应用气象学报

Cold Air Influence on the Tibetan Plateau Vortex Moving out of the Plateau

Yu Shuhua, Xiao Yuhua, Gao Wenliang

2007, 18(6): 737-747.

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Abstract:
Storm rainfall and torrential storm rainfall and flood to the east of the Tibetan Plateau and even over a large area of China can be led to by some vortices that move out of the main Plateau region. Much attention is paid by meteorologists to the research on Plateau vortex moving eastwards, but the study of cold air influence on the Tibetan Plateau vortex moving out of the Plateau is few. Based on analyzing the different vortex activities which lead to the severe flood in large area of China, the middle troposphere level cold air influence on the Plateau vortex moving out of the Plateau and by using the synoptic diagnose, numerical simulation and experiment, the cold air influence on the Plateau vortex moving out of the Plateau is discussed.By investigating and analyzing the different east moving processes of Plateau vortices during 1998—2004, typical Plateau vortex processes leading to the severe flood disasters over different region of China are selected. By synoptic analysis and using 4 times daily 1°×1°NCEP data and the same time upper air observational data, the potential vorticity of Tuole Plateau vortex moving out of the Plateau during August 12—14, 2002 is analyzed. By using the MM5 version 3.4 PSU/NCAR high resolution non-static mesoscale model, a series of numerical experiments are conducted. The following results are obtained. There is cold air influence both before and after the Plateau vortex moving out of the Plateau which has long active time (more than 36 hours). The Tuole Plateau vortex moves with shear line and moves out of the Plateau by influence of the cold air flow invasion from the northeast. By potential vorticity analysis on the Tuole vortex moving out of the Plateau, it is found that the Plateau vortices is influenced by cold air flow of northeast region of China and moves out of the Plateau when there is high level potential energy air moving into low level potential energy air and the cold air flow is forced close to wet and warm air flow. It is demonstrated through the numerical simulation of cold air influence on Tuole Plateau vortex that when there is no cold in Plateau vortex area or no cold temperature trough, the northeast main cold air is made lean to east and weak and less influence to Tuole vortex of northeast China cold air flow. The baroclinic instability is made small.The speed of the Plateau vortex moving out of the Plateau will also be slowed down, and the intensity of the vortex will be weaker and the maximal wind speed will be lowered. The influence of the China northeast cold temperature trough is especially much obvious and the Plateau vortex region will be small when there exists a China northeast cold temperature trough, and the Plateau vortex will draw back to the west and float around the Plateau edge.

Application of On-board GPS Data and High-precision Orbit Model to Polar Satellites Orbits Calculation

Guan Min, Yang Zhongdong

2007, 18(6): 748-753.

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Abstract:
A high precision orbit model based on numerical integration is introduced. Satellite's instantaneous position and velocity are derived from the position data measured by on-board GPS receiver, and then they are used as initial value to predict the orbit by high precision numerical integration. The six orbital elements which are used to describe the motion of satellite can be transformed to the satellite's position and velocity, and vice versa. The satellite's instantaneous orbital elements at time t₁ can be calculated from satellite's two position vectors and at time t₂ and t₂ respectively, then the satellite's instantaneous position and velocity at time t₂ can be obtained. There are many perturbing terms that have been considered in the satellite's high precision orbit model, including the aspherical gravitations of the earth, the perturbations that arise from the gravitational attraction of the sun and the moon, the solar radiation pressure and the atmospheric drag. The earth gravity model that is used is the EGM-96 model of degree and order of 360. Numerical methods are used to solve the equation of the satellite's motion. The variable order and stepsize method DE/DEABM are used for the numerical integration.This new method are applied to Terra/Aqua-MODIS satellite's orbit calculation. Satellite Terra's position vectors r₁ at time t₁ and r₂ at time t₂ are used to compute the instantaneous velocity vector. The result shows that the departure between the calculated observation and the GPS measurement is very small with the error of instantaneous speed less than±0.1 m/s. Then they are used as initial input to predict one of Terra/MODIS' further 10-minute orbit by applying the high precision orbit model. It shows that the satellite's position and velocity vectors and range which are predicted by this method are all consistent with the measurements by GPS. The following results are gained that the position error is between-20 m and +5 m, the velocity error is less than±0.2 m/s. The same method are used to compute Aqua/MODIS' orbit. The Aqua's position vectors error between the predictions from high precision orbit model and the GPS measurements is less than 40 m, the error of predicted velocity vectors is less than±0.4 m/s.Because of the high precision and the continuous stability in certain time, the high precision orbit model based on numerical integration can be used to verify the reliability of GPS measurement results if the initial input is correct, and substitute the wrong GPS measurement value. Further more, the new method is suitable for FY-3 satellite's orbit computation.

Application of Generalized Moist Potential Vorticity in Non-uniformly Saturated Atmosphere to Torrential Rain Forecast

Zhou Yushu, Cao Jie, Wang Donghai

2007, 18(6): 754-759.

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Abstract:
The introduction of generalized potential temperature and tendency equation of generalized moist potential vorticity into the thermodynamic framework is based on the non-uniform saturation of real atmosphere. The generalized moist potential vorticity (GMPV) equation is deduced by absorbing the generalized potential temperature. The water vapor and its gradient effect can be manifested in the GMPV equation, which indicates the convergence mechanism of water vapor at lower levels when torrential rain occurs. The GMPV anomaly is used in diagnostic studies of torrential rain both in North China and Yangtze River Basin. The results show that dynamic identification and forecasting of torrential rain from the perspective of generalized moist potential vorticity and its anomaly are effective, which maybe provide a new thought for the operational application of the GMPV.

CISK Inertia-gravitational Wave Related to Horizontal Wind Shear Intensity Nonhomogeneous

Wang Xiaofang, Cui Chunguang, Hu Bowei

2007, 18(6): 760-768.

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Abstract:
In the Meiyu season most of the severe MCSs (mesoscale convective systems) with torrential rain may form, develop, move and regenerate down-stream along such Meiyu front in the Yangtze River basin. The kind of wave disturbance most relevant to these activities of MCSs is not only likely the deep mesoscale inertia-gravitational waves in company with the macroscopic cumulus cloud ensemble heating (inertia-gravitational wave CISK briefly), but also that relates to horizontal wind shear and wind shear intensity nonhomogeneous. The so called Meiyu front in Yangtze River basin is actually an equivalent barotropic zone wherein the horizontal thermal gradient is negligibly weak and rather the humidity gradient is very strong particularly in the lower troposphere. A three-dimensional linear model in a dimensionless pseudo-height (Z ≡-ln (p/p₀)) coordinates with a simple parameterized cumulus heating expression is most suitable to be applied to discuss the deep mesoscale disturbances analytically in Yangtze River basin. The behaviors and the weather influences of the CISK inertia-gravitational wave relating to horizontal wind shear instability near Meiyu front on the MCSs activities over Yangtze River basin are investigated. The results show that the horizontal wind shear and horizontal wind shear intensity nonhomogeneous characters have the important influences on the instability of CISK inertia-gravitational wave. In the dry stratified atmosphere without cumulus heating, practically in almost all cases, the effect of horizontal wind shear and its horizontal nonhomogeneous characters can not make the inertia-gravitational waves instable. And only in the nearly CISK situation and the weak stability condition, the horizontal wind shear and its horizontal nonhomogeneous characters have a positive contribution to the instability of the wave disturbances. Such additional instability is mainly attributing to the second order derivative of basic flow in meridional direction. So the most favorable instable location is near the low-level jet stream on the south of the Meiyu front where the MCSs are likely most active. It does not mean that the instability and dispersion of the inertia-gravitational wave-CISK are the only mechanism of the genesis of the MCSs. Other mechanisms, including the dry inertial-gravitational wave in some stable-stratification atmospheric layer, may also lead to the MCSs development.

Aridity-wetness Characteristics over Northwest China in Recent 44 Years

Wang Pengxiang, He Jinhai, Zheng Youfei, Zhang Qiang

2007, 18(6): 769-775.

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Abstract:
Northwest (NW) China covers Xinjiang, Qinghai, Ningxia, Shaanxi and the western part of Inner Mongolia; it is located to the north and northeast of the Qinghai-Tibetan Plateau, far away from oceans. This extensive region is one of the aridest areas in the world and also a principal arid and semi-arid expanse in China, including totally 85%of such land in China. This region is under the impacts of westerly, plateau and monsoon climates so that rainfall undergoes great variability and there is a high frequency of drought, serving as a zone sensitive to climate change and ecologically vulnerable. The inference is presented by Shi Yafeng that the NW climate is changing from a dry, warm one to a moist, warm stage one, which is awaited for further studies with more climate elements. Whether climate pattern changes or not depends completely on the change in hydrological cycle whose critical ingredient is evaporation, by which, in combination with rainfall and runoff, a regional hydrological equilibrium is determined. Rainfall is focused on by previous studies on NW China climate change and the pattern conversion and it is considered by few researchers whether the climate is changing from a warm, dry one to a warm, moist pattern by means of rainfall and evaporation in combination, which are two no negligible aspects of water equilibrium on a regional basis. It is apparent that drought is led to by deficient precipitation and evaporation would increase such that it is feasible to take into account the budget of rainfall and precipitation in the study on transformation of arid-moist climate for the NW China, which is of far-reaching strategic and practical significance to NW China socio-economic development. Based on 1960—2003 rainfall and small-sized evaporation pan measurements from 131 stations in NW China, an aridity-wetness homogenized index of rainfall and evaporation is proposed as the crucial components of hydrological equilibrium, with EOF, REOF, tendency analysis, M-K sudden change check and Morlet wavelet analysis, the aridity-wetness evolution characteristic is analyzed over northwest China in recent 44 years. Results show that a regional consistent anomaly serves as the paramount mode of the 1960—2003 yearly dry and wet features, as well as the opposite feature in the NW (NE) to the SE (SW) which is also the important mode for the annual dry and wet abnormality. The space patterns for the arid and moist anomaly include the westerly, tableland and monsoon climates. The annual arid and wet features display greatly humidification trends in the whole NW, westerly and tableland climate zones, with the westerly climate humidification stronger than the trend of the tableland sub-zone, their abrupt change is from arid to moist in the mid-1970s. While the area on the fringe of monsoon climate in the southeast of NW China shows a trend of turning aridity, their abrupt change is from moist to arid in the early 1990s. In spite of the period surge which is not the same as in NW and three key climate zones, inter-decadal oscillation of over 8-year is a main period in all regions, 3—5-year inter-annual surge is also shown in all regions, but the intensity of amplitude is weak.

Interdecadal Change of East Asian Winter Monsoon and a Numerical Experiment on Its Possible Cause

Shi Xiaohui, Xu Xiangde

2007, 18(6): 776-782.

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Abstract:
In the recent more than 20 years, the surface air temperature (SAT) is obviously increasing over the globe. More and more scientists believe that it is caused by greenhouse effect. Many researches reveal that the warming trend is heterogeneous in space and time, and the most obvious warming appears in high latitude and winter. Under this heterogeneous warming background, the sea-land thermal contrast would be changed and then may lead to the variation of East Asian winter monsoon (EAWM). Based on this hypothesis, the interdecadal variation of EAWM is analyzed and the influence of the change of sea-land thermal contrast caused by greenhouse effect on the variation of EAWM is verified by a numerical experiment. In order to study the interdecadal variation of EAWM in the latest few decades, an annual index of EAWM intensity is defined, briefly I_WI, by means of the NCEP/NCAR reanalysis monthly mean sea level pressure (SLP) data during 1961—2000. The variation of the interdecadal component (11-year running mean value) of I_WI is investigated. The result shows that EAWM has an obvious interdecadal variation in the period of 1961—2000. It weakens from 1960s to early 1970s and strengthens after that, then obviously weakens from early 1980s again. This interdecadal variation of EAWM is consistent with the wintertime warming trend in the north of East Asia. To investigate the possible causes of the interdecadal variation of EAWM, the correlation coefficients of the interdecadal components of I_WI with the mean SAT over the east of East Asia and the west Pacific are calculated separately. The results show that on the interdecadal scale, the correlation of the I_WI with the SAT over the land is more significant than that over the sea. It reveals that the interdecadal warming in the northeast of East Asia is closely related to the interdecadal weakening of EAWM. So, a possible mechanism of the interdecadal variation of EAWM is that the warming over the East Asia and the weakening of sea-land thermal contrast between the East Asia and the West Pacific are led to by the greenhouse effect, and then the weakening of EAWM is induced. Because the greenhouse effect is mainly caused by the decreasing long-wave radiation effect of increasing greenhouse gases, to verify this possible influence of greenhouse effect on the interdecadal variation of EAWM, a sensible numerical experiment with decreased long-wave cooling rates over northeast of East Asia in the regional climate model (RegCM3) is performed. The simulation results show that the reduction of the eastwest orientation SLP difference and the weakening of northerly on the low level atmosphere in winter, i.e., the weakening of EAWM, could be led to by the decreasing of long-wave cooling rates over northeast of East Asia. Summing up the above diagnosing and simulation results, such conclusion can be drawn that the interdecadal weakening of EAWM might be a regional response to the global warming caused by greenhouse effect.

Spatial and Temporal Characteristics of Dry/Wet Land Surface in Anhui Province with Their Impacts on Agriculture in Recent 30 Years

Ma Xiaoqun, Zhang Hui

2007, 18(6): 783-790.

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Abstract:
The reference evapotranspiration (E_T0) in Anhui for the period from 1971 to 2000 is calculated using FAO Penman-Monteith equation, in which the term of net radiation is modified utilizing the observation data of radiation in Anhui. Aridity index (I_a) is calculated by E_T0 and precipitation of the same period, and variation of area land surface arid and humid condition and its impact on agriculture are analyzed based on aridity index in different time scales. The results indicate that the isoline of I_a=1 is the boundary of the humid and semi-humid zones, and it has a good consistency with the isoline of 1000 mm annual precipitation. Also, the isoline has clear agricultural meaning. The isoline (I_a=1) fluctuates in the direction of south and north during 1970s, 1980s and 1990s, and this fluctuant zone is just Jianghuai watershed where is apt to drought and waterlog. Temporal variation of land surface arid and humid condition in Anhui shows obvious regional characteristics. On the one hand, because of temporal variation trends of the precipitation and the reference evapotranspiration, aridity indices present significant increasing trend in fluctuant zone, and significant decreasing trend in semi-humid and humid zones. On the other hand, influenced by great interannual variability of precipitation, interannual variability of aridity indices is also great, which is most remarkable in the fluctuant zone, and second remarkable in semi-humid zone. Therefore, drought is the most serious menace in the fluctuant zone; and drought and waterlog both exist in the semi-humid and humid zones, which are remarkable in 1990s. Temporal variations of land surface arid and humid condition root mostly in summer half year in each region. Temporal variation of land surface arid and humid condition affects increasingly on agriculture in each district. In semi-humid zone, affected by the water shortage and high rainfall variability, the frequencies of summer waterlog, summer-autumn and autumn-winter drought are quite high. In Jianghuai watershed liabledrought fluctuant zone the variation trends of precipitation and aridity index are opposite to those of the other two areas, the rice and autumn harvested crops are threatened by drought evidently. In humid zone, although the average condition is humid, variations of precipitation and aridity index are even high than those of the semihumid area in summer half year and the frequencies of drought are increasing. The normal growth of rice and semi-tropical fruit trees is threatened increasingly by seasonal droughts. Anhui belongs to the transition area of semi-humid and humid zones. The spatial and temporal characteristics of land surface arid and humid condition in Anhui Province are thoroughly analyzed. The results are useful to understand the variation of semi-humid and humid climate and its influences, as well as to guide the agriculture. Limited by data, the variation of semi-humid and humid is only discussed in the recent 30 years. In fact, the variation of land surface arid and humid condition status is a gradual process. The analysis on data of a longer time period helps to get the more scientific and objective results. Therefore, it is very necessary to keep on complementing the data for a long-time research.

The Method of Diagnosing the Onset of Meiyu Based on the Moisture Data

Cao Xiaogang, Ding Jincai, Ye Qixin, Wang Jun, Qiu Lihua

2007, 18(6): 791-801.

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Abstract:
Meiyu is an important transition period from spring to summer in the Huaihe and Yangtze River Reaches. The traditional methods to diagnose the onset of Meiyu are mainly based on rainy days, temperatures and position of subtropical high, etc. But because of the discontinuous rainy days and variable synoptic background, the traditional methods can't reach consistent results to the onset of Meiyu in many years. A new method is introduced to diagnose the onset of Meiyu using moisture. Characteristics of moisture variation during Meiyu season in recent four years are analyzed based on the precipitable water vapor data from GPS Meteorological Network (thereafter as GPS/PWV) in the Yangtze River Delta. It is founded that the GPS/PWV changes significantly on the beginning of Meiyu, which shows a seasonal change of moisture. The following three indexes of GPS/PWV are concluded to diagnose the onset of Meiyu:Everyday average and five-day average of GPS/PWV ascend to more than 40 mm; five-day average of GPS/PWV is stably under 40 mm before the onset of Meiyu, occasionally over 40 mm, after the onset of Meiyu, five-day average is stably over 40 mm, occasionally under 40 mm; the difference of five-day average shows a peak more than 20 mm at about the onset of Meiyu.If the three requirements are met by the GPS/PWV variation, it can be considered as the onset of Meiyu. This method is tested by PWV from 1980 to 2000 based on radiosonde sounding data. Results show that the onset days of Meiyu diagnosed by new method are more reasonable than those by traditional methods; the seasonal transformation can be better illustrated by the moisture data. This method is also successfully applied to diagnose the onset of Meiyu in 2006. The onset day of Meiyu in 2006 over the lower reaches of the Yangtze River issued by different observatories is different, such as 13—14 and 22 of June. Through analysis of GPS/PWV data from June to July, June 22 is more reasonable as the onset day of Meiyu in 2006.In addition, analysis shows the increasing of water vapor is directly led to by north-moving of subtropical high, which is advantageous to the establishment of Meiyu front.

The Morphological Characteristic and Spatial Behavior of the Meteorological Disaster Event

Hu Haibo, Wang Yingchun, Liu Weidong

2007, 18(6): 802-809.

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Abstract:
The surface formed by the influence of the meteorological disasters is no more than a polygon in its geometry shape. And the assimilatory meteorological elements, the character of the underlying surface, the habitat and accumulative assets of human beings are all combined on the characteristic influencing dimension of disaster, so that the condition indicates significant difference on the distribution and space background. However, the spatial analysis and the method of morphology to initialize the digitized dynamical convolution operator are generally implemented, according to the multi-types of land use and the land cover represented by the complexity of underlying surface on the urban area. Supported by the combined GIS and the morphology technique, the gridded atlas of the meteorological map is handled by the operation of erosion or dilation. Moreover, with the dynamical erosion and dilation operation to the grid map derived from the map containing the contour lines of these meteorological elements, such as the temperature, the precipitation, the humidity, and any of those observations when the disasters occur, the gridded atlas for the urban area influenced by the disaster could be set up, it would be a good way to evaluate the meteorological disasters. The research on the high temperature event occurred on July 22, 1999 is carried out as a case study, and it shows that the grids which near or contain the water or green land have been applied with the erosion operation. On the contrary, the grids which are mainly made up of buildings, roads, or cement surfaces are applied with the dilation. The conclusion drawn by the research is conformity with the characteristic of the land surface processed in the urbanized underlying surface, and even the responding behavior is extremely similar. The effectiveness of the case study is very good by applying the spatial evaluating model, and the outcome by the form of atlas is consistent with the actual situation influenced by the disaster. It is also demonstrated that the disaster evaluation with the morphological method is easy to operate, and has the ability to deal with the multi-factors that bring about the loss of disaster, by which the characteristic of the distribution is embodied.

The Structure of Tropical Cyclone from Advanced Microwave Sounding Unit

Qiu Hong, Fang Xiang, Gu Songyan, Zhang Wenjian, Zhu Yuanjing

2007, 18(6): 810-820.

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Abstract:
Strong sounding abilities of atmospheric temperature and moisture, cloud and precipitation are provided by the Advanced Microwave Sounding Unit (AMSU) on-board the new generation polar orbit meteorological satellite series—NOAA-KLM. Two parts are included in the AMSU: AMSU-A and AMSU-B. The frequency of 50—60 GHz O₂ absorption band is mainly covered by AMS-A channels, and is used to retrieve the temperature profile. The water vapor absorption line centered at 183.31 GHz is covered by AMSU-B and is mainly used to get moisture vertical distribution of atmosphere. The AMSU-A and AMSU-B data from NOAA series satellites are used to analyze the thermal and cloud structure of tropical cyclone and the relation between TC intensity and its central warming and the change of could and rain structure.The AMSU-A and AMSU-B data are limb adjusted based on Wark and mapped at the center of the tropical cyclone (TC) to prepare for analysis of TC thermal and cloud structure. Firstly, the warming anomaly of two TC cases occurring over the northwestern Pacific Ocean in 2003 is analyzed with AMSU-A channel 6—9 data from NOAA-16/17 satellites, it is found that the warming anomaly of the weak TC Kronvan at its most intensive stage is only about 2.5 K and occurs at lower layers, but Maime, the strongest TC of that year, had more than 5 K anomaly and the warming occurs at all levels from 350 hPa to 100 hPa. The statistic relation between the intensity of TCs and their strongest warming anomaly is analyzed with TC cases in 2001—2003, it shows that the anomaly increases as the TC intensity becomes stronger, with related coefficients of 0.778.Then the cloud structure of the TCs is analyzed based on AMSU-B data. The data from AMSU-B window channel at 150 GHz are used to show the total cloud and rain structure of TC and that from high level channels centered at 183.31 GHz are used to show its convection distribution. The results show that the strong convection occurs at the eyewall and the outside rainband has obvious characteristics in the microwave images at 183.31 ±1 GHz , the low level stratus cloud would be viewed in window schannel image. The time series data of Dujuan are used to analyze the change of cloud structure of TC and its relation to the intensity, it is found that the highest intensity of TC is got after the convection burst out.It is concluded that the observation from AMSU-A temperature channels, especially for those weighting functions at upper troposphere has good response to the TC warm core. The observation from high frequency channels of AMSU-B shows the structure of could and the distribution of deep convection. The warming anomaly and the deep convection structure of TC have a close relation to the TC intensity. Further research would be done for this target.

Ocean Chlorophyll-a Derived from Satellite Data with Its Application to Red Tide Monitoring

Zhang Chungui, Zeng Yindong, Zhang Xing, Pan Weihua, Lin Jing

2007, 18(6): 821-831.

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Abstract:
The signal-to-noise ratio of ocean color channels of MODIS sensor is higher than SeaWiFS sensor and the bandwidth is narrower than SeaWiFS, thus MODIS data are more suitable for the retrieval of chlorophyll-a in ocean. Many standard empirical algorithms and semi-analytical algorithms are supplied to calculate ocean chlorophyll-a by the SeaDAS software which is distributed from NASA. Considering the characteristic of MODIS sensor, the two standard empirical algorithms SeaDAS OC2 and OC3, two semi-analytical algorithms SeaDAS Clark and NSMC-CASE2 are used to calculate ocean chlorophyll-a based on MODIS data, the correlation of MODIS chlorophyll-a and ten stations measured chlorophyll-a is analyzed in Fujian coastal red tide monitoring region in 2004. The statistic result of MODIS chlorophyll-a and ten stations measured chlorophyll-a shows that the correlation index of OC2 standard empirical algorithms is 0.787, and OC3 is 0.839, and Clark semi-analytical algorithms is 0.510, and CASE2 is only 0.133. Although the ocean chlorophyll-a calculated by SeaDAS based on MODIS data is high compared with the chlorophyll-a measured in locale, the chlorophy ll-a variational curve of SeaDAS OC2 and OC3 and Clark is similar to the chlorophyll-a variational curve measured in locale. However, the chlorophyll-a counted by CASE2 semi-analytical algorithms is much higher than the chlorophyll-a measured in locale, and the chlorophyll-a variational curve of CASE2 is very much different to the chlorophyll-a variational curve measured in locale. The red tide occurring in Fujian coastal region at one time with the MODIS chlorophyll-a during 2002—2005 is analyzed also, and the possibility of monitoring red tide based on 250 m and 500 m resolution ratio MODIS visible light data is discussed. The ratio of MODIS red (250 m)and green (500 m) channel obviously changes in the whole course of red tide disaster, the ratio is much higher when the red tide disaster occurs than before and after the red tide disaster occurs. The results show that there is inconsistence high estimate for chlorophyll-a derived from two standard empirical algorithms and two semi-analytical algorithms. On the opposite, SeaDAS OC3 standard empirical algorithms are suitable to calculate ocean chlorophylla in Fujian coastal region based on MODIS data. On the basis of accumulating the chlorophyll-a data measured in locale, the relevant inversion mode for quantitative monitor of remote sensing data of chlorophyll-a on Fujian coastal water will be established with the 250 m and 500 m resolution ratio of MODIS visible light data, and atmospheric correction process will be carried out in MODIS data, thus it is possible that the change of chlorophyll-a on Fujian coastal water will be accurately predicted .

The Response of Typical Vegetation Growth to Climate Conditions in North Tibetan Plateau

Chu Duo, Deji Yangzong, Pubu Ciren, Bian Duo, Li Chun

2007, 18(6): 832-839.

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Abstract:
Based on the scanned and georeferenced vegetation map of North Tibetan Plateau from 1：1000000 China Vegetation Atlas and grassland resource map of the North Tibetan Plateau, alpine steppe in the western North Tibetan Plateau, alpine meadow in the central North Tibetan Plateau and alpine shrub meadow in the eastern North Tibetan Plateau are selected as three most typical vegetation types in the North Tibetan Plateau. First, the climate conditions in North Tibetan Plateau are analyzed. Secondly, the ten-day mean temperature and precipitation and SPOT VEGETATION ten-day maximum composite NDVI (normalized difference vegetation index) of three typical vegetation regions from 1999 to 2001 are studied. Finally, the relationships between vegetation growth based on the SPOT VEGETATION ten-day maximum composite NDVI and the ten-day mean temperature and ten-day precipitation as two key climate variables that affect vegetation growth in these regions are analyzed. The spatial distribution of the precipitation decreases from southeast to northwest and that of the temperature decreases from south to north in the North Tibetan Plateau. Contrary to the precipitation, evaporation is higher in west than that in east in the North Tibetan Plateau. SPOTV EGETATION NDVI variations can represent the three typical vegetation growth patterns. In two important vegetation growth periods, the date of the green-up initiation and withering of vegetation represented by NDVI is consistent with the vegetation growth phases by calculating from accumulated temperature. The coefficients between NDVI and corresponding temperature from 1999 to 2001 in the alpine steppe is 0.66, in alpine meadow 0.81, and in alpine shrub meadow 0.79, while the coefficients between NDVI and precipitation in three different vegetation types are 0.53, 0.68 and 0.54, respectively. It means that NDVI variations in the North Tibetan Plateau are more sensitive tothe temperature than to precipitation. Because of the high altitude and frigid climate in the North Tibetan Plateau, the impact of the temperature on the vegetation growth markedly is higher than that of the precipitation. The temperature is the main confining factor for vegetation growth in the North Tibetan Plateau. Response degree of three typical vegetations to climate variations in the North Tibetan Plateau from high to low arealpine meadow, alpine shrub meadow and alpine steppe, respectively .

The Synoptic Conceptual Model of 6-hour Tropical Cyclone Rainfall and Its Application in Guangxi

Wang Jiechun, Jiang Jixi, Feng Jianbi, Deng Yujiao, Li Yu

2007, 18(6): 840-848.

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Abstract:
Every 6-hour rainfalls of 9 tropical cyclones (TC) that influence Guangxi Autonomous Region in three years from 2001 to 2003 with the number of 0103, 0104, 0107, 0212, 0214, 0218, 0220, 0307 and 0313 are selected for the study. The characteristics and the mechanism of the heavy rainfall caused by landing tropical cyclones are analyzed in detail, using the information from Tropical Cyclone Annual, observational precipitation data, NCEP/NCAR reanalysis data and black-body temperature (TBB). Based on the study, methods for diagnosing and forecasting the intensity and distribution of precipitation in 6-hour over Guangxi are developed.Every 6-hour rainfalls within the 9 tropical cyclones are analyzed. The regions with 6-hour rainfall amount over 5 mm are picked up, especially those areas of over 50 mm rainfall caused by TC are divided into four types: zonal, meridio nal, NE—SW and NW —SE orientated kinds. Then, the detailed analyses on the main physical factors at upper-level , middle-level and low-level related to the heavy rainfall in each type are made and the relationship between the rainfall in future 6-hour and each factor is investigated. The result shows that the rainfall distribution and intensity in 6-hour relate closely to the physical factors such as divergence field at upper-level, the field of vorticity at middle-level, convergence and ascending motion and the low-level jet, the moisture flux convergence and so on. On the other hand, different type of rainfall distribution and precipitation intensity is formed by the different allocation of these factors. With this understanding, the conceptual models of 6-hour precipitation forcasting and its main transforming direction are summarized. And the forcasting method on the rainfall distribution and intensity in 6-hour is presented. The method can be simply described as below. The location of TC center, the trend of low-level jet and the physical factors such as divergence field at upper-level, the field of vorticity at middle-level, convergence and ascending motion at low-level can help to find out the rainfall type. Then with the location of low-level jet, the distribution of TBB and the moisture flux convergence, themain area of rainfall can be fixed on. Finally, based on the results above and combined with the evolution of cloud systems, the allocation of physical factors and the negative variate zone of TBB, the intensity of precipitation can be worked out.The method is tested on two TCs in 2006. The test results indicate that the false fo recasts are made up of more false-alarm than miss, and the fo recasting of heavy rainfall is not so good .

Differences Between Automatic and Manual Observation

Wang Ying, Liu Xiaoning, Ju Xiaohui

2007, 18(6): 849-855.

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Abstract:
Manual observation is being replaced by automatic observation in China gradually. Till 2006, there are altogether 1904 automatic weather stations (AWS) in the country. Great changes have taken place in the observational rules and methods of AWS comparing with manual observations. Inhomogeneity of observational time series may be caused by many reasons and the change of observational instrument is an important one. The records of AWS and manual parallel observation in a certain period of time may be used in analyzing the observational differences between AWS and manual.Based on the data of automatic and manual parallel observations in 700 stations during 2001—2005, the differences of temperature, precipitation, pressure, relative humidity, wind speed, wind direction and ground surface temperature are calculated and the characteristic differences between automatic and manual observation in different areas are analyzed. Results show that certain differences exist in all the meteorological elements between automatic and manual observation, but in most areas the differences in temperature, precipitation, pressure, relative humidity, wind velocity and direction and ground surface temperature fall in the accepted error rang of AWS. In most stations in China the difference is of ±0.1℃ in the annual mean temperature. To be exact , the difference of annual mean maximum and minimum temperature is a little larger than annual mean temperature. More significant system error appears in the automatic observation of a few stations, and when the automatic observational data of temperature are used the instrument systematic error should be corrected. The difference of all elements between automatic and manual observation has different distribution features in China, and the same element may vary greatly in different climatic situations. In dry areas or in the seasons with little precipitation, there is a great differences between auto and manual precipitation observation. The areas with difference of 0.2—0.6 hPa in pressure are mainly distributed in the western areas with high sea level elevation. In the wet areas in the south of the Yangtze River, Tibetan Plateau, northeastern area and mountain stations of the northeast, big difference appears in the auto and manual observation of relative humidity. In the north during snowing period there is a significant difference between auto and manual observation of ground surface temperature. The use of automatic stations exerts certain influence on the continuity of annual mean temperature, so it is necessary to test whether the significant difference exists in the auto and manual observation time series if manual and auto observation data are used. Homogeneity correction is needed if the significant difference appears.The difference between auto and manual observation is unavoidable. Any instrument change in history will bring the data difference, especially the change from manual observation to automatic observation with quite different observational instrument and method. The time series of automatic observation are short in China and the replacement by automatic observation just starts, so with longer observational time series and more automatic stations further analysis is needed to know the causes for the difference between automatic and manual observation as well as correcting methods .

The Artificial Intelligence Identification and Filtering Methods for Non-meteorological Radar Echo in Ningbo

He Caifen, Huang Xuanxuan, Ding Yeyi, Zhu Longbiao

2007, 18(6): 856-864.

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Abstract:
The products of Doppler weather Surveillance Radar are occasionally contaminated by non-meteorological echo. For example, the accuracy and reliability of the precipitation-estimating products are reduced significantly by the clutter contamination. For the purpose of improving the accuracy of the products, the clutter removalwork should be firstly done before further developing new radar products. Statistical analysis of non-meteorological radar echo in Ningbo from 2003 to 2006 shows that these clutters mainly are normal propagation ground clutters (NPGC) and abnormal propagation ground clutters (APGC) . The radar-derived products are contaminated by the two types mostly. The following characteristics are shown: they are mostly common in low elevations, discrete distribution of reflectivity products, radial velocity values and spectrum widths values in clutter around zero occasionally mixing with high values and significant horizontal and vertical gradient. Based on echo characteristics and the traditional experience on clutter identification, a stationary safe multidimensional linear approximation algorithm simulating manual eyes' fuzzy logic is designed, which takes full account of the relationship between computation efficiency and data quality. The following three rules should be obeyed by clutter removal. The first is conservation, which is to avoid removing precipitation echoes improperly. The second is independency, that is different clutter is identified and filtered respectively. The third is diversity, that is to utilize three moments of R, V, W of more than two elevations (now use 0.5°and 1.5°) as many as possible and other real time data. The flow chart of clutter removal quality control is given and key points are as below: to build echo background to classify the echoes such as clear or light rain, moderate rain, heavy rain, the edge of strong echoes, strong echoes and strong clutters and so on, identification of isolated clutters, clutter filtering based on the horizontal and vertical reflectivity gradient, identification of small region where the reflectivity values have a sharp change. 190 cases have been tested with the techniques under weather conditions including clear sky, showers and deep convections. Results show that it works well, and has good performance to remove the nonmeteorological radar echoes completely and accurately within the range of 150 km. But out of the range, it doesn't operate well while the radial velocity is fussy. Because of the great horizontal and vertical gradient in small scale deep convective systems, for the sake of conservation, not only a very strict threshold is set but also the removal work is given up to protect the real precipitation echo where fussy radial velocity exists. The cases in the article prove that it doesn't cause wrong removal in small-scale deep convections. If satellite data, real time surface and sounding data can be combined together with radar base data, and time continuity of radar data is taken into account as well, the technique may probably be applied up to a valid range of 200 km even further away in the future.

Estimation of Wheat Development Periods on a Grid Scale upon Potential Temperature

Zhang Xuefen, Wang Chunyi, Chen Dong, Zou Chunhui, Chen Huailiang, Fu Xiangjian

2007, 18(6): 865-869.

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Abstract:
Wheat development period (WDP) data of different scales on grids are necessary in monitoring by remote sensing and quantitative assessment during late freezing. Taking Henan Province as an example, the calculation of WDP on grids is proposed upon potential temperature by GIS considering the elevation of different grids, which is a strong mechanism. At first, it is divided into five different ecological regions according to different climatic types, which is Ⅰ area (the north of Henan) , Ⅱ area (the west of Henan) , Ⅲ area (the middle of Henan) , Ⅳ area (the plain in eastern Henan) and Ⅴarea (the south of Henan) , respectively. The equation of accumulated temperature (E-AT) between turning green and jointing is constructed based on more than two decades WDP records. To consider the effect of elevation upon interpolation, equations of potential temperature and stateas well as ARCGIS software are used to calculate grid potential temperature; to reckon air pressure etc. on grids; to deduce grid temperature data based on the above results; to perform winter wheat elongation stage on grids which are matched with remote sensing data according to E-AT at last. The results show that the method to calculate WDP indirectly has much new idea and strong mechanism; the way to perform data of wheat turning green in grids by means of meteorological index is more theoretical and accurate than that of setting the same date of WDP in the same climatic region during the calculation of WDP; the error resulting from this method is two days or so, and is within the permitted error which is about 5 days during monitoring wheat late freezing; the error by the indirect way to calculate WDP after obtaining potential temperature and air pressure is lowercompared with results from directly interpolating temperature and other ways considering terrain height. And the result can be used during monitoring late frost by remote sensing.

Application of NetFlow Technology to Network Data Flow Monitor and Analysis in Guangdong Meteorological Bureau

Xiao Wenming, Lang Hongliang, Chen Xiaoyu

2007, 18(6): 870-876.

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Abstract:
For a network administrator, it is essential to understand the traffic characteristics and the user behavior which is typically achieved by the traffic measurement. The basis of the NetFlow technology are reviewed. The function, application, switch features and datagram format of NetFlow are further analyzed. NetFlow's application in the network of Guangdong Meteorological Bureau is introduced in detail. In order to make the network administration convenient, straightforward, and easy for decision making, a Network Monitoring System (NetFlow Analysis System of Guangdong Meteorological Bureau) is designed based on NetFlow for network monitoring. The health of network can be quickly determined by the system, statistics are compiled for each user, and warnings of impending network issues are given. The selection of monitoring nodes is based on the structure ofthe network. Depending on the application, special care is put on how to collect network traffic data. For the ease of use, a host of web application is developed to automatically collect statistics, generate real-time report, and compile statistics. The system has the characteristics that network running situation can be looked over bythe network administrator conveniently, the statistics of the user habits of using the internet and the trouble of network can be found in time. The time that the network administrator needs to search and to get rid of the network breakdown will be evidently reduced by the completion of the design.An analysis is made on a case happened in Guangdong Meteorological Bureau Network on Dec 5, 2006 on how the NetFlow Analysis System of Guangdong Meteorological Bureau is used to quickly identify the network breakdown, and to find the root cause, and to recover it by using the traffic measurement. By using the NetFlow Analysis System of Guangdong Meteorological Bureau to analyze the data stream of NetFlow, it is easy to find the IP address of virus, and the infected computers. Since the worm virus can initiate massive scanning connection during their spreading process, using SNMP and the switch ports linked with the computers those use these IP addresses can be located and the virus-infected computers can be isolated from the network by closing the corresponding switch ports. In this case, not only those kinds of abnormities of different networks in different time segment exactly can be detected by the system, but also the efficiency and bottleneck of the running network can be analyzed on time. So the network performance can be optimized by network managers more promptly and reasonably.

Concurrent Multiprocess Application to Domestic Telecommunication System

Hu Yingmei, Shen Wenhai, Song Zhiguang

2007, 18(6): 877-884.

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Abstract:
As the national meteorological telecommunication center, Beijing Meteorological Telecommunication System (BMTS) is mainly responsible for the collection and dissemination of national meteorological data. With all kinds of means of exploration and products of weather service teeming, domestic meteorological telecommunication software cannot satisfy the meteorological data real time transmission needs, so meteorological data can not be used in time. Communication software is imperative to improve the ability to exchange information to meet the ever-increasing demand for the exchange of real-time weather information. Along with the computer technology development, the multi-advancements technology also obtained the widespread application and development. By analyzing the causes and treatment of the zombie process, function waitpid ( ) is used to avoid the zombie process. Furthermore, corresponding strategy is formulated by analyzing the quit status information and it is made sure that meteorological data exchange accurately, timely and efficiently in BMTS. On the other hand, by comparing many interprocess communication technologies and combining domestic communications features and the actual business, message queue is adopted. Now the processing time of newly data on BMTS decreases to 43%. After solving the problems above, multi-process technology is applied on BMTS, by which the transmission efficiency of domestic meteorological data is improved. This software has been running reliably and stably in the system since 2005 and real-time exchanging and sharing of the nationwide newly meteorological data are ensured.

2007, 18(6) DOI: 10.11898/1001-7313.20070618

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Abstract:

Vol.18, NO.6, 2007