Abstract:The paper proposes to judge the working condition of a ground-based microwave radiometer for atmospheric remote sensing by observing the brightness temperature (TB) at 08:00 BST on clear days according to atmospheric temperature seasonal variation features.Radiative transfer theory was briefly introduced and the data of temperature at 08:00 BST observed at Nanjing during the period of November 27,2010 to May 29,2011 were used to make a statistical comparison between the observed TB with a ground-based microwave radiometer and the simulated TB with radiosonde profiles as input to radiative transfer calculation in order to judge the working condition of the radiometer.The radiometer has 12 channels including 5 channels at 22.235,23.035,23.835,26.235 and 30.000 GHz for sensing humidity and liquid water content and 7 channels at 51.25,52.28,53.85,54.94,56.66,57.29 and 58.80 GHz for sensing temperature profiles.The results showed that the former 5 channels worked well in the period while the latter 7 did not.The methodology may be applied to radiometers' working condition monitoring as well as observation data quality control.

Abstract:The characteristics of the 30—60 d intra-seasonal oscillation(ISO) over the South China Sea(SCS) and its relationship with ENSO cycle are diagnosed by using the NCEP/NCAR reanalysis data,NOAA outgoing long wave radiation(OLR) data and extended reconstructed sea surface temperature from 1979 to 2009.The results are as follows:(1)The 30—60 d period of the ISO over the SCS is significant from May to October.The ISO over the SCS during normal years,which is represented by the convection in company with the ISO,presents eastward and westward longitudinal propagation and seasonal latitudinal sway between the two hemispheres.The ISO intensity over the SCS represented by the low frequency kinetic energy(KE) shows interdecadal variation with an increasing trend during the past 31 years as well as monthly change with a peak from July to August.(2)The ENSO cycle has a significant influence on the ISO convection over the SCS,and the convection intensity tends to be suppressed(intensified) during El Niño(La Niña) years.In contrast with normal years,the westward propagation of the ISO convection over the SCS weakens while the northward spread is notable during both El Niño and La Niña years.The northward spread is characterized by the northward leap of active convection band from the Southern Hemisphere to the Northern Hemisphere in the spring(from April to May),and the band can reach 35°N during La Niña years.However,the spread direction in the Northern Hemisphere is distinctly different from that in the normal years around September.(3)The ISO intensity over the SCS has a close relationship with ENSO cycle.The ISO intensity would weaken(strengthen) during El Niño(La Niña) years and has about half a year(6—8 months) lag correlation with the occurrence of mature El Niño(La Niña) event.The correlation between ISO intensity and the sea surface temperature anomaly over the Niño3 region is the most striking over the western and central Pacific in the spring and autumn before the mature El Niño occurs.The correlation centers also spread eastward accompany with the high value centers of low frequency KE.

Abstract:Using the three dimensional observation test data of urban heat island(UHI) in Nanjing in summer 2010,spatial and temporal distribution characteristics of urban heat island under typical weather conditions were analyzed.The results showed that daily mean UHI intensity on sunny days was over 1 ℃ in Nanjing in summer.UHI intensity was stronger and more stable during nighttime than that in daytime,with UHI distribution displaying directional characteristic and corresponding well to urban land-use conditions.During daytime,mixed layer in urban areas developed faster and was higher than that in the suburbs.During nighttime,there existed a long lasting convective mixed layer at low altitude in the city due to the unstable atmospheric stratification and the roughness of the underlying surface,which was as thick as more than 250 m.Owing to the storage of a large amount of heat and strong turbulent transport in urban underlying surface,heat island came into being in urban boundary layer,with UHI intensity decreasing with height.Heat island in boundary layer extended up to 900 m in daytime and maintained at 300 m at nighttime.

Abstract:Based on the data of daily wind direction and surface temperature over the China Southern Coast and the wind velocity over the northern South China Sea (NSCS),the northerly cold surge criterion and the occurrence frequency of the cold surge over NSCS were defined.In addition,the interannual variation of the cold surge over NSCS and the variation of its associated circulation have been investigated.The results show that the occurrence frequency index of the cold surge over NSCS can describe the cold surge system characteristics more comprehensively.It is closely associated with the outbreaks of cold air which influence most part of China,and results from the interaction between the middle and high latitude circulation and lower latitude circulation.When the ridge over the west of the Lake Baikal is stronger than normal,the meridionality of the circulation over middle and high latitudes becomes larger,at the same time the subtropical western Pacific high becomes weaker and is located further east than normal.Both of these are beneficial for the southward movement of the cold air,and lead to the cold surge's formation over the NSCS.When the cold surge occurs,the Hadley cell becomes stronger and it adjusts the air quality over the middle and high latitudes.Meanwhile,the subtropical westerly jet resulting from the high-level air northward movement under the action of the Coriolis force becomes stronger than normal.Both of these elements are beneficial for the maintenance and strengthening of the cold surge.

Abstract:The model and assimilation scheme of the second generation Global Oceanic Data Assimilation System of Beijing Climate Center(BCC_GODAS2.0) are introduced in this paper.Two experiments are designed to test the effect and stability of the assimilation system.One experiment is assimilated with the GTSPP observation from 1990 to 2008,while the other is performed without any observation in the same period.Comparison of the experiment results with the OISST and SODA(Simple Ocean Data Assimilation) datasets indicates that the assimilation of GTSPP can improve the simulation of sea surface temperature(SST) and sea surface salinity(SSS).In detail,the error of SST and SSS in the ocean,especially in the tropical Pacific,is reduced effectively.Moreover,the experiment with assimilation can better represent the temporal evolution of SST in the Nino3 and Nino4 regions as well.Also the assimilation amends the simulation in vertical.Specifically in the mixed layer near 200 m,the root mean square errors of temperature and salinity are decreased by 1.5 ℃ and 0.6 psu,respectively.

Abstract:By using the daily precipitation data of 392 stations over eastern China from 1959 to 2008,which passed 5% quality control,the characteristics of extreme precipitation are studied.The studied time period is divided into 1948—1976 and 1977—2008,and the differences of MPV(moist potential vorticity) and atmospheric stability are discussed during the two periods.Results indicate that the significant south-north differences of extreme precipitation are found over eastern China.The extreme precipitation and its percentage decrease in north of eastern China,especially in east of North China,which increase in south of eastern China,especially in the middle and lower reaches of Yangtze River.MPV exhibits a reduction in north of eastern China and an increase in south of eastern China.Both the convective stability and the baroclinic stability weaken in the south and strengthen in the north.The siginificant variation of atmospheric property is a main reason of the change trend of the extreme precipitation over eastern China.The further study demonstrates that the temperature anomalies are negative at 300 hPa over the high latitudes after 1976,which leads to the difference of thermodynamic properties of upper air in eastern China and affects the convective stability.Meanwhile,the negative temperature anomalies make the decrease(increase) of west wind in the north(south) side of the cold center,and the baroclinic stability weakens(strengthens) accordingly.

Abstract:Based on the NCEP 1°×1° reanalysis data and the precipitation data from AWS in Zhejiang Province,the relationship between precipitation resulting from distant typhoon(PDT) and the perturbation kinetic energy dispersion (PKED) of typhoon Krosa is analyzed.The results show that the mechanism of PDT in Zhejiang Province is different from that in north region of China because the PDT here is formed by the distant propagation of disturbance kinetic energy of typhoon while the PDT in north region of China results from the interaction between westerly trough and outer circulation of typhoon.The PKED of typhoon occurs both before and after its landfalling in Zhejiang Province.The intensity of disturbance kinetic energy is different at lower,middle,and upper levels in troposphere.The larger the amplitude of disturbance kinetic is,the longer of the wave propagation distance will be.The intensity of disturbance kinetic energy at middle and upper levels is larger than that at lower level in troposphere,so the PKED at middle and upper levels in troposphere can exert impact on the precipitation in Zhejiang Province when the typhoon location is far from it but that at lower level can not.The PKED from distant typhoon can produce a positive vorticity area at the upper level in precipitation region.And then the local cyclonic circulation comes into being because of the downward propagation of the positive vorticity from upper level.Finally,the combination of local cyclonic cell with the moisture flow from the east sea of China leads to the enhancement of local precipitation.

Abstract:Using the monthly mean temperature data of 160 stations from NCC,the NCEP/NCAR reanalysis data and NOAA global sea surface temperature(SST) data,the causes of winter temperature anomaly and its precursors in 2011/2012 are analyzed on the basis of associated mechanisms since 1986.The results show that the Siberian High,East Asian winter monsoon and the abnormal circulation systems around the Ural Mountains and the region South to the Lake Baikal at 500 hPa are the main circulation systems at high latitudes which exert important impact on the wintertime surface air temperature in China;the circulation systems at low latitudes mainly include the Western Pacific Subtropical High and the India-Burma Trough;the sea surface temperature anomalies(SSTA) of key regions in tropical Indian Ocean and the middle-east equatorial Pacific are closely related to the circulation system variation associated with the winter temperatures in late winter.The July and August SSTA of higher temperature in the western Indian Ocean mainly corresponds to the enforcement of winter circulation anomalies of Siberian High,which makes the winter monsoon stronger and the wintertime air temperature lower in China.August,September and October SSTA of higher temperature over the middle and east equatorial Pacific mainly causes the enforcement of Western Pacific Subtropical High and India-Burma Trough.The location of Western Pacific Subtropical High is to the west and north,and the India-Burma Trough becomes stronger at the same time,which causes the temperature in China to be warmer,and vice versa.The influences of the SSTA in these two key regions on the subsequent circulation are somehow independent,and the winter surface air temperature anomalies are jointly affected by the two factors.

Abstract:After the homogeneity test and correction,the meteorological data from 96 observation stations in Hunan province during 1960—2010 were used to analyze the climate change facts there.The results showed that getting warm was the main characteristic in climate change in Hunan,which was consistent with the global trend.The warming tendency in Hunan also presented seasonal and regional differences:the linear warming trend was significant in winter,spring and autumn and the most significant warming region appeared in northern areas;the factors sensitive to warming were closely related to temperature such as seasonal mean temperature,annual mean minimal temperature and active accumulated temperature.The abrupt change times of temperature presented a good logical relation;the linear trend of precipitation in Hunan was not significant but it presented regional differences and the extreme preicipitation events was increasing.There was an increasing trend in precipitation in eastern areas of Hunan and the annual days with daily precipitation of more than 100 mm were increasing significantly.The annual sunshine hours,annual mean wind speed and annual mean relative humidity in Hunan presented a significantly decresing trend in recent 61 years.

Abstract:By using the monthly NCEP/NCAR data and the data of thunderstorms in Jiangsu Province from 1981 to 2010,the main causes for anomalous thunderstorms in Jiangsu in winter 2010 are analysed on the basis of the possible mechanism of typical episodes occurring in recent 30 years.Results show that there were more thunderstorms in winter of 2010 than normal in most areas of China,which was negatively related with the teleconnection circulation anomaly of the Arctic Oscillation (AO).When the AO was weaker than normal,the air pressure in Central Siberian and West Siberian were higher than normal while that in middle-latitude area was lower.At the same time,Ural blocking high played a supporting role,so the East Asia winter monsoon was stronger,which meant the cold air was stronger than normal.There was an anomalous warm center at 30°N of lower troposphere,which caused the intensification of water vapor transfer at Bay of Bengal and thus there would be a water vapour convergence center in Jiangsu.The distribution of "cold and dry upper-layer and warm and wet lower-layer" triggered upward movement of the air,which was beneficial for the occurrences of thunderstorms.The negative anomalies of SSTA in such regions as central and eastern North Pacific caused anomalous divergence,resulting in the anomalous downward movement of the air.It then caused anomalous convergence in the area of the same latitude in East Asia via Walker pattern and enhanced cyclonic circulation in both areas.

Abstract:Visibility variation trends from 1980 to 2005 have been constructed using four different statistical methods:Ridit analysis,cumulative percentiles,frequency of "very good" visibility,and annual and seasonal means.Improvements in visibility were experienced from 1980 to 1984.A decline trend can be observed after 1985 with some fluctuations in the process.In these 26 years,the mean daily visibility was 8.59 km with the maximum at 29.25 km and the minimum at 0.55 km,respectively.There were obvious seasonal and daily variation features in visibility.It was worst in winter and best in summer in one year while it was worst at 08:00 BST and best at 14:00 BST in one day.Visibility showed a positive correlation with wind speed and a negative correlation with relative humidity.However,temperature and atmospheric pressure showed comparatively little correlation with it.PM₁₀ was the major pollutant in Nanjing.Curve estimation of daily mean PM₁₀ mass concentration and the visibility presented a negative correlation and the coefficient was the largest in autumn and the smallest in summer.A regression model based on relative humidity,PM₁₀,wind speed and temperature has been developed.There were seasonal differences in the coactions of air pollution and meteorological condition on visibility,which was worse in summer than that in the other three seasons.

Abstract:An ensemble fog forecast system was designed based on WRF and a high resolution numerical 1-D model called PAFOG,whose initial perturbation conditions were obtained from the simulation of WRF.Comparison between prediction and observation was made during a typical radiation fog event that occurred in Nanjing during 13—14 December 2007.The results show the ensemble forecast system is better than single forecast.By using this method,the predictions for both visibility on surface and vertical structure of fog are better than those utilizing the model only initialized by radiosonde observation.The initial time of simulation played an important role in prediction accuracy.Because most radiation fog occurs at night and it takes some time for the model to stabilize,the best time to start the one-dimensional model is 14:00.The standard deviation between ensemble member and observation is 0.516 and the absolute error of ensemble average is 0.287 km.

Abstract:Using MICAPS routine data,TWR01 radar data and the observation echo data of the Doppler radar in Shiyan,combined with hail reports on the ground,this paper analyzed the weather background and radar data of two hailstorm processes in Baokang on 6 June and 26 August 2009.The results showed that upper cold chamfer trough and low shear line were the main impact systems.The hail on 6 June was caused by strong cell hail cloud and the hail cloud echo presented supercell echo characteristics.The initial radar echo was high and the hail cloud developed fast.The strong center was in the shape of a spindle.Low middle layer have WER(weak echo region);vertically integrated liquid water values before the hail showed obvious responses.The hailstorm on 26 August occurred in the subtropical high internal circulation situation and was generated by the merged and strengthened hail clouds.

Abstract:Paddy rice is one of the main crops in China.Timely information acquisition of rice planting area and spatial distribution at a large scale is of great significance in guiding rice production and regulating regional balance of supply and demand.In order to obtain paddy field area of Jiangsu Province,three types of vegetation indexes(including NDVI(normalized difference vegetation index),EVI(enhanced vegetation index),and LSWI(land surface water index)) are calculated by using the MODIS09A1 data from 2009 to 2011.Based on the temporal variation characteristics of EVI in different growth stages of rice,the key growth period of rice area extraction extracts is determined.According to the characteristics of rice transplanting period with high soil moisture,NDVI,EVI and LSWI are used to identify potential planting area of rice.The linear spectral mixture model is applied to decompose the mixed pixel of potential rice area,and the rice spatial distribution is obtained in Jiangsu Province from 2009 to 2011.Finally,selecting the typical sample area of rice,the rice planting area and spatial distribution are extracted by using HJ-1 CCD(30 m) data,and the results are used as reference data to verify the extraction accuracy.Meanwhile,the statistical rice planting area of Jiangsu Province from the statistical department is also used to verify the rice area.The error is within 10% by two methods of the statistical data and HJ-1 CCD(30 m) data.The research shows that it can more accurately extract a large range of rice planting area by using MODIS09A1 data and the linear spectral mixture model.

Abstract: