应用气象学报

Statistical Estimation of Dynamic Balance Constraints in GRAPES Variational Data Assimilation System

Wang Ruichun, Gong Jiandong, Zhang Lin

2012, 23(2): 129-138.

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Abstract:
Dynamic balance constraints that govern the atmospheric circulation play very important roles in the analysis of atmospheric state. These constraints indicate how it might be possible to determine one variable from another. As a result, they could help to avoid noise caused by gravity waves, and enable maximum information to be extracted from the observations.The existing GRAPES three-dimensional variational data assimilation system, which is defined on sigma coordinates, uses linear balance equation to ensure that mass and wind analysis increments to be geostrophically coupled. In this formulation, to deal with difficulties in solving the balance equation at sigma levels, analysis variables need to be interpolated to a series of auxiliary isobaric surface to calculate balanced components. A new formulation of estimating dynamic balance constraints is developed in the variation assimilation system. In the new scheme, regression coefficients between stream function and dimensionless pressure (Exner function), instead of the geostrophic balance equation in the original scheme, is used to describe the balance relationship between rotational wind and mass field. In addition, the balance relationship between rotational wind and divergent wind is similarly described by regression coefficients between stream function and velocity potential. Compared to the old scheme, the new formulation avoids repeated interpolations along the vertical direction, which would make the estimation simpler and more accurate.In the new formulation, the balanced coefficients are computed using NMC method, which is found to produce a useful approximation to the true balance constraints in atmosphere. Based on 24 h, 48 h GRAPES forecast differences, linear regression is carried out for each level and for each latitude. By doing this an implied latitude-dependent structure in the dimensionless pressure is directly included in the analysis. Statistical results show that the explained variance of dimensionless pressure is primarily in the extratropics with the variance best explained below 100 hPa in this new formulation. And the explained velocity potential ratio has a maximum in the middle and high latitudes near the surface. Results of randomization and single-observation experiments indicate that, in regions where geostrophic balance is appropriate, the new formulation behaves similarly to the original scheme. However, in regions where geostrophic balance is not appropriate, the new formulation could allow for a smooth decoupling of stream function and dimensionless pressure, while the original scheme can not. Such properties of the new formulation could help variational data assimilation system get more reasonable analysis results in tropics and tropopause. Moreover, by adding the balance relationship between rotational wind and divergent wind, the new formulation could derive a more reasonable wind field in boundary layer.

The Applicability of NCEP Reanalysis Data to Severe Convection Environment Analysis

Wang Xiuming, Yu Xiaoding, Zhu He

2012, 23(2): 139-146.

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Abstract:
Operational sounding observation is carried out twice per day, but four similar vertical profiles can be obtained from NCEP reanalysis data. Therefore, the vertical profiles obtained from NCEP reanalysis data are assessed and its applicability in diagnosing severe convection environment is analyzed. Sixty soundings in close proximity to supercell storms are investigated. These supercell storms are observed in China and identified by Doppler weather radar. The soundings which may be polluted by storm are replaced by soundings from its downstream area or upstream area. The profiles obtained from NCEP data are at the same time and as close to the observation soundings as possible. The vertical profile data that obtained from NCEP reanalysis data are compared with soundings. The ingredients-based methodology is used to discuss the potential for severe convection. Vertical wind shear is the first element to check. NCEP wind in middle and high troposphere is almost consistent with observation, so the deep and middle vertical wind shear (0—6 km, 0—8 km and 0—3 km) and other related dynamical parameters can be calculated from NCEP data except for 0—1 km low vertical wind shear, because wind difference is significant in planet boundary layer (PBL). To study instability of storms, convective available potential energy (CAPE), temperature lapse rate (temperature difference between 850 hPa and 500 hPa), and K index are investigated. The statistic results show that the difference of CAPE between observation and NCEP profiles is significant, because CAPE is sensitive to dewpoint and temperature of lifting air mass. On average, 1℃ temperature increment of lifting airmass brings 200 J·kg^-1CAPE augmentation, 1℃ dewpoint increases CAPE by nearly 500 J·kg^-1, and the augmentation can vary from 0 to 1000 J·kg^-1. Moisture is one of the three ingredients for thunderstorm. The error of NCEP moisture parameter is significant, especially within planet boundary layer, the average dewpoint difference between NCEP and observation is 2℃ in low troposphere, which results in nearly 1000 J·kg^-1CAPE difference. To calculate CAPE from NCEP data, moisture should be corrected according to observation. Temperature lapse rate can be used to diagnose atmospheric instability instead of CAPE, as temperature profile can be used to analysis severe convection. The difference of K index is small in most cases. NCEP output variable CAPEsfc (surface CAPE) is unreasonably small, but the tendency can indicate the change of CAPE. Most lifting processes are within PBL, where the difference of the atmospheric parameters especially the wind direction between observation and NCEP data is significant, so it's not suitable to use NCEP data to study lifting mechanism of thunderstorm. On average, the NECP moisture profile is much drier at low level and wetter at middle level than observation, and wind speed above 925 hPa is weaker than observation, which lowers the possibility of severe convection.

Identification of Non-precipitation Meteorological Echoes with Doppler Weather Radar

Li Feng, Liu Liping, Wang Hongyan, Jiang Yuan

2012, 23(2): 147-158.

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Abstract:
When it is clear or there are just clouds without rain, wide spread non-precipitation meteorological echoes are often observed near the radars, which have notable effect on rainfall estimation and radar data assimilation. To discriminate these echoes efficiently, a Non-Precipitation Meteorological echo Detection Algorithm (NPMDA) based on fuzzy logical and SCIT is developed. Using surface and star data, a standard to identify non-precipitation meteorological echoes is established. With data observed by the SA radar in Beijing, after analyzing the statistical characteristics of non-precipitation meteorological echo, membership functions are obtained. Echoes are assembled to pieces using SCIT. If an echo piece meets one of some special conditions, the whole PPI would be recognized as precipitation echoes. If no piece meets any of the special conditions, the threshold is set as 0.5, for the echoes which can't be assembled to pieces. If the area of an echo piece is less than 2000 km², the echoes in the piece are also recognized with a threshold of 0.5. If the area of an echo piece reaches 2000 km², the attribute value of this echo piece would be calculated with an algorithm based on fuzzy logical. The threshold of echoes in the piece would be calculated with the attribute value of this echo piece. If the attribute value of one piece is greater than or equal to 0.5, the echoes in the piece would be recognized with the threshold of 0.5. If the attribute value of one piece is less than 0.5, the echoes in the piece would be recognized with a threshold obtained by subtracting the attribute value of the piece from 1. The echoes would be recognized as non-precipitation meteorological echoes if their attribute values are greater than the threshold or equal to it. After using dynamic thresholds, the thresholds of most precipitation echoes would be greater than 0.5. The method can efficiently avoid this situation that the precipitation echoes are recognized as non-precipitation echoes. It should also be noticed that the thresholds of some non-precipitation echoes would also be greater than 0.5, which would decrease the identifiable accuracy for non-precipitation echoes to some extent. The algorithm does well with most of non-precipitation meteorological echoes and precipitation echoes, but it does not handle some weak precipitation echoes well. Compared with the ICADA used by NCAR, the identifiable accuracy for non-precipitation echoes can be improved remarkably with NPMDA, and the erroneous recognition for precipitation is also decreased obviously.

Indirect Comparison of Two Types of Radiosonde Systems Deployed in Xinjiang Using First Guess Fields

Yao Wen, Ma Ying, Wang Zhan, Huang Bingxun

2012, 23(2): 159-166.

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Abstract:
The consistency of upper-air observations in serial of space and time is attached more and more importance especially by the users and upper-air observation operators. Generally, the systematic differences of different types of radiosondes can be obtained using the method of direct comparison when the compared radiosondes are suspended below the same balloon. However, as these errors are more or less related with the releasing place, time and method, the results of a few direct comparisons cannot reflect the differences properly.It is found that FG (first guess) fields can reflect the regional differences of meteorological element arose by weather process generally and such differences can be removed indirectly using FG. If two different types of radiosonde systems are equipped at neighborhood stations for quite a long time, they can be compared indirectly using FG.Average bias is analyzed between the observations and FG from neighborhood stations of Urumqi, Yining, Klamayi, Beitashan (4 stations which use P-band radiosonde system), Altay, Aksu and Kuerle (3 stations which use L-band radiosonde system) during 2007—2010. The result reveals that the differences of average bias between observations and FG from L-band stations are small during both daytime and night. The differences of average bias at the same sounding time from the 4 P-band stations are normal, but the differences are very large between 0800 BT and 2000 BT.And the differences of average bias are very small between P-band and L-band at 2000 BT but large at 0800 BT.It shows that observations at 0800 BT by P-band radiosonde system might be problematical, which call for more attention when using these data in Xinjiang. Statistical results are also given as reference for correcting the systematic error.

Comparative Analysis on Tropical Cyclone Numerical Forecast Errors of T213 and T639 Models

Ma Suhong, Wu Yu, Qu Anxiang, Xiao Tiangui, Li Xun

2012, 23(2): 167-173.

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Abstract:
The vortex initialization scheme used in the operational global model T213L31 for tropical cyclone (TC) track prediction is implemented in higher resolution global spectral model T639L60 in 2009, which is the new generation model for medium range forecast in National Meteorological Center. The vortex initialization scheme used in T213L31 typhoon model includes three parts. One part processes the initial vortex formation using bogus vortex technique when TC being first named in the northwest Pacific Ocean, another part relocates the vortex in the following backgrounds according to the correct position analyzed by the forecasters, and the third part modifies the intensity according to the maximum wind or the minimum sea level pressure analyzed by the forecasters. The comparative analysis of the performance of TC track forecasts for T639L60 and T213L31 typhoon models is carried out using the TC track data from 2009 to 2010 in order to evaluate the ability of TC track prediction of T639L60. The results show that the mean distance errors of T213L31 and T639L61 are close within 72 h forecast, but for 96 h and 120 h forecasts, T639L61 brings a little bit larger errors. The errors of T213L31 and T639L61 for No.0907—No.0922 and No.1001—No.1014 TCs are 120.2 km and 124.8 km (24 h), 211 km and 203.8 km (48 h), 314.7 km and 320.7 km (72 h), 416.3 km and 436.6 km (96 h), 556.3 km and 602.1 km (120 h). The intensity errors of T639L60 are much smaller than those of T213L31 because of the higher resolution of T639L60. The track errors are also analyzed by group all the TCs into five different types of tracks: North-westward moving, northward moving, westward moving, recurvature and unusual track TCs. The results show that T639L60 has better performance for the north-westward moving and recurvature TCs than T213L31, but the track errors are much larger for the northward moving TCs and west moving TCs especially the west moving TCs in the South China Sea. For abnormal track TC forecasts, T639L60 can well forecast the adjustment of the environmental flow and has much smaller mean track errors than T213L31. For the systematic direction errors of landing TC forecasts, T213L31 has the systematic bias of northeast-north and T639L60 has the systematic bias of northeast-east.

Climate Characteristics and Cause of Long Continuous Rainstorm Process in June of Guangdong Province

Xie Jiongguang, Ji Zhongping, Gu Dejun, Li Xiaojuan, Hu Litian

2012, 23(2): 174-183.

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Abstract:
Long continuous rainstorm is one of the extremely catastrophic events, and its cause and forecast are of many concerns. April to June is the main rainy season in Guangdong Province, and large scale and long continuous rainstorm can easily induce flood-causing catastrophe. Data analysis shows that long continuous rainstorm lasting for over 7 days causes serious flood disaster. Daily precipitation and rain pattern from 86 meteorological stations in Guangdong Province during 1961—2008 are investigated. The climate characteristics of the annual longest continuous rainstorm is analyzed, and the preceding field of circulation and sea surface temperature (SST) with or without long continuous rainstorm are studied using composite analysis and correlation analysis.The results show that the longest period of heavy rain days in Guangdong Province mainly manifests inter-decadal stage change with weak linear increasing trend. The longest period of heavy rain days in Guangdong Province are less from the mid-1970s to the 1980s than that in the other period, and long continuous rainstorm that continues for more than 7 days occurs mostly after the year of 1990.The 500 hPa height field characteristics during long continuous rainstorm are high in the west and low in the east at high-latitudes, and high in the east and low in the west at low-latitudes. European trough deepens at mid and high-latitudes and a clear ridge occurs around Balkhash and Baikal. These results show that the meridional circulation is strong and cold air is frequently active. South branch trough is active at low-latitude and subtropical high is strong. These distributions are advantageous to meeting of cold and warm air along the coast of South China Sea and form long continuous rainstorm. SST anomalies (SSTA) in Niño4 region is negative, SSTA in Niño3 region is weak positive, SSTA in the Kuroshio region is clearly positive, and SSTA in West Wind Drift region is weaker negative in composite SSTA with long continuous rainstorm. The composite difference of 500 hPa geopotential height and SST in March and April between long continuous rainstorm and no long continuous rainstorm shows that they have significant distinction. It also reveals that SST fiercely evolve from March to June and SSTA in Niño3 and Niño4 regions changes from negative to positive value for long continuous rainstorm, but distributive pattern of El Niño SSTA persists from March to June for no long continuous rainstorm.

Wind Characteristics Study in Surface Layer of Typhoon Morakot (0908)

Zhang Rongyan, Zhang Xiuzhi, Yang Xiaosheng, Wu Jincheng, Qu Haibin

2012, 23(2): 184-194.

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Abstract:
The observations from 33 anemometer tower within Typhoon Morakot (0908) affected area are analyzed. As the typhoon moves closer, the wind asymmetry becomes more apparent. Morakot has a counterclockwise shift of wind direction on the left flank, and a clockwise shift of wind direction on the other flank. Near the landing area, the wind reaches maximum and the direction is northerly before landing. When landing, the wind slows down, its direction rapidly changes and air pressure drops rapidly. Southerly gale appears when landing and northerly gale appears to the north of the location where it enters the sea.In the place far away from Morakot, wind direction is steady and the turbulence intensity changes are correspondingly stable. Its value is decided by sub-layer attribute, complex surface conditions lead to strong turbulence intensity.Near the landing area, the wind direction, the wind speed and the turbulence intensity may all changes suddenly. In the mountainous region, turbulence intensity change is most complex. Influenced by Morakot, the turbulence intensity curves do not look like the IEC standard curve which reduces stably along with the wind speed increasing. The turbulence intensity reaches a peak with wind speed of 7—17 m·s^-1when I₁₅achieves Level A, B or above. No matter southerlies or northerlies, each layer turbulence intensity difference tends to reduces with wind speed. Given the same wind speed and height, the turbulence intensity of southerly gale is bigger than that of the northerly gale. Turbulence intensity decreases first then increases with wind speed increasing at Morakot landing area northern flank, finally surpassing IEC the standard Level A curve. But to the south of landing location, turbulence intensity along with the wind speed changes much smaller than the north side and increases along with the wind speed, showing the standard Level A curve tendency. On the north side turbulence intensity is bigger than the south side and at each height the turbulence intensity difference reduces remarkably compared to south side. It indicates that the north side vertical direction the perturbation is stronger.Morakot gust coefficient is between 1.2 and 1.7. The average gust coefficient changes with height and regional terrain, and it also becomes larger when the typhoon center draws near. In general cases, the gust coefficient reduces with height. But over complex terrain especially the knoll mountainous region it reduces with height below 50 meters, and increases with height above 50 meters.

The Identification and Changing Characteristics of Regional Low Temperature Extreme Events

Gong Zhiqiang, Wang Xiaojuan, Cui Donglin, Wang Yanjiao, Ren Fumin, Feng Guolin, Zhang Qiang, Zou Xukai, Wang Xiaoling

2012, 23(2): 195-204.

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Abstract:
When an extreme low temperature event occurs, it generally impacts a certain area and lasts for some time, which means that it is a regional extreme event. How to identify a regional extreme low temperature is the basis for studies in this area. An objective identification technique for regional low temperature extreme events (OITRLTE) is developed. This technique consists of four parts: Defining the threshold value of extreme low temperature for single station; identifying abnormality belts; distinguishing temporal continuous process of the event; an integrated index system. The index is specially developed based on the features of regional events, which includes 5 single indices: Extreme intensity, accumulated intensity, accumulated area, maximum impacted area and duration, as well as an integrated index. Case studies show that OITREE is skillful in identifying regional low temperature extreme events (RLTEs). It can objectively and automatically capture daily impacted areas of a regional event for its duration, and reasonably putting them in a "string" to shape an entire regional event. Then based on the winter daily minimum temperature from 1960 to 2009, spatial distribution and temporal changes of RLTEs is also investigated. Results show that probability distribution of lowest temperature and latitude of geometrical center of RLTEs both obey the two-peak distribution, and the center of RLTEs mainly locates at two belts of 32°N and 42°N. The annual accumulative value of the frequency, intensity and max covering area of RLTEs is decreasing, and during the end of 1980s this trend changes and the trend becomes stationary after 1990s. These characteristics might be caused by the RLTEs with long duration and wide space range that accounted for top 10% of all events. Considering the good correlation between RLTE indexes, economic loss and the number of stricken people on cold disasters, an integration index is defined based on RLTE indexes. The weighted coefficients of the first-grade integrated index are defined based on the correlation between the yearly cumulative value of first-grade index, the corresponding yearly index of economic losses and the number of stricken people on cold disasters. So, in this way the weight coefficients denote the correlation between regional low temperature extreme events and corresponding disaster losses to some extent.

The Ideal Density and Distribution of China Climate Network for Monitoring Surface Climate Change

Ren Yuyu, Ren Guoyu, Zhou Jiangxing

2012, 23(2): 205-213.

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Abstract:
The China national climate observation network composed of 2416 stations are taken as the reference station network, and correlations of surface air temperature series precipitation series between the reference station network and analyzed station network are used to investigate the monitoring ability for surface climate change. The relationships between the monitoring requirements and the station number are analyzed for 2.5°by 2.5°, 2.5°by 3.5°, 5.0°by 5.0° latitude/longitude grid cells. Results show that the needed amount of stations decreases rapidly with the lowing of ability (standard) required for monitoring. Taking 2.5° by 2.5° grid cell for example, the needed amount of stations decreases from 750 to 377 when the monitoring requirements for temperature change from 0.99 to 0.95, and the needed amount of stations decreases from 670 to 417 when the monitoring requirements for precipitation change from 0.95 and 0.90. With the increase of grid cells, fewer stations are needed for the same monitoring requirement. In areas of rugged terrain, undulating terrain and transition zone from mountains to the plains and plateaus, higher station densities are generally needed. The areas where need high-density stations are mainly located in the mountainous regions, including the Sichuan Basin, the Wuyi Mountains, the Loess Plateau, the Qinling Mountains, the Southeast Hills, and the eastern mountainous areas of Northeast China. The more complex the terrain is, the lower the spatial consistency of climate change is, and the more stations are required. In general, monitoring for precipitation change requires higher density of stations. For 5° by 5° grid, however, the difference of station densities needed between temperature and precipitation is relatively small. The cause needs further study. The distributions of stations at the central and the west parts of Tibetan Plateau and Taklimakan Desert are not enough due to the harsh natural environment. Further research is needed in these regions, favorably in combination with other methods. In addition, the current stations are often located in the valleys and foothills rather than those on the slopes or on the peaks in mountainous regions, which has lowered the representativeness and enlarged the uncertainties.

Retrieval of Land Surface Temperature and Dynamic Monitoring of a High Temperature Weather Process Based on FY-3A/VIRR Data

Dong Lixin, Yang Hu, Zhang Peng, Tang Shihao, Lu Qifeng

2012, 23(2): 214-222.

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Abstract:
Split-window algorithm is mainly used for retrieving land surface temperature in thermal infrared remote sensing. Around seventeen algorithms have been published in recent years, but few have been applied to Chinese meteorological satellite data such as FY-3 series. FY-3A, the first of this series is launched from Taiyuan Satellite Launch Centre in China on 27 May, 2008. This new generation satellites series provide three dimensional, quantitative, multi spectrum global remote sensing data under all weather conditions, which will greatly help the operational numerical weather prediction, global change research, climate diagnostics and prediction, and natural disasters monitoring. The visible and infrared scanning radiometer (VIRR), medium resolution spectral imager (MERSI) and microwave imaging instrument (MWRI) aboard this satellite can all be used for retrieving the land surface temperature (LST) and monitoring the process of high temperature weather.Daily LST products are retrieved by the improved Becker algorithm using the FY-3A/VIRR data. And the first process of high temperature weather in 2009 is monitored and the changes of thermal environment in different land types are analyzed. First, a modified Becker's split window retrieval algorithm is developed using VIRR thermal infrared spectral response function for retrieving LST from the FY-3A/VIRR data. A new set of parameters for Becker's LST algorithm is proposed. The algorithm is developed from a surface brightness temperature dataset generated from the MODTRAN program, which uses a range of surface parameters (294.2 K, 294.2 K±5 K, 272.2 K, 272.2 K±5 K, 287.2 K, 287.2 K±5 K, 288.2 K, 288.2 K±5 K) and four kinds of atmospheric model (mid-latitude summer atmosphere, mid-latitude winter atmosphere, sub-polar summer atmosphere and American standard atmosphere 1972) as inputs. The daily brightness temperature data of the Channel 4 and Channel 5 of FY-3A/VIRR (1-km resolution) are used to generate the model parameters of Becker's split window inversion algorithm. Second, as a validation of the algorithm, the retrieved VIRR LST is compared with the instrument measurement data in satellite transit period in Dunhuang radiometric calibration and validation test site and MODIS LST of the same period and area. The results show that the error of LST products is-0.17 K and 1.77 K by two validations in Dunhuang site. The two LST products are found to be consistent, and the root mean square error between FY-3A LST and MODIS LST is 2.64 K. By histogram comparison, the two frequency distributions show no difference. Finally, the retrieved daily FY-3A LST is applied to monitor the first high temperature weather process in 2009, indicating two high-value regions: North China (Shijiazhuang, Zhengzhou, Beijing, etc.) and Northwest Territories (Xi'an, etc.). Land surface temperature in some regions exceeds 320.2 K. There are some spatial distribution differences in different urban land types. The profile data of VIRR LST in main cities verify the existence of the phenomenon of urban heat island. And the heat island of industrial mining land is reflected especially clearly in the LST spatial distribution because the vegetation around the industrial mining land is destroyed seriously.These results show VIRR LST production meet the real-time demand of operation. This also would provide scientific basis data for further study of local climate change, and greatly help the operational numerical weather prediction and global change research.

Temperature-sounding Microwave Channels for FY-3(02)

Zhang Miao, Lu Naimeng, Gu Songyan, Zhang Wenjian

2012, 23(2): 223-230.

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Abstract:
The new generation of Fengyun polar orbiters FY-3(02) satellite will be launched in 2012. Using Non-hydrostatic Modeling System (UW-NMS) cloud resolving model by University of Wisconsin, in conjunction with the VDISORT microwave radiative transfer model to simulate the upwelling brightness temperatures, the basic atmospheric parameters of Katrina are estimated, and the precipitation characteristics of sounding channels from two oxygen absorption complexes at 50—60 GHz and 118.75 GHz, which will be installed on FY-3(02) satellite are preliminarily analyzed. The two channels are combined to make use of their differential response to absorption and scattering by hydrometeors. To optimize the channel combination, four pairs of channels which show similar weighting functions in clear-sky atmospheric profiles are chosen (i.e., 50.3 GHz and 118.75±5.0 GHz, 51.76 GHz and 118.75±3.0 GHz, 52.8 GHz and 118.75±2.5 GHz, 54.40 GHz and 118.75±1.1 GHz), with the largest differences occurring at the lowest channels as a result of their different sensitivity to moisture that significantly affects observations below 500 hPa. To study the potential use of these frequencies, the relationships between the simulated TBs and the microphysical properties of the UW-NMS simulated precipitating clouds are analyzed. The sensitivity analysis shows that, all channels are very sensitive to hydrometeor species, and they are most sensitive to the graupel, then the snow, followed by the rain. Due to the scattering of the frozen hydrometeors, the TBs of 118.75 GHz decreases more than 50—60 GHz. After that, a Bayesian retrieval framework is used to retrieve the rainfall intensity and vertical structure of hydrometers, and three different sets of frequencies have been chosen to perform the retrieval: Using only the 50—60 GHz channels, using only the 118.75 GHz channels and a combination of all the channels respectively. Then the root mean square (RMS) and the correlation coefficient have been considered to analyze the behavior of the retrieval relative to the columnar liquid/ice water contents of rain, graupel, snow and surface rain rate. The results show that the 118.75 GHz channels are better in retrieving the columnar ice water contents of graupel, the 50—60 GHz channels are better in retrieving the columnar liquid/ice water contents of rain and snow, and the combination of all the channels always presents the highest correlation coefficient and the smallest RMS, so the combination of all channels will improve the precipitation retrieval precision. Then a second set of statistical indexes (correct rate, critical success index, probability of detection, false alarm rate) have been employed to evaluate the rain detection capability, discriminating between the raining and non-raining pixels. The results show that the correct rate and critical success index of all the channels are closer to 1, and the false alarm rate are closer to 0, so the combination of all the channels can better discriminate between the raining and non-raining pixels. After the launch of FY-3(02) satellite, this method will be further verified. And for global applications, more flexible retrieval approaches are required, which should be capable of constraining the algorithm according to the local situation.

The Applicability and Modification of Takahashi Formula for Evaporation Estimation in Lhasa

Fu Jing, Fan Guangzhou, Zhou Dingwen

2012, 23(2): 231-237.

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Abstract:
Researches on the latent heat, the process of water balance and the dry climate of Tibetan Plateau are of great significance. But due to the limits of estimation methods, observation instruments and lack of stations, there is no long, accurate evaporation data on Tibetan Plateau. Therefore, it is important to choose a more efficient, simple formula to estimate evaporation. The data of the Lhasa can represent the average state of the entire Plateau. In order to calculate the evapotranspiration, several methods including Takahashi formula are adopted and the results are compared with data of the Asian Monsoon Experiment. The result shows that the calculated values are close by PM formula, Remanenko formula, Blaney-Criddle formula and Hargreaves formula. The values calculated by PM formula and Remanenko formula begin to increase from January, reaching the maximum in May, and then decreases. But for the values calculated by Blaney-Criddle formula and Hargreaves formula, the maximum appears in July, two months later. The values of Remanenko formula and PM formula are closest, so the Remanenko formula can be used for the area lack of data. The maximum of potential evapotranspiration appears in May, but the evaporation is smaller due to lack of water, though the sun radiation is strong. As the relative humidity increases with precipitation, the potential evapotranspiration decreases, while the actual evaporation reaches maximum in July. The value estimated by the Takahashi formula has large bias comparing with the observation, indicating that Takahashi formula is not suitable for Lhasa. The bias is greater when the temperature is higher, because the frozen soil, ice and snow thaw on Tibetan Plateau have added the uncertainties. Considering the direct proportion between the temperature and the gapbias, the temperature is divided into 5 grades: Lower than 0℃, 0—5℃, 5—10℃, 10—15℃ and higher than 15℃. Without changing the original coefficients of the Takahashi formula, a coefficient is introduced on the precipitation part, which leads to results closer to the observations. The maximum of actual evaporation appears in summer, reaching 100 mm or above, which is slightly less than the measured value of the Asian Monsoon Experiment, and the minimum appears in winter. The value calculated with the modified formula is significantly higher than the original formula, closer to the observed data. But the value in winter is significantly higher than the original value, slightly higher than the observation.

Development of DAR Metadata for Meteorological Data in WIS

Zhu Ting, Li Xiang

2012, 23(2): 238-244.

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Abstract:
As the use of automated and web based systems increasing, metadata has become the key to sharing information between people working in different disciplines. As the interest of other earth science communities in meteorological data increases, there is a great deal of meteorological data which need to be transferred and shared. Traditionally weather data has been exchanged without metadata, i.e., the information about the data itself. It is assumed that the recipient understands the abbreviated message format, and has access to any metadata needed to determine the meaning of the transmitted data. This mode of data exchange works well within the meteorological community. However, it will be a problem for users outside of the meteorological community. Meteorological metadata will be the key to resolve the problem.The standardization of metadata within the meteorological community is becoming an important task during the last couple of years. WMO has recognized the importance of standardized metadata. A CBS expert team has been established after the CBS conference in 2000, aiming to develop a proposal for a WMO metadata standard. The team came up with the draft WMO Core Metadata Profile, version 0.2 at the end of 2003, based on the geographical standard ISO 19115.During the 14th World Meteorological Congress (Cg-XIV, 2003), a plan is approved for developing an overarching, integrated WMO Information System (WIS) that could meet the requirements of all WMO programs, affiliated international organizations and programs. The WIS architecture, functions and services will provide the solution for information exchange, management and access. Its main functional organizations include National Centers (NC), Data Collection or Product Centers (DCPC), and Global Information System Centers (GISC). China Meteorological Administration (CMA) has joined WIS program and achieved the core function requirement of GISC, including providing entry points and data service, through Beijing GISC and comprehensive metadata catalogues.In Beijing GISC, DAR (Discovery Access and Retrieval) meteorological metadata is the foundational information used for managing data resource and providing service of data discovery and access. It's also the reference information used for users to discover and retrieve data and products in WIS. An introduction is given on the background of applying DAR meteorological metadata in WIS, the WMO Core Metadata Profile, the metadata template applied in Beijing WIS portal, and how to generate DAR metadata instance in CMA. There are about 120000 corresponding DAR metadata for all the meteorological data provided by Beijing GISC.

The Design of Typhoon and Marine Meteorological Information System with Its Implementation

Chen Zuan, Li Haisheng

2012, 23(2): 245-250.

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Abstract:
A Typhoon and Marine Meteorological Information System with spatial-temporal model for heterogeneous multi-source weather products is introduced. The system focuses on multi-function typhoon track querying, weather information fusion and integrated web publishing based on WebGIS and rich internet application (RIA). The system also aims to expand typhoon and marine weather information service applications, and to develop a fast integrated multi-source weather data publishing platform. This system has been deployed on a website (typhoon.weather.com.cn).The overall system design idea is to develop a spatial-temporal model based on web electronic map and manage a series of weather data such as typhoon information, satellite images, radar images, live wind data, live precipitation data, offshore weather forecast and high-altitude surveillance data. The system fuses and overlays all kinds of the data, then publishes all the contents on the web. The system tries to complete and improve traditional weather service mode on the Internet, and attempts to provide richer and more professional meteorological services.The system aims to accomplish 4 primary targets. The first one is to process several weather data products into an integrated one, thus a product can convey a variety of weather information. The second aim is to popularize the meteorological information, and let the public understand the development of typhoon better. The third one is to fuse weather monitoring data and forecast data as an integration in order to provide references for the professional users and decision-making departments. The fourth one is to provide different services depending on different target users. As for ordinary users, the system can be accessed quickly, representing meteorological information easy to understand, allowing massive concurrent visits. As for professional users, this system will provide more professional and comprehensive weather information superimposed applications and more flexible user interaction.The system uses C/S and B/S combination of technical architecture based on spatial databases. The C/S section provides data import, edit and electronic map management functions. The B/S section represent marine meteorological information such as typhoon tracking, monitoring data and other integrated information based on WebGIS technology. All the various types of meteorological information are organized and managed according to a unified spatio-temporal data model.Compared to the traditional typhoon information systems, this is a user-friendly and feature-rich system which will process and apply a wide range of information including news, typhoon track data, satellite images, radar data, weather alerts, etc. Its designed daily visits are more than 5 million page views. The service framework of the system is valuable for further promotion.

The Operational System of Provincial Meteorological Instrument Calibration

Zhang Jianmin, Luo Chang, Wang Jiansen, Zhang Xiaodong, Bao Bingsheng, Yang Anliang

2012, 23(2): 251-256.

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Abstract:
As an application platform of provincial meteorological service, the operational system of provincial meteorological instrument calibration is applied to improve professional management, working efficiency and calibration quality. This system consists of two parts: The management subsystem and automatic calibration subsystem. With B/S construction and the classic C/S structure technology adopted respectively in the two subsystems, the operational system brings digitization, and automation of calibrating into effect. In detail, the management subsystem is combined with the module of data receiving and distributing through apparatus, instrument maintenance, system management, warning inspection beforehand, report form processing, comprehensive inquiry and statistics, and administrative control of measuring instruments. The automatic calibration subsystem includes the automatic detection of temperature, humidity, pressure, wind and precipitation sensors, which can carry out automatic calibration and performs intelligently in data processing. On the whole, the application of this system shows that the calibration efficiency and quality have been significantly improved.

Vol.23, NO.2, 2012