应用气象学报

The Interdecadal Variability of Summer Precipitation over North China

Liu Haiwen, Ding Yihui

2011, 22(2): 129-137.

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Abstract:
Based on the daily precipitation data from 740 stations and NCEP/NCAR reanalysis daily datasets, the interdecadal variability and their causes for summer rainfall over North China are analyzed by means of composite analysis method.Interdecadal variability of rain belt is found closely related with the decrease of rainfall over North China after 1978. Meanwhile, the rain belt over eastern China also has a significant interdecadal variability in summer. In wet period of summer over North China, there is a broader area with smaller amount of precipitation between the northern and southern rain belt in eastern China. But in dry period of summer, the area becomes smaller. In wet period, the rain belt over North China can extend westward to 115°E at most time and nearly reaches the west boundary of North China. However, in dry period, the precipitation amount is much smaller. And the rain belt can hardly maintain to the west of 115°E not to mention 110°E, so the stretch of westward of rain belt over North China is not obvious.Interdecadal variability of atmospheric circulation and East Asia summer monsoon are the direct cause of interdecadal variability of rain belt over North China in summer. In wet period, anomalous southerlies from the sea develop into convergence with upward motion under the influence of the terrain, and the anomaly high pressure over the Bohai Bay urges the rain belt over North China to extend westward. However, in dry period, the anomalous northerlies develop into divergence and anomalous downward motion, which are not favorable for the westward extension of rain belt over North China.

Threshold Values on Extreme High Temperature Events in China

Li Qingxiang, Huang Jiayou

2011, 22(2): 138-144.

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Abstract:
The threshold values are very important to define the indices of extreme climate events. Usually, the 90 percentile threshold value is used as the threshold values of extreme high temperature events, while the specific methods of categorization and calculation lead to different threshold values. In order to find the most suitable method, the quality controlled and homogenized daily maximum temperature data in China for the period of 1951—2008 are checked, and some missing data are reconstructed. Analysis is conducted using a new data for 1961—2008 in 224 selected stations. The preliminary analysis shows that the daily data series of most stations are not fit for normal distribution as generally believed. Based on the analysis above, the comparison for the threshold values falling into the percentiles of the extreme events of maximum temperature is accomplished using three different methods (including two traditional methods of calculating threshold values based on the assumed normal distribution and a new method by which the threshold values are calculated based on the sample probability distribution).The results show that the evaluation of the threshold values on the method using the real sample frequency distribution to simulate the probability distribution (the new method) has got the best results than using the other traditional threshold values calculating methods. Based on the comparisons, the threshold values of extreme events of maximum temperature in China have been developed with the 30-year sample climate phase. The following inspection shows the threshold values can reflect the real threshold values on the maximum temperature in daily use, and they are more stable and representative. In addition, the distribution charts of the threshold values developed by the different methods are drawn, and it's found that except for in Southwest and Northeast China, Qinghai, Inner Mongolia, the threshold values of extreme high temperature events for most part of China are all above 35 ℃, which proves that it is reasonable of using the threshold 35 ℃ as the standard of high temperature disasters.

Characteristics and Evolutions of Probability Distribution of Summer Extreme High Temperatures in China

Zhou Yun, Qian Zhonghua, He Wenping, Feng Guolin

2011, 22(2): 145-151.

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Abstract:
In view of the non-normal distribution existed in summer extreme high temperature (SEHT) in China, a skewed probability distribution function is proposed to study the SEHT, which derived from Box-Cox Transformation of SEHT data. Based on a skewness index (SI) and the most probable extreme high temperature (MPEHT), the characteristics and evolutionary rules of the probability distributions in the SEHT are described before and after 1980s. The results show that from 1961 to 2008, the probability distributions of the SEHT at most meteorological stations are positive skew, and particularly in the southeastern Southwest China. While the probability distributions show negative skewness in most areas of the south to the middle and lower reaches of the Yangtze River. The highest magnitudes of the SEHT lie in the central-eastern China and the western Northwest China, secondary magnitudes lie in Northeast China and most of Inner Mongolia, and the smallest magnitudes in the central Northwest China and most parts of Southwest China.Before and after 1980s, the probability distribution changes greatly in most parts of central-eastern China, central Southeast China, most of Xinjiang, and northeastern Inner Mongolia, respectively. The results indicate that there are some weakening trends for both positive skewed distribution pattern and negative skewed distribution pattern, and the MPEHT has a common trend to approximate the mean values of the SEHT, which show that the changes of the distribution patterns can reflect some change direction of the MPEHT. There is a significant cooling trend in those areas especially for the MPEHT, while in the secondary or smallest magnitudes regions, obvious warming trend is found.Further study on the responses of SI and MPEMT to different time scales of SHET suggests that sliding removing some sequential SEHT has influences on SI and MPEMT.The SI is affected obviously to south of the Yangtze River, but changes relatively less in other areas. The larger time scale of SEHT is removed, the more significant impact appears on the probability distribution. MPEMT nearly remains the same when removing different time scale of SHET, so it is a relatively stable value, and can be regarded as a possible new way to define a threshold of extreme high temperature events.

The Application of AOD's Spectral Curve Parameter to Judgment of Aerosol Particle Size

Yang Su, Shi Guangyu, Wang Biao, Yang Honglong, Zhao Jianqi, Qin Shiguang

2011, 22(2): 152-157.

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Abstract:
Aerosols play important roles in earth's climate system by scattering and absorbing radiance and changing surface radiation budge, so they are recognized as one of the most important factors inducing global dimming during 1960 to 1990. On the other side, aerosols can also act as cloud condensation nuclei, changing the optical and micro-physical property, altering hydrological cycle. The aerosol particle size is an important factor which could determine the aerosol physical and optical characteristic, so the knowledge of the particle size information is an urgent and necessary job for aerosol research. Angstrom exponent (α) is a convenient parameter for describing particle size, in general, as α < 1.0, it means coarse particle is dominant; as α > 1.0, it means fine particle is dominant. However, this application is based on Angstrom power law which is just valid for the Junge size distribution, not suitable for all environments and locations. Improper application would introduce considerable uncertainty and lead to misunderstanding. Fortunately, previous measurements note that when the aerosol doesn't meet Junge size distribution, the Angstrom exponent would vary with wavelength, and the spectral curvature of the Angstrom exponent (a₂, a₁) is useful for describing particle size. Analysis is conducted to find the relationship between these parameter and particle size based on Aeronet Level 2.0 data from Beijing, Taihu, Xinglong, Xianghe sites. The data contain 440 nm, 675 nm, 870 nm, 1020 nm AODs, and particle volume concentration, the data temporal series of each site is more than one year, α, a₂, a₁ are derived by least square method. The results show that although the aerosol is mixed by fine and coarse particle sometimes, α is still larger than 1.5 which indicate that aerosol mainly consists of fine particle in typical Angstrom law. Correspondingly, median α (0.8 < α < 1.2) also appears for fine particle condition at which α should be larger than 1.2 in typical Angstrom law. On the other side, when α is less than 0.75, the aerosol is dominated by coarse particle certainly which is in accord with Angstrom law. It means that α is a good particle size indicator for coarse particle but not for all conditions. Although a₂, a₁ contain particle size information, they are not sufficient for describing particle size just by themselves, they could be nice complement to α. There is significant relationship between particle size and α, a₂, a₁, when α > 0.75, a₂ < -0.5 or a₂ < -0.5, a₁ < -1.0, it means that aerosol is dominated by fine particle (V_fine/V_total > 0.7); when α < 0.75 or a₂ > -0.25, a₁ > -1.0, it means that aerosol is dominated by coarse particle (V_fine/V_total < 0.2). It has been proposed that a₂-a₁ is a first approximation of α, which could also be a good particle size indicator. But the examination shows that a₂-a₁ does not perform as well as expected, especially when 1 < a₂-a₁ < 2, the particle size is very complicated, thus a₂-a₁ provides no assistance to judgment.

Comparison of Black Carbon Aerosols in Urban and Suburban Areas of Shanghai

Xiao Xiuzhu, Liu Pengfei, Geng Fuhai, Gao Wei, Zhen Canming, Zhao Chunsheng

2011, 22(2): 158-168.

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Abstract:
Black carbon (BC) aerosols influence climate by absorbing incoming solar radiation resulting in a warming effect with large uncertainties. To better understand the anthropogenic BC pollution and its transport in the region of Shanghai, the BC mass concentrations are measured at Pudong (the urban site) and Dongtan (the suburban wetland site), during a one-year period from December of 2007 to November of 2008. The diurnal and seasonal variations of BC mass concentration and the wind-concentration relationships at two sites are compared. According to the Aethalometers, the hourly BC mass concentration of Pudong is 1.2—7.6 μg·m^-3 (10%—90% percentiles), with an average value of 3.8 μg·m^-3, which is significantly higher than that of Dongtan (0.1—4.3 μg·m^-3, with an average of 1.7 μg·m^-3). The BC concentrations show similar variation patterns at both sites in seasonal scale, with the highest concentrations usually observed in winter and the lowest concentrations in summer. However, different diurnal patterns are usually observed at different sites. The average diurnal variation measured at the urban (Pudong) site revealed a dual-peak pattern, with peaks between 09:00 and 10:00 and between 20:00 and 21:00, while the minimum values generally appear in the afternoon and midnight. The morning peaking is attributed to enhanced traffic during rush hour, while the evening rush hour combined with the collapse of convective boundary layer result in the evening peak. Additionally, pronounced "weekend effect" is observed at the urban (Pudong) site, when the average BC concentration of non-workdays is about 13% lower than that of workdays. These results indicate that the BC concentration at Pudong site is mainly influenced by the local anthropogenic emissions. In contrast, neither significant diurnal variation nor significant "weekend effect" is observed at the suburban (Dongtan) site, indicating that the local anthropogenic emissions at Dongtan are relatively weaker. Surface wind direction and wind speed has substantial effects on the BC concentrations. Wind could either dilute BC aerosols or transport them from other places and contribute to the measured concentration, depending on different wind directions and speeds. Different characteristics of wind-concentration relationships are observed for urban and suburban areas in which the BC concentrations are mainly influenced by the local emissions and by the regional pollutant transport, respectively.

Parameterization of Turbulent Orographic Form Drag and Implementation in GRAPES

Xue Haile, Shen Xueshun, Su Yong

2011, 22(2): 169-181.

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Abstract:
Due to the limited model resolution, scales of topographies below the model resolution are called sub-grid scale orography. Sub-grid scale orography plays important roles on the atmosphere from the thermal and dynamic aspects, and these effects are fed back to the model atmosphere through parameterization.Generally, the dynamic effects of sub-grid scale orography includes: Sub-grid orographic turbulent form drag caused by turbulent flow over hills; sub grid-scale form drag of orographic flow blocking, separating and lee vortex; buoyancy waves drag caused by breakdown of gravity-waves that excited by flow over mountains and transmitting upward in the upper atmosphere. With resolution raised, turbulent form drag becomes more important which is associated with small-scale orography. Given these facts, the characteristics and effects of the sub-grid orographic turbulent form drag and its parameterization are studied.Usually, effects of the turbulent form drag due to sub-grid scale orography in numerical models are simply considered as enhancing surface roughness, known as the effective roughness method. In recent years, according to asymptotic theory and numerical simulations, a new scheme of sub-grid orographic turbulent form drag is developed. As an independent physical process, the new scheme is of three-dimension features in the model, while the effective roughness method is only considered being on the surface level.It is significant to consider turbulent form drag in NWP model for completing physical processes of model and improving the model prediction of the surface layer. A single-column model is used to simulate the characteristics of turbulent form drag, comparing the advantages and disadvantages between the effective roughness method and direct parameterizing method. Two direct parameterization schemes are also compared, one is developed and applied in NWP model recently, and the other is based on ideal terrain. Finally, the form drag scheme that developed and applied in NWP model is implemented into the GRAPES regional model. Case studies are conducted to investigate the possible influences of form drag on the forecast of near surface wind fields and other variables.

Error Analysis of the Numerical Value Forecast for Tropical Cyclone Paths with the T213L31 Model

Wu Yu, Ma Suhong, Xiao Tiangui, Qu Anxiang, Jiang Xiaoyun

2011, 22(2): 182-193.

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Abstract:
The numerical forecast result for tropical cyclone paths from 2006 to 2009 is fully checked from mean distance error, distance error distribution, system error of the model, mean full-shift velocity error and the mode forecast error to circumstance fields by using T213L31 model of China National Meteorological Center. The analysis shows that the model forecast distance errors of 24, 48, 72, 96 hours forecasts are 135.8, 250.1, 376.3, 515.9 and 695.1 km. For the TC path of different alignment, the forecast for west path type is the best, followed by excrescent path and path of going up north. The biggest forecast error path is the path going up northeast, with the path east to change direction in second. Classifying the tropical cyclone strength indicates that the forecast error to tropical cyclone decreases as the strength increases, and the forecast is most efficient when the strength attains super typhoon. The forecast error to strong tropical storm is significant when forecast time increases, and the error to the tropical storm is also notable. The T213 produces a system deviation of northwest to west path among all average forecast samples. For northwest line and path to west cyclones the deviation is northeast to east and northeast to north. For cyclones changing direction to the northwest, middle, west and northeast, the deviation is northwest path, northwest to west and west system deviation respectively. But for the east changing direction and path going up north, the deviation is southwest to west and southwest respectively. Calculating the mean moving velocity, it's found that forecast for northeast path cyclones generates great error on initial velocity, reching up to 1.11 m/s, which leads to forecast error of distance. For the northwest, west, going up north type path cyclones the error of velocity is smaller, but for all changing direction type ones the velocity deviation is bigger. From the cases of T213 model which forecasts TC tracks with larger error in 2009 (such as No.0904, No.0906, No.0907), by examining the model prediction error of the background field, it shows that the model overestimates westerly trough in middle and higher latitude regions. For forecasts of two close cyclones, the Fujiwhara Effect can happen easily, which will cause forecast deviation for TC tracks.

Establishment and Application of Random Lightning Leader Model

Ren Xiaoyu, Zhang Yijun, Lü Weitao, Tao Shanchang

2011, 22(2): 194-202.

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Abstract:
Lightning occurred in the atmosphere is a kind of long-distance discharge phenomenon, and it often causes a variety of disasters which become more serious by the extensive use of electronic devices particularly. With deep understanding on physical processes of lightning occurrence and development, lightning leader model is established based on observational facts to study development of lightning leader and its interaction with structures and provide reference for lightning protection. According to characteristics of CG lightning, a model of random lightning leader is established. The connection process of lightening leader is simulated. The model of lightning leader is developed by simulating ambient potential distribution using an over relaxation method. In the model, the direction of next leader step depends on the probability, and final connection location of downward leader is chosen randomly by the probability formula.The induced charge of downward leader increases with the propagation of downward leader. Simulation results of a random model show that the induced charge of downward leader is about 10^-4 C/m. With the development of the downward leader, the branch of downward leader increases. There are diversiform forms in connection process. Downward leader can connect with structure or ground which do not produce upward leader besides upward leader. Downward leader can connect with one of the upward leaders on the ground, and even connect with the ground which does not produce upward leader. Downward leader does not always connect with the tip of upward leader, and it can connect with one branch or middle of the upward leader. Lightning rod may do not produce upward leader and the downward leader above doesn't always connect with the lightning rod, sometimes it connects with structure and ground. The downward leader far away from lightning rod can also connect with the lightning rod. In most conditions, lightning rod can protect the structure from lightning. With fixed distances from downward leader and lightning rod, wider and lower structure is less likely protected by lightning rod.These simulation results are achieved with two-dimensional random lightning leader model within the range of limited space. More simulation and analysis are needed for three-dimensional random lightning leader model within larger spatial extent to find out the behavior characteristics of lightning rod and investigate the protection of lightning rod to buildings. A large number of natural lightning and triggered lightning observations are also needed to further check the reasonableness of the simulation results.

Precipitation Characteristics in Tropical Cyclone Katrina Using TRMM Precipitation Radar

You Ran, Lu Naimeng, Qiu Hong, Li Xiaoqing

2011, 22(2): 203-213.

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Tropical cyclone is a primary disastrous synoptic system in China. Its monitoring mainly depends on optical data, i.e., visible and infrared data. These sensors observe the albedo and temperature of cloud top which is somewhat related with the precipitation, but leave the precipitation particles inside the precipitation-cloud system unseen. Fortunately, the microwave sensor can penetrate into the cloud and sense precipitation particles in and even below the cloud system, and observe precipitation more directly.Based on TRMM PR (Precipitation Radar) product, 6 orbit data in four days covering the main part of the cyclone are analyzed to study the characteristics of near-surface precipitation and vertical precipitation profile of stratiform and convective cloud in nascent, developing, and recessionary stages of the cyclone Katrina. Results indicate that the convective rain percent is 15%—22% and stratiform rain occupies 78%—85%. The average stratiform rain rate is 2.7—5.9 mm·h^-1, the convective rain rate is 7.7—17.5 mm·h^-1, and the total rain rate is 3.5—7.7 mm·h^-1. During the life cycle of the cyclone, the pixel number with convective rain is one fourth of stratiform one's, while the average intensity/rain rate of convective rain is four times of stratiform rain. The average rain rates of convective and stratiform precipitation gets larger along with the developing of cyclone, gets a little weaker just before landing, and enhances after landing except that stratiform rain become a little weaker.During nascent stage, weak precipitation of 1—2 mm·h^-1 is dominant, and there are no pixels with rain rate larger than 31 mm·h^-1. During developing stages, the rain rate intensifies. More rain pixels appear, some with very high rain intensity. After landing, because of the strong friction effects with land surface, the proportion of pixels with rain rate between 5—10 mm·h^-1 increases, and the pixel number with rain is almost doubled except the ones between 30—50 mm·h^-1 becoming a little less.During the nascent and recessionary stages, the max precipitation height is 10 km. During the developing stages, it reaches as high as 16 km. Most precipitation profiles vary first larger (to 4 km) then smaller with height, and reach minimum at 6—7 km because of the freezing level. The profiles of nascent and recessionary stages diminish equably with height. The profiles of developing stages vary very uneven with height because of the violent upwelling airflow in cyclone. The analyses on TRMM data provide a perception to precipitation type, horizontal distribution, and intensity of data-sparse oceanic tropical cyclone where conventional radiosonde measurements are not available. These results are useful information for future quantificational precipitation retrieval of cyclone.

Regional Representativeness Analysis of National Reference Climatological Stations Based on MODIS/LST Product

Wang Yuanyuan, Li Guicai, Zhang Yan

2011, 22(2): 214-220.

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Abstract:
Observations of reference climatological stations plays an important role in climate change research and disaster warning, which requires the stations to be representative enough for their surroundings. Furthermore, representativeness is important in optimizing meteorological observation network and selecting locations for new meteorological stations. However, researches on meteorological stations representativeness are still limited, especially from regional point of view.A new method to quantify reference climatological stations representativeness based on remote sensing data is proposed. The representativeness of a reference climatological station is measured using its explained variances for the LST (land surface temperature) anomaly series extracted from different sizes of windows centered on that station. MODIS/LST products (MOD11A2, 1 km spatial resolution) from 2001 to 2007 are used. MOD11A2 is 8-day average composite of MODIS daily LST product (MOD11_L2) which is produced using split-window algorithm. The product accuracy is better than 1 km according to previous validation, providing quality guarantee. The selected window size ranges from 3×3 km² to 51×51 km², with a step of 2 km. For each window size, explained variances of all the 142 national reference climatological stations are calculated. Through investigating the trend of explained variances with window size increments, a threshold is selected, according to which the maximum area a station can represent is determined. When 0.75 is set as the threshold, about 41% stations have good representativeness, representing areas larger than 51×51 km² which are mainly located in the north regions. About 21% stations have low representativeness, representing areas less than 7×7 km² that mainly located in the south regions. Other stations with moderate representativeness are found to distribute in both north and south regions. In order to explore the factors influencing representativeness, two indices are defined. One is land cover diversity based on Shannon-Weiner index formula and retrieved from MODIS land cover product. The other one is terrain undulation, which is defined as the difference between the maximum and minimum elevation and retrieved from DEM data. It is found that as far as all reference climatological stations are concerned, land cover diversity and terrain undulation are negatively correlated with representativeness, and when window size increases this correlation strengthens accordingly. Land cover diversity has greater impacts on representativeness than terrain undulation. Using land cover diversity and terrain undulation as independent variables, linear regressions can model representativeness pattern of most stations very well. For several stations whose representativeness cannot be explained well, fast urban expansion maybe an important factor, which needs further research. Finally, the representativeness for climate zone to which a station belongs is also studied. The results reveal that in areas featured with complicated climate, such as southwest region and part of Xinjiang, the representativeness of reference climatological stations are low, suggesting more meteorological stations are needed.

Satellite Remote Sensing Drought Monitoring Methods Based on Different Biophysical Indicators

Yu Min, Wang Chunli

2011, 22(2): 221-231.

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As a frequent natural hazard, drought causes the heaviest damage to daily life and ecological environment among all natural disasters. The large scale and dynamic drought monitoring has been frontier and hot topic in the global climate change and food security research. Satellite remote sensing is the main method of obtaining distributed information of the land surface. However, the applicability of a drought monitoring method varies by region and period. So it's necessary to inspect and evaluate the drought monitoring method to ensure the validity and accuracy in drought monitoring.Vegetation index based I_VC, land surface temperature based and Surface Temperature-Normalized Difference Vegetation Index space (T_s-I_NDV space) based are compared to analyze and evaluate their characteristics and applicability in drought monitoring. The MODIS 16-day NDVI (MOD13A2) and 8-day T_s (MOD11A2) provided at 1 km spatial resolution as a gridded level-3 product in the Sinusoidal projection are used, and the Heilongjiang Province, the main food production area in China, is chosen as the study area. The monitoring period is from 9 May to 9 June of the year 2000 to 2008. The correlation between I_VC, I_TC, I_VTC and relative soil moisture in 10 cm and 20 cm depth, the correlation between I_VC, I_TC, I_VTC and the precipitation in the satellite monitoring period and the cumulative precipitation in the last 1-, 2-, 3-, 4-period time scales, the difference and the relationship between I_VC, I_TC, I_VTC are analyzed.Significant linear correlation is found between I_VTC and the relative soil moisture in 10 cm and 20 cm depth, especially for the 10 cm depth. The correlation between I_VTC and relative soil moisture is obviously better than that between I_TC, I_VC and the relative soil moisture. So, it can be judged that I_VTC may mirror the soil moisture better than I_VC and I_TC, and is more sensitive to shallow soil moisture. I_VTC is also found linearly correlated with precipitation in current monitoring period, as well as the cumulative precipitation in the last 1-, 2-, 3-, 4-period timescales. The correlations are better than those between I_TC, I_VC and precipitation as well as corresponding cumulative precipitation, which show that I_VTC is more sensitive to precipitation than I_VC and I_TC, and is closely related to not only current precipitation but also past cumulative precipitation. In the early growing season, I_VTC and I_TC are applicable in drought monitoring, while the fractional I_VC cover is too low to monitor drought. It is difficult to compare the drought among different areas with I_VC and I_TC, while based on the energy conservation principle, combining the I_NDV and T_s, I_VTC can reflect soil moisture better and is comparable in different areas. Furthermore, the land surface temperature implied by I_VTC gives more direct hint of drought than the I_NDV implied especially on the grassland, then in the crop land, brush land and forest land in sequence.

Seasonal and Spatial Variability of Vegetation and Land Surface Temperature in Anhui Province

Zhang Hongqun, Yang Yuanjian, Xun Shangpei, He Binfang, Zhang Aimin, Wu Wenyu

2011, 22(2): 232-240.

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Abstract:
Anhui Province lies in the transitional area between temperate zone and subtropical zone, so the climate here is warm and moist, and the four seasons are distinct. The north of the Huaihe River possesses a half-moist monsoon climate of warm temperate zone while the south of the Huaihe River possesses a subtropical moist monsoon climate. As a result, the climate is very suitable for various kinds of crops and plants. On the other hand, many kinds of natural disasters, such as drought, flood, and cold happen frequently every year in Anhui Province, influencing agriculture, ecosystem and people living significantly.Land vegetation and surface temperature play important roles in climate change, resource and environment change, agricultural monitoring and so on, while their in-situ investigation is very limited. Fortunately, satellite remote sensing is used widely to monitor macroscopical, large-scale, dynamic continuous vegetation and surface temperature during recent years. Using MODIS data from 2001 to 2008, seasonal, monthly and spatial variability of normalized difference vegetation index (NDVI) and land surface temperature (LST) of Anhui Province are explored. Furthermore, the relationship between NDVI and LST is analyzed. Also, spatiotemporal variability of NDVI and LST in 4 cities of Anhui Province are analyzed. The results show that spatiotemporal variability of NDVI and LST in Anhui Province are obvious. Due to local climate, the differences of vegetation lead to different seasonal changes and spatial distribution characteristics of LST in Anhui. For instance, due to evergreen broadleaf forests in South Mountain area and Dabie Mountain area, both NDVI and LST seasonal variations are smaller and they are positive correlated. However, in the north and middle most areas, the deciduous broad-leaved vegetation and seasonal crops (rice, wheat, corn, soybean, rape, etc.) have greatly enlarged the seasonal variations of NDVI and LST, and their positive correlation is less obvious. Moreover, in cities and their surrounding areas, the correlation of NDVI and LST is negative, with urban LST significantly higher than rural values, which is notable characteristics of the urban heat island. The distribution feature of LST has been proved depending on local climate and spatiotemporal variability of NDVI in Anhui Province. These results offer an important reference for the reasonable zonation of farm belt, monitoring of ecological resource environment, the valid assessment of land use and characteristics of the urban heat island in Anhui Province.

The Influence of Climate Change on Suitability of Shaanxi Apple Growth

Li Xingmin, Bai Qinfeng, Zhu Lin

2011, 22(2): 241-248.

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Based on the meteorological data from 1961 and phenological observations data from 2001 of the northern part of Shaanxi Province, the main meteorological factors that influence apple production and quality, the features of frosts over the apple blooming periods and the average days of high temperature as well as the impact of climate change on apple growth during the past 50 years are analyzed, using the methods of time series analysis and agricultural climatic indices and grade criterion for apple planting demarcation of China. The results suggest that among the factors affecting apple planting, the annual mean temperature is in a rising trend. The rate of rising trend is about 0.23—0.37℃/10 a across Yan'an and the north area of it, and is about 0.14—0.24℃/10 a in Guanzhong and Weibei apple planting areas. The minimum mean temperature from June to August is in a smaller rising trend, too. The mean relative humidity in the same period doesn't change much. The mean annual precipitation is in a decreasing trend. In the recent 30 years (1979—2008), the mean annual precipitation becomes obviously less than the average from 1961 to 1990.Analysis on apple growth during the three periods of 1961 to 1990, 1971 to 2000 and 1979 to 2008 show that the grades of climatic suitability of apple growth remains in former climatic suitability range. Due to the rising of annual mean temperature, the grade of the west Guanzhong apple planting area decreases, but the grade of the north apple planting area increases. Due to the minimum mean temperature of summer rising, the years of grades are not in suitable range in Huanghe River bank and Guanzhong areas are increasing years. Precipitation change results in the grades decreasing in part of Guanzhong and the east of other apple planting areas. That is to say, in some regions the rising of the annual average temperature and the declining of the mean annual precipitation have resulted in the grades change of climate suitability for apple growth. Increasing frost frequency, especially in the second ten days of April in recent years since 1961, increases the possibility of frost damage on apple flowering in Yan'an and the west of Weibei apple planting areas where the date of apple flower is ahead of before. Since the 1990s, the increasing high temperature days have caused growing damage on apple production and should be noticed.

Real Time Observing and Forecasting System for Soil Moisture in Anhui Province

Chen Jinhua, Yang Zaiqiang, Yang Taiming, Li Yongxiu

2011, 22(2): 249-256.

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In order to meet the needs of flood control and drought relief, the operation of soil moisture observation is launched routinely in meteorological department, by artificial boring stick all the time or by automatic measurer in recent years. However, the use of soil moisture data is always lagging with poor matching service and continuity. Based on the soil water observation network (including the manual and automatic network) and many kinds of approaches for data transmission, Real Time Observing and Forecasting System for Soil Moisture in Anhui Province (SMRTOFS) is developed. SMRTOFS is composed of data observation and transmission subsystem, forecast subsystem, and display subsystem. In data observation and transmission subsystem, the data from manual observers and automatic observation stations is collected in real time and stored in standard soil moisture database, and the data from unexpected transmission approach is also automatically gathered and conserved by defining an intermediate file. In forecast subsystem, predicting models of soil water content for each season are established, and soil moisture forecast is achieved using the latest soil water observation data and the coming 10-day weather information. In the display subsystem, based on the secondary development of Golden Software Surfer 8.0 and line bar chart control, the results of soil water observation and prediction in different seasons and different depths are exported and displayed dynamically, with the patterns of data table, the filled contour in spatial scale, bar chart, and so on. In the system, four-level files from observation to application are constructed including observation raw data, standard database, primary products and user products. The operation flow of soil moisture observation and forecast is reduced to transforming the four-level files. With higher applicability and compatibility, the system is applied triumphantly to the service of agricultural drought and waterlogging operation in Anhui Province. The information could be used to avoid the loss of flood and drought disaster. However, the soil moisture forecasting is based on statistical method, so the model parameters need modification for other regions. Implementing better Soil-Plant-Atmosphere Continuum model can also improve the performance of this system.

Vol.22, NO.2, 2011