Abstract:A process-based model (Agricultural Production systems SIMulator, APSIM), which was developed in Australia, was used to study the spatiotemporal changes in agricultural soil organic carbon (SOC) across the North China Plain (NCP) from 1980 to 2010. The modeling results suggested that the calibrated APSIM model generally performed well in terms of simulating changes in yields of wheat and maize and SOC under different treatments at three selected long-term experimental sites: Xuzhou, Zhengzhou, and Changping. The regional simulations showed that most croplands of NCP experienced an increase in SOC, except several areas of the northern part of Hebei Province, and central and eastern parts of Shandong Province. The average rate of change of SOC was 0.35 Mg(C) ha^-1 a^-1, and the total increase in the SOC pool was 257.43 Tg (with a total cropland area of~24.52 Mha in NCP). Spatially, the cropland SOC pool increased by 102.05, 59.82, and 95.56 Tg in the Beijing-Tianjin-Hebei area, Shandong Province, and Henan Province, respectively. The increase in cropland SOC was mainly attributed to the increasing amount of carbon input during the past several decades.

Abstract:Using the PRECIS (Providing Regional Climates for Impacts Studies) regional climate modeling system driven by five members of QUMP (Quantifying Uncertainties in Model Projections) model ensembles developed by the Hadley Center/Met Office, this study analyzes the simulations of the surface air temperature and predicts the temperature during 2021-2050 under the IPCC SRES A1B emissions scenario over China. The result shows reasonable capabilities of PRECIS-downscaled QUMP members in simulating the baseline (1961-1990) climatology of surface temperature over China, though general overestimations of temperature values compared with observation were found over several regions. The projection shows increases in surface temperature simulated by all of the ensemble members, but differences of the warming tendency were also found among these members. The simulated annual mean daily minimum temperature showed the most significant warming compared with the annual mean daily mean temperature and the daily maximum temperature. Besides sensitivity test Q10, the warming simulated by each member corresponded with the climate sensitivity of the driven GCM. Overall, the most significant projected warming was shown over Northwest China with a range of 2.08-2.61℃, while the lowest range (1.33-1.84℃) was located over South China. However, differences of projected regional-scale warming were also shown among each member.

Abstract:Based on the highest daily temperature records of boreal summers from 1960 to 2011, this study analyzes interannual variations of the extremely high temperature days (EHTDs) in the Yangtze-Huaihe River basins of East China and their associated anomalous atmospheric circulations and sea surface temperature anomalies (SSTAs). Composite results of the summers in which the occurrence frequencies of EHTDs are higher (lower) than normal show that: (1) There is anomalous quasi-barotropic anticyclonic (cyclonic) circulation over the Yangtze-Huaihe River basins accompanied with anomalous descending (ascending) motion due to middle and upper troposphere thermal wind vorticity advection; (2) the position of the westerly jet has a northward (southward) displacement and a Silk Road Teleconnection-like wave train is found embedded in the upper troposphere; (3) prior summer, the central equatorial Pacific Ocean, South China Sea, Bay of Bengal, and Arabian Sea feature significantly positive (negative) SSTAs, while at the same time the SSTAs of the East China Sea and South Sea of Japan are significantly positive (negative). This study also evaluates the abilities of eight models involved in the Coupled Model Intercomparison Project Phase 5 (CMIP5) in simulating the EHTDs of the Yangtze-Huaihe River basins of East China, and the trend of EHTDs under different future emissions scenarios. The results suggest that the boreal summer EHTDs of the Yangtze-Huaihe River basins could reach about 20 d by the end of the 21st century under the 2.6 W m^-2 representative concentration pathway (RCP2.6), and 40 d and 70 d under RCP4.5 and RCP8.5, respectively.

Abstract:In order to better understand the relationship between lightning activities and nitrogen oxide (LNO_x) in the troposphere, and estimate the lightning-generated NO_x production in China more precisely, monthly means of lightning density and tropospheric NO₂ vertical column densities (VCD) from the Tibetan Plateau, where there is a sparse population and underdeveloped industrial activity, are analyzed in terms of their distribution and correlation. The data are obtained from LIS (Lightning Imaging Sensor) measurements and GOME-2 (the Global Ozone Monitoring Experiment-2) from January 2009 to February 2012. The LNO_x production in inland China is estimated based on Beirle's LNO_x estimation method. The results show that the tropospheric NO_x over the selected region of inland China is influenced little by anthropogenic sources. Lightning densities over the region are in reasonable agreement with tropospheric NO₂ in terms of annual, spatial and seasonal variations. Combined with the correlation coefficient of 0.84 calculated by linear fitting, LNO_x production in inland China is evaluated as 0.15 (0.03-0.38) Tg(N) a^-1. It is indicated that the Tibetan Plateau is an ideal area to study LNO_x. The conclusion further reduces the estimation uncertainty range of LNO_x production in previous work, helping us to more clearly recognize the important role of lightning in climate change in China.

Abstract:Air temperature is a basic element of conventional surface meteorological observations, and its method of observation and data errors are directly related to our understanding of atmospheric processes and forecast accuracy. Carrying out comparative analyses of different temperature observing systems and ensuring the accuracy and comparability of the observed data is important for the study of atmospheric science and the forecasting of weather and climate. Based on a side-by-side field comparison of a natural ventilation Louvred screen Temperature System (LTS) and an Aspirated shield Temperature System (ATS), from September 2009 to August 2010, the differences between the data obtained from them were analyzed. In addition, the relationship between the system biases and temperature, and the relationship between the radiation biases and solar radiation and wind speed, were discussed. Subsequently, a model to modify the system biases and radiation biases was proposed and, finally, the effects examined. The results showed that the LTS possessed warm biases of 0.19℃ and 0.29℃ at nighttime and during daytime, respectively; and the ambient-temperature-dependent systematic biases were a linear function of temperature, which increased by about 0.006℃ when temperature increased by 1℃. The ambient-solar-radiation- and ambient-wind-speed-dependent radiation biases were the result of the mutual coupling effect between solar radiation and environmental wind speed. With the warming effect, solar radiation was a good approximate parabolic function of the radiation biases; and with the cooling effect, the wind speed was a good approximate negative exponential function of the biases. After modification, both the biases at night and during the day dropped to 0.0℃. The consistency rate increased up to 92.3% and 96.0%, and the samples whose biases were between -0.2℃ and 0.2℃ increased from 64.5% and 45.3% to 83.7% and 80.6% at night and during the day, respectively.

Abstract:The East Asian summer monsoon has a significant impact on climate change in the Chinese monsoon region, but the responses and mechanisms of the terrestrial net primary productivity (NPP) to summer monsoon climate change are still not clear. In this paper, an atmosphere-vegetation interaction model (AVIM2) is used to simulate the NPP in the Chinese monsoon region. The correlation between NPP and summer monsoon index is analyzed, and the response mechanisms of NPP to the variations of summer monsoon are discussed. It is found that the vegetation responses and mechanisms to the variations of the summer monsoon are very different in North China and South China. Corresponding to strong summer monsoon years, the NPP in North China increases, while the NPP in South China decreases. The East Asian summer monsoon can affect precipitation over the North China Plain during vegetation growing seasons, and thus also affects the local NPP. Due to the superimposed effect of temperature and precipitation on NPP, Beijing, Tianjin, and Hebei become the most sensitive areas to the variations of the summer monsoon in the North China Plain region. During strong East Asian summer monsoon years, the NPP in South China decreases, and the main impact factors correlated to a strong East Asian summer monsoon are different: In Jiangsu, Anhui, Hubei, Hunan, and Jiangxi provinces, it is the reduced solar radiation; in Guangdong and Taiwan provinces, it is the lower temperature; and in Zhejiang and Fujian provinces, the major factor is the superimposed effect of reduced solar radiation and lower temperature.

Abstract:Version 3.6 of the online-coupled meteorology-chemistry model WRF-Chem (Weather Research Forecasting Model with Chemistry) was applied to simulate the feedback effect of a heavy haze episode (15-17 February 2013) on the synoptic conditions, based on optimization of the model scheme with observed data. We focus on the contribution of anthropogenic emissions, including primary particles, inorganic gas compositions, and volatile organic compounds (VOCs), to the formation of fine particulate matter (PM2.5), and the feedback effect on meteorological variables. The model results show that the contribution rate of anthropogenic emissions to the regional average PM2.5 concentration is 91.27% over North China and 96.9%, 95.9%, and 97.2% in Beijing, Qinhuangdao, and Cangzhou, respectively, leading to a 15.99% decrease in regional downward shortwave radiation, with regional radiative forcing at the surface estimated to be -26.51 W m^-2. Consequently, the 2-m temperature decreases by 0.14℃ (3.68%), and the inversion intensifies so that the vertical temperature gradient (∂T/∂z) increases by 0.026 K km^-1, which leads to a boundary layer height reduction of 18.92 m (8.77%). The 10-m wind speed decreases by 0.014 m s^-1 (0.35%), surface relative humidity increases by 0.51%, and surface pressure reduces by 0.86 Pa. For the haze episode during 15-17 February, the feedback effect of anthropogenic emissions on downward shortwave radiation plays a leading role in the weather process, which has a great influence-but not a leading role-on boundary layer height, and has little influence on temperature, wind speed, relative humidity, and surface pressure. As the precursors of secondary organic aerosol (SOA), volatile organic compounds (VOCs) contribute 99.6% to the concentration of SOA; moreover, VOCs transform inorganic gas into inorganic salt by adjusting the reactivity of the atmosphere, and they contribute greater than 50% of sulfates and nitrates. Even so, the contribution of VOCs to the PM2.5 concentration is less than 1/4 of the contribution of all anthropogenic emissions. The feedback effect of anthropogenic VOCs is about the same as anthropogenic emissions, but the effect of VOCs on surface pressure is led by thermal factors and all the anthropogenic emissions are led by dynamic factors. These results imply that the meteorological feedback effect induced by haze pollution was not conducive to the dispersal of air pollutants but contributed to local accumulation, which resulted in a more prolonged and serious pollution episode than might otherwise have been the case. Hence, the self-adjustment of air pollutants is an ineligible factor in analyzing the formation mechanism of regional haze.

Abstract:Two first thunderstorms at Beijing Capital International Airport caused by warm shear was analyzed. The feasibility and success in forecasting the storms is also reported. The results can be summarized as follows: 1) During the two warm-shear thunderstorms, a shallow trough appeared at the 500 hPa level, and the time that the positive vorticity in the 500 hPa layer arrived at the airport was consistent with the timing of the thunderstorm. Furthermore, there was strong convergence in the lower uplift region. 2) From the radar images, it can be seen that an obvious convergence speed appeared near the airport, and the radar echo was generated locally when the thunderstorms occurred. 3) The lower the Black Body Temperture (TBB), the stronger the thunderstorms. Therefore, the convection development trend can be inferred from the TBB contour map. 4) During the thunderstorm periods, the thunderstorm index value from FY-2E satellite ranged from 0 to 0.5. The value accurately characterized the timings of the thunderstorms.

Abstract:A two-wavelength polarization lidar, developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences, was used to measure cirrus cloud over Geermu City from December 2013 to December 2014. In this paper, the authors first introduce the lidar structure and data type, as well as the data processing methods. Then, a particular observation case is used to discuss the characteristics of the cirrus cloud. The results showed that the cirrus cloud was located from 4.7 km to 7 km, with a small optical depth of less than 0.1. The mean lidar ratios at 532 nm and 1064 nm were 24.3 Sr and 29.9 Sr, respectively, and the color ratio was concentrated between 0.8 and 1. The depolarization ratio measured for this case of cirrus cloud varied from 0.1 to 0.4, with maximum frequency between 0.25 and 0.3. This lidar has the ability to measure cirrus cloud, and can be used to study the long-term spatial and temporal distribution of cirrus cloud over the Tibetan Plateau.

Abstract:Based on the monthly mean surface dataset from 315 weather stations during 1963-2012, the spatial distribution characteristics of specific humidity (SH) and relative humidity (RH) over East China are analyzed. The results are as follows: 1) In winter months, the mean values of SH (0.4-7 g kg^-1) show zonal spatial distribution decreasing with latitude, while the mean values of RH (41%-82%) present the feature of a lower value in the central than in the northern and southern sides of the region. The relative variability of SH and RH are also discussed, revealing higher values of relative variability in areas with a lower value of SH and RH during the winter months. 2) In summer months, the values of SH (7-20 g kg^-1) are generally higher than in winter months, but the RH values (44%-89%) have little changes. Both SH and RH decrease from the southeast coast to northwest inland over East China. The spatial distribution of relative variability in summer months shows the lower mean values of surface humidity denoting lower mean values of SH or RH denoting higher values of SH or RH relative variability. 3) The spatial distribution of surface humidity in winter is deeply affected by the geographical location over East China. Specifically, surface humidity in winter is mainly dependent on latitude, but longitude also plays a role. However, surface humidity is not sensitive to elevation. Moreover, the distribution characteristics of SH are more dependent on the geography than RH in winter. 4) In contrast, the influence of geographical factors on the surface humidity distribution is more obvious in summer than in winter. In summer, surface humidity is also largely dependent on latitude, but the influence of elevation on SH and longitude on RH becomes more significant in summer than in winter. The geographical characteristics of the SH distribution are also stronger than for RH in summer.

Abstract:Using NCEP/NCAR reanalysis data, Hadley Centre SST data, station precipitation data, and Objectively Analyzed Air-sea Fluxes (OAFlux) latent and sensible heat flux data, the impacts of Kuroshio Current latent heat flux on Chinese precipitation anomalies in spring during 1960-2010 are investigated. Firstly, the results of air-sea interaction in the Kuroshio region indicate a forcing of the atmosphere to the ocean in the summer, and a forcing of the ocean to the atmosphere in the winter and spring. There is no clear signal for the air-sea interaction in the autumn. In spring, the sensible heat and latent heat fluxes in the Northwest Pacific are sensitive to the Kuroshio Current, and the maximum of both the sensible and latent heat appears in the region of the Kuroshio Current. The climate mean sensible and latent heat fluxes in the Kuroshio Current area are 30 and 120 W m^-2, respectively. Large standard deviation values of latent heat flux in spring are mainly distributed in the East China Sea and to the southeast of Japan, which is the Kuroshio Current region. However, large standard deviation values of sensible heat flux are mainly distributed to the west of Japan. The spatial pattern of the first EOF mode for the latent heat flux in the East China Sea and surrounding areas shows a large-value area located just inside the Kuroshio Current region. Further linear correlation analysis and composite studies confirm that the spring rainfall is above normal in South China and below normal in central China when the Kuroshio Current Latent Index (KLI) is larger than 0.8. The atmospheric circulation associated with the KLI indicates a significant change in the wind anomaly over China. When the KLI is larger than 0.8, northerly wind anomalies occur over China. The southwesterly wind in the northwest of the subtropical high is mainly distributed in southern China. Hence, water vapor cannot be transported northward, resulting in accumulation of water vapor in southern China. In this case, more rainfall is observed in southern China and less rainfall in central China. The situation is roughly the opposite when the KLI is smaller than -0.8.