应用气象学报

Impacts from the Processing of Vegetation Types Within a Model Grid Cell

Zhang Zhengqiu, Sun Shufen

2008, 19(2): 129-136.

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Abstract:
Traditionally, when coupling a land surface model into a GCM, the vegetation types within a model grid cell are grouped as one type, by which some discrepancy of model results to the reality are certainly led to. To better understand the impact, the simulated study through offline experiments of two cases in the same grid cell are conducted. Underlying surface in the cell is considered in one case as the coexistence of multi-vegetation types and the other as one single typical vegetation type.A practical scheme is suggested for this kind of coupling, i.e., a model grid cell is divided into several subgrid cells with each one being called "Tile" according to the number of vegetation types within the grid cell in the form of high resolution data. Meanwhile the land surface model is designed to be able to run simultaneously at different subgrid cells, rather than further to group the vegetation types from the high resolution data. By doing so, the same forcing is shared by all the subgrid cells within one grid cell as in the conventional way, but the ground fluxes need to be integrated from the subgrid cells by percentage of vegetation area coverage. As a matter of fact, the approach can be easily realized. In the meantime, the way to estimate effective ground temperature, effective sensible and latent heats and so on is proposed.In the offline experiments, the land surface model of SSiB and the field observation data of HAPEX-MOBILHY, which are generously provided by Xue who is also the SSiB author, are used to carry out the study. As for real condition, the field of HAPEX-MOBILHY which consists of forest with the percentage of 40% and mixed agricultural crops with the percentage of 60%should be categorized to grass land according to the classification in SSiB. Outputs of simulations show that there are big differences in the effective ground temperature, effective sensible and latent heats predicted respectively by three cases of the land surface including forest, grass and the coexistence of forest and grass. Also, the outputs show that the vegetation type with less percentage cover in a grid cell may make more contribution to the latent or sensible heat in the cell than the vegetation type with more percentage cover in the same grid cell. The validity of the method which considers the vegetation with more percentage in a cell as one representative vegetation type in the cell for some previous land surface model should be reevaluated.

Particle Sizing Analysis on AgI Pyrotechnics with the Electron Microscope

Su Zhengjun, Zheng Guoguang, Guan Liyou, Zhang Jihuai, Huang Geng

2008, 19(2): 137-144.

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Abstract:
Pyrotechnics flares, containing silver iodide (AgI) as active ice-nuclei (IN), are widely used for seeding in hail suppression and precipitation enhancement operations over China nowadays. The idea and procedure for developing newly high efficient AgI pyrotechnics widely used in weather modification in China are given. The different nucleation mechanisms are strongly depended on the size of the nuclei aerosols. Furthermore, it must be known how long it is possible to work with one and the same aerosol before coagulation has seriously altered the spectrum. Five formulations of pyrotechnics with high nucleating effectiveness, containing 1.5%—5% by weight of AgI, including the flare is made according to the given formulation of silver spare (USSR), are examined their particle size with the environmental scanning electron microscope FEI Quanta 200 (ESEM) and transmission electron microscope (TEM). At the same time, their nucleating effectiveness and temperature thresholds are tested. The characteristics of five kinds of AgI-type pyrotechnics are investigated and compared with other widely used product-silverspare, or A2 USSR.From the electron microscopic analyses, the size distributions of the particles produced from all five types of flares are found to be similar. For each of pyrotechnics, more than 98% of AgI effluent concentration is contained in particles less than 0.5 μm in diameter, and more than 90% is contained in particles less than 0.3 μm. Because of the particle sizes, a diffusive contact and condensation-freezing mechanism is probably playing an important role in the nucleation of water droplets. Different kinds of AgI-type pyrotechnic has differ size distribution. Based on TEM micrographs or five kinds of AgI-type pyrotechnics particles, several less AgI particles adhered on a KCl particle and the structure characteristics is maybe the cause that resulted in a high nucleating effectiveness. The AgI contents and temperature thresholds of five kinds of pyrotechnic nucleate and Ice crystal formation kinetics for AgI aerosols in the isotherm al cloud chamber at given temperature are studied in the research. For five kinds of AgI agents, their thresholds temperature change in the range of -4.4—-3.5 ℃. Their differences are less, in other words, the temperature thresholds of AgI pyrotechnics are mainly decided by AgI itself. The interaction of cloud, CCN and AgI artificial ice nuclei (AAIN) is important to the formation of cloud, precipitation and weather modification. The size distribution of AgI effluent from the five flares appears to be similar based on the carbon membrane samples that are collected static subsidence and analyzed with an ESEM. The deactivation of AgI smoke in contact with liquid water above -4.4 ℃ is considered, it therefore should not be introduced for cloud-base seeding at warm temperatures. The chemical composition of the pyrotechnic is another important factor that directly affects the effectives and nucleating mechanism of the AgI pyrotechnics. In the future research, the experimental study on the chemical composition of flares at the main mode is helpful to interpret the nucleating effectiveness differences in the flares. The interrelation of them is complex and further study is needed.

Characteristics of Tropical Convection Intraseasonal Oscillation Anomaly and Their Relationship with Sea Surface Temperature

Li Liping, Wang Panxing, Guan Zhaoyong, Yang Song

2008, 19(2): 145-152.

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Abstract:
The seasonal and interannual variability of intraseasonal oscillation (ISO) intensity of tropical convection is investigated by using NCAR/NOAA outgoing longwave radiation (OLR) data, along with the relationship with sea surface temperature (SST). It shows that there are two strongest ISO areas, namely, tropical Indian Ocean and tropical western Pacific Ocean, companied with large SST zonal deviation in climatological fields for any seasons. There are three noticeable areas of interannual anomaly of OLR ISO intensity, i.e., tropical middle and eastern Pacific (TMEP), tropical northwest Pacific (TNP) and tropical southwest Pacific (TSP). In these areas, there are noticeably positive correlation relationships between anomalies of OLR ISO intensity and SST interannually, along with the circulation anomaly convergence (divergence) in the low (high) level at the same time, which is also closely related to El Niño (La Nina) events according to the time coefficient series. In addition, the ISO enhances and moves eastward gradually before El Niño event takes place, and weakens later in the tropical Indian Ocean and tropical west Pacific, which links up with the areas of OLR ISO interannual anomaly intrinsically, because OLR ISO weakens in TNP and TSP and enhances in TMEP after the El Niño event occurs. In the climatological fields, OLR ISO is weak in TMEP, TNP and TSP, whereas the SST interannual anomaly is notable in these areas. It shows that SST interannual anomaly is very important for that of OLR intensity and an even crucial factor. It is well known that ENSO is the strongest interannul signal of SST, which is most notable in the winter and spring, so it is easy to understand that there is a close relationship between the above local relations of ISO intensity and SST interannual anomaly with ENSO. SST interannual anomaly is too weak to produce the marked ISO anomaly in the western Pacific, so there is weak relation between ISO intensity and SST interannual anomaly. Comparing the seasonal with interannual variation of OLR intensity, it is found that SST is a key factor to determine the seasonal and interannual variations of OLR intraseasonal oscillation intensity.

The Prelimiary Application of Radar Data to the Lightning Warning of Isolated Storm Cells

Wang Fei, Zhang Yijun, Zhao Junzhuang, Lǜ Weitao, Meng Qing

2008, 19(2): 153-160.

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Abstract:
The radar data, the sounding data and the lightning location data of 20 isolated cells in Beijing from July to August in 2005 are analyzed. Considering the analysis and the overseas studies, it is concluded that 40 dBz is an appropriate predictor for the regional lightning warning, because the difference of 40 dBz echo top between thunderstorms and non-thunderstorms is maximal among various echoes. The application of this predictor is not as simple as other research results. According to the analysis on the evolution of various echoes, it is considered that the threshold of 40 dBz echo top height should be located at the 0 ℃ stratification level. In the meantime, whether 40 dBz echo top height reaches the -10 ℃ stratification level, the proportion of some kinds of echo should be taken into account. The forecast accuracy will be improved markedly when the factors mentioned before are taken into consideration. Based on the above studies, a forecast process of lightning is given. First, it is checked that whether the 0 ℃ stratification level is reached by the 40 dBz echo top height or not. If it is affirmative, the cell will have the great potential of becoming a thunderstorm. If not, the cell will be concluded to be a non-thunderstorm. Then, checking whether the -10 ℃ stratification level is reached by the 40 dBz echo top height will be necessary to judge the thunderstorm further. If that height is reached, the first lighting in the cell will occur in 15 minutes. If not, the P value should be used for subsidiary discrimination. If the P value exceeds 5% and keeps above this level for a period of time, the first lightning will also occur in 15 minutes. A prediction test for this method is carried out using the data of the other 22 isolated cells in Beijing in the same period. The test result shows that the method is effective in judging whether a normal cell will become a non-thunderstorm cell or not and predicting the time of the first lightning in a thunderstorm. In addition, a linear relationship is found between two time intervals. One interval is between the occurring time of the first intercloud flash (IC) and the first cloud-to-ground (CG) in a cell. Another is between the appearing of the first 25 dBz in the cell and the V value (change rate of 35 dBz echo thickness in the cell) reaching its maximum. A reference is given for the CG prediction.

The Lag Relationship Between Winter NDVI over Tibetan Plateau and Temperature of the Southwest China

Li Xuemin, Zhou Dingwen, Fan Guangzhou, Li Hongquan, Hua Wei, Liu Yaqin

2008, 19(2): 161-170.

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Abstract:
Many studies show the importance of vegetation to climate. Southwest China neighbors to Tibetan Plateau, by which climate of this region is influenced by its own system. Therefore, taking account of both factors it is considered that climate of Southwest China is affected by vegetation over Tibetan Plateau to some extent. The lag relationships between NDVI over Tibetan Plateau and temperature of Southwest China are discussed by using statistical methods. Empirical orthogonal function (EOF) analysis is made first to describe temporal and spacial characteristics of mean temperature, highest temperature and lowest temperature in summer over Southwest China during the period of 1982—2001. The results show that there is a coincidence between mean temperature and highest temperature, especially Sichuan and Chongqing are in a cool period during 1980s and getting warm in 1990s. Based on the monthly Normalized Difference Vegetation Index (NDVI) data that is made by GIMMS (Global Inventory Modeling and Mapping Studies) workgroup and the monthly mean air temperature, maximum air temperature and minimum air temperature data of 96 stations in Southwest China, the relationships between NDVI over Tibetan Plateau and temperature of Southwest China and key regions are analyzed by applying correlation, composite and singular value decomposition (SVD). The results show that mean temperature and highest temperature are more sensitive to vegetation change, and the correlation between temperature and preceding NDVI has a significant difference between tow parts of the Plateau, vegetation over the West Plateau shows a stronger influence on temperatures than the east part. Compared with the years of abnormally low NDVI, abnormally high NDVI in winter over the Plateau corresponds to a warming in Southwest China in summer, highest temperature increases most obviously, the maximum increase occurs in July in north of Southwest China. The best coupled patterns of NDVI and tem peratures are showed respectively, the extent of vegetation's impact on temperatures and key regions are distinguished. The strongest correlation is found between the Plateau NDVI of winter and mean temperature of summer; mean temperature is driven by vegetation in northeast part of the Plateau, Lhasa and Linzhi predominately. For highest temperature the area of remarkable correlation is located in west of the Plateau and the large area along the north edge of the Plateau, and for the lowest temperature is the belt region along the north edge of the Plateau. The regions sensitive to the change of winter NDVI are mainly located in Sichuan Basin and the vicinity of it.

Interannual Variation of Summer Precipitation in Xinjiang and Asian Subtropical Westerly Jet Stream

Yang Lianmei, Zhang Qingyun

2008, 19(2): 171-179.

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Abstract:
The relationships between Asian subtropical westerly jet stream (ASWJS) and summer precipitation in Xinjiang are examined using the NCEP/NCAR reanalysis dataset and 75 stations monthly precipitation data in Xinjiang from 1960 to 2003. Summer precipitation in Xinjiang is closely related to meridional displacement of west Asian jet stream and quasi-stationary wave activity along ASWJS. It is confirmed by Eliasson-Palm flux diagnoses that stationary waves propagation over Scandinavian Peninsulan-middle Europe has important impacts on stationary waves activity along ASWJS. It is found that anomalous summer more (less) rainfall in Xinjiang is related to the West Asian Westerly Jet axis moving to Southern (Northern) rather than normal, and subtropical westerly front also migrates southward (northward) over the whole troposphere. As a result, anomalous convergence and divergence occur over Xinjiang. The composite plots show the troposphere atmospheric steady wave weakens or strengthens over West Asia and strengthens or weakens over Xinjiang which are associated with more or less rainfall in Xinjiang. It is investigated that the horizontal wave vector propagation is obviously different between more and less rainfall years. During more (less) rainfall years, it is found that horizontal wave activity flux divergence center over Scandinavian Peninsula-middle Europe is favorable for moving eastward (westward and southward), and horizontal wave activity propagation strengthens (weakens) toward eastward leading to turning to southeastward near Ural mountain and entering ASWJS at Aral Sea-Xinjiang and the wave propagation strengthens (weakens). In the meantime, the direct wave propagation toward southeastward enters ASWJS in the east Mediterranean and Black Sea and weakens (strengthens) because of which quasi-stationary wave activity along West Asian westerly jet stream weakens (strengthens). Xinjiang summer rainfall is closely related to wave activity and propagation over Scandinavian Peninsula-middle Europe-ASWJS. Furthermore, the meridional wave train along 60°E connecting the two hemispheres is revealed, and this wave train which propagates meridionally upward from lower-troposphere in polar region to low-latitude tropopause and continues turning downward to mid-latitude in northern hemisphere is associated with west Asian jet variation. This wave train EP flux divergence performs opposite the variation near the south and north along 40°N, leading to different west Asian westerly jet stream intense variation near the south and north along 40°N for drought/flood years. EP flux divergence to the south (north) of 40°N and convergence to the north (south) of 40°N enhances (weakens) in flood (drought) years leading to the enhanced (weakened) upper level westerly to the south of 40°N and weakens (enhances) upper level westerly to the north of 40°N.

Mountain-based GPS Occultation Observation Experiment at Mt Wuling

Gong Xiaoyan, Hu Xiong, Wu Xiaocheng, Zhang Xunxie, Song Shuli

2008, 19(2): 180-187.

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Abstract:
Mountain-based GPS occultation technique is referred to as receiving the radio signals of GPS satellites with very low elevations and negative elevations using a GPS receiver at the top of high mountain and retrieving the lower atmospheric refractivity profiles. A mountain-based GPS occultation observation experiment is performed at Mt Wuling (40.60°N, 117.48°E, 2118 m) in Hebei Province during August 1—29, 2005. The campaign is organized by China Meteorological Administration, a few other organizations participate in the experiment. Totally 576-hour raw observation data are collected by JAVAD two-frequency GPS receiver provided by Center for Space Science and Applied Research, Chinese Academy of Sciences, and 1136 occultation events are recorded. Out of the total occultation events, 621 are rising occultation events and 515 are setting occultation ones. There are about 2 occultation events observed in one hour on average. Detailed statistics and analyses are made to show features of all the observed occultation events, such as the distribution of the occurring time, the duration, minimum elevations and azimuth. The results are as follows. The distribution of the occurring time of the observed mountain-based occultation events is nearly random uniform, and it seems that there are more observed occultation events for two periods of time, one is from 20:00 (local time) to 22:00, and the other is from 04:00 to 06:00. The duration of most occultation events is from 15 minutes to 20 minutes, and about 18 minutes on average. The range of azimuth of observed occultation events is between 110° and 290°, the peak of the distribution of azimuth is between 180° and 195°. These features are related to some important factors, such as the distribution of GPS satellites' orbits, the location of GPS receiver and the direction which the antenna points to. The minimum elevations of most occultation events are between -3° and -2.5°, the lowest negative elevations of all the events is -4.994° from south direction, which is possibly resulted from the landform around the observation station. The minimum elevations of setting occultation events are lower than that of rising occultation events obviously. It shows that the ability to track rising occultation events of commercial GPS receiver is weak. If the same GPS satellite is occulted, it is occulted mostly from the same azimuth, and their occurring time is close (their differences are usually less than two hour). This is determined by distribution of GPS satellites' orbits, cycle and features of movement. A new effective method is provided by mountain-based occultation observations for monitoring lower atmospheric environment. This emerging technique has potential applications. Above are the first statistic and analytic results from observed data by which reference can be provided for mountain-based occultation observation's operation application.

Automatic Identification Methods of Ground Raindrop Spectrum Observation and Image

An Yingyu, Jin Fengling, Zhang Yunfeng, Zu Xuemei

2008, 19(2): 188-193.

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Abstract:
The ground raindrop spectrum observation method is studied. The traditional filter paper sampling method is improved through enlarging the sample area, and increasing the methods of auxiliary observation. The image automatic identification software is designed and put into application in the processing of the raindrop spectrum data. Not only the sample member to obtain stable raindrop spectra data is enlarged by these ways, but also the mutual coordination and the analysis of the data are benefited. It is tested and result error analysis on its image position variation, the shape change, the drop spectrum overlaps and so on is made. The pattern recognition results are not influenced by the location and shape changes of single drop image in the data of the raindrop spectra data. The automatic image procedure is stable and reliable. It is very sensible when the separated drop spectra data are dealt with by the procedure. When many scattered drops formed from big drops, a large member of independent small raindrops will be formed, and it manifests that the splash problem can't be solved. The intelligence of the procedure is not high on the problem of raindrop overlapping each other together and it can't be recognized if the phenomenon of overlap really exists, the overlapped raindrops can't be separated and the overlapped drops can't be taken as one drop, so the member of the observing drops is small. From the error analysis of the raindrop spectra data, the relative error of spot mark diameter is smaller than 6% from 3 mm to 18 mm and the error is controlled within 6% for drops smaller than 4 mm, the error is even smaller when handling the small droplets. The result is obtained that this method is of great accuracy, stable performance, and very practical in the ground raindrop spectrum observation and the data processing. A new thought for the raindrop spectrum data processing analysis is provided and can be applied to the practical work.

Estimation of Linearized Vertical Diffusion Scheme in GRAPES Model

Zhang Lin, Zhu Zongshen

2008, 19(2): 194-200.

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Abstract:
Four-dimensional variational data assimilation (4DVAR) is an optimal method to obtain a best estimate of the initial conditions for a forecast model. A cost function is defined that involves a model trajectory as compared with three-dimensional variational data assimilation. The minimization requires an adjoint model in order to solve the problem at a reasonable computing cost. A four-dimensional variational data assimilation system (GRAPES 4DVAR) based on regional GRAPES model is developed by Chinese Academy of Meteorological Sciences. There are only several 4DVAR systems based on the non-hydrostatic model as GRAPES worldwide. GRAPES 4DVAR also has the ability to assimilate the observations, including the new non-conventional satellite and radar data. For the operational implementation in the future, GRAPES 4DVAR system is designed in the incremental formulation. The tangent-linear and adjoint model are both required to calculate the cost function and its gradient in the inner-loop. As the starting point, an adiabatic version of the linerized model is developed in 2005. Recently, much more effort is spent in the development of the linerized physical parameterization scheme for the application in GRAPES 4DVAR system. The linearization of vertical diffusion scheme used in GRAPES model is discussed.MRF nonlocal boundary layer scheme is used by GRAPES model to describe the vertical diffusion within and above the mixed boundary layer. The vertical diffusion scheme for the free atmosphere is linearized. After the straightforw ard linearization of vertical diffusion scheme, the standard tests are carried out to check the correctness of the tangent-linear model with vertical diffusion. It is well known that all physical processes are characterized by discontinuities and nonlinearities by which the departures of their linearied schemes can be significantly increased. To evaluate the validity of tangent-linear approximation for vertical diffusion scheme, twentyone cases during August 7—27, 2005 are run to calculate the mean departure between the tangent-linear model and the nonlinear model. It is found that the discontinuity resulted from the "on-off" switch has little influence on the mean departure between the tangent-linear model and the nonlinear model. Indeed, significant departures caused by the nonlinearity of vertical diffusion scheme may be lead to by a straightforward linearization of vertical diffusion scheme. This is a clear demonstration of the possible detrimental impact on the perturbed pressure and wind fields. The problem is solved by neglecting the perturbation of the surface flux for momentum. After the simplification, a better agreement between the tangent-linear model and the nonlinear GRAPES model with full physics for all variables is resulted in by the inclusion of the linearized vertical diffusion scheme. In conclusion, the results are encouraging, and the linearized vertical diffusion scheme is applicable in GRAPES 4DVAR systems. More linearized physics parameterization schemes will also be developed in the near future.

The Application of Dual Kriging Interpolating Method to Meteorological Data Analysis

Zheng Yongjun, Jin Zhiyan

2008, 19(2): 201-208.

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Abstract:
Kriging method is an interpolating method based on the spatial statistical correlation of the samples. The core idea implicated in Kriging method is that each sample is assigned with different weight according to the spatial correlation among the sample points, and the estimated error is minimized. So, it can be summarized to be the best linear unbiased estimator of a random function. Non-dual Kriging method is a local interpolator for the interpolation at each node and the solution of a new Kriging linear system is required by which the location of interpolating node is explicitly depended on. Therefore, non-dual Kriging method is quite time consuming for the solution of a new Kriging linear system for every interpolating point. By equivalent transform, the Universal Kriging method can be transformed to Dual Kriging method, which is a global interpolator for its Kriging linear system is independent of the interpolating point. Therefore, the Kriging linear system is solved by the Dual Kriging method only once to interpolate all points, so the computational efficiency is significantly improved and is of great value in meteorology and oceanography where large data sets are to be interpolated. Furthermore, the result of the numerical experiment shows that Dual Kriging method is not only equivalent to Universal Kriging method in accuracy and comparable to or superior to the Cressman method built in GrADS, but also far superior to Universal Kriging method in computational efficiency. In order to improve the accuracy, efficiency and flexibility of Dual Kriging method, several unique techniques are adopted in the implementation of the computational scheme:the solution of Dual Kriging linear system using partial pivoting LU decomposition and iterative improvement, the fitting of the trend by SVD linear fitting method, Levenberg-Marquatdt iterative method for the non-linear parameters fitting of the semivariance model, and the flexible parameter configuration by the FORTRAN 90 modular interface. Finally, four kinds of semivariance expressions are obtained by fitting the statistical sample semivariance derived from the statistics of summer precipitation in the Eastern and Southern China, and the sensitivity of these four kinds of semivariance models to the accuracy of precipitation interpolation is analyzed using the Dual Kriging method. It is found that exponential semivariance model is resulted in the best analysis, spherical semivarance model is better, Gaussian and linear semivariance is the worst. It is reasonable since the exponential semivariance model is the smoothest and its range is the longest, then the interpolation is made more accurate by the smooth weight contributions from more samples around the interpolating point. Therefore, the longer the range is, the more smooth the semivariance varies, the more accurately the precipitation within the isotropic range is interpolated by the Dual Kriging method. In summary, the Dual Kriging method is superior to non-dual Kriging method and Cressman method, and as an efficient and accurate best linear unbiased interpolator, more applications in meteorology and oceanography will be gained.

Numerical Simulation and Diagnosis Analysis on Heavy Rain in East Hebei by Typhoon Matsa

Chen Yan, Su Hailiang, Shou Shaowen, Jia Zibing, Wang Liping

2008, 19(2): 209-218.

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Abstract:
A heavy rain occurs in east Hebei during August 8—10, 2005. It is caused by a tropical storm which is resulted from the weakened typhoon Matsa. Mesoscale numerical model MM5 V3 is used to simulate the case. The precipitation time and intention as well as the synoptic situations are compared with the observation. Similarities are found. Based on mesoscale numerical model products, the physical mechanisms of the heavy rain are analyzed.The results show that the water vapor on low-level is quasi-saturated and the humidity layer is deep and stationary during the heavy rain. There are upper-level atmosphere divergence and the low-level atmosphere convergence over the rainstorm area, and they result in strong ascending motion which is the dynamical mechanism of the initiation and maintaining of the heavy rain.The meso-and low-level air circulation and the θ_e field are analyzed. Results indicate that the thermal structure of typhoon is asymmetry. Its eastern region is warm and the western is cold. The strong easterly low-level jet sustains in north of the typhoon. Energy and warm vapour are transported toward the rain-storm area.In meso-and low-level troposphere the values of helicity over the rainfall center are always positive. The precipitation center is corresponding with the maximum helicity center, and its movement follows the maximum helicity center. The maximum helicity center has certain designation function for the center of the heavy rain in the future. The values of local helicity are large probably because of the large horizontal wind velocity or the horizontal vorticity or of the both. Abnormity of air is lead to, and so is the rainstorm. The results also indicate that the rainstorm occurs in the maximum SRH (storm relative helicity) center or in its southeast isoline denseness area. At the same time, the values of SRH in the rainstorm area always exceed 120 m²/s² before or during the heavy rain. It means that the rotary environment wind field is advantageous to strengthen ascending motion. Enough flotage energy is provided for the convection.

The Experimental Detecting and Adjusting of the Precipitation Data Homogeneity in the Yangtze Delta

Li Qingxiang, Jiang Zhihong, Huang Qun, You Yong

2008, 19(2): 219-226.

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Abstract:
Annual and monthly precipitation data over 36 stations in Yangtze Delta are chosen in the experimental homogeneity studies. It is expected to find a method to homogenize the annual and monthly historical precipitation series over China. Two road maps are adopted to test the homogeneity of the precipitation series, one is a traditional standard normal homogeneity test (SNHT) and the other is a method based on EOF of filtered normalized monthly precipitation series which do not rely on the reference series. In the first method, the first step is to create a homogeneous reference series for each station with series from those stations that are near the checking station and have good correlations with the candidate series. Then the second step is to test the homogeneity of the candidate series with SNHT. Testing results show that some inhomogeneities exist in the precipitation data series in the selected region. Although the stations distribution is well-proportioned and the landform is relatively even in the study region, the density of the stations in the region is not enough, the references series might be questioned. Then the later references-independent method is used to check the potential discontinuities detected by SNHT. The precipitation data are normalized by calculating the cubic root of the monthly value, and the variations under inter-annual time scales are filtered. Then EOF is conducted to the fields where month is used as variables, the abrupt change points in time coefficients of the significant first eigenvectors are detected as the discontinuities of the series. Only those discontinuities which are detected by both of the two methods are regarded as real inhomogeneities. Finally, the confirmed discontinuities are adjusted in both annual and monthly series. Comparison analysis shows that the adjustment is reasonable and acceptable. Based on the earlier studies and operational practices of the network in China, a combination of the two different methods is proved to be necessary and possible, and it shows reasonability and application values in the homogeneity study of precipitation series in China, especially for the regions where the station densities are not enough. Further more, stations metadata are relied little on by these methods. In some context, the puzzles of lack of station metadata of precipitation data are avoided by these methods.

Contact Anemometer Self-recording Records Digitization Processing System Design and Realization

Qu Zhiyi, Hu Wenchao, Kong Lingwang, Wu Huanxia

2008, 19(2): 227-232.

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Abstract:
Contact anemometer self-recording instrument is the main wind measurement equipment in meteorological department. In the past, identifying the automatic recording curve is mainly depended on manual work. It is impossible for manpower to obtain all wind data because of the tremendous workload. Therefore, it is essential to design an automated processing system for self-recording curve to save the precious wind data. The wind data denoted by anemometer automatic recording curve are withdrawn by automated processing system making use of pattern recognition technique and digital image processing method.The digitization of paper-based record curve is a very significant research task in the field of pattern recognition. The technique of recording curve digitization has a wide application prospect; it can be applied to many different fields such as medical treatment, meteorological data and so on. A digitized processing system for contact anemometer self-recording curve of wind in the field of meteorological data is studied and implemented. The digitization process can be divided into four stages:curve image inputting, preprocessing of curve image, curve image segmentation, and curve tracking and recognition.The TWAIN standard compile image scanning program for scanner is applied by the automated processing system. The programming connection is provided by the TWAIN standard that imaging applications is allowed to communicate with scanners and digital cameras. In the process of preprocessing of curve image, median filter and regulated straight square drawing are introduced. In the curve image segmentation step, the traditional method of gray level threshold segmentation and color space segmentation is elaborated. In the step of curve tracking and recognition, a new method of contour tracing to extract the data in the curve image is presented. The wind speed data can be extracted more quickly and rightly by this method based on these characteristics of the wind speed curve image.The method mentioned above has practical signification. The system is tested by the consumers, and it has excellent effect.

The Spatial and Temporal Distribution of Insolation Duration over Rugged Terrains in the Guizhou Plateau

Yuan Shujie, Miao Qilong, Qiu Xinfa, Gu Xiaoping

2008, 19(2): 233-237.

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Abstract:
Due to local terrain factors such as slope, aspect and terrain inter-shielding, the insolation duration over rugged terrain is different from over horizontal surface. Calculating the insolation duration over rugged terrain is very difficult. In the mountainous regions of complicated landform and great height difference, the observation data of the existing weather stations are far from enough to reflect the spatial distribution of the complicated sunshine time.Guizhou Province, which is from 24°37′N to 29°13′N and from 103°36′E to 109°35′E, lies in the plateaus and mountains in the western China. The physiognomy of the whole Province falls roughly into the categories of plateaus, mountains, hilly land, and basins. 92.5% of the total land area is mountains and hilly land. Based on Digital Elevation Model (DEM) and Geographical Information System (GIS), the distributed models for calculating insolation duration over rugged terrain are developed. Applying the models to Guizhou Plateau with 100 m×100 m DEM data, the elaborated spatial distributions of insolation duration over rugged terrain are generated. The insolation duration over rugged terrain of considering slope, aspect and terrain inter-shielding is analyzed.The influences of slope, aspect and the terrain inter-shielding on sunshine duration are very big. The spatial distribution of sunshine duration has apparent terrain feature over rugged terrain. The solar altitude angle is quite low in January; the effect of slope, aspect is very apparent. The shadow areas of topography are relative large and the spatial difference of sunshine time is big. The insolation duration varies spatially from 16 to 142 hours, and the maximum is about 9 times as the minimum. The solar altitude angle is quite high in July; the shadow areas of topography are relative small. The insolation duration varies spatially from 133 to 210 hours, and the maximum is about 1.6 times as the minimum. But the sunshine time over horizontal surface is much in July, and the influence of local terrain on the insolation duration is still obvious. The insolation duration and its amplitude of variation vary between in January, July and in April, October. The annual average insolation duration varies spatially from 768 to 1824 hours, and the maximum one is about 2.4 times as the minimum one. The effect of slope, aspect and the terrain inter-shielding on annual sunshine duration is quite great. The spatial difference of it is very evident. Therefore, the effect of complex topography on insolation duration should be considered.

The Relationship Between East Asian Winter Monsoon Meridional Anomaly and Meiyu Precipitation of Jiaxing

Lu Chenli

2008, 19(2): 238-242.

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Abstract:
Using NCEP/NCAR reanalysis monthly average SLP data, a winter monsoon meridional change index (WMMCI) is defined to show the intensity difference of winter monsoon between mid and high-latitudes. The index is well in accordance with the East Asian winter monsoon index (EAWMI). Generally, when WMMCI is strong, so is EAWMI. And WMMCI is weaker when EAWMI is weaker, too.The correlation between WMMCI and Meiyu precipitation of Jiaxing is studied. The results show that the abnormal Meiyu precipitation in the coming summer is caused by the abnormality of East Asian winter monsoon and the influence lasts two or three years. There is a positive correlation between the WMMCI and later Meiyu precipitation of Jiaxing on both interannual and interdecadal scales. Jiaxing Meiyu precipitation is generally heavy (light) when preceding winter monsoon is strong (weak). The variation trend of the Jiaxing Meiyu precipitation is behind the index. The Meiyu precipitation of Jiaxing is continuously heavy (light) when WMMCI continuously strengthens (weakens) for 2 years and the winter monsoon is strong (weak). The effect on later precipitation caused by weak winter monsoon is slower than that caused by strong winter monsoon.The composite anomalies of 500 hPa height show that the development of meridional (zonal) circulation over mid-and high-latitudes is favored by the pattern of north positive (negative) and south negative (positive). The southward movement of the cold air is benefited (not benefited) by the meridoinal (zonal) circulation. Also, the pattern has a persistent effect on the circulation, by which the Meiyu precipitation is favored (not favored). A possible explanation of the continuous effect of the winter monsoon meridional abnormality on the Meiyu precipitation of Jiaxing is that the abnormality of westerly (easterly) in the equatorial Pacific Ocean is caused by the continuously strengthening (weakening) strong (weak) winter monsoon, by which the occurrence of El Niño (La Niña) through abnormal variation in sea surface temperature is triggered.

The Evolution of Lustre File System and the Perspective of Application to the Meteorology Filed

Yang Xin, Shen Wenhai

2008, 19(2): 243-249.

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Abstract:
Very high performance computer (HPC) systems are needed to run modern Numerical Weather Prediction (NWP) model. More and more meteorological applications, especially NWP Models have already been and will be run in these large scale cluster systems. As the HPC development has stepped into the mature phase, computing power is never a big problem any more. However, the data processing and data services are becoming a conspicuous issue, since a more powerful HPC would demand and generate much more data. One of the key elements in a HPCs environment to address the issue is the Cluster File System Technology.To improve the HPC's comprehensive utilization and the operational efficiency for meteorological applications, when data processing becomes a restrictive factor, several problems must be solved, such as, how the data can be efficiently moved into or out of a HPC, how a large application can be input or large amount of output data be generated fast; how the data can be exchanged or shared effectively among multiple HPCs? Cluster File System is the answer, and Lustre is one of the best Cluster File System solutions currently in the market. The advantages are as follows. First, Lustre is designed to be a very flexible, scalable and stable file system. In practice, it can be configured with a large variety of machines, as well as different network technologies; the number of nodes can range from several to tens of thousands. Second, Lustre software experiences for over 6 years in many important HPC environments, including the largest lab in the Department of Energy (DOE) in America. It has been widely developed, tested and then put into production for some highest mission-critical applications. During the latest one to two years, it has been recognized by the HPC world and successfully adopted by a majority of Linux based Clusters. One of the core technologies of Lustre is Object Storage which is usually implemented as Object Based Storage Devices (OSD) that aims at achieving both high performance and cross-platform features by offering an entirely new way of abstracting storage-objects. The concept of Object Storage is implemented by Lustre by introducing the Metadata Server (MDS) which is both the hardware and the software component in a Lustre Cluster.A couple of HPCs are currently maintained by National Meteorological Information Center for China Meteorological Administration users. A concept framework is proposed that is designed to establish a globally unified parallel file system by which multiple Linux clusters can be spaned in our environment, hence the operational workflow is optimized and the utilization of the storage resources among the clusters is improved. The global Business Continuity of mulitple HPC clusters can also be greatly improved with the help of this framework.

The System Development and Applications for Space Weather Monitoring and Warning Based on FY-2 Geostationary Meteorological Satellite

Shan Haibin, Guan Min, Liu Yujie, Yu Tao, Rong Zhiguo

2008, 19(2): 250-256.

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Abstract:
The FY-2 satellites are a series of geosynchronous meteorological satellites, which are instrumented to observe high-energy particles and solar X-ray fluxes except for meteorological observation. The spatial particle detector and solar X-ray detector are carried by the satellites. The high-energy particles detector has 7 energy channels to detect ³He (3.5—26 MeV), ⁴He (3.5—26 MeV), P1(3.5—26 MeV), P2(10—26 MeV), P3(26—100 MeV), P4( > 1.1 MeV) and E ( > 1.4 MeV). And the solar X-ray detector has 10 energy channels which range from 4 keV to 100 keV to detect the solar X-ray fluxes. The solar activity level is directly revealed by these observations, and a real-time monitor of the X-ray storm, proton event and electronic event is provided. Additionally, these X-ray detection data can be used to make early-warnings of space environment disasters. The design of the FY-2 geostationary meteorological satellites data processing software for space environment monitor is introduced, which is a part of the first-phase project of space weather monitoring and warning system, supported by China Meteorological Administration. It is presented how to process the data from energetic particle detector and solar X-ray monitor. Through some examples, the X-ray energetic spectrum characteristics of proton events and the hard X-ray change characteristics during whole proton event are analyzed. Several proton event forecast rules are also summarized. It is detected by the FY-2 satellite that there are X-ray storm and high-energy proton event caused by the solar strong activities from Oct 28, 2003 to Oct 29, 2003.The first X-ray storm is on from 10:57 to 11:49 on Oct 28, and the hard X-ray storm is stronger than the soft. A strong storm lasts from 12:40 to 13:51 on Oct 28, during which the high current of X-ray is kept about 20 hours. From the X-ray power spectrum, it is found that the hard X-ray flux has an impulsive increase corresponding to the hard X-ray flux. The proton event begins on Oct 28, 13:55, and lasts for 24 hours. From Nov 1 to Nov 3, 2003, two solar flares are found by the FY-2 satellites, one of which is not a proton flare, and the other is. Some different rules of the two flares can be found from the FY-2 data. The no-proton flare lasts for more than ten hours from 21:00 on Nov 1 to 14:00 on Nov 2, but its X-ray spectrum is stable, and the hard X-ray has similar changes to the soft. The X-ray current enhances on Nov 2, 18:20, and the hard X-ray becomes stronger than the soft. Then, the proton event happens at 20:40 on Nov 2. The X-ray power spectrum shows that the hard X-ray has an impulsive increase corresponding to the hard X-ray flux.

Vol.19, NO.2, 2008