, including wave emission of monopole, dipole and quadrupole types. On the other hand, within or near to the "source" field, the near field form can serve as an approximate expression of the slow manifo ld. These results indicate that the convergence/divergence fields accompanied wi th vortical flows is composed of two main parts, i.e., the spontaneous emission o f inertia gravity waves from vortical flows and slow varying convergence/diver gence filed slaved to the adjustment of balanced flow. Although higher order ap proximation solution has already been given by Ford (2000) using method of match ed asymptotic expansions, the Green function solution can depict the spontaneo us emission in a more physical way.

Simplification of an Inorganic Salt Thermodynamic Equilibrium Model and Its Application

Li Shu, Wang Tijian, Xie Min, Zhuang Bingliang

2010, 21(1): 89-94.

[FullText HTML] (884) [PDF 2498KB](1812)

Abstract:

In order to simulate the spatial distribution and temporal variation of volatile nitrate aerosols, it is necessary to introduce a thermodynamic equilibrium model and calculate the concentration under the state of equilibrium from the viewpoint of chemical thermodynamics. However, it costs much time to carry out a large scale and long term simulation because the thermodynamic equilibrium model contains a lot of species and reactions. The inorganic salt thermodynamic equilibrium model ISORROPIA is simplified using look up table method. A look up table for concentrations of 5 species (sulfate, nitrate, ammonium, nitric acid and ammonia) under the state of equilibrium is constructed according to various conditions of effecting factors (temperature, relative humidity, NH₃+NH₄⁺, HNO₃+NO₃^- and HH₂SO₄+SO₄^2-). The regional climate chemistry modeling system (RegCCMS) is an on line coupled modeling system which contains the regional climate model (RegCM3) and the tropospheric atmosphere chemistry model (TACM). The look up table scheme and the thermodynamic equilibrium model are introduced into TACM to treat nitrate, sulfate and ammonium. These two schemes are respectively adopted in RegCCMS to investigate spatial distribution of nitrate aerosol over China in January and July of 2003. Nitrate aerosol is mainly distributed in Sichuan, Yunnan, Guizhou, Hebei, Henan, Shandong in January and Henan, Hebei, Shandong, Jiangsu in July, which is roughly consistent with the distribution of the industry development. Influenced by temperature on thermodynamic equilibrium, wet scavenging of precipitation and the monsoon climate, the nitrate concentration is high in winter, and is very low in summer. The results of monthly average surface concentration show that look up table method has a good agreement with the thermodynamic equilibrium model in both quantity and distribution. The effect of look up table method is better on land than on ocean. Look up table method can save about 80% of the computing time compared with the thermodynamic equilibrium model, greatly improving the computational efficiency. The surface concentrations every 6 hours in several cities got from the look up table method and the thermodynamic equilibrium model are compared. The correlation coefficients of these two schemes in Chongqing, Xi'an and Xiamen are 0.99, 0.99, 0.97 in January and 0.75, 0.81, 0.86 in July. The results show that look up table method is able to simulate the characteristic of temporal variation. Due to higher temperature and humidity, differences between these two schemes are more obvious in July than those in January. As a whole, the look up table method can deal with the thermodynamic equilibrium processes successfully and reduce time for calculation significantly, therefore it has broad application prospect in research of climate effects of aerosols.

An Altitude triggered Lightning with Multiple Branches and Ground Contacts

Li Jun, Lǜ Wei tao, Zhang Yijun, Dong Wansheng, Zheng Dong, Chen Shaodong, Qiu Shi, Wang Tao, Liu Hengyi, Chen Luwen

2010, 21(1): 95-100.

[FullText HTML] (1352) [PDF 1291KB](2238)

Abstract:
Field experiments on artificially rocket triggered lightning are conducted in summer of 2007 in Conghua, Guangdong Province by Lightning Physics and Protection Engineering Laboratory of Chinese Academy of Meteorological Sciences. The lumin osity characteristics of lighting are captured simultaneously by a Redlake Motion Pro HS 4 high speed camera at 5000 frames per second (fps) 630 m away. Field mill, magnetic loop antenna, broadband interferometers, slow antenna and fast an tenna are installed at the experiment site. The time constants of slow and fast antenna are 6 s and 2 ms respectively, and the bandwidth of broadband interferom eters to locate the lightning is from 25 MHz to 290 MHz. One lightning is succes sfully triggered at 13:58:33 30 June 2007. The top of the wire is 335 m height and the bottom of it is 170 m height at that time. The records of the electric field on the land surface show that it is a negative altitude triggered lightning. No return stroke is observed in luminosity, and the initial continue current p rocess of this flash is 178.6 ms. Bi directional leader process occurs be fore mini return stroke and upward stepped leader branches of this altitude triggered lightning occur after that. The upward positive leader appears 4.93 ms earlier before the downward negative leader. The upward stepped leader propagates at an average speed of the order of 10⁴ m/s in its initial stage, and then becomes 1 0⁵ m/s in magnitude. After the downward negative leader appears, the upward po sitive leader channel becomes brighter than before. The downward negative leader has 3 bifurcation points and produces 4 different ground contacts, and two bran ches connects to ground persisted during the initial continue current process. T he average speed of the downward stepped leader is 1.69×1 0⁵ m/s. After mini r eturn stroke, the upward positive leader above the wire channel propagates along several different branch channels into the cloud, and the average speed of it is 1.05×1 0⁵ m/s. In this experiment, the inducing charge provides the charge of the leader to spread, and the environmental electric field may play a decisive role to the multiple branches and multiple ground contacts of this altitude tr iggered lightning.

The Actuality and Progress of Whole Sky Cloud Sounding Techniques

Gao Taichang, Liu Lei, Zhao Shi jun, Sun Xuejin, Liu Jian

2010, 21(1): 101-109.

[FullText HTML] (3693) [PDF 445KB](4490)

Abstract:
Clouds are regular and important weather phenomenon which play important role on the earth's radiation budget and climate change. The shape, size, distribution and movement of them indicate the condition of the atmosphere, thus cloud observ ation is important. Clouds can be observed by means of both satellites and ground based instruments. Satellite cloud images provide global coverage data which are used widely in weather forecast. Ground based cloud images are very localones which contain more details. Ground based cloud sounding instruments have not been put into actual operations by far though. Some cloud base height measurem ents such as ceilometers and the newer laser beam ceilometers are developed in order to determine local cloud base height, however cloud coverage and typology are still determined with a subjective aspect by human observers.In recent years, a number of ground based sky imagers have been developed due to the improvements in both hardware and digital image processing techniques. Many well known instruments are developed and used for cloud coverage estima tion and scientific experiments. For example, the all sky imager (ASI), total sk y imager (TSI) and whole sky camera (WSC) measure visible skylight from the entire sky dome during daytime, while the whole sky imager (WSI) provides hemispheri cal coverage with different detection techniques during day and night. The WSI has approximately 70 nm wide imaging bands centered at 450, 650 nm and 800 nm, ide ntifying clouds from red/blue ratios during the day and from star maps at night (with gaps in operation near sunrise and sunset).The infrared cloud imager (ICI) and the Whole Sky Infrared Cloud Measuring System (WSIRCMS) are ground based passive sensors that measures downwelling atmospheric radiance in the 8—14 μm wave length band. These two instruments can identify clouds and calculate cloud am ount continuously with accordant sensitivity during day and night. Some key techniques are analyzed, such as obtaining whole sky images, camera lens protection, cloud detection, cloud coverage calculation, cloud base height calculation and cloud type classification etc. It shows that, visible light based apparatus can hardly be applied in actual operation because they can't work well during night. The WSI can provide data at night, but the consistency can't turn up trumps because of the algorithmic difference during day and night. Images from cloud infrared radiometers have bad spatial resolution which goes aga inst cloud classification. Sensors using infrared detector array can work with no difference in sensitivity during day and night and have good spatial resolution, but needs improving in stability. Fully considering whole sky cloud sounding theories, techniques and applications, there are still a lot of problems before these instruments to be used in actual operations. Their performance should be more firmness. The whole sky cloud base height should be lucubrated. The instrume ntal cloud form classification principle should be proposed to classify cloud with ground based instruments.

Fog Forecast Experiment of Single Station Based on LVQ Neural Network

Wang Yanlei, Cao Bingwei, Huang Bing, Dong Zhaojun, Lu Zeting, Chen Xingming

2010, 21(1): 110-114.

[FullText HTML] (865) [PDF 583KB](2206)

Abstract:
The generating and dissolving of fogs are too complex for empirical and linear s ystems methods to forecast and these methods cannot meet the needs of flight tra ining. To meet this end, a new fog predicting model is proposed based on learnin g vector quantization neural network. The forecasting model of fog weather event s is established using sequential forecast idea, adopting principal component an alysis (PCA) and learning vector quantization network too. 186 cases of heavy fo g, mist or fog free weather events on a certain airport is studied. Temperature, pressure, moisture, wind and other elements observed at 08:00, 14:00, and 20:0 0 the day before the foggy weather are selected as prediction factors. Based on Learning Vector Quantization neural network, the prediction model of airport fog gy weather events is established using sequential forecast idea (fog versus fog free, heavy fog versus mist), and the prediction factors can be simplified usi ng the principal component analysis.In the network training process, the model forecasting capability is improved in accordance with fitting accuracy to dynamically adjust neurons scaling paramete rs of the network. Adopting "to stop" technology of the timely termination tra ining in accordance with testing the accuracy, generalization ability of the mod el is effectively improved. Forecasting experiments show that, the proposed mode l can effectively distinguish fog, mist and fog. Both the fitting rate and the f orecasting accuracy are satisfactory so the model is practical.

The Design of Operation Monitoring System for L Band Upper air Meteorological Sounding Network

Li Wei, hang Chunhui, Meng Zhaolin, Liu Fengqin, Liang Haihe

2010, 21(1): 115-120.

[FullText HTML] (826) [PDF 670KB](2124)

Abstract:
The operation monitoring system aims to monitor L band upper air meteorological sounding network running conditions including instrument running status and sounding data quality. Based on B/S structure, Windows platform and Oracle database, it can ensure users visit the monitoring system website at anytime and anyplace. The surface radar running condition monitoring file will be automatically generated 5 minutes after balloon releasing, and upper air sounding data monitoring file that contains upper air sounding statistics results and upper air sounding minutely data will be generated when upper air sounding process finishes. The TTAA message arrival information is used to judge whether L band upper air sounding system is working, the surface radar running condition monitoring file i s used to judge whether the surface radar working status is normal, the TTAA mes sage and upper air minutely data are used to check data quality. The monitoring system is developed fully considering monitoring information and sounding data provided by upper air meteorological sounding system, integrated operational running experience and users' requirements. The sounding parameter, surface instan taneous observation data and surface radar running status parameters can be displayed and checked, and sounding result can also be displayed and analyzed by th e system. During the sounding data quality control, first the message format is checked, and then based on WMO's reference criteria for AWS instantaneous extreme value check the surface instantaneous extreme value check is carried out. The nationwide monitoring area is divided into northeast, northwest, middle and south subareas. The geopotential height and temperature thresholds of each subarea are set using compiled upper air sounding data of CMA. Spherical coordinate data including elevation, azimuth, slant range and height are added to the monitoring file, and they are used to check the consistency of upper air sounding data and quality of the wind data. The sounding data quality check diagnoses the facility problems automatically and can improve its performance. The results show that the surface radar and radiosonde problems and current running status can be found immediately through the monitoring system integrated with sounding data quality check. The system can guarantee the operational stability of upper air mete orological sounding network, and improve meteorological sounding data quality effectively. But during the sounding data quality assessment the thresholds are found to be too strict, so it should be modified to avoid too much false warning information through further running assessment.

Distributed Synchronization System of Meteorological Metadata: An Exploratory Development

Zhou Zheng rong, Wang Cheng, He Wenchun

2010, 21(1): 121-128.

[FullText HTML] (784) [PDF 1028KB](2833)

Abstract:
The current meteorological information system will be unable to meet the telecommunicating, storing and computing requirements of enormous weather radar data in the near future. Therefore, the New Generation Weather Radar Information Sharing Platform (WRISP) has been planned, the main target of which is sharing the meteorological data countrywide. The project should begin with sharing and exchanging the meteorological metadata, then it's imperative to set up a meteorological metadata synchronization system across WAN. A research is conducted on some related conceptions such as meteorological metadata, synchronization protocol of metadata and data consistency, etc. Meteorological metadata, as the subject carried on the synchronization system is interpreted including its characters and defects, then methods are provided to improve it. Mechanism of metadata synchronization, models of data consistency, and metadata harvesting protocols such as OAI PMH are analyzed and feasibility studies are carried out. The general design thought of the synchronization system, which consists of topological design, conceptive model, data flow and technical architecture is proposed. Two performance tests are taken on the test prototype, and the obtained data is evaluated and leads to a preliminary conclusion. The meteorological metadata synchronization system on the meteorological dedicated WAN described in the prototype is a distributed data exchange platform. It's able to synchronize and exchange the metadata conformed to the WMO Core Metadata Profile among multiple nodes under the distributed WAN environment, and ensures the FIFO and monotonic write consistency as well. The prototype may help to promote the research on WIS and build a cornerstone of WRISP which facilitate the sharing of the meteorological data nationwide.

Vol.21, NO.1, 2010