Vol.17, NO.4, 2006

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Doppler Radar Analysis on a Series of Downburst Events
Yu Xiaoding, Zhang Aimin, Zheng Yuanyuan, Fang Chong, Zhu Hongfang, Wu Linlin
2006, 17(4): 385-393.
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Abstract:
For the first time a downburst event is analyzed in detail with Doppler weather radar in China. A severe multi-cell storm develops near the border between Dingyuan county and Feidong county in Anhui Province, and produces a series of downbursts accompanied by severe hails on 6 June 2003. As for the synoptic background, the axis of the trough tilts eastward, so that the dry and cold air mass from the rear of high-level trough superposes upon the moist and warm air mass in front of the lower level trough, building up the convective instability. The lower troposphere is moist with weak vertical wind shear, while the mid and upper troposphere is dry. This is a situation favorable for wet downburst. This series of downburst consists of three sequential bursts of strong downdrafts, produced by three convective cells developping in the multi-cell storm. From 16:14 to 16:33, the continued descending of reflectivity core of the first cell occurs, and at 16:33, a significant midlevel convergence appears. At 16:39, the first downburst hits the ground, with significant divergence on the lowest elevation (600 m height above ground). The same precursor appears before the second and third consecutive downbursts. Before each burst of the downdraft, the core of the corresponding cell descends, accompanied by the convergence above cloud base. This fact can be used to issue downburst warnings with a lead time of about 5 to 6 minutes. At the same time, a rotation appears on the midlevel in the storm. These facts are in agreement with those discovered by Roberts and Wilson with the statistics of 31 microbursts occurred in Colorado, USA. When the downburst attains its maximum strength, the largest velocity difference along the 0.5° scan over a distance of 6 km is 44 m/s, corresponding to a divergence value of 1.5 ×10-2s-1. The downburst series, consisting of three sequential downbursts, lasts 74 minutes, with each lasting 25 minutes on average. During the whole period, the storm moves very slowly, due to the cancellation of the advection and propagation, leading to the occurrence of the three downbursts at nearly the same site. Analysis shows that it is the hail and rain's descends that initiate the downdraft, which is then greatly enhanced by the entrainment of dry air into the downdraft and subsequent evaporative cooling, for the environmental air is relative dry at mid troposphere. Furthermore, the steep decrease rate of environmental temperature from surface to 0 ℃ level is quite large, around 8 ℃/km, keeping the downdraft with negative buoyancy down to the ground.
The Relationship and Influence Mechanism Between Circulation Anomaly in Southern Hemisphere and Summer Precipitation Distribution in China
He Min, Sun Linhai, Ai Wanxiu
2006, 17(4): 394-402.
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Abstract:
To introduce signal on southern hemisphere circulation anomaly for diagnose and forecast of precipitation trend during flood season, the relationship between southern hemisphere circulation anomalies and its influence mechanism on summer precipitation distribution patterns in China is studied using SVD (Singular Value Decomposition), correlation and analogue methods. Also, the 500 hPa height field and zonal wind shear anomaly from high-level to low-level troposphere (Δu850-Δu200) in southern hemisphere, and summer precipitation distribution patterns in China are analyzed. Results show that:① When the ridge of Australian high is stronger and zonal wind shear anomaly in the southwest Pacific tropical region is negative, the cold air that comes from the southern hemisphere is weaker. It should be beneficial to the stronger subtropical monsoon and weaker tropical monsoon. And the northwest Pacific subtropical ridge shifts southward, and summer precipitation over the Yangtze River and south of the Yangtze River should be above normal. The rainbelt is located in southern China. On the other hand, when the ridge of Australian high is weaker, the zonal wind shear in southwest Pacific tropical region is positive anomaly, more precipitation appears in northern China. ② The possible mechanism for the influence of circulation anomaly in southern hemisphere on the summer precipitation distribution patterns in China is as follows:there is a close relationship between the anomaly of circulation and cold air activity in southern hemisphere and the monsoon circulation system activity in East Asia. It may also influence positions of the Northwest Pacific subtropical ridge and the rainbelt in China. ③ Furthermore, Australian winter monsoon index is defined. It indicates the circulation anomaly and the intensity of cold air activity in southern hemisphere troposphere. When Australia winter monsoon index is negative, precipitation is richer over the Yangtze River and the north part in the south of the Yangtze River in summer, and less than normal in Northern China. ④ The differences in the origin and intensity of water vapor transfer between strong and weak Australia winter monsoon years may cause the difference of the summer precipitation patterns in China. In weaker Australia winter monsoon year, water vapor is mainly transferred from the Pacific and reaches lower latitudes, and the main rainbelt is over the Yangtze River and south of the Yangtze River. In stronger Australia winter monsoon year, water vapor is mainly transferred from the India Ocean and the South China Sea and reaches high latitudes, and the main rainbelt is in Northern China.
Diurnal Cycles of the Boundary Layer Structure Simulated by WRF in Beijing
Chen Jiong, Wang Jianjie
2006, 17(4): 403-411.
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Abstract:
The planetary boundary layer (PBL) is directly affected by the presence of the earth's surface, responding to such forcing as frictional drag, solar heating and evapotranspiration. The PBL over land generally undergoes significant diurnal cycles. The daytime PBL develops when the upward net surface heat flux increases after sunrise. The mass and wind fields in this mixed layer adjust quickly to produce a state of equilibrium until the PBL reaches its maximum depth in the late afternoon. After sunset, the rapid radiative heat losses occur at the ground so that a second temperature inversion starts to grow near the bottom surface.Although many studies focus on the sensitivity of the structure of the PBL simulation to the PBL parameterization, little attention has been paid to the land surface processes' contribution to the development of the PBL, especially the wind field in surface layer. Two planetary boundary layer parameterizations and 3 land surface model (LSM) in WRF model are used to simulate the PBL structures in Beijing area during July 1—4, 2004. The diurnal cycles of surface winds and temperatures and PBL height are analyzed, which shows the temperature and wind fields in the surface layer are sensitive to both the PBL parameterization and the land surface process. The simulations show MYJ scheme gives the more reasonable results than YSU. Noah land surface model considers the soil moisture variation in addition to soil temperature, as the result, the sensitivity of the temperature and wind in surface layer to the PBL scheme becomes strong as the rain appears when use Noah LSM. Noah LSM can produce the heat island phenomenon because it couples a single layer urban canopy model. As a new LSM implement in WRF, RUC cannot describe the variation of the PBL very well. All results of the PBL schemes and land surface models simulated wind speeds in surface layer are much stronger than observations in urban area due to insufficient consideration of the urban building effects. Not only the urban area-averaged potential temperature vertical profiles but also the wind vertical profiles are sensitive to both the PBL schemes and land surface processes.
Quality Check and Analysis on the Historic Global Surface Synoptic Observations
Ren Zhihua, Xu Song, Sun Huanan, Zhang Qiang
2006, 17(4): 412-420.
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Abstract:
The primary purpose of the quality check is to verify the data validity and correct the wrong ones on time. Global surface synoptic data are one of the largest quantities and the most frequently used data in meteorological observations. As the climatic data received and saved in the Climatic Data Office of NMIC (National Meteorological Information Center) in China, the global surface synoptic data are made up of 45 meteorological variables, 4 times observations in term hour daily from approximately 6000 stations around the world. The data have to go through visual observation, instrument reading, recording, encoding transmission by GTS, and decoding etc. It is generally agreed that error data may come into being as a result of each of the above processing stages. Data message format detection and error station number correction are processed to decrease error data induced by data transmission prior to the quality check. The quality control (QC) regulations of global surface synoptic data have been developed in China. The QC procedures in the regulations have been implemented in the operation on global surface synoptic observations' real-time receiving and saving. Using the QC procedures, the historic global surface synoptic dataset stored in Climatic Data Office of NMIC is quality-checked. At the same time, large amounts of data decoded by errors are corrected and then historic global surface synoptic dataset version 2 with quality flags is made. Also, the result of quality check and quality analysis of historic global surface synoptic data from 1980 to 2003 is presented.A large number of error data detected at the stages of data message format check, error station number check and data quality check are corrected or deleted. The quality of the historic global surface synoptic dataset version 2 has been improved greatly. By quality check, the suspect data are 20.3‰, error data is 2.0‰ in historic global surface synoptic dataset version 2. Both the total number of doubtful messages and that of error data of various main variables decrease gradually from 1980 to 2003, which shows their qualities in the dataset are improved. The main variables are those whose percentage received during the hour following the time of observation in term hour is more than 80%. After quality check and some error data processing, the suspect data and the error data of dataset version 2 from 1982 to 1999 are about 18.3‰ and 1.8‰ respectively. Due to the wrong decoding of air temperature and dew point temperature, the error data of dataset version 2 are up to 3.5‰ or so from 1980 to 1981.The percentage of suspect data after 1999 increases to about 30.2‰ as a result of inconsistency between precipitation amount collected in various time intervals, inconsistency between minimum air temperatures and ground surface status.
Numerical Simulation Analysis on the Meso-β-scale Systems Structure of a Heavy Rain over the Huaihe River
Liao Yishan, Li Wujie, Min Airong, Wang Yehong
2006, 17(4): 421-430.
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Abstract:
By analyzing and numerical simulation of a heavy rain event, the physics process and spatial structure of the meso-scale convective system are revealed. Such studies help to get ideas beneficial to and then improve heavy rain forecast. A heavy rainfall occurred over the Huaihe River during 29—30 June 2003 is simulated by using AREM model which is the advanced LASG η-coordinates numerical meso-scale heavy rainfall prediction model with horizontal resolution of 37 km and 28 levels vertically. Comparison between hourly simulated results and observed development shows that the main rainfall period and the main precipitation system are successfully simulated. As indicated by the simulation results:① Though southwest low vorticity is not the direct influencing system, the shear line and low pressure trough area stretching out from the low vorticity provide favorable background condition for the development of meso-β-scale system. ② Southwest low-level jet is the main cause of this weather course. The fast movement of the axis of Southwest low-level jet stream enhances the gradient of the wind and the cyclonic shear in the north of the axis of low level jet, bringing sharp transformation of the vorticity. A strong column of positive vorticity leads to the occurrence and development of the meso-β-scale depression and cyclone at lower level near the vorticity column, whereas a meso-β-scale high pressure developes at the midhigh level of the troposphere without the assorted meso-scale anticyclone. ③ The geostrophic deflection caused by the new meso-high changes the wind field near the meso-high and produces the strong meso-β-scale divergence center around the high. It results in the development of a strong updraft combined with the powerful convergence at lower layer. ④ The strong updraft occurs near the south boundary of the strong frontal zone of θse at lower layer. Meridional vertical cell across the strong frontal zone of θse firstly originates in the boundary layer then develops upwards slowly. And a meso-β-scale cyclone comes into being circling the ascending branch. ⑤ With the development of the meso-β-scale convergence in lower layer and meso-β-scale divergence in higher layer, water vapor in low layer accumulates to the meso-β-scale system area, thereby forms a narrow vapor convergence band, which ultimately leads to the strong rainfall under the effect of strong updraft.
The Relationship Between the South-west Monsoon Tide and the Rain Storms over South China in May 2004
Li Zengzhong, Fang Xiang, Zhu Fukang, Zheng Xinjiang, Li Feng
2006, 17(4): 431-437.
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Abstract:
The relationship between the south-west monsoon tide (SWMT) and the precipitation from April to June in China is analyzed in terms of the examples of two rain storms in South China on 8 and 11—21 May 2004. The preliminary result shows that the outbreak of the SWMT is connected with the cross-equator flow (CEF) coming from the south hemisphere immediately. By means of the weather map, grid wind data, satellite cloud images as well as the Quikscat wind fields at 10 m level over sea surface, evidence shows that the main northern precipitation influencing systems including cold front, occluded front, ground small high pressure, upper troposphere cold vortex, inclined trough, shear line and so on. The cold air guided by these systems moves southward and plays an important role in the formation of the heavy rainfall. The southern precipitation systems are the water vapor and the cloud band caused by the outbreak of the SWMT leaded by the CEF at 85°~95°E (the longitude degree of the bay of Bengal) and 105°E, and the tropical cloud cluster is formed by the interaction between the SWMT and Himalaya Mountains. These cloud clusters with high temperatures, high humidities and high instabilities are transferred to the south and southwest of China and interact with the cold air, cause the rain storms and persistent precipitations. The analysis shows that the precipitation systems are closely connected with the "large-scale system between the two hemispheres". They are the primary cause of strong convective weather, rain storms and tornados generated over southern China.The precipitation progresses is mainly connected with SWMT over the bay of Bengal region. But the South China Sea monsoon tide hasn't occurred at that time. So the South China Sea monsoon tide can be regarded as one part of the Asia south-west monsoon tide. In order to get the final conclusion, more studies on this question should be done in the future.
Research on Climate Warming and Urban Heat Island in Xi'an
Tian Wuwen, Huang Zuying, Hu Chunjuan
2006, 17(4): 438-443.
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Abstract:
The length of meteorological records in most weather stations over China is less than 50 years. To do researches on the climate variation on time scale of a hundred years, stations selected are those mainly centralize in big cities with longer records. The fastest growing period of global warming is exactly the rapid city expansion time in China, during which the farmland around the weather stations turned into cities. The urban heat island could lead to the rising temperature, so the variation of temperature in cities is the jointly affected result of urban heat island and climate change. In order to analyze the contributions of each, mean monthly temperature anomaly from 1961 to 2003 in Xi'an (city) and 4 stations around (town) are selected to do contrast analysis. That is to say, the contribution of urban heat island in Xi'an is analyzed on the assumption that it only exists in Xi'an station. Result shows that the average value of mean monthly temperature anomaly from 2000 to 2003 increases 1.55 ℃ more than that from 1961 to 1972, and the average value of the other 4 stations at the same time only increases 0.48 ℃. It indicates that the warming mainly results from the urban heat island, and the climate change warming is minor in Xi'an. In the process of warming, obvious difference between Xi'an and the other 4 stations mainly exists in two periods. It can be reflected perfectly in the moving average curve (36 samples) of mean monthly temperature anomaly distributed according to the time. According to the investigation on urban construction, the two periods are consistent with the time of rapid city expanding towards the meteorological stations. The urban heat island model in Xi'an based on the analysis above is set up, and the cause of the increasing temperature in Xi'an is separated into the city urban heat island and the climate variation respectively. Increasing temperature in Xi'an aroused by urban heat island is 1.07 ℃, and that by climate variation is 0.48 ℃. Balance between mean monthly temperature of Xi'an and the 4 stations around is also analyzed for testifying the result, and the rising range in Xi'an is about 0.93 ℃ higher than the latter. When focusing on the climate warming, the urban heat island raised by change of surrounding environment which is brought by extending of city can not be ignored. Range of rising temperature aroused by urban heat island is larger than that of climate variation. Because the extending time of different city is not the same, corresponding model should be set up separately so as to eliminate the contribution of urban heat island to increasing temperature.
Study on Three-dimensional Wind Fields of Mesoscale Convective Systems in Xinjiang
Zhuang Wei, Liu Liping, Wang Nan
2006, 17(4): 444-451.
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Abstract:
The dual Doppler radar system constructed by two C-band Doppler radars in Urumqi and Wujiaqu is used to detect convective systems in Xinjiang Uighur Autonomous Region in 2004, it is supported by the project of National Natural Science Foundation of China (NSFC) "Study on Meso-scale Kinetic and Thermodynamic Feature of Precipitation System with Dual Doppler Radar in Xinjiang". It focuses on the three-dimensional wind field retrieved with dual Doppler radar technique in the strong mesoscale convective systems that produces relatively heavy rainfall within the observational network from 22:30 (BT) 7 August to 02:30 8 August 2004, and the three-dimensional wind structure of these systems as well as their evolution processes are analyzed. Moreover, the radar data quality and reliability of the wind retrieval algorithm with dual Doppler radar are also examined.The positions and structures of radar echoes captured by the two radars are well matched, the radial velocities observed by the radars above the radar baseline are mostly the same, the dual Doppler radar technique is reliable and suitable for the observations of mesoscale convective systems. The sensitivity analysis of the interpolation algorithm on wind retrieval framework demonstrates that the influence radius of Cressman interpolation does not play a significant role in determining the wind structures of mesoscale convections. Even though the wind retrieval errors resulted from the radial velocity measurement errors are associated with their relative positions to the radars, however, such type of errors within 1 m/s on redial velocity would not change the major shapes of the mesoscale wind structures.According to the evolutions of these mesoscale systems, the several convective cells develop into convective precipitation band. Some new cells are generated along the left side of the old ones, whose reflectivity vary from 50 to 55 dBz with the maximum 8 km top height, and finally develop as a band-shaped convective cluster (with 90 km length) after 4 hours. The convective band is corresponding with a strong convergence produced by a branch of strong northeasterly wind and a weak westerly wind, and the updraft is just located at the maximum reflectivity center. The different convective cells actually have their independent wind structures respectively, but they would subsequently interact with each other to engender heavy rainfall weathers. Besides, there are limits to the measurements on this type of mesoscale convective systems in the conventional observations, such as radio sounding, whose spatial and temporal resolutions are limited at hundreds kilometers and 12 hours respectively. Consequently, it is not sufficient to determine their dynamic structures, which develop quickly and have relatively short lifecycle. Fortunately, due to the retrieved wind fields of these mesoscale convections with dual Doppler radar observations, it would be easier to analyze their kinetic features and therefore study the initiation and development mechanism of the mesoscale rainfall systems.
The Doppler Radar Velocity Image Features and Its Application in a Snowfall Process
Wang Lirong, Tang Dazhang, Hu Zhiqun, Zhao Ruijin
2006, 17(4): 452-458.
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Abstract:
A Doppler weather radar radial velocity PPI image identifying technique in large-scale rainfall is introduced:① The image characters of the cold (warm) advection combined with large-scale divergence (convergence) are that the bending degree increases on a side while decreases on the other, which forms the zero-speed line differing in bending on both sides of the display center. ② The wind direction-related convergence or divergence features display an bow-like zero-velocity line, thereby the convergence or divergence can be determined. If the bow's ends bending towards the positive (negative) speed area, the negative (positive) area is larger than the positive one (negative), which means pure convergence (divergence). ③ The wind speed-related convergence (divergence) character can be estimated by means of the positive and negative speed areas and measures in a same distance ring. It is convergence if negative velocities are bigger than positive ones, otherwise it is diver-gence. The bigger the different value between positive and negative, the stronger the convergence or divergence.Furthermore, a method is introduced to quantitively calculate the atmospheric average divergence and vertical speed using EVAD technique:① Extract average divergences in each height level from radar base data utilizing Thomas weighted coefficient method. ② In order to diminish the error added up while integrating along height when calculating air vertical speed by continuous equation, divergences are adjusted according to variation method. ③ Adjusted divergences are considered in continuous equation to calculate air vertical speeds.Applying the image identifying and EVAD techniques, a large-area snowfall process is analyzed in detail in Shijiazhuang, Hebei Province, in the winter of 2004, which suggests that there are obvious convergence (divergence) features during the process, radial velocities are small, convergences and divergences are weak and there is always the warm convection. In addition, the snowfall intensity is closely related to the divergence and vertical speeds, snowfall strengthens as soon as the thickness of convergence levels increases and divergence ascends up; otherwise snowfall weakens when the height of convergence and divergence levels descends down. The quantitive divergence calculated by EVAD is corresponded with those quality analyzed by radial speed picture produced in the same time.
Fuzzy Clustering Diagnosing and Forecasting on Subtropical High Intensity Index
Hong Mei, Zhang Ren, Wu Guoxiong, He Jinhai, Yu Dandan
2006, 17(4): 459-466.
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Abstract:
In order to analyze and diagnose the correlative characters and phase relation between subtropical high and the east-Asia summer monsoon circulation and thermal factors as well as southern hemispheric pressure field, an idea of synthetically combining FCM, GA with FSC to make clustering analyze and diagnosis on subtropical high and its influence factors is presented. Based on observational and statistical facts, some initial subtropical high influence factors in east-Asia monsoon system are chosen to form a high-dimensional feature spaces. Firstly, the FSC technique is used to objectively estimate the clustering number of samples in the feature space, then the GA technique is used to make global optimization search and the FCM technique is used to make further local optimization searching and adjusting on the GA global optimization results. Finally, the synthetical optimized clustering results of subtropical high indexes and its influence factors in the feature mapping space are taken as the classification criterion for subtropical high intensity index classification. By the clustering analyze and diagnosis of using above synthetical techniques, some important portentous characteristic facts of subtropical high changing are revealed and discovered, and a corresponding clustering diagnosis and prediction are carried out.On the basis of above researches, some examples of subtropical high index and its monsoon influence factors are analyzed, diagnosed and predicted by using the synthetical clustering technique, the experiments results show that the classification correctness and forecast precision of 5 grades subtropical high indexes are superior to 60%, especially, the correctness and precision in the case of the weakest and the strongest subtropical high indexes are better than 80%, and similar better subtropical high classification results are also gotten by different examples clustering experiments, the validity and reliability of the synthetical clustering technique are well supported and approved by above experiments.The idea and technique presented not only can overcome the shortcoming of GA/FCM short of sufficient local/global optimization, but also can objectively determine the number of clustering centers. In the actual application, by calculating and judging the mapping location of monsoon influence factors in their high-dimensional feature spaces, the intensity grade of subtropical high index are accordingly determined, and that the subtropical high index diagnosis and forecast are also carried out.
The Equilibrium of the Water Vapor in an Air Bubble and the Principle of the Humidity Generator with Saturated Aqueous Salt Solution by Means of the Air Bubbles
Zhou Weixin
2006, 17(4): 467-472.
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Abstract:
The constant humidity property of some saturated saline solution can be used to design humidity generators. Current humidity generators using saturated saline solution usually require complex equipments and a long time to reach equilibrium, and are prone to environmental influences. On the other hand, air bubbles are characterized by good air-tightness and short inside mean diffusion distance, which is defined as the volume above the solution divided by the surface area of the solution in a closed container. Therefore, it is easier to achieve vapor equilibrium within an air bubble, which can then be collected pneumatically and used to calibrate humidity sensors.The conditions under which water vapor reaches equilibrium within air bubbles are quantitatively analyzed in this study. An air bubble can be modeled as a closed cylinder container with solution at the bottom. Assuming that the gradient of vapor density is distributed linearly along the axis of the cylinder, the time τ required to reach vapor equilibrium within the air bubble can be deduced from the relationship that the vapor mass diffused from the solution surface into the container within a unit time equals the increased vapor mass within the container. From the forces exerted on the air bubble during its ascent, the time t for the air bubble to remain in the solution can be calculated. In order to reach vapor equilibrium within the air bubble, τ must be smaller than t (τ < t). It follows that the diameter of the air bubble r and the depth of the solution h should satisfy the inequality below: in which ρ is the solution density, g is the gravity acceleration, D is the vapor diffusion constant, η is the viscosity of the solution, U0 is the normal humidity at the surface of the saturated solution, U1 is the initial humidity in the air bubble, and U2 is the humidity of the air released from the air bubble when it bursts.To test the new humidity generator described above, a test set is calibrated against a M4 hygrometer (General Eastern Instrument) with the dew point temperature uncertainty of 0.2 ℃. The absolute values of the differences between readings from the test humidity generator and those from the reference hygrometer are no bigger than 1%. The response time is typically 10 minutes under common application conditions.The sources of error for the humidity generator using the air bubble method are also discussed. The analysis and the test show that a humidity generator based on air bubbles from saturated saline solution is simple, fast, accurate, and less affected by environmental factors, and is a real utility humidity reference, in particular can be used in onsite calibration of humidity sensors at automatic weather stations.
Analysis on Typhoon Rananim Using Products Retrieved from ATOVS
Liu Zhe, Han Zhigang, Zhao Zengliang, Zhang Fengying, Li Wanbiao
2006, 17(4): 473-477.
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Abstract:
Nowadays, the most widely used tropical cyclone estimation and position analysis techniques employed by operational forecasters are to analyze the infrared and visible satellite imagery. While these products provide invaluable information about the overall structure and strength of tropical cyclones, they often can't penetrate clouds to ascertain low-level storm structures. Relatively, certain waveleng ths of microwave energy are able to penetrate ice clouds (such as the cirrus above the storm). Therefore, it offers a unique perspective into tropical cyclone structures. Advanced TIROS Operational Vertical Sounding (ATOVS) is composed of the Advanced Microwave Sounding Unit (AMSU) and the High-resolution Infrared Radiation Sounder (HIRS/3), which are aboard the NOAA-16-18 satellites. With the International ATOVS Processing Package (IAPP) by Cooperative Institute of Meteorological Satellite Studies (CIMSS) of the University of Wisconsin (UW), the ATOVS data can be finally translated into the retrieval products including the atmospheric temperature profile, moisture profile in both clear and cloudy atmospheres. The domain of typhoon center cloud field is determine according to the coincident infrared image, and then the temperature anomalies are calculate by subtracting the average temperature of outer radius from the temperature at each grid in the domain. By analyzing the cross-section of temperature anomalies, the warm-core of typhoon Rananim can be seen in the upper-troposphere clearly as well as the distribution of strong precipitation in the lower altitude due to its contamination to the upper microwave radiation. But the area range of ATOVS data received by National Satellite Meteo rological Center (NSMC) is not wide enough, which can only receive the data of part of the Western North Pacific besides the mainland. By analyzing the area range of ATOVS retrieval data mapped with the tracks of Rananim from National Meteo rological Center (NMC), four ideal sets of ATOVS retrieval data are recieved. Under hydrostatic assumption, using the nearest NCEP/NCAR reanalyzed data as initial parameter and four sets of ATOVS data mapped with Rananim, the minimum sea level pressure (MSLP) is calculated respectively and compared with the typhoon warning report of NMC estimated from the visible and infrared method, the mean discrepancy of MSLP is found to be 11.8 hPa, showing similar time-variant tendency of Rananim as described by NMC. Therefore, by using ATOVS retrieval products, the thermal structure under the Center Dense Overcast of typhoon Rananim is better displayed; what's more, the relatively accurate intensity of typhoon is obtained when compared with the result of the operational departments.
Preliminary Researches on Digitizing Paper Meteorological History Archives
Lan Ping, Zang Haijia
2006, 17(4): 478-482.
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Abstract:
Realizing the digitization of the meteorological archives with the secure scanning and the OCR (optical character recognition) is an effective way to save and develop the papery historic meteorological archives. Based on the investigation and the experimentation on the digitization technique, a conception about the digitization of the papery historic meteorological archives is presented. Aiming at the character of the content recorded in the meteorological archives, the application of the handwritten numeral recognition of OCR is analyzed, and the resolution strategy of OCR recognition of the meteorological archives is presented, which provides a technical idea and effective technical reference for the construction of the digitization of the papery meteorological archives in the area.The scientific and effective way of the meteorological archive digitization is to utilize the technique of the integrated carrier and the OCR which are advanced at home and abroad, and to found a system platform of the digitization of the meteorological data. The platform is consisted of the high/low secure scanner, personal computer, the storage device, the managing software, the OCR software and the applied software etc. The system integrates the scanning process, the quality control, and the statistical process of the various papery archives and the microfilm archives, creates the electronic files in the unified format and the same medium, realizes the extraction of the data information from the meteorological data in the form of long sequence with OCR technique, and finally solves the problem of protection and the digitization of the library papery meteorological data.The construction of the meteorological archive digitization is not only simple data processing, but also relates to a series of associated techniques including the classification of the meteorological archives, the construction of the standard specification, the secure scanning, OCR technique, the data storage, the construction of the data set and the retrieval and application of the information etc. The construction of the meteorological archive digitization integrates the archives on the different carrier in order to realize the overall application of the protection and digitization of the archives. The resulting electronic documents and the long term digitizing documents have important significance for the protection of the archives and the climatic analysis in the various fields.The primary analysis of the strategy of the digitization of the papery meteorological archives indicates that it is feasible to apply the secure scanning and the OCR technique to the digitization of the papery meteorological archives. At present, the system of the meteorological archive digitization has stepped into the performing phase, and the digitization of the papery historic meteorological archives will provide the foundation for the conservation and the application of the historic meteorological data.
Investigation and Analysis on Surface Air Temperature of Sloping Fields of Lianjiang County in 2004/2005 Winter
Cai Wenhua, Pan Weihua, Zhang Hui, Lan Zhongming
2006, 17(4): 483-487.
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Abstract:
The technique of inverse temperature of sloping fields as an effective method to prevent the frozen loss is applied to protect these fruit trees in practice. Comparison of results from the traditional methods which are laborious and costly in protecting fruit trees shows that the maximal increasing temperature effect of inverse temperature of sloping fields is excellent. By analyzing the characters of inverse temperature of sloping fields, to select appropriate regions for planting these fruit trees is significant in avoiding or mitigating the freezing harm to them. According to the investigation statistics data of low temperature of 2004 and 2005 in Lianjiang, the effect of low temperatures in sloping fields is studied. The results reveal that the temperature gap (Δtd), which denotes difference between the low temperature of observation spot in sunlight days (td) and the temperature at the bottom of sloping fields, is increasing with the increase of altitude where the hills with relative total altitude gaps (ΔH) are 49 m. Along with the distance close to the top of the sloping fields, Δtd and td are larger and larger. Furthermore, td is the highest, and the inverse temperature is prominent where the middle or upper parts of the hills with ΔH are 100 m and relative altitudes ratios, which is the ratio (G) between the relative altitudes gaps of observation spot and ΔH are 0.90 approximately. As a result, based on the investigation in the study, a conclusion can be drawn that the inverse temperature of sloping fields has three characters as follows: in unclouded nights, the inverse temperature phenomenon that the temperature at the top or middle of the sloping fields is higher than at the bottom of the sloping fields exists at the hills. If ΔH≤60 m, the formula can be acquired: Δtd=b0+b1×G (b1 > 0), which means td at the top of the sloping fields is the highest, and the maximum of inverse temperature (ΔTd) can be calculated from the formula: ΔTd=b0+b1. Else if 300 m > ΔH≥80 m, they reveal that Δtd can be calculated from the formula: ΔTd=b0-b1×(G-b2)2 (b1 > 0, b2 > 0), when G equals b2, td is the highest and ΔTd equals b0; considering the hills where the relative altitude gaps are less than 300 m, the location of the ratio (G) where the maximum inverse temperature exists is opposite to ΔH, and with the increase of ΔH, G is descending; ΔTd is correlated with the amount of push-join (B) (which denotes the ratio between the azimuth of the push-join and 360°) and ΔH of hills. When the B are identical, with the increase of ΔH, ΔTd is increasing acco rdingly. When ΔH are identical, because of the restrictive condition 1≥B > 0, with the decrease of B, ΔTd is increasing contrarily.
A New Weighted Average Method on Ensmble Mean Forecasting
Duan Mingkeng, Wang Panxing
2006, 17(4): 488-493.
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Abstract:
The ensemble mean forecasting is one of the major forecasting products in an ensemble prediction system. Compared with the results from a single deterministic forecast, the ensemble average forecast has higher forecasting skills. For the forecasts starting at the same initial time, the ordinary ensemble mean forecasting is the arithmetic mean of all ensemble members. In the ensemble, each of ensemble members has the same weight. A new ensemble average method considering the different weight of ensemble members (known as "the weighted ensemble average method") is presented. In this method, the ensemble average is calculated from all the ensemble members, which has the same initial time and lead time, with the different weight. Through this method, it is expected to get the better forecasting performance than the ordinary ensemble mean forecast (known as "the common ensemble average method").Some research conclusions indicate that the results of the ensemble forecasting are more inclined to the value of major ensemble members; at the same lead time, the higher success rate of ensemble forecasting always correspond to the more consistent members of the forecasting results (the prerequisite of this result is that the ensemble prediction system has better reliability and the initial ensemble perturbations have enough spread so that the forecasting results can more comprehensively cover the possibilities of forecasting errors).The starting point of the weighted ensemble average method is to adjust the weight of ensemble members in order that the members with consistent forecast results have larger weights. By this process, the consistence among the ensemble members is emphasized. Here, the weighted ensemble average method uses the climatologically likely intervals to group the ensemble members according to the proximity extent each other; then according to the size of the climatologically likely interval and the ensemble members in it, the corresponding weight is adjusted; eventually, based on the adjusted weight, the calibrated ensemble mean forecasts are gotten.Based on the NCEP EPS forecasting dataset, the verification methods of ACC and RMSE are used to prove the performance of the weighted ensemble average method. The test results at the various regions show that the method can upgrade the ensemble mean performance in a way. Even in the worst situation, the effects of the weighted ensemble average method do not appear below the ordinary ensemble average method. Compared to the resolution improvement of the numerical weather prediction or development of enormous ensemble prediction system further, the enhancement of the weighted ensemble average method is significant.In addition to the medium-range ensemble average forecasting, this method can also be used in the ensemble mean of the continuous variables during the other types of forecasts, predictions to improve the forecast performance.
Analysis on Specification of FY-3 Meteorological Satellite Data Transmission
Zhu Aijun
2006, 17(4): 494-501.
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Abstract:
The specification of FY-3 meteorological satellite data transmission between FY-3 satellite and user ground stations is analyzed. It helps user stations to understand specification and performance requirements of FY-3 meteorological satellite data communications interface. FY-3 will provide three types of data transmission capabilities. When FY-3 satellite passes the receiving station, the three downlinks transmit simultaneously. The three downlinks include: real time direct downlink of HRPT (high resolution picture transmission); real time direct downlink of MPT (moderate resolution picture transmission); direct playback for delay time data link of DPT (delay picture transmission). HRPT transmission adopts L-band and QPSK modulator and data rate of 4.2 Mbps and EIRP (effective isotropic radiated power) of 41 dBm; MPT transmission adopts X-band and QPSK modulator and data rate of 18.7 Mbps and EIRP of 46 dBm; DPT transmission adopts X-band and QPSK modulator and data rate of 93 Mbps and EIRP of 46 dBm. Their channel coding adopts telemetry channel coding standard (CCSDS 101.0-b-5) and advanced orbiting systems-networks and data links architectural specification (CCSDS 701.0-B-2) (consultative committee for space data system (CCSDS) recommendations). DPT is transmitted only when satellite passes over China area and Svalbard area. FY-3 Meteorological Satellite will be launched in 2007, it will provide services for users to replace FY-1. National ground stations of FY-3 consist of Beijing ground station, Guangzhou ground station, Urumqi ground station and Svalbard ground station. They can receive HRPT, MPT and DPT data of FY-3. Other ground stations can receive only HRPT and MPT data of FY-3.The application data provided by the HRPT of FY-3 link are as follows: VIRR data, IRAS data, MWTS data, MWHS data, SBUS data, TOU data, MWRI data, SIM data, ERM data and SEM data. The application data provided by the MPT of FY-3 link only include science instrument data of MERSI. The application data provided by the DPT of FY-3 link are as follows: MERSI data, VIRR data, IRAS data, MWTS data, MWHS data, SBUS data, TOU data, MWRI data, SIM data, ERM data and SEM data. The transfer frames and Source Packet structure of data are consistent with CCSDS.An introduction to the physical layer on HRPT/MPT is given in this paper. The physical layer includes: RS encoding serial to parallel conversion convolution encoding synchronization and modulating. After ReedSolomon encoding and pre-pending the attached Sync Marker, data are divided into I channel and Q channel, then rate 3/4 convolution encoding for HRPT and 1/2 convolution encoding for MPT are applied, then data are modulated with QPSK modulation.The main principle, calculating method and analyzing method of FY-3 HRPT link budget and FY-3 MPT link budget are also given. The differences of data transmission among FY-3 and METOP and NPP/NPOESS are discussed. Primary strategy to design the user stations is given: when direct read out user stations design their ground stations, the ability of acquiring data must be considered. It is very important that direct read out users stations must acquire the HRPT data and MPT data of FY-3, AHRPT data of METOP and HRD data of NPP.
NOAA/ATOVS Data Obtaining, Processing and Displaying Based on DVB-S System
Ran Maonong, Qu Jianhua, Sha Li, Yuan Wanping, Zhang Fengying, Wu Xuebao
2006, 17(4): 502-507.
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Abstract:
DVB-S (digital video broadcast by satellite) remote sensing satellite data sharing platform is essentially a data transmission system which collects the data from DB (direct broadcast) acquisition stations and re-broadcasts by a communication satellite in near real time. On the current DVB-S system in China, CMA/NSMC broadcasts the data free of charge not only of the required EOS/MODIS data from both CMA (Beijing, Guangzhou, Urumchi and Lhasa) and SOA (Beijing and Sanya) DB receiving stations, but also all the FY-1/HRPT and NOAA/HRPT data of CMA (Beijing, Guangzhou, and Urumchi) 3 DB stations in very short time through a rented geostationary communication satellite (ChinaStar-1). Users in China and East-Asia area have the benefit of this DVB-S data sharing platform. The DVB-S system in user-end consists of three parts: receiving PC with data ingest card and a small dish; data pre-processing PC, data product and application.ATOVS, a set of vertical sounding instruments aboard on NOAA series satellites (NOAA 15 and later), with its data stored in HRPT data stream, has 40 channels covering spectrum of visible, infrared and microwave bands for atmosphere temperature and moisture sounding. ATOVS consists of 3 independent instruments: HIRS/3, AMSU-A and AMSU-B. It can be greatly improved on atmospherical temperature profile by using HIRS/3 and AMSU-A combination as well as on moisture profile with HIRS/3 and AMSU-B retrieval together, particular in cloud area. In addition, the window channels in AMSU-A and AMUS-B can be improved on the surface sounding ability of NOAA satellite, such as more precise atmosphere precipitable water and some the surface products.ATOVS data receiving, processing and displaying systems at the DVB-S user-end are introduced briefly. The ATOVS data processing system includes the software of pre-processing (AAPP) and retrieval packages (IAPP). The original AAPP software (AVHRR & ATOVS Pre-processing Package) is developed by EUMSAT under UNIX or LINUX operational system, and here the modified AAPP has been transferred into PC/WinXP/2000. It includes 4 steps to pre-process ATOVS data: decommutation, geolocation, calibration and re-preprocessing. ATOVS level 1c data (HIRS/3, AMSU-A, and AMSU-B stored as temperature brightness by channels) produced by AAPP package can be directly applied to NWP or some variable assimilation models. If user wants to get some meteorological elements such as temperature profile, moisture profile, total ozone amount from ATOVS instruments, the IAPP (International ATOVS Processing Package from Wisconsin, USA) software must be executed. Here the IAPP is also modified from UNIX into PC/WinXP/2000. The accuracy of temperature and moisture profiles in DVB-S ATOVS system is similar to the result of the running operational system in NSMC. The RMS compared with RAOB data is 2K less for temperature and 20% for moisture, respectively. NSMC also develops ATOVS data displaying system under PC/WinXP/2000. It is easy for users to use the software displaying and analyzing ATOVS retrieval data as the temperature and moisture profiles, contour lines, vertical section planes, elements and so on.Examples of typhoon Crabapple in July 2005 and a heavy rain in June 2002 are selected for displaying and analyzing, the extraordinary advantages of meteorological satellite vertical sounding are presented by the ATOVS displaying system. The completed DVB-S system is sure to make the applications of ATOVS data in meteorological and related fields even more effectively.
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