应用气象学报

The Conductivity Additivity of Ionic Components in Precipitation and Its Application to the Data Evaluation of Acid Rain Monitoring

Tang Jie, Xu Xiaobin, Yang Zhibiao, Ba Jin, Wang Shufeng

2008, 19(4): 385-392.

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Abstract:
Conductivity of precipitation (K) is a primary parameter in acid rain/precipitation chemistry monitoring. As the conductivity of ions in precipitation is an addible quantity, the conductivity data is commonly used in the quality check/assessment on the analysis data of ionic components in precipitation, by comparing the measured K with the calculated K from the ionic concentration data obtained from the chemical analysis. This method is referred normally as conductance percent difference (CPD) method and widely used. A national monitoring network has been run by China Meteorological Administration for more than 15 years for the acid rain monitoring, which is called Acid Rain Monitoring Network (ARMN/CMA), as an important supplement to its Global Atmosphere Watch (GAW) program with 4 Global/regional stations. Only pH and conductivity of precipitation are measured by those ARMN/CMA stations, with a total number nearly 300 by the end of 2006. To meet the need for quality check/assessment on the basis of pH and K data obtained from ARMN/CMA, the K-pH inequality method is proposed based on the same principle of conductivity additivity with CPD method, viz. : the K calculated from H⁺ concentration reduced from pH must be smaller than the measured K.The usage of K-pH inequality method in different pH value range is discussed and it shows that this method is an effective and easy-to-use tool for the on field check and afterward data evaluation, especially for the data with pH values below 5.0. With K-pH inequality method, the historical pH and K data of ARMN/CMA from 1992 to 2005 are checked. The results show that part of the calculated K is larger than the measured K, which means errors either in pH measurement or in K measurement, or both. The distributions of the differences between the measured and the calculated K in different pH bins show that the differences with pH≤4.0 tend to be more and more negative as pH getting lower. It suggests that the errors be mainly associated with pH measurements. With this assumption, the errors in pH measurements for those data are estim ated to be from-0.1 to-0.3. This estimate is in consistence with results of the annual blind sample inter-comparison within ARMN/CMA.The CPD values of all precipitation samples from 4 GAW stations are also calculated and the frequency distributions of CPD values in different pH bins are studied to check/evaluate the data quality of the ionic component data. The results show that CPD values for samples with pH≤4.0 tend to be positive and those for samples with pH>4.0 tend to be negative. This tendency also suggests errors in pH measurements for 4 GAW stations, but the magnitude is smaller than data of ARMN/CMA, with an estimate of-0.05.

Characteristics of Lightning Exposure in China from 1997 to 2006

Ma Ming, Lü Weitao, Zhang Yijun, Meng Qing, Yang Jing

2008, 19(4): 393-400.

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Abstract:
A more complete national climatic description of lightning casualties and damages is essential to improving awareness and education concerns of this hazard. By using China Meteorological Administration (CMA) lightning accident data, lightning-related disasters, injuries, and property damages reported in China from 1997 to 2006 are summarized. Climatic characteristics of lightning casualties and damages are analyzed. The data contain 4488 deaths, 4320 injuries, and 27784 property damage cases, which show that severe casualties and economic loss are caused by lightning damage during the past ten years. The annual average number of death in China between 2004 and 2006 is 0.53 per million people, 26% more than in the United States, ten times more than in the United Kingdom. Lightning disasters in China frequently occur in eastern coastal areas and southern areas, but relatively rare in western areas. Guangdong Province has the most deaths (772), injuries (662) and damage reports (7993) from lightning, which makes it the worst damaged areas from lightning all over the country. Yunnan Province comes second with 1025 deaths and casualties from lightning damage.There are also severe deaths and casualties from lightning damage in Guizhou, Jiangxi, Guangxi, Shandong, Jiangsu, Sichuan, Hubei and Hunan provinces, whereas Tibet, Shanghai, Shanxi, Beijing, Gansu, Xinjiang, Ningxia and Tianjin rank relatively low in the list. When population is taken into account, Hainan Province has the highest casualty rate. Tibetan Autonomous Region, with its population of only over 2 million, ranks the second top in terms of casualty rate. Qinghai Province rises to the fifth, whereas Hubei, Hunan and Shandong, with large population, fall in the ranking. Lightning disaster in China may occur in any month of the year, with less damage from October to March. 65% of the year's lightning casualties and damages occur in summer, reaching a maximum in July. The diurnal variations show that 73% of the lightning casualties and 62% of the lightning damages occur between 13:00 and 20:00. The peak of lightning casualties and damages occurs at 16:00. Compared with lightning damages, lightning casualties are affected by people's life routines and habits, with more incidences during working hours in the day time.Peasants account for 93% of lightning casualties, with urban residents of 7%, which makes peasants the major population of victims. In the report with known locations for lightning victims, farmland account for 32% of the total locations as the largest category, buildings is 23%, open fields 13%, water related fields 10%, under-tree fields 8%, on telephone 6% and storage 3%, respectively. Additional information is provided about lightning victims and objects.

Observation of a Natural Cloud-to-ground Lightning with Multiple Return Strokes

Li Jun, Zhang Yijun, Lǜ Weitao, Dong Wansheng, Chen Shaodong, Li Bin

2008, 19(4): 401-411.

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Abstract:
A field experiment on artificially rocket-triggered lightning and natural lightning observation is conducted in summer of 2006 in Conghua, Guangdong. The luminosity characteristics of lighting discharges are observed simultaneously by using a video camera and a Redlake MotionPro HS-4 high-speed camera which consists of a 512×512 pin photodiode array module. A cloud-to-ground (CG) lightning with 13 return strokes (RS) is observed by using the high-speed camera with a frame rate of 5000 frames per second at 16:52:51 Aug 1, 2006. The distance from the high-speed camera to the flash is about 2.1 km. The record of the electric field on the surface of the earth shows that this CG lightning discharge transports the negative charge in cloud to the ground. All of the 13 strokes propagate along the same main channel and have one ground termination.The duration of this flash is 822.4 ms. The peak luminance of the 2nd, 3rd, and 8th return strokes are brighter than that of the first one, being 25% of all 12 subsequent return strokes. Of the 13 strokes, 6 (46 %) present some luminosity persistence after the return stroke frame. The durations of 2 persistence luminosity are in excess of 40 ms (CC (continuing current) following 9th stroke:157.6 ms; CC follow ing 10th stroke:221 ms).There are 17 Mcomponents occurring during the 6 continuing current occurrences. The luminosity characteristics of 3 leaders are examined. The average speed of the stepped leader is 2.23×106 m/s. It is a β-type leader according to the previous results which the stepped leader emerges from the cloud base and develops with a high average speed of the order of 10⁶ m/s. The speed of the attempted leader before the 4th return stroke exhibits the decrease as it develops down toward the ground.The speed of the dart-stepped leader before the 13th return stroke appears to increase as it approaches the ground. Cut-off time is the time when the lightning channel shows no luminosity between two adjacent return strokes. In other words, it is the sum of the time from the frame that the previous return stroke and the CC followed disappears to the frame that the next return stroke is observed. Total luminosity is the sum of luminance of the frames including the return stroke and the CC followed. It is found that the cut-off time before a subsequent return stroke exhibits a consistent trend with the total luminosity of this subsequent return stroke and the CC followed (although there is no fixed proportionality between them), especially there is a proportionality relationship between them after the 9th return stroke. The geometric average of 17 Mcomponents' lasting time is 1.28 ms, and that of 11 intervals between the consecutive M-components is 1.69 ms.

Tropospheric Water Vapor Profiles Using GPS Network in Hainan

Bi Yanmeng, Mao Jietai, Mao Hui

2008, 19(4): 412-419.

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Abstract:
Water vapor plays a key role in atmospheric processes. Water vapor field is also one of the initial conditions needed by numerical weather prediction. Its distribution remains difficult to quantify due to water vapor's high variability in time and space and the deficiency of available measurements. The GPS has proved its capacity to measure the integ rated water vapor at zenith with the same accuracy as other methods, such as radiosonde and water vapor radiometers, which has been demonstrated by many experiments and GPS precipitable water vapor has been operated in many areas. Recent studies also show that it is possible to quantify the integ rated water vapor in the direction of signals of the GPS satellite. These observations can be used to study the water vapor tomography using GPS network. That is to use the water vapor amount along slant path of GPS satellites to form observation equations and to obtain the vertical profile information over GPS sites by solving these equations.The principle of tomography is introduced in which slant path observations from ground-based GPS is used and the method of calculating the observation equations is presented. During November in 2005, a small GPS network experiment is carried out in Hainan. The purpose of this experiment is to study the tomography tropospheric water vapor profiles based on GPS slant path observations. Without a priori information of water vapor, the absolute value of water vapor is difficult to resolve. After the method of GPS raw data processing is summarized, how to use a priori information is also analyzed. The period of tomography is from Nov 17 to 21 in 2005. Three different vertical tomographic resolutions of 600 m, 800 m and 1000 m are tested and analyzed. Results show that these resolutions have no large difference. Therefore, tomographic resolution from 500 m to 1000 m can be applied in practical use. In the experiment, tomographic vertical resolution of 1000 m is selected. Three different plans using a priori information are described.In the first plan, priori information is the earliest radiosonde at 00:00 on Nov 17, 2005. In the second plan, the latest radiosonde before the retrieved time is used as priori information. The average radiosondes are used in the third plan during the experiment. In the first and the third plan, priori information is hold but in the second plan priori information is changed and regenerated. Water vapor vertical profiles derived from GPS tomography are compared with that measured by radiosonde in Haikou site. The results show that they agree well with each other and the root-mean-square error (RMSE) is about 0.5 g·m ^-3. The process of water vapor decreasing and atmosphere drying is well reflected by GPS tomography. The tomographic results from different priori information used in tomographic method are also analyzed. It is demonstrated that water vapor priori information is obviously adjusted by GPS observation. And some problems in tomography are also discussed. Vertical profile distribution of tropospheric water vapor can be retrieved from GPS measurements with high time resolution through tomography inversion.

Offsetting Image Rotation System in FY-3 MERSI's Geolocation

Guan Min, Guo Qiang

2008, 19(4): 420-427.

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Abstract:
45°rotating scan mirror is one of the most popular scanning modes in optics and fine mechanics, but out-of-axis misalignment will be brought about for the multi-detector combined scanning system because image rotation is caused by 45°rotating scan mirror. In order to obtain high resolution, multi-detector or linear sensor techniques are often adopted by current remote sensing instruments. For example, Chinese Ocean Color and Temperature Scanner (COCTS) on HY-1 satellite is a four-detector combined scanning scheme, 10 detectors and 40 detectors for sampling are adopted by the Medium Resolution Spectral Imager (MERSI) on FY-3 satellite. In order to eliminate this misalignment of image rotation, K mirror is applied in COCTS and MERSI to offset image rotation from 45°rotating scan mirror. A larger out-of-axis error in geolocation of remote sensing image will also be produced if the rotation and reflection of 45°rotating scan mirror is considered only but not the K mirror.An algorithmic model in the remote sensing image's geolocation is introduced. In the model, K mirror's reflection matrix is deduced and the error in remote sensing image's geolocation has been eliminated by vector reflection and rotation. First, the cause of image rotation from 45°rotating scan mirror is analyzed, then the processing method of "45°mirror & K mirror" offsetting image rotation system in the geolocation, including building the coordinate system and calculating the reflection matrix of 45°rotating scan mirror and K mirror, is presented. This model has been applied in FY-3 MERSI's geolocation. The categories of land and water have been searched from global Land Water Mask database according to longitude and latitude. It is proved by the geolocation results that this method can offset the error of image rotation. Finally, the error resources which are produced from "45°mirror & K mirror" offsetting image rotation system in geolocation are discussed.This model is also fit for the geolocation of other remote sensors that use 45°mirror and K mirror and multiple detectors.

Arbitrary Baseline Radar Reflectivity Vertical Cross Section Algorithm

Xiao Yanjiao, Liu Liping, Li Zhonghua

2008, 19(4): 428-434.

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Abstract:
Reflectivity vertical cross section is an effective tool to monitor and analyze severe convection weather and identify convective and stratiform cloud. A one-time request can be issued by the PUP (Principle User Processor) user to the RPG (Radar Product Generator) for the product whose vertical resolution is 0.5 km in new generation weather radar system. But this manner isn't convenient to generate the product from historical volume scan radar data, and its vertical resolution is not high. Therefore, a high-resolution reflectivity vertical cross section algorithm based on volume scan radar data has been developed. The algorithm has three steps. First, a random beeline is drawn by mouse on radar image on computer screen, the distance from radar and the azimuth from the begin-point to the end-point and all the other points with 1 km spacing on the beeline are calculated. Second, the elevation angle, azimuth and slant range of any grid point on reflectivity vertical cross section on the space location in radar polar coordinates is calculated. Last, the analysis value of grid point is obtained by using an objective analysis method. In view of the function of reflectivity vertical cross section for analyzing the three dimension structure of severe convective weather, the reflectivity analysis field obtained by the objective analysis method is required to be spatially consecutive while high-resolution structure comparable to the raw volume scan radar data is retained as much as possible. A linear interpolation in vertical direction combined with a nearest neighbor scheme on range-azimuth planes is used. Two schemes are employed for linear interpolation in vertical direction. In the first scheme, two reflectivities in dBZ of the same azimuth-range bin between adjacent tilts are averaged with distance-weight. In the second scheme, firstly reflectivity in dBZ is converted into reflectivity in mm⁶ /m³. Then two reflectivities in mm⁶/m³ between adjacent tilts are averaged with distance weight. Last, reflectivity in mm⁶/m³ is converted into reflectivity in dBZ again. Through comparison between reflectivity PPI and vertical cross section, it's found that the echo intensity and space position in reflectivity vertical cross section generated using the algorithm is reasonable. Through image continuity examination, it's found that the reflectivity analysis field obtained using interpolation with reflectivity in dBZ is spatially consecutive, but the reflectivity analysis field obtained using interpolation with reflectivity in mm⁶/m³ is inconsecutive in vertical direction. Through comparison between reflectivity analysis values and observations, it's found that reflectivity analysis values obtained using interpolation with reflectivity in dBZ are more close to observations than in mm⁶/m³. Because the space between adjacent tilts in low elevation angles is lesser than that of high elevation angles, the interpolation results in low elevation angles are better than that of high elevation angles.

Concentrations and Size Distributions of Inhalable Particles in Summer and Winter in Shenyang

Yan Wenlian, Zhou Deping, Wang Yangfeng, Yang Jun, Li Zihua

2008, 19(4): 435-443.

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Abstract:
Inhalable particles which refer to particles with aerodynamic diameters less than 10μm are the main pollutants in many cities. They are crucial to human health, visibility of atmosphere and radiation balance, and are also the good bearer of atmospheric chemistry reaction.Some studies about inhalable particles are made in Shenyang, but the studies on the number concentration of the surface layer aerosols and the polluted characteristic are scarce, especially the synchronous observation and research about the number and mass concentration of PM₁₀ and PM_2.5 are not enough. Atmospheric component monitoring station of Shenyang has begun to continuously and synchronously monitor the PM₁₀ and PM_2.5 with ambient dust monitor (Grimm 180) since July 2006. Based on continuous observations of inhalable particles including number and mass concentration data in the atmosphere in August 2006 (summer), in December 2006, and in January 2007 (winter), data are processed by mathematical statistics to obtain the average hourly, daily and seasonal concentration. In order to reveal pollution characteristics of Inhalable Particles in Shenyang, particle spectrum distribution and variations of concentration are analyzed.In addition, the relations to meteorological factors are investigated. Results show that the diurnal and inter-daily variations of concentration are obvious, and diurnal variations of summer and winter both show the characteristics of single peak and single vale. Peak value in summer is earlier than that in winter, but vale value is later. Number and mass concentrations reach the highest point at about 10:00 in winter, and the lowest point is between 13:00 and 14:00. The spectrum distribution conforms to the Junge distribution well, and the average relative error is 9.4%. Number of days that PM₁₀ and PM_2.5 mass concentration is above air quality standards, and is 77% and 87% of total days in winter respectively, and number of days that exceeds third class standard is 43%.The mean number density is 6668.7cm^-3, and the mass concentration reaches 252.8μg/m³, 3.0 and 2.4 times of summer respectively. Average mass percentage about PM_2.5/PM₁₀ of winter and summer respectively are 0.647 and 0.603, PM_2.5 average quantity accounts for over 99%of PM₁₀.Concentration variation has a good connection with wind speed, temperature and relative humidity. The spectrum distribution is different as well as the conditions of the different weather, and the precipitation and snowfall could wipe off aerosol concentration obviously, especially of the high clear rate for the fine particles, and the near ground temperature inversion and fog are important for aerosol increase. The visibility in the city is affected evidently by pollution of the airborne particulate matters.

Characteristics and Maintaining Mechanisms of Sustained Cold-air Outbreak Snowstorm Processes in Shandong Peninsula During December 3—21, 2005

Zhou Shuling, Cong Meihuan, Wu Zengmao, Yan Shulian, Yang Chengfang, Zhu Junjian

2008, 19(4): 444-453.

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Abstract:
The analysis of characteristics and maintaining mechanisms of heavy snow events occurring in Shandong Peninsula during Dec 3—21, 2005 is undertaken using Doppler radar data, FY-2C satellite VIS image, observational station data and NCEP/NCAR reanalysis data. The results show when outbreaks of winter cold air occur from the Eurasian Continent, snow clouds develop over the Bohai Sea.The meso-scale coastal front along the north of Shandong Peninsula is the meso-scale system which causes the sustained cold-air outbreak heavy snow events. The spatial distribution of real precipitation during Dec 3—21, 2005 is different from the north to the south in Shandong Peninsula, and the precipitation per 6 hours on Dec 4 and 7 2005 in Weihai shows the day variation of snowstorms. Doppler radar data show that the reflectivity at 0.5° elevation of the heavy snow-band extends from Bohai sea toward Shandong Peninsula is about 35 to 40 dBz. In the velocity field, the anticlockwise movement of wind vectors with height presents cold air current and a coastal front is studied by analyzing the Doppler radar data also. In reflectivity cross section data, most radar echo tops are less than 3 km. Velocity cross section shows the vertical structure characteristics of the horizontal wind velocity of the snowstorm.The FY-2C VIS satellite image shows the cloud streaks which the alignment of SW to NE is almost perpendicular to the northwesterly wind in the lower troposphere. It shows that there exists a close relationship between the evolution of the circulation over the mid-high latitudes and the heavy snowstorm processes. Once the dry cold air originates from the mid-high latitudes, the heavy snowstorm event develops.There is a weak south-northerly wind area when heavy snow events occur in Shandong Peninsula.The relative humidity is more than 90% between 850 hPa and 750 hPa, and the line of 90% relative humidity change with a wave movement. The snowstorms are in close relationship with the relative humidity. The horizontal convergence distribution at 850 hPa and the updraft along 122°E plays an important role in the spatial distribution of real precipitation. The updrafts and the convergence in the lower layer are the dynamic maintaining mechanism of the snowstorms by analyzing the time-height cross section of vorticity and horizontal divergence from Dec 3 to Dec 21 2005.The difference between sea surface temperature and temperature at 850 hPa over Bohai Sea is more than 20℃, and the distribution of θ_se at 850 hPa shows the convective instability in Shandong Peninsula during the snowstorm processes.

A Case Comparison Between the TRMM Data and Airborne Radar Data in Rainfall Retrieval

Chen Tingdi, Wang Lianzhong, Dou Xiankang

2008, 19(4): 454-462.

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Abstract:
Precipitation radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) is the first spaceborne instrument capable of producing three dimensional structure of rainfall. Information about each individual tropical cyclone (TC) can also be provided by airborne radar. Both airborne and spaceborne radars have a lot in common and their observing data are comparable. But it's difficult to get proper cases with good coincidence to perform significant comparison. Only hurricane Bonnie is selected as a study case. On August 26, 1998, a flight is made by NOAA/P3 plane at 11:30 along the east coast of America, and a close observation on hurricane Bonnie is made by the dual beam airborne radar placed on it. Almost at the same time the TC core is fully observed by TRMM orbits.Before comparing with TRMM, P3 radar data need to be processed. The measured reflectivity factor (Z-field) of P3 radar is corrected for path attenuation using the hybrid dual beam/stereoradar algorithm. The absolute error in the radar calibration is also corrected. The typical sampling time of a hurricane by the airborne P3 radar is about one hour, while it is one or two minutes for the TRMM PR. Therefore, the nearly instantaneous rain pattern observed by the PR may evolve and move during the airborne radar sampling. Such an effect is reduced by restricting the region for comparisons to a domain where the maximum time lag between the two samplings do not exceeding 600 s. Also, the rain pattern is corrected for advection using a model of horizontal tangential speed (V_t) of individual rain cell versus the radial distance to the eye center. Considering different cross range resolution, TRMM is interpolated on the P3 grid.Then a serial of comparisons is made between P3 and TRMM data. Comparisons of vertical cross section of TRMM and P3 corrected reflectivities are given, and the data agree with each other well within the comparison domain. Outside this area, a large part of the hurricane where the time lag between the two samplings exceeds 600 s can't be used for significant comparisons. Point to point comparis ons of all rain, stratiform rain and convective rain show that most of the data points are along the diagonal and have a standard deviation of 3.9 dBz. The associated histogram of differences ΔZ is sharply peaked, the mean difference is 0.7 dBz with a standard deviation of 6.1 dBz. The mean vertical rainfall density profiles retrieved from the P3 and TRMM show they agree with each other very well above 5 km and have a little difference within 2—5 km. All the comparison results show that these data are in good agreement.By comparing the data of P3 and TRMM in hurricane Bonnie, the TRMM results a re validated, so is the hybrid algorithm and also the understanding of TC precipitation field is improved.

Comparative Analysis on Automatic and Manual Evaporation Measurements in China

Shen Yan, Ren Zhihua, Wang Ying, Liu Xiaoning

2008, 19(4): 463-470.

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Abstract:
Automatic Observation System (AOS) has been set up since 2002 and Manual Observation System (MOS) will be substituted gradually. The results show that data quality will be influenced by the changes of either the measurement instrument or the manner. So it is necessary to conduct AOS-MOS parallel observations to determine the discrepancy and correlation. For evaporation observations the difference is great between the manual and automatic observation. In fact manual evaporation is measured once a day at about 20:00, the difference of the two days measurements is the daily evaporation quantity. However, automatic measurements have been implemented to record continuously water surface height which is then used to calculate the hourly and daily evaporation at a given station. It is wanted by many meteorologists to know how much is the difference and the relationship between the amount of evaporation measured by automatic and manual observations and what is the main causes of the difference.There are 130 stations by 2005 conducting evaporation parallel measurements in China. The monthly or annual value is often used for evaporation analysis. Moreover the contrast coefficient is defined as the ratio between automatic and manual value and often used, too. Based on the monthly, annual value and contrast coefficient, various analyses are carried out on evaporation difference arising from two observation systems. The results are as follows: Monthly difference doesn't satisfy normal distribution pattern. The average monthly evaporation a mount observed by automatic way is 5.74 mm (or 5.51%) more than that by manual way. The standard deviation of the difference is 9.02 mm. In the 1050 evaporation comparison observations, 3.33% of data observed in the two ways is identical, 19.71% of data observed by automatic way is smaller, 76.95% of data observed by automatic way is larger. Namely, about 80% of automatic monthly data is greater than corresponding manual ones. Super sensitive of automatic ultrasonic probe and the measurement time discrepancy may be the reasons. When manual amount is small, its associated difference between automatic and manual is large, especially in the Wanyuan station in Sichuan Province. The monthly evaporation by automatic observation is obviously a linear function of that by manual one with the correlation coefficient passing 0.01 significant level test. The annual contrast coefficient is within the range of 1.0 to 1.2, with two high value regions centered at Douan and Nanxian stations in Guangxi and Hunan provinces, respectively. The change of monthly contrast coefficient is similar to bi-parabolic distribution pattern with highest and lowest value in January and June or July, respectively. Meteorological factors influencing the monthly contrast coefficient include the monthly average relative humidity and monthly average wind speed. There is a trend to merge the different kind of data to compose high quality evaporation dataset which deserves further research in the future.

Forecasting Precipitation Experiment with KNN Based on Crossing Verification Technology

Zeng Xiaoqing, Shao Mingxuan, Wang Shigong, Liu Huanzhu

2008, 19(4): 471-478.

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Abstract:
In order to improve objective precipitation forecasting level, non parameter estimate technology is used in research in application and interpretation of numerical prediction products. T213 numerical prediction products from national meteorological center are used as primary data from April to September during 2003 to 2005. By diagnostic analysis and Stepwise Regression, 10—20 factors are selected frommany factors of different levels and various times. The factors from numerical prediction products are well relevant to the rain observation precipitation data. An improved K-nearest neighbor approach (KNN) is used to forecast precipitation and that more than 10 mm at dissimilar area stations from April to September in 2006. In searching K-nearest neighbor process, different types of weather events such as rain free days, drizzle days and moderate rain days, have diverse probability. Then, the different K (K⁺ and K^-) values are computed to match the different weather events. The number of exiting weather event is represented by the value of K⁺. The number of no weather event is represented by the value of K^-. It is reasonable for different weather event to use KNN method. Forecasting and test patterns are selected in turn from history patterns by crossing verification method. Forecasting and test pat terns are replaced by other ones in historical patterns. Until all historical patterns are gone through thoroughly as forecasting and test patterns before an accuracy rate and a summary rate of forecasting are computed. To reduce the rate of miss forecast and to put the main emphasis on accuracy rate and summary rate of forecasting, the values of K⁺ and K^- are continually adjusted. Different accuracy rate and summary rate of forecasting can be computed for different K⁺ and K^- value. The result of tentative forecasting is compared. When both the accuracy rate and summary rate of forecasting are comparatively better, one optimal K is selected from a number of the accuracy rates and the summary rates of forecasting, which are corresponded with optimal K⁺ and K^-. After K⁺ and K_- are chosen, historical patterns are revised. The forecasting and distinguishing value of some stations is computed by comparing the results. To a certain extent, the rate of false forecasting decreases. Based on the forecasting experimentation from April 1st to September 30th in 2006 to forecast 24 hour and 48 hour qualitative prediction of 0 mm and 10 mm precipitation in different area stations, the improved KNN approach obtains a much higher technical score than KNN approach used before. The forecasting results of the improved KNN method are compared with the results of direct model output (DMO) and the result of MOS precipitation prediction. KNN approach gets more technical score than that of DMO and MOS, especially the rate of false forecasting of KNN approach sharply decreases, which is superior to DMO and MOS precipitation forecast, and better than KNN approach used before. It is a useful model for the actual operational forecasting of precipitation.

Application of Cross Wavelet Transformation to Analysis on Regional Climate Variations

Sun Weiguo, Cheng Bingyan

2008, 19(4): 479-487.

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Abstract:
By combining the cross spectrum with the wavelet transform, the cross wavelet transform method is adopted to analysis on variations of regional climate. Compared with the traditional cross spectrum method, more advantages for the correlation analysis of coupling oscillations between regional climate variation and atmospheric circulation system are provided by the cross wavelet transform method. Not only the limitation of the classical cross spectrum method is made up, but also the technical predominance of the wavelet transform method is exerted on displaying the localized distributing characteristics of climate signal in time and frequency space. This method possesses the ability to distinguish coupling signals of two time series and the excellence to describe the distributing of coupling signals in time-frequency space, it can be applied to diagnose and forecast the variations of regional climate in the work of provincial meteorological bureaus. As an example, this method is used to study the associated statistical characteristics and time-frequency correlations between the anomaly series of monthly Arctic Oscillation Indices (ΔI_AO) and monthly precipitation (ΔR), temperature(ΔT) in Henan Province in the last 56 years. The influences of Arctic Oscillation on climate variations in Henan Province are analyzed by means of wavelet cross-correlation coefficient, wavelet coherence spectrum and wavelet phase spectrum. The results show that there are significant correlative oscillations at multi-time scales between the variations of precipitation, temperature in Henan Province and Arctic Oscillation. The wavelet cross-correlations between ΔI_AO and ΔR, ΔI_AO and ΔT on inter-decadal timescale are obviously higherthan on inter-annual timescale in frequency space, and the correlation measure decreases with the increasing of coupling oscillation frequencies. In time domain, positive and negative correlations between ΔI_AO and ΔR, ΔI_AO and ΔT display the staggered distributing characteristics, and the correlation measure varies with the inter-annual and inter-decadal timescale. It is estimated that the negative correlation between ΔI_AO and ΔR, the positive correlation between ΔI_AO and ΔT will be maintained for 1—2 years by the varying tendency of wavelet cross-correlation coefficients. Analysis on the wavelet coherence spectrum shows that the coherent significances depend on the associated statistical characteristics of ΔI_AO and ΔR, ΔI_AO and ΔT in time and frequency space. There are localized distributing characteristics of wavelet coherence and phase in time space. The significant syntonic periods between ΔI_AO and ΔR are quasi-2-year, 3—5-year, 6—8-year and above 20-year timescales, interdecadal correlation distributes in all time space and inter-annual correlations presents at different stages in time space. The significant correlations between ΔI_AO and ΔT are showed on the periods of about 1a, 2—4-year, 6—8-year and above 16-year, the coherent significance increases obviously after 1974 for inter-decadal correlation and it is different for inter-annual correlations at different stages in time space. The cross-wavelet phases of correlative oscillation between ΔI_AO and ΔR, ΔI_AO and ΔT vary with the syntonic frequencies. The phase differences of correlative oscillation on inter-decadal timescale are lager than on inter-annual timescales, and the phase variations are inphase basically before 1975 and inverted clearly after 1975 in time space.It shows that Arctic Oscillation anomalies of inter-annual and inter-decadal timescale have significant influence on climate variations in Henan Province.The relationship and coherent significance between the variations of precipitation, temperature in Henan Province and Arctic Oscillation depend on their associated statistical characteristics in time-frequency space.

Effects of Thermal Forcing on the Local Circulation

Huang Xianlun, Li Guoping

2008, 19(4): 488-495.

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Abstract:
Many factors have impact on local circulation such as surface friction, topography, thermal forcing and so on. Attentions are paid to the spatial and temporal variation of wind, temperature, divergence and vorticity which is at the bottom of thermal forcing. Thermal forcing has effect on surface and atmosphere. In order to conduct research on the effects of thermal forcing on local circulation, based on the two dimension Bossinesq equations of mesocscale incompressibile at mospheric motion including surface heating, a set of perturbation solutions that mainly including perturbations of vertical motion, horizontal motion, pressure and temperature forced by surface heating is obtained. Then the perturbation effects on the local circulation forced by thermal heating, and temporal and spatial variations of the perturbation fields are qualitatively discussed by using dynamics method. The main conclusions are as follows: The intensity of moment turbulence is positive correlation with the thermal forcing, but in stable stratification, it is negative to stability parameter. Under the condition of fixed altitude and time, differential surface heating is beneficial to the formation of horizontal gradient of temperature or horizontal shear of wind, there is ascending motion in the heating center and sinking motion in both sides of heating center. The horizontal wind disturbance, distribution of vertical wind shear and variation of horizontal divergence resulted from surface heating are opposite to those from atmospheric heating. The distribution of horizontal vorticity is caused by surface heating, there is negative vorticity in the west side of heating center and positive in the east side. But for atmospheric heating, there is negative vorticity in both sides of heating center. The variation tendency of horizontal vorticity with time is opposite in the two kinds of heating. A simple physical model can be concluded by researching and analyzing. The horizontal gradient of temperature can be caused by the uneven heating of surface and the structure of wind can be changed, by which divergence, vorticity and vertical shear of wind can be caused. Because of the ascending motion caused by convergence of airflow in the center of heating, it is beneficial to releasing latent heat of condensation in atmosphere. The horizontal wind disturbance, distribution of vertical winds hear and variation of horizontal divergence resulted from atmospheric heating are opposite to those from surface heating. And two symmetry local vertical circulation cells are formed which are the central axes of surface atmospheric heating. The results not only strengthen people's understanding of the mechanism and the rule of local circulation, but also hold the theoretical significance leading to many local circulation problems(such as urban heat island, valley breeze, land and sea breeze and air turbulence)and the influences of thermal forcing on these local circulations.

The Inhomogeneity Test Method of Atmospheric Pressure Sequences Based on Γ-distribution

Wu Biwen, Wen Huayang, Hui Jun

2008, 19(4): 496-501.

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Abstract:
Climate change research is built on the basis of homogeneity sequence data which can reflect the real changes. Therefore the homogeneity and/or the inhomogeneity of the meteorological observation data should be tested before using the data for climate change research. Currently, the main methods of homogeneity test are based on the hypothesis that the data sequences obey the normal distribution. However, in Anhui Province, it is found the average pressure sequence homogeneity test for 23 representative stations from 1961 to 2006 that some sequences are not subject to normal distribution, which can not be tested by the common method based on normal distribution. At the same time, it is found that some sequences obey Γ-distribution (pass the significant level of 0.05 Kolmogorov goodness of fit tests). A new homogeneity test method, Γ-test, for atmospheric pressure sequences is presented, in which the hypothesis should be met at first that the sequence is subject to Γ-distribution. Firstly, some reference stations are used to construct a reference sequence; then the ration sequences of stations which will be the test sequences to reference sequences are gotten; thirdly, the ration sequences are tested by Γ-test sequence homogeneity test; finally, the cause of the inhomogeneity sequences are analyzed by checking the history of the stations.The method is briefly introduced, and the data of Tongcheng are taken as an example, the concrete process of Γ-testing and analysis are given. Furthermore, the result of Γ-test is compared with SNHT which is a widely use method. The results show that the 23 stations can be tested by Γ-test and the accuracy rate reaches 78.3%. In contrast, four stations can not be tested by SNHT and the accuracy only reaches 53.8%. In other words, Γ-test is superior to SNHT in scope and accuracy. Nevertheless, Γ-test also has some problems such as the high computational complexity and missing of some change points. The Homogeneity test results show that the change of barometer height and the station location is the main reason of the significant inhomogeneity of atmospheric pressure sequences in An hui Province.

Modification of Palmer Drought Severity Model Based on Improving Water Loss Pattern and Increasing Sample Stations

Guo Anhong, Liu Weiwei, An Shunqing, Liu Gengshan

2008, 19(4): 502-506.

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Abstract:
After the modification of Palmer Drought Severity Model in 2003, it is found that the soil water loss pattern needs to be improved according to the actual soil water loss process. Also, in order to apply the Palmer Drought Severity Model more practical and more suitable in most arid and semi arid regions in north parts of China, Palmer Drought Severity Model is once again modified from the aspect of optimizing the soil water loss pattern and increasing the sample numbers of modeling stations.From the aspect of soil water loss pattern, in consideration that in most arid and semi arid regions in north parts of China, evapotranspiration will stop when soil water content in 0—20 cm layer is about 5% of available water consumption (C_aw). Thus in the soil water loss pattern in modeling Palmer Drought Severity, it is supposed that the soil water loss in upper soil layer will be no less than 5% of C_aw.Besides Jinan, Zhengzhou, and Taiyuan stations, Qiqihaer station in Heilongjiang Province and Haiyuan station in Ningxia Province are selected and added to the modeling process. Totally 25 stations in north parts of China are used to modify the weight factors (4 new selected stations, in addition to 21 stations in modeling in 2003). The drought index calculated by latest modified Palmer Drought Severity Model is compared with that modified in 2003 and the actual drought and wetting records in history. The result indicates that the latest modified Palmer Drought Severity Model can better evaluate the drought and wetting situations, especially in de scribing the extreme drought and extreme wet development processes, and can be better applied in most arid and semi arid regions in north parts of China.

A Fine-grained, Real Time HPC Resource Management System

Wang Bin, Zong Xiang, Wei Min

2008, 19(4): 507-512.

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Abstract:
In contrast to the rapid development of capability construction, resource management of national meteorological high performance computers is left behind. Absence of operational software in resource management keeps system administrators from having a detailed knowledge of what's going on in national meteorological high performance computers and exerting effective control over resource allocations. Regarding existing problems, a fine grained, real time high performance computer resource management system is proposed. The system is designed to be a real time, fine grained one with cross cluster (Grid) support. The system works closely with CPU hours resources under keen competition. With the introduction of GCU (General Computing Unit), a resource virtualization unit, to measure computing resources, diversities of computing resources in different high performance computer systems are shielded and fine grained uniform quantitative management is enabled by the system. The target users of the system include resource users, leaders of user organizations, resource system administrators, decision makers etc. The system comprises three layers, namely, user interfaces, resource management, and high performance computer systems. Resource management layer, the primary layer, can be divided into resource accounting and allocation manager, Grid plat form, and resource information database. With open source software from supercomputing centers abroad, Grid project funded by MOST, and RDBMS employed, the system has seen an implementation, deployment and experimental running in National Meteorological Information Center. Fundamental functions of resource accounting and allocation management have been implemented, including cluster system job accounting, resource accounts management, management, allocation and query of user and organizations, providing command line interface for users. PostgreSQL database technology is adopted as the resource information database, on which accounts, users, organizations, computer systems, job records, accounting and allocation relation tables are created. The software system has been deployed into the three partitions of IBM high performance computer system, Sunway 32I cluster, Sunway 32P cluster, IBM SP system, working with LoadLeveler, PBS. Information of users on national meteorological high performance computer systems have been sorted and updated, resulting in uniform UID and GID, and inserted into databases. Two layers of management, organizations (projects) and individuals, are established. Computing resources are evenly allocated to user organizations according to 200 percent of the total available resource in terms of GCUs. Only resources allocated to their department can be used by individual users. The validity of resources are set to a season. Overdraft is allowed. Based on partial data collected during experimental run, initial statistical analyses are made to probe resource usage by user organizations and individuals. At present, the high performance computer resource system has been put into operational run and successfully applied to operation management.

Vol.19, NO.4, 2008