应用气象学报

Inter-decadal Variability of the Relationship Between Winter Temperature in China and Its Impact Factors

Li Weijing, Li Yi, Chen Lijuan, Zhao Zhenguo

2013, 24(4): 385-396.

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Abstract:
The inter-decadal variation characteristics of winter temperature in China and its key impact factors are analyzed by using monthly temperature data of 160 stations in China, NCEP/NACR reanalysis data, extended reconstructed sea surface temperatures data, and Arctic sea ice extent data from 1951 to 2012, focusing on the inter-decadal changes of the relationship between key influencing factors and winter temperature in China. Results show that the winter temperature in China before 1985 is in a cold period, and then a warm period follows. A significant inter-decadal variability has occurred for winter temperature anomalies. The scope and intensity of warming tendency has weakened significantly from 2004 to 2011.The main diagnostic analysis conclusions are summarized as follows. The majority of impact factors of winter temperature anomalies in China shows significant inter-decadal shift from 1970s to 1980s, most of which changes ahead of that of winter temperatures in China, such as Arctic Oscillation (AO), the East Asian winter monsoon (EAWM), Western Pacific subtropical high (WPSN), Arctic sea ice cover in September, and Niño3 SST index. But the inter-decadal variability of Siberian High (SH) and the basin-wide SSTA variation in the tropical Indian Ocean (IOBW) has the same pace with that of the winter temperature. The inter-decadal variability of relationship between winter temperature and its impact factors have changed on temporal and spatial scales. On temporal scale, the relationship between the winter temperature and IOBW index has weakened significantly from cold to warm period. But the influences of EAWM index, SH index and the WPSH area index on winter temperature have strengthened. On spatial scales, distributions of correlations between winter temperatures and affecting factors have changed from cold to warm period. The high correlation coefficient regions between EAWM and winter temperature have enlarged significantly. The correlation coefficient between AO index and winter temperature is negative in central-southern China in warm period. The inter-decadal variability of relationship between the impact factors has changed, the relationship between EAWM index and tropical SSTA in winter are significantly weakened from cold to warm period.Based on the basic facts of inter-decadal variations, a multi-factor regression prediction model of winter temperature can be established respectively in cold and warm period. This regression prediction model can reflect inter-decadal characteristics of relationship between the winter temperature and its impact factors. Such strategy may keep the stability and effectiveness of the prediction skill for winter temperature in China.

Modulation Effect of MJO on the Precipitation over Guangdong and Its Link with the Direct Impact System in June

Lin Ailan, Li Chunhui, Zheng Bin, Gu Dejun

2013, 24(4): 397-406.

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Abstract:
A distinguishing method of 500 hPa circulation systems influencing Guangdong is established, and the changes in modulation effect of MJO on the precipitation over Guangdong with the low latitude 500 hPa circulation system in June is analyzed using 30-year (1979—2008) 86-station observational daily precipitation of Guangdong and daily atmospheric data from NCEP-DOE Reanalysis 2. It is found that each phase of strong MJO may correspond to various levels of precipitation, of which the third phase has the highest probability of heavy precipitation (49.3%). The third phase is the only phase among 8 phases of MJO that strong precipitation days outnumber weak precipitation days. The 500 hPa circulation systems in low-latitude impacting Guangdong directly mainly include westerly trough, shallow westerly trough, flat westerly or border of subtropical high, subtropical high and tropical low or trough. The most strong modulation effect of MJO on the precipitation over Guangdong occurs in the case impacted by westerly trough, while the modulation effect is quite weak in the other cases. The precipitation anomaly percentage averaged over Guangdong is peak (valley) in the third phase (the sixth phase) under the case impacted by westerly trough. The changing in modulation effect of MJO on the precipitation over Guangdong with the low latitude circulation system is substantiality due to the changing of dynamic ascending motion and the water vapor transport, both of which are necessary for rainfall. In the westerly trough case, the subtropical high is strong and westward, water vapor transport to Guangdong increases significantly, and the dynamic ascending motion and high level divergence conditions are also enhanced, which results in Guangdong precipitation strengthening in the third phase of MJO. But in the sixth phase of MJO, the subtropical high is weak and eastward, water vapor transport to Guangdong decreases significantly although the dynamic ascending motion is enhanced, leading to weaker precipitation than that in the third phase of MJO. However, in the case without westerly trough, although water vapor transport to Guangdong increases in the third phase of MJO, the geopotential height anomaly is positive over East Asia and Western Pacific, therefore the dynamic ascending motion is reduced, so the precipitation is not much stronger than the other MJO phases. Therefore, the modulation of MJO on the precipitation over Guangdong needs the cooperation of westerly trough. The direct impact of westerly trough and remote correlation effect of the third phase of MJO are good prediction indicators for large domain heavy precipitation over Guangdong.

Preliminary Estimation of Specific Humidity Profiles with Wind Profile Radar

Sun Kangyuan, Ruan Zheng, Wei Ming, Ge Runsheng, Dong Baoju

2013, 24(4): 407-415.

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Abstract:
As a new type of detection instrument, wind profile radar (WPR) can detect meteorological factors such as wind profiles, spectral width, and refractive index structure constant and so on. The special detecting ability of WPR decides its broad application in atmospheric science research, meteorological operation application, climate research, aviation security and many other areas. With the advances of detection, a new specific humidity profiles retrieving method with WPR is proposed.Based on the turbulent backscattering theory, the method of estimating specific humidity profiles using boundary layer wind profile radar characteristics of clear-air echoes is devised. A retrieving test of specific humidity profiles are carried out with the data of observational campaign conducted from 15 Aug to 10 Sep in 2011 at a meteorological station of Dali, Yunnan Province, analyzing the main factors of retrieving accuracy. In the low atmosphere the refractive index gradient (M) is mainly influenced by three factors: dq/dz by 80.39%, the atmospheric temperature (T) by 12.75%, and the specific humidity q by 6.86% on average, respectively. Obviously, the dq/dz item is the most important factor, namely, there is a close relationship between the refractive index gradient and specific humidity.It is the measurement of refractive index gradient that turns out to retrieve specific humidity profiles with the help of WPR. The volume reflectivity (η) of turbulence echoes can indicate the fluctuation of atmosphere specific humidity due to the good correlation with M. Another factor that matters is the atmospheric turbulence dissipation rate which is under the influence of the signal spectral width observed by WPR. Radio Acoustic Sounding System (RASS) provides virtual temperature in retrieving of specific humidity profiles with the measurement of acoustic speed; PWV from GPS provides a method to obtain the initial boundary specific humidity; estimation of specific humidity profiles comparing with radiosonde data at the same time is conducted with WPR, RASS and GPS data.Results show that WPR can successfully retrieve specific humidity profiles with a certain degree of error. Among many factors that affect the retrieving accuracy, the determining of the sign of M, the refractive index structure constant and turbulence spectral width plays the key role, while the temperature and pressure are not so important. This new method can retrieve specific humidity profiles simply with the remote sensing instruments. The specific humidity retrieving from WPR, temperature profilers and initial boundary specific humidity from radiosonde shows the same trend comparing with which observed by radiosonde. The mean deviation and standard deviation turns out to be 0.75 g·kg^-1 and 0.8 g·kg^-1 respectively, both showing an increasing trend with height. With the assistance of WPR, GPS/PWV and RASS data, the retrieving mean deviation and standard deviation of specific humidity is 0.64 g·kg^-1 and 0.85 g·kg^-1 comparing with the observation of radiosonde.

The Experiment of Hydrologic Probabilistic Forecast Based on the Precipitation Forecast Calibrated by Bayesian Model Averaging

Liang Li, Zhao Linna, Qi Dan, Wang Chengxin, Bao Hongjun, Zhang Yujie

2013, 24(4): 416-424.

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Abstract:
Based on 24-h accumulated precipitation data of the Huaihe Basin from 1 June to 31 August in 2008 and the corresponding ensemble forecast of 24 h, 48 h, 72 h from T213 model, the method of Bayesian Model Averaging (BMA) is used to calibrate quantitative precipitation forecasts of 15 members from the ensemble forecast based on the training data of 30 days. The calibrated results are verified by continuous ranked probability score (CRPS) and mean absolute error (MAE). Second, the Dapoling—Wangjiaba Catchment in the upper stream of the Huaihe River, which is subdivided into Dapoling—Xixian Catchment and Xixian-Wangjiaba Catchment, is investigated with the hydrological simulation experiment. The Xixian and Wangjiaba hydrologic stations in the upper stream of the Huaihe River are selected as representative stations. The rain process occurring from 23 June to 3 August in 2008 is investigated to simulate the runoff tendency. Then, the 25th and the 75th percentiles of 24-h, 48-h and 72-h precipitation ensemble forecast which are calibrated by BMA are used to force the Variable Infiltration Capacity (VIC) hydrological model respectively to obtain the corresponding runoff, and finally the simulate results are analyzed comparing with daily runoff observations.Results show that the precision of 24-h, 48-h, 72-h precipitation forecast of BMA model is improved after the calibration. The raw ensemble forecast of 24 h is calibrated well by BMA model. As the leading hours increase, the calibration of 48 h and 72 h is as good as that of 24 h. Although BMA calibrates on the raw ensemble forecast, the improvement of calibrated forecast depends on the accuracy of raw ensemble forecast. The valid interval given by BMA model, namely the interval from the 25th percentile to the 75th one of ensemble forecast, is more likely to contain the true value of observations according to the verification analysis of hydrological probabilistic forecast. From this aspect, the performance of BMA forecast outperform deterministic forecast. It can improve the accuracy of forecast and reduce the error by BMA, describing forecast uncertainty in the form of a probability distribution. Known from the analysis of verification index of hydrologic probabilistic forecast, it shows that the hydrological simulation forced by the calibrated precipitation is almost consistent with the runoff tendency of observations. It is effective to grasp the trend of runoff change. It indicates that the precipitation forecast calibrated by BMA can be established coupling with the VIC hydrological model as well as increasing the forecast accuracy significantly. It can meet the more and more objective, quantitative needs of decision-making service, and improve the benefit of weather forecast greatly.

Influences of Sensitive Initial Error on the Numerical Forecast of Typhoon Kammuri (0809)

Huang Jiangping, Dong Peiming, Li Chao, Liu Jun

2013, 24(4): 425-434.

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Abstract:
Initial error is one of the key factors that have great effects on the accuracy of numerical forecast. To study the characteristics of initial error and its influence on the numerical prediction, an analysis procedure of the sensitive initial error of numerical forecast is developed based on WRF adjoint model and is used in the investigation of typhoon Kammuri (0809). The validity of the linear assumption on the study of typhoon case is firstly assessed prior to discussing any adjoint analysis results. It is done by evaluating the evolution differences of the perturbation between linear and nonlinear development, showing that the nonlinear perturbation evolution is well represented by the linear assumption during 24-h forecast. The sensitive initial error is then constructed using the information derived from adjoint sensitivity analysis, finding that the reference coefficient from 0.01 to 0.08 is proper to build the sensitive initial error. The result of 0.08 is the best in this case study. The numerical forecast error could be reduced and the prediction bias of typhoon trace could be improved greatly by removing the sensitive initial error from the initial field. This effect of the sensitive initial error derived from 24-h numerical forecast error affects the numerical forecast even within 60 hours. In addition, the analysis reveals that the sensitive initial error of regional short-term numerical forecast concentrates mainly around the weather system. It goes with typhoon circle and the pattern is almost consistent for all physical variables. The sensitive initial error in the middle-upper troposphere has slightly more contribution to the forecast than that in lower troposphere. Comparing the contribution of different physical variable, it is found that wind is the main contributor with pressure and humidity following.

Assimilation Experiment of LIS Based on AMSR-E Soil Moisture Products

Yang Xiaofeng, Lu Qifeng, Yang Zhongdong

2013, 24(4): 435-445.

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Abstract:
Soil moisture is an important part of the soil, playing an important role in energy and mass exchange between land and atmosphere. It is an important environment factor and the process parameter of hydrology, meteorology and other researches. In order to accurately depict and understand the interaction between land and atmosphere, precise and high resolution soil moisture contour information is needed. But whether using the objective measurement or numerical prediction of land surface process simulation, soil moisture contour line with spatial-temporal continuum and good precision can't be obtained. In order to eliminate the error, data assimilation method (EnKF) is used to process passive microwave inversion products (AMSR-E) and land surface model (NOAH) outputs, and then shallow soil moisture information is transmitted to deeper soil layers by land assimilation system (LIS). These methods are used to calculate soil moisture with high precise, high resolution and low error. Through these methods, 4-layer (10 cm, 30 cm, 60 cm, 100 cm) soil moisture data with spatial resolution of 0.25° by 0.25° for the year of 2003 are obtained.Agro-meteorological-station soil moisture data and ecological-station data are used to verify the 4-layer soil moisture results. The simulation accuracy of the land surface model is improved when data assimilation method is used, the simulation accuracy in different layers is different, and the accuracy in the grassland ecosystem is higher than that in crop and forest ecosystems. The spatial characteristics of assimilation results match with real values, which is high in the southeast and low in the northwest. Assimilation soil moisture data has more detailed information in horizontal scales compared to station data and has more detailed information in vertical scales compared to the passive microwave inversion products.The accuracy of the assimilation process depends on the passive microwave inversion products (AMSR-E). However, AMSR-E has stopped running and inversion errors of passive microwave inversion products will be accumulated in data assimilation run. In order to solve these problems, passive microwave inversion products of FY-3B can be used experimentally. Besides, assimilation experiment can be started by directly assimilate radiation brightness temperature of microwave channels. Simulation accuracy of soil moisture can be further improved through these processes. Effect of assimilation experiment is different in different vegetation, which mainly depends on capabilities of land surface model. Therefore, improving the land surface model is also an effective means to improve soil moisture simulation accuracy.

Current and Electromagnetic Field of M Component in Triggered Lightning

Xiao Tong, Zhang Yang, Lü Weitao, Zheng Dong, Zhang Yijun

2013, 24(4): 446-454.

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Abstract:
Based on data obtained in the triggered lightning at Conghua, Guangzhou during the period of 2008—2010, the characteristics and correlations of base current and electromagnetic field of M component are analyzed.Lightning M components are transient enhancements in the continuing current and in the associated channel luminosity after the return stroke. A typical M component is characterized by a more or less symmetrical current pulse at the channel base. The M component characteristics of each charge is examined using multiple station measurements of electric and magnetic fields at distances of 80 m, 2 km and 9 km from triggered lightning channels, respectively. Different bandwidth between the current and the electromagnetic field could lead to the differences between different data waveform, affecting the accuracy of the extracted parameters. Furthermore, the relation between the current and the close electromagnetic field is complex since it includes the static field, the induction field and radiation field. The ranging from 500 Hz to 20 kHz band pass filter is designed to filter these data, in order to obtain the valid data within the bandwidth of the M component.Results show that the geometric mean values of duration, 10%—90% rise time, decline time and half-peak width for electric field waveform of M component are 0.49 ms, 0.12 ms, 0.28 ms and 0.15 ms, respectively. The geometric mean values of duration, 10%—90% rise time, decline time, half-peak width and peak for current waveform of M component are 0.53 ms, 0.11 ms, 0.31 ms, 0.17 ms and 0.34 kA. The geometric mean values of duration, 10%—90% rise time, decline time, half-peak width and peak for magnetic field waveform of M component are 0.65 ms, 0.16 ms, 0.37 ms, 0.21 ms and 2.76×10^-5 T.In addition, the following relationship exists between the current, electric field and magnetic field waveform of M component. The correlation coefficient of duration, 10%—90% rise time, decline time, half-peak width, peak between the electric field and current are 0.64, 0.69, 0.39, 0.77 and 0.86, respectively. The coefficients between the magnetic field and current are 0.62, 0.86, 0.55, 0.76 and 0.93, respectively.In summary, there is a relatively strong correlation between the peaks of current and electromagnetic field waveform, and their geometry is comparable. As a result, the current waveform of M component can be calculated by the electromagnetic field data.

The Relationship Between Power Load and Meteorological Factors with Refined Power Load Forecast in Shanghai

Liu Hongya, Cao Liang

2013, 24(4): 455-463.

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Abstract:
The forecast value of power load is an important reference for the power dispatch, and meteorological conditions have a significant impact on the diurnal and seasonal variation of the power load. Therefore, power load data of every 15 minutes in Shanghai and observations of Baoshan weather station (ID:58362) every 3 hours from 2004 to 2008 are analyzed to study the correlation. It's found that the meteorological power load is most closely related to the temperature. When the daily mean temperature (DMT) is great than 25 ℃, the daily mean meteorological power load rate (DMMPLR) is positive, DMMPLR increases with the increasing of DMT; while DMT is great than 18 ℃ and less than 25 ℃, DMMPLR is negative, DMMPLR increases as the DMT rises too; when DMT is between 6 ℃ and 18 ℃, DMMPLR is negative, DMMPLR decreases with the increasing of DMT; and while DMT is less than 6 ℃, DMMPLR is positive, the magnitude of changes with DMT is slightly. Moreover, the characteristics of power load diurnal variation curve display significant differences in different temperature ranges or under different weather types. Taking the summer season (T≥25 ℃) as an example, the peak of power load rate appears around 1100 BT in rainy-day, appears at about 1400 BT in the day with rainy-afternoon, and appears in the afternoon in the day with sunny-morning; the diurnal variations of hourly mean meteorological power load rate (HMMPLR) are basically the same in the day with rainy-morning or overcast-morning, suggesting that precipitation is not very important, but the sky condition has the main influence.Stepwise regression method is adopted to get the prediction equations of DMMPLR in each temperature range, and then the forecasting values of HMMPLR, under different weather types, calculated by multiplying the statistics coefficients (HMMPLR/DMMPLR) obtained in advance. The forecast test results in 2009 show that, using the 3-day average (before the forecast date) of the trend power load as the trend power load of the forecast date, the mean of absoulute relative error (MARE) of daily mean power load forecast value (DMPLFV) is about 3.6%. The MARE of DMPLFV of non-working days is larger than that of working days. In working days, while DMT is greater than 18 ℃, the MARE of DMPLFV is lower, when DMT is less than 18 ℃, the MARE of DMPLFV significantly increases. The MARE of hourly power load forecast value is about 4%.

Developing of Beidou Radiosonde System and Analysis on Its Wind Measuring Performance

Zhang Enhong, Cao Yunchang, Zhu Bin

2013, 24(4): 464-471.

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Abstract:
As an important constituent of the integrated meteorological observation system, the upper air meteorological observations have extremely important effects on weather forecast, climate change research and other work, and it plays an irreplaceable benchmark function in atmospheric remote sensing observation authenticity verification and calibration of testing. The development of Beidou radiosonde and the ground receiving system is based on Beidou Satellite Navigation System with completely independent intellectual property rights, and the prototypes are assembled. By the end of 2012, Beidou Satellite Navigation System can provide preliminary service with 14 satellites in orbit, including 5 Geostationary Earth Orbit (GEO) satellites, 4 Medium Earth Orbit (MEO) satellites and 5 Inclined Geosynchronous Satellite Orbit (IGSO) satellites in 3 inclined orbits. On this basis, Beidou radiosonde is examined, and comparative analysis are carried out on its different patterns of wind measuring, i.e., single Beidou, single GPS and mixed mode. The results show that the wind measuring performance of Beidou and GPS radiosonde is quite close. The deviation of Beidou radiosonde compared to the GPS radiosonde is as follows: The standard deviation of the north velocity is 0.05 m·s^-1, the average deviation is-0.05 m·s^-1, the standard deviation of the east velocity is 0.03 m·s^-1, the average deviation is-0.01 m·s^-1, the height standard deviation is 6.88 m and the average deviation is 7.48 m. The PDOP value in single Beidou mode is large compared to GPS radiosonde and the accuracy of positioning is poor, because the current constellation is not fully deployed. Beidou radiosonde performance is relatively stable in the lower atmosphere, but a violent wave happens in the high level atmosphere, which means that the stability of the national dual-mode chip and module needs improving.

Datasets and Rain Gauge Precipitation over Yunnan and the Surrounding Areas

Wang Fen, Cao Jie, Li Fuguang, Tang Haopeng

2013, 24(4): 472-483.

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Abstract:
The precipitation over Yunnan and the surrounding areas are analyzed from spatial and temporal distributions aspects using several datasets, including data from meteorological stations, APHRO data from Asian Precipitation-Highly Resolved Observational data integrations towards evaluation of water resourced, GPCC data from Global Precipitation Climatology Center, CRU data from Climatic Research Unit, CMAP data from CPC Merged Analysis of Precipitation, and GPCP data from the Global Precipitation Climatology Project. Assessments are carried out to examine the quality of APHRO, GPCC, CRU, CMAP and GPCP precipitation in Yunnan and the surrounding areas from space distribution, inter-annual and monthly variation.Five grid precipitation datasets show similar distribution of precipitation amount to station data, which can reflect the distribution characteristics of spatial distribution of precipitation. There exists the maximum horizontal gradient center in the south of Yunnan, but CRU, CMAP and GPCP cannot represent it. The EOF analysis results of the five datasets show similar spatial distributions of precipitation amount to station data, the first eigenvector space distribution is positive, but in the northwest of Yunnan and the south of Sichuan is negative. The first eigenvector in January is basically positive, but in July, it is negative in the southeast and southwest of Yunnan, the south of Sichuan, and that of other regions is opposite. APHRO and GPCC distributions of positive and negative value are consistent with those of STN, there is a significant difference between the spatial distribution of CRU, CMAP and STN, negative area is not seen in January and July, GPCP is more significant different compared with STN. Correlation coefficients of five precipitation dataset to STN have better consistency, and for most regions, correlation coefficients pass the test of 0.05 level, the correlation coefficient in January is higher than that in July, and the mean square error in July is higher than that in January. APHRO and GPCC underestimate the trend of precipitation, but the weak amplitude of GPCC is less than APHRO, GPCP precipitation estimation is significantly higher, which reaches the highest 18.73% in April, the trend of CRU and CMAP is not very clear.Above all, the application effects of five precipitation datasets in south of Yunnan, northwest of Yunnan, boundary of Yunnan, Guizhou and Sichuan, and boundary of Yunnan, Guizhou and Guangxi are poor, waves of five precipitation datasets in EOF leading time series, correlation coefficients and mean square error is coincident, integral application effect of APHRO is the best, with GPCC, CMAP and GPCP followed, but CRU is the worst in terms of spatial distributions, correlation coefficients and square errors. In terms of the leading modes, the first-three-variance contribution of APHRO is the lowest, then is GPCC, CRU, CMAP, GPCP, the difference in the second mode is not clear, APHRO and GPCC data underestimate, but CRU overestimates the intensity, and GPCP overestimates the trend largely. When the precipitation become larger, the trends is more clear.

Spatial-temporal Characteristics of Urban Heat Island in Typical Cities of Anhui Province Based on MODIS

Shi Tao, Yang Yuanjian, Ma Ju, Zhang Li, Luo Sufeng

2013, 24(4): 484-494.

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Abstract:
Anhui Province is a place with great economic development and potential that lies in the hinterland of the Yangtze River Delta. The topography and climate of Anhui Province present obvious variousness, which can be divided into three natural regions: North China plain, Jianghuai hills and mountain areas of south Anhui. Anhui Province covers an area of 139600 km². The population of Anhui Province reaches 68.62 million by the end of 2010. Since the 1990s, great changes have happened in Anhui Province, e.g., the tremendous growth of urban sprawl, population, vehicles and economy. In recent years, great increase in urban heat island (UHI) intensity also takes place in the areas with the most rapid urbanization due to fast economic growth and the increasing desire of people for an urban lifestyle. Hefei, the capital of Anhui Province, locating between the Yangtze River and the Huaihe River with hilly terrain, the non-rural area population and urban built-up area of which reaches 1800000 and 326 km² in 2010, respectively. Wuhu, the economic center of southern Anhui, locating to the south of the Yangtze River with mountainous terrain, the non-rural area population and urban built-up area of which are respectively 950000 and 135 km² in 2010. Fuyang, the economic center of northern Anhui, locating to the north of Huaihe River with a flat sub-layer, the non-rural area population and urban built-up area of which are 490000 and 76 km² in 2010, respectively. Land surface temperature (LST) retrieved from MODIS data is used to explore the characteristics of urban heat island (UHI) in Province during 2001 to 2010. Considering some factors (climate, geography and urbanization), three cities mentiened above are first selected to study the UHI. Moreover, diurnal and seasonal variations of LST in these cities are captured by MODIS with GIS technology. Finally, spatial-temporal characteristics of urban heat island are analyzed in representative cities of Anhui Province. The result shows that the heat island effect of Hefei is the most significant. The intensities of UHI in representaty cities of Anhui is stronger in the south area than in the north. Especially, diurnal and seasonal characteristics presented significantly. In recent 10 years, the UHI area and UHI intensity in representative cities maintain increasing tendency, while the extreme UHI intensity (more than 3 ℃) has a weaker enhancement in Hefei. Large bodies of water have a significant role in weakening the city heat island effect in daytime, while have no impacts on UHI effect in nighttime, even becoming high value center of LST. LST and NDVI show significant negative correlation in summer, so it is very important for improving vegetation coverage of the city to reduce land surface temperature and weaken the effects of UHI.

Characteristics of Shaanxi Summer Precipitation Anomalies in ENSO Developing and Decaying Stages

Zhao Qiang, Yan Huasheng, Cheng Lu

2013, 24(4): 495-503.

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Abstract:
Based on Shaanxi summer precipitation data from 1961 to 2008, NCEP/NCAR monthly reanalysis data, the influence of developing stage and decaying stage of ENSO events on Shaanxi summer precipitation is analyzed through composite analysis. It shows that the response of Shaanxi summer precipitation to ENSO in developing stage is very different from that of the decaying stage. During El Niño developing stage and La Niña decaying stage, the precipitation in Shaanxi is less than normal. During La Niña developing stage and El Niño decaying stage, Shaanxi has more precipitation than normal, and the most significantly impacted period by ENSO is July. The response of Shaanxi summer precipitation anomalies to La Niña developing stage and El Niño decaying stage is more remarkable than that of El Niño developing stage and La Niña decaying stage. There is a significant difference in atmospheric circulation in developing and decaying stages of ENSO, especially with regard to the western Pacific subtropical high and the East Asia monsoon strength. During El Niño developing stage and La Niña decaying stage, the western Pacific subtropical high is stronger and more west than normal and the East Asia monsoon is weaker than normal. During La Niña developing stage and El Niño decaying stage, the situation is the opposite. When the subtropical high is stronger and further west, Shaanxi has southwest wind anomalies which transport water vapor, the northern part has the north wind anomalies that bring cold air, and the precipitation would be higher. ENSO developing and decaying stages affect on the change of atmospheric circulation and the East Asia monsoon, and contribtute to Shaanxi summer precipitation. During El Niño developing stage and La Niña decaying stage, the East Asia monsoon is stronger, and Shaanxi has less precipitation. During La Niña developing stage and El Niño decaying stage, the East Asia monsoon is weaker and Shaanxi has more precipitation. In comparison, the East Asia summer monsoon is greatly affected by El Niño events than La Niña events. At the same time, Shaanxi summer precipitation is also affected by El Niño events more greatly. This is an evidence that ENSO affect Shaanxi summer precipitation through changing the East Asia summer monsoon strength.

Nowcasting & Warning Operational System in the Middle Reaches of the Yangtze with Its Implementation

Wan Yufa, Wang Zhibin, Zhang Jiaguo, Wu Cuihong, Wu Tao, Wang Jue

2013, 24(4): 504-512.

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Abstract:
In order to meet the need for modern operational forecasting of severe storm events in the middle reaches of the Yangtze, MYNOS (Nowcasting & warning Operational System in the Middle reaches of theYangtze), an advanced and useful nowcasting system, is originally established in 2007 based on the experiences of the advanced nowcasting systems Auto-Nowcaster and WDSS-II of USA and GANDOLF of UK. MYNOS combines the resources of new generation radar network in China with the data from numerical weather prediction. Several advanced techniques and methods are developed and adopted as follows: Quality control of radar reflectivity field and the precipitation echo classification are achieved by identifying the structures of the vertical gradient and horizontal textures of radar reflectivity echoes. Real time formation technique of vertical reflectivity profile (VPR) is developed and used for vertical calibration of precipitation reflectivity factor. Important concepts of "quasi same-rain-volume sample" and "hourly equivalent reflectivity factor" are proposed, and the synchronously integrated method of radar and rain gauge (RASIM) is established. The cell gravity potential energy, as an important physical component of radar for describing the life span of storms, is proposed. The technique for automatic identification and tracking of severe weather is developed by means of radar derived parameters and the meso-scale output of physical parameters. The multi-scale characteristics of storm echoes through their life courses are analyzed and the echo filtering technique is studied, and the multi-scale precipitation nowcasting confined to the life time of each scale echo is realized. Potential forecasting products for severe convection meteorological phenomena (torrential rain, hail, thunderstorm, etc.) are developed based on numerical models and fuzzy logics. The problem of image registration and animation in ordinary GIS (Geographic Information System) is solved by introducing custom layer, and the nowcasting workstation equipped with the function of GIS along with numerical prediction, radar, satellite, lightning data and various quantitative monitoring, forecasting and warning products is developed from the bottom. MYNOS is put into operational experiments in May 2006 and has been in concentional operation since the flood season of 2007. The real-time generated output of MYNOS, such as valley quantitative precipitation estimation and nowcasting, strong convective weather classified potential diagnosis and identification warning products, provide an important foundation and reference for routine nowcasting operation.

Vol.24, NO.4, 2013