Li N.,Nanjing University of Information Science and Technology |
Wei M.,Nanjing University of Information Science and Technology |
Niu B.,Wuhan Central Meteorological Observatory |
Mu X.,Jiangsu Institute of Meteorological science
Meteorological Applications | Year: 2012
A new storm identification and warning technique is proposed which exclusively uses radar data as input. The new identification method assembles contiguous storm points to constitute 2D storm components and improve the vertical association of storm components to construct 3D storms, which can overcome the deficiencies existing in traditional identification methods. Based on the evolution properties and characteristic distributions, strong storms and general storms are specified to train support vector machines (SVMs) which then can be used to discriminate storms. The performance of the SVM shows that it can indicate the intensity and development of a storm, providing an important aid in severe weather warning. © 2011 Royal Meteorological Society.
Sun J.,Institute of Heavy Rain |
Shi Z.,Nanjing University of Information Science and Technology |
Chai J.,Hubei Lightning Protecting Center |
Xu G.,Institute of Heavy Rain |
Niu B.,Wuhan Central Meteorological Observatory
Atmosphere | Year: 2016
The effects of the liquid water content (LWC) and mixing ratio of hydrometeors in the simulation of convective precipitation in Wuhan, Hubei Province, China, are investigated using a three-dimensional convective rainstorm model. The microphysical processes of warm and cold clouds are considered into microphysical parameterization. The warm-cloud process is dominated by the combined effects of condensation and drop coalescence. The cold-cloud process is initiated mainly by production of graupel, and the microphysical parameterizations are used to predict the mixing ratio of cloud droplets, rain, ice crystals, snow, and graupel. The simulations results show that 80% rainfall is derived from warm cloud microphysical processes, and the rest is produced by cold cloud microphysical processes. The mixed phase microphysical process can invigorate the production of convective rainfall and enhance the liquid water content (LWC). In addition, the vertical distribution of LWC is mainly concentrated at the height isotherms of -10 to -20 °C in precipitation and the concentration area of LWC matches the distribution range of graupel particles. However, the growth of graupel particles depend on the microphysical processes of nucleation and propagation between rain and graupel particles (NUrg) and collision and coalescence between cloud droplets and graupel (CLcg), in which NUrg is a major source of graupel particles and the contribution of the process accounts for 77% of the amount of graupel particles.
Tao L.,Nanjing University of Information Science and Technology |
Li S.-J.,Wuhan Central Meteorological Observatory
Journal of Tropical Meteorology | Year: 2014
In this work, an index of tropical 20-90 d oscillation (intra-seasonal oscillation; ISO) in the western North Pacific (WNP) was determined via the combined empirical orthogonal function (EOF) method using daily outgoing longwave radiation (OLR) field data from the National Oceanic and Atmospheric Administration (NOAA), daily wind field data (at 850 hPa) from the European Centre for Medium-Range Weather Forecasts (ECMWF) and referencing the Madden-Julian oscillation (MJO) index proposed by Wheeler and Hendon. An in-depth investigation was conducted to examine the impact of the ISO on changes in tropical cyclone (TC) tracks in the WNP during different ISO phases. The research results indicate that during the easterly phase of the ISO, under the impact of the northeastern airflow of anti-cyclonic ISO circulation, the easterly airflow south of the western Pacific subtropical high is relatively weak, and TCs generated in the subtropical high tend to change their tracks east of 140°E; during the westerly phase, there is a relatively high probability that TCs change their tracks west of 140°E. This work also analyzed the ISO flow field situation in cases of typhoons and determined that the track of a tropical cyclone will experience a sudden right turn when the center of the ISO cyclonic (anti-cyclonic) circulation coincides with that of the cyclone.
Wan Y.,Institute of Heavy Rain |
Wu C.,Wuhan Central Meteorological Observatory |
Jin H.,Wuhan Central Meteorological Observatory
Acta Meteorologica Sinica | Year: 2010
A technique for real-time synchronous integration of radar and raingauge measurements based on the concept of the quasi same-rain-volume sampling (QSVS) is presented. Because of the temporal and spatial discrepancies and resolution differences, the integration of radar measurements with raingauge observations has long been a difficult task. Observations indicate that there exists a correlation that conforms to the power law between hourly accumulated raingauge measurement (QG) and detected radar echo (ZOH) over the raingauge. On the basis of this, a concept of the QSVS and five direct correspondent formulas of radar and raingauge samples are built up, aiming to eliminate the temporal and spatial discrepancies. A convenient and practical sampling method-the time integral vertical synchronous sampling (TIVS) is proposed and the ZOH- QG relationship is studied. It is significant that under the fixed exponent, the coefficient AB or AM varies flexibly in accordance with the temporal and spatial variability of natural precipitation, having the function of synchronously integrating the Z- R conversion and the gauge adjustment into a single equation, and thus the precipitation estimation errors caused by detecting resolution differences between radar and raingauge can be obviously mitigated. The real-time synchronous integration technique using the ZOH- QG relationship to estimate the ground hourly rainfall accumulation is called the radar-gauge synchronous integration method (RASIM). The experiments of two cases show that the accuracy of estimated surface hourly rainfall accumulation within 230 km is about 90%, and the average relative error for the point estimation over the whole process is about 20%. Through the detailed analysis of the applicability of TIVS in three environmental fields with various wind drifts, the physical essence of TIVS is explored: it is an approximate QSVS. By analyzing the data pairs of radar and raingauge, an effective quality-control procedure is established, which can greatly improve the stability and rationarity of the ZOH - QG relationship. The forecasting product of hourly rainfall accumulation derived from the RASIM has been put into operation. It is demonstrated that the RASIM plays an important role in the quantitative monitoring and forecasting of short-term torrential rainfall.
Lin W.,Chinese Academy of Meteorological Sciences |
Xu X.,Chinese Academy of Meteorological Sciences |
Ma Z.,Institute of Urban Meteorology |
Zhao H.,Chinese Academy of Meteorological Sciences |
And 2 more authors.
Journal of Environmental Sciences | Year: 2012
SO 2 measurements made in recent years at sites in Beijing and its surrounding areas are performed to study the variations and trends of surface SO 2 at different types of sites in Northern China. The overall average concentrations of SO 2 are (16.8 ± 13.1) ppb, (14.8 ± 9.4) ppb, and (7.5 ± 4.0) ppb at China Meteorological Administration (CMA, Beijing urban area), Gucheng (GCH, relatively polluted rural area, 110 km to the southwest of Beijing urban area), and Shangdianzi (SDZ, clean background area, 100 km to the northeast of Beijing urban area), respectively. The SO 2 levels in winter (heating season) are 4-6 folds higher than those in summer. There are highly significant correlations among the daily means of SO 2 at different sites, indicating regional characteristics of SO 2 pollution. Diurnal patterns of surface SO 2 at all sites have a common feature with a daytime peak, which is probably caused by the downward mixing and/or the advection transport of SO 2-richer air over the North China Plain. The concentrations of SO 2 at CMA and GCH show highly significant downward trends (-4.4 ppb/yr for CMA and -2.4 ppb/yr for GCH), while a less significant trend (-0.3 ppb/yr) is identified in the data from SDZ, reflecting the character of SDZ as a regional atmospheric background site in North China. The SO 2 concentrations of all three sites show a significant decrease from period before to after the control measures for the 2008 Olympic Games, suggesting that the SO 2 pollution control has long-term effectiveness and benefits. In the post-Olympics period, the mean concentrations of SO 2 at CMA, GCH, and SDZ are (14.3 ± 11.0) ppb, (12.1 ± 7.7) ppb, and (7.5 ± 4.0) ppb, respectively, with reductions of 26%, 36%, and 13%, respectively, compared to the levels before. Detailed analysis shows that the differences of temperature, relative humidity, wind speed, and wind direction were not the dominant factors for the significant differences of SO2 between the pre-Olympics and post-Olympics periods. By extracting the data being more representative of local or regional characteristics, a reduction of up to 40% for SO2 in polluted areas and a reduction of 20% for regional SO2 are obtained for the effect of control measures implemented for the Olympic Games. © 2012 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences.
Modeling convective-stratiform precipitation processes on a Mei-Yu front with the Weather Research and Forecasting model: Comparison with observations and sensitivity to cloud microphysics parameterizations
Luo Y.,Chinese Academy of Meteorological Sciences |
Wang Y.,Wuhan Central Meteorological Observatory |
Wang H.,Chinese Academy of Meteorological Sciences |
Zheng Y.,CAS Institute of Atmospheric Physics |
Morrison H.,U.S. National Center for Atmospheric Research
Journal of Geophysical Research: Atmospheres | Year: 2010
Deep convective-scale simulations of the linear mesoscale convective systems (MCSs) formed on a Mei-Yu front over the Huai River basin in China on 7-8 July 2007 were conducted using the Advanced Research Weather Research and Forecasting model to investigate impacts of cloud microphysics parameterizations on simulated convective-stratiform precipitation processes. Eight simulations were performed with identical configurations, except for differences in the cloud microphysics parameterizations. Measurements from rain gauges, ground-based weather radars, and the Tropical Rainfall Measuring Mission satellite Precipitation Radar were used to quantitatively evaluate the model results. While all of the simulations largely capture the observed large-scale characteristics of the precipitation event, notable differences among the simulations are found in the morphology and evolution of the MCSs at mesoscale and cloud scale. Significant influences on the coupling between dynamical and microphysical processes at the resolved deep convective scale by the various microphysical parameterizations are evident. On the one hand, the different microphysical schemes produce not only substantial differences in intensity of convective precipitation but also distinguishable vertical distributions of latent heating and condensate loading in the deep convective regions, which in turn results in significant differences in the vertical distributions of vertical air velocity and in the heights and strength of detrainment from deep convective regions. Consequently, detrainment of hydrometeors and positively buoyant air from the deep convective regions to the stratiform regions is significantly different, which impacts the formation and growth of ice-phase hydrometeors at the upper levels and thus surface rainfall rates in the stratiform regions. On the other hand, prediction of rain size distribution significantly impacts the simulated rain evaporation rates and mass-weighted rain fall speeds, and hence rain flux. Improper determination of the intercept parameter of rain size distribution can result in unrealistic features in the morphology of the storm and can have substantial impacts on precipitation distribution and evolution. Copyright 2010 by the American Geophysical Union.
Liu K.,Wuhan Region Climate Center |
Liang Y.,Wuhan Region Climate Center |
Zhou J.,Wuhan Central Meteorological Observatory |
Liu M.,Wuhan Region Climate Center
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2014
In recent years, drought events in Honghu lake have shown a significant increasing trend, which has had a tremendous impact on local ecological and agricultural production. We conducted an analysis based on Honghu's hydrology and land-use data over the past 30 years and climate data from 1960 to 2011, using the water balance principle and statistical methods. The results showed that the Honghu water resource is most vulnerable in the spring. The water level at this time of year is just slightly higher-with 2 to 3 times the mean standard error-than that in winter, which leads to frequent and severe drought in Honghu. With global climate change, however, the local annual precipitation is increasing; the rainfall is concentrated in summer and is less in spring, especially in spring drought years, with a decreasing rate of 12.57 mm/ 10a, significant at 0.1. The precipitation in summer increases, but it is negatively correlated with the water level in the following spring, which means that an increase in precipitation in summer can aggravate the severity of the spring drought. The Honghu lake water level in May is highly dependent on spring rainfall, with a rate of 0.36 m/ 100 mm. Over the past 20 years, the agricultural structure in Honghu has changed significantly, with increasing aquaculture areas and decreasing dry crop areas. The aquaculture area of the two counties surrounding Honghu has increased nearly 7 times and, because of this, the agricultural irrigation water requirement has increased by more than 414 million cubic meters in the case of low rainfall, which is equivalent to 45% of the total water in Honghu lake's annual income. Increasing aquaculture consumes much of the water resource in spring and the coefficient between aquaculture and water level of Honghu is about -0.158 m/ 104 hm2 with a correlation coefficient of - 0. 4954, which is significant at 0. 1. Human activities, especially excessive aquaculture and climate change, are the main reason for the increasing frequency and severity of spring drought in Honghu, with aquaculture having the greatest impact. In order to maintain Honghu's ecological function and reduce the drought effects, measures should be taken to change both the agricultural structure and the way in which land is used.
Lin W.,Chinese Academy of Meteorological Sciences |
Lin W.,Meteorological Observation Center |
Xu X.,Chinese Academy of Meteorological Sciences |
Ge B.,CAS Institute of Atmospheric Physics |
Liu X.,Wuhan Central Meteorological Observatory
Atmospheric Chemistry and Physics | Year: 2011
Gaseous pollutants, NOy/NOx, SO2, CO, and O3, were measured at an urban site in Beijing from 17 November 2007 to 15 March 2008. The average concentrations (with ± 1;sigma;) of NO, NO2, NOx, NOy, CO, SO2, and O3 were 29.0 ± 2.7 ppb, 33.7 ± 1.4 ppb, 62.7 ± 4.0 ppb, 72.8 ± 4.5 ppb, 1.99 ± 0.13 ppm, 31.9 ± 2.0 ppb, and 11.9 ± 0.8 ppb, respectively, with hourly maxima of 200.7 ppb, 113.5 ppb, 303.9 ppb, 323.2 ppb, 15.06 ppm, 147.3 ppb, and 69.7 ppb, respectively. The concentrations of the pollutants show "saw-toothed" patterns, which are attributable mainly to changes in wind direction and speed. The frequency distributions of the hourly mean concentrations of NOy, SO 2, CO, and O3 can all be decomposed in the two Lorentz curves, with their peak concentrations representing background levels under different conditions. During the observation period, the average ratio NO x/NOy was 0.86 ± 0.10, suggesting that the gaseous pollutants in Beijing in winter are mainly from local emissions. Data of O 3, NOz, and NOx/NOy indicate that photochemistry can take place in Beijing even in the cold winter period. Based on the measurements of O3, NOx, and NOy, ozone production efficiency (OPE) is estimated to be in the range of 0-8.9 (ppb ppb-1) with the mean(± 1σ) and median values being 1.1(± 1.6) and 0.5 (ppb ppb-1), respectively, for the winter 2007-2008 in Beijing. This low OPE would cause a photochemical O3 source of 5 ppb day-1, which is small but significant for surface O3 in winter in Beijing. Downward transport of O3-rich air from the free troposphere is the more important factor for the enhancement of the O3 level in the surface layer, while high NO level for the destruction of O3. The concentrations of SO2, CO, and NOx are strongly correlated among each other, indicating that they are emitted by some common sources. Multiple linear regression analysis is applied to the concentrations of NOy, SO2, and CO and empirical equations are obtained for the NOy concentration. Based the equations, the relative contributions from mobile and point sources to NOy is estimated to be 66 ± 30 % and 40 ± 16 %, respectively, suggesting that even in the heating period, mobile sources in Beijing contribute more to NOy than point sources. © 2011 Author(s).
Liu X.-W.,Chinese Academy of Meteorological Sciences |
Liu X.-W.,Wuhan Central Meteorological Observatory |
Xu X.-B.,Chinese Academy of Meteorological Sciences |
Lin W.-L.,Chinese Academy of Meteorological Sciences
Zhongguo Huanjing Kexue/China Environmental Science | Year: 2010
Surface O3 and other pollutants were observed from June, 2008 to May, 2009 simultaneously at the compound of China Meteorological Administration (CMA) in Beijing urban area, Shangdianzi background station (SDZ) northeast of Beijing, and Gucheng station (GCH) southwest of Beijing. The observational data are used to study the variation characteristics of surface O3 and the relationships between O3 concentration and other pollutants concentrations as well as meteorological parameters. The results show that surface O3 at SDZ has clear seasonal and diurnal cycles, which are obviously different from those at other two stations, while the seasonal and diurnal cycles at GCH and CMA are similar. O3 is negatively correlated with NO, NO2, NOx, RH, and the correlations in winter are more significant than in summer. In addition, air temperature and wind speed are positively correlated with O3, and the correlation coefficient between wind speed and O3 at CMA changes very much from winter to summer. The O3 concentrations show some dependence on the local wind direction at the sites, with higher O3 concentration being observed under southerly winds and lower O3 concentration under northeasterly winds.
Lin W.L.,Chinese Academy of Meteorological Sciences |
Lin W.L.,Tibet Institute of Plateau Atmospheric and Environmental Science |
Xu X.B.,Chinese Academy of Meteorological Sciences |
Sun J.Y.,Chinese Academy of Meteorological Sciences |
And 2 more authors.
Science China Earth Sciences | Year: 2011
Lorentz curve fittings are applied to frequency distributions of the concentrations of O3, CO, NOx and SO2 recorded at the Jinsha regional atmospheric background station (JSH) from June 2006 to July 2007, and the peak concentrations of these species for the different seasons are obtained. The peak concentrations are considered to be representative of different background levels for certain processes. The peak concentrations are compared with the corresponding mean (median) concentrations, and the suitability and limitations of the mean (median) values as the background levels are discussed. The mean (median) values might represent the background concentrations in the region under some circumstances, but in other cases these values often underestimate or overestimate the true background concentrations owing to the transport of pollutants and other factors. The effects of air masses transported from different regions on the pollutant background concentrations are obtained by analyzing the 72-hour backward trajectories of air masses 100 m above the ground at JSH. These trajectories are estimated using the HYSPLIT model and then clustered for the measurement period. The spatial distribution and seasonal variations of trajectories and the corresponding mean concentrations of O3, SO2, NOx and CO for different clusters are analyzed. After filtering the seasonal changes in pollutant concentrations, the relative influences of air masses from different regions are obtained. The results show that JSH can be used to obtain the atmospheric background information of different air masses originating from or passing over the Yangtze River Delta, Central South China and the Jianghan Plain. Air masses from Central China, South China, and the western Yangtze River Delta contribute significantly to O3 at JSH. Air masses from the north and northeast of JSH (i. e., the Jianghan Plain, Huang-Huai Plain and North China Plain) and the south (Central South China) contribute significantly to SO2, CO and NOx concentrations. Air masses originating from the ocean often bring clean air. Air masses originating from high altitudes over northwestern regions often have lower CO and NOx concentrations, lower relative humidity, and higher concentrations of O3 and SO2. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.