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Wu J.,Yunnan University | Wu J.,Yunnan Institute of Geography | Zha J.,Yunnan University | Zhao D.,CAS Institute of Atmospheric Physics
Climate Dynamics | Year: 2015

Long-term changes in surface wind speed (SWS) are influenced by both large-scale circulation and relative resistance. The effects of large-scale circulation are embodied by the pressure-gradient force (PGF), which is mostly a natural factor, whereas the resistance is due to the drag between the air and the surface as well as in the different boundary layers, which is mainly caused by the anthropogenic land use and cover change (LUCC). We performed experiments using a simple dynamical method in which a balance among the PGF, Coriolis force, and drag is reached to separate the effects of the PGF and LUCC on the SWS, and then, to quantitatively estimate the influence of the LUCC on the SWS over the East China Plain (ECP) during the period 1980–2011. The results show a distinct decrease in the SWS in the station observation data with a rate of −0.13 m s−1 (10 year)−1, but there is no statistically significant long-term trend in the reanalysis data. At the same time, the drag coefficient induced by the LUCC shows an increasing trend, which is consistent with the 30 % increase in the rate of urbanization during the study period. In addition, the PGF fluctuates with distinct seasonal and interannual changes, and it has an insignificant long-term increasing trend during the period 1980–2011. At the same time, the spatial distribution of the linear trend coefficient of the normalized PGF is inconsistent with that of the SWS, but the linear trend coefficient of the normalized drag coefficient shows a similar spatial distribution as the SWS. Therefore, the increase in the drag coefficient induced by the LUCC should account for the long-term decrease in the SWS. The difference between the model wind speed, in which the drag coefficient is constrained to its value in the year 1980, and the observed wind speed at each station (SWSD) can reflect the influence of the LUCC on the SWS. Furthermore, the long-term changes in East Asian monsoons may not completely account for the observed wind speed decrease near the surface in the ECP region, but it is an important factor in the SWS. © 2015 Springer-Verlag Berlin Heidelberg Source


Wu J.,Yunnan University | Wu J.,Yunnan Institute of Geography | Guo J.,Yunnan University | Guo J.,Nanjing University of Information Science and Technology | Zhao D.,CAS Institute of Atmospheric Physics
Atmospheric Research | Year: 2013

We used daily aerosol simulations for the period from 2001 to 2003 that were generated by the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model to characterize aerosol transport and distributions in East Asia. In comparison with the AERONET, MODIS, and visibility observations, the model can capture the main distribution features of the aerosol optical depth (AOD) and its temporal changes with a correlation coefficient of 0.75 and 0.85, respectively. It was found that high AODs occur in Central China, the Sichuan basin, the Indo-China peninsula, the Indian subcontinent, and the Bay of Bengal because of black carbon, organic matter, and sulfate, whereas in the Taklimakan desert and its adjacent regions, high AODs occur because of dust. The potential effects of the hygroscopicity of aerosol particles on the AOD were mainly observed in the Sichuan basin, the Bay of Bengal, the Indo-China peninsula, and Central and Southern China. The East Asian aerosol transport was distinctly affected by the flux divergence induced by aerosol advection (AFD) and by the flux divergence induced by wind divergence/convergence (WFD). For black carbon, organic matter, and sulfate, the effect of AFD was a factor of 2 or 3 larger than that of WFD in the divergence region, whereas AFD dropped to 70% of WFD in the convergence region. The high AOD of black carbon, organic matter, and sulfate over the Sichuan basin related to the circulation characteristics of convergence in low altitudes and divergence in high altitudes, which can collect aerosol from adjacent regions at altitudes below 300. hPa and cause them to diverge easterly at higher altitudes. © 2013 Elsevier B.V. Source


Wu J.,Yunnan University | Wu J.,Yunnan Institute of Geography | Zhang L.,Yunnan University | Zhao D.,CAS Institute of Atmospheric Physics | Tang J.,Nanjing University
Climate Dynamics | Year: 2015

Based on daily rainfall data collected at 395 gauge stations over eastern China during 1979–2009, the variation in light rain days with intensities of 0.1–10 mm day−1 in the summer half of the year was analyzed. Results indicate that both the light rain amount and the number of light rain days decline distinctly, with trends of −4.89 mm (10 year)−1 and −2.48 days (10 year)−1, respectively. The first two principal components of EOF analysis on light rain days not only show a long-term decrease, but also depict regional differences; specifically, light rain days decline more distinctly in northeastern and southern regions of eastern China. Spatial and temporal features, as well as the periods derived from the EOF analysis of temperature, precipitable water content, and relative humidity in the lower troposphere, coincide with those of light rain days. Composite analysis also suggests that there are fewer light rain days in years with lower relative humidity and precipitable water content in the lower troposphere, while there are fewer light rain days in years with higher tropospheric temperatures. According to the Clausius–Clapeyron equation and the relative humidity equations, relative humidity over eastern China during the period studied decreases by 5.5 % due to lower-tropospheric warming, and decreases by 0.16 % because of the decrease in specific humidity in the same period. Both warming and water vapor content are the reasons for light rain reduction, and warming is deemed the primary cause. © 2014, Springer-Verlag Berlin Heidelberg. Source

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