Ma Z.,Institute of Urban Meteorology |
Xu H.,Zhejiang Institute of Meteorological Science |
Meng W.,Institute of Urban Meteorology |
Zhang X.,Institute of Urban Meteorology |
And 3 more authors.
Environmental Monitoring and Assessment | Year: 2013
Vertical ozone and meteorological parameters were measured by tethered balloon in the boundary layer in the summer of 2009 in Beijing, China. A total of 77 tethersonde soundings were taken during the 27-day campaign. The surface ozone concentrations measured by ozonesondes and TEI 49C showed good agreement, albeit with temporal difference between the two instruments. Two case studies of nocturnal secondary ozone maxima are discussed in detail. The development of the low-level jet played a critical role leading to the observed ozone peak concentrations in nocturnal boundary layer (NBL). The maximum of surface ozone was 161.7 ppbv during the campaign, which could be attributed to abundant precursors storage near surface layer at nighttime. Vertical distribution of ozone was also measured utilizing conventional continuous analyzers on 325-m meteorological observation tower. The results showed the NBL height was between 47 and 280 m, which were consistent with the balloon data. Southerly air flow could bring ozone-rich air to Beijing, and the ozone concentrations exceeded the China's hourly ozone standard (approximately 100 ppb) above 600 m for more than 12 h. © 2012 Springer Science+Business Media Dordrecht.
Jia B.,CAS Institute of Atmospheric Physics |
Xie Z.,CAS Institute of Atmospheric Physics |
Dai A.,University at Albany |
Dai A.,U.S. National Center for Atmospheric Research |
And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013
Surface solar radiation plays a crucial role in surface energy and water budgets, and it is also an important forcing for land hydrological models. In this study, the downward surface solar radiation (DSSR) from two satellite products, the Fengyun-2C satellite (FY-2C) and the Fast Longwave and Shortwave Radiative Fluxes project (FLASHFlux), and two reanalysis datasets, NCEP-DOE and ERA-Interim, was evaluated against ground-based observations (OBS) from 94 stations over mainland China during July 2006 to June 2009. It is found that the mean DSSR derived from FY-2C is comparable to OBS, with small positive biases of 3.0 Wm-2 for daily data and 3.5 Wm-2 for monthly data and moderate RMSEs of 49.3 Wm-2 (daily) and 31.9 Wm-2 (monthly). These results are comparable to those for FLASHFlux, which has the lowest RMSEs (43.2 Wm-2 and 30.5 Wm-2 for daily and monthly data, respectively) and the strongest correlations with OBS (r = 0.90 and 0.93 for daily and monthly data, respectively) among the four products. The DSSR from the reanalyses has much larger RMSEs and generally lower correlations with OBS than the satellite products, especially for the NCEP-DOE products. Results also show that daily DSSR values are sensitive to the averaging grid size, while monthly mean DSSR is largely insensitive to the averaging scale. The DSSR from the four datasets over East Asia shows similar spatial patterns with large seasonal variations but differs in magnitude. In summer, high DSSR is observed over western China, while low DSSR is seen primarily over South Asia and the Sichuan Basin associated with extensive cloud cover (CC) and large precipitable water (PW). In winter, the high DSSR center shifts to South Asia due to decreased CC and PW, and the DSSR decreases from the South to the North. Deficiencies in the parameterizations of clouds, aerosols, and water vapor, as well as errors in atmospheric and surface properties for the retrieval algorithms contribute to the lower correlation of the DSSR derived from FY-2C (r = 0.82 and 0.90 for daily and monthly data) with OBS than those from FLASHFlux product. Further improvements to the representation of clouds and aerosols in the FY-2C retrieval algorithm are needed. © 2013. American Geophysical Union. All Rights Reserved.
Chen F.,CAS Institute of Atmospheric Physics |
Chen F.,Zhejiang Institute of Meteorological Science |
Xie Z.,CAS Institute of Atmospheric Physics
Climate Dynamics | Year: 2012
In this study, the CERES phenological growth and development functions were implemented into the regional climate model, RegCM3 to give a model denoted as RegCM3_CERES. This model was used to represent interactions between regional climate and crop growth processes. The effects of crop growth and development processes on regional climate were then studied based on two 20-year simulations over the East Asian monsoon area conducted using the original regional climate model RegCM3, and the coupled RegCM3_CERES model. The numerical experiments revealed that incorporating the crop growth and development processes into the regional climate model reduced the root mean squared error of the simulated precipitation by 2.2-10.7% over north China, and the simulated temperature by 5.5-30.9% over the monsoon region in eastern China. Comparison of the simulated results obtained using RegCM3_CERES and RegCM3 showed that the most significant changes associated with crop modeling were the changes in leaf area index which in turn modify the aspects of surface energy and water partitions and lead to moderate changes in surface temperature and, to some extent, rainfall. Further analysis revealed that a robust representation of seasonal changes in plant growth and developmental processes in the regional climate model changed the surface heat and moisture fluxes by modifying the vegetation characteristics, and that these differences in simulated surface fluxes resulted in different structures of the boundary layer and ultimately affected the convection. The variations in leaf area index and fractional vegetation cover changed the distribution of evapotranspiration and heat fluxes, which could potentially lead to anomalies in geopotential height, and consequently influenced the overlying atmospheric circulation. These changes would result in redistribution of the water and energy through advection. Nevertheless, there are significant uncertainties in modeling how monsoon dynamics responds to crop modeling and more research is needed. © 2011 The Author(s).
Yu Y.,CAS Institute of Atmospheric Physics |
Yu Y.,Zhejiang Institute of Meteorological Science |
Xie Z.,CAS Institute of Atmospheric Physics |
Zeng X.,University of Arizona
Journal of Geophysical Research D: Atmospheres | Year: 2014
To remove the deficiency of the numerical solution of the mass conservation-based Richards equation for soil moisture in a regional climate model (RegCM4 with its land surface component Community Land Model 3.5 (CLM3.5)), a revised numerical algorithm that is used in CLM4.5 is implemented into CLM3.5. Compared with in situ measurements, the modified numerical method improves the ground water table depth simulations in RegCM4. It also improves the temporal and spatial variability of soil moisture to some extent. Its impact on simulated summer precipitation is mixed, with improvements over three subregions in China but with increased errors in three other subregions. The impact on the simulated summer temperature is relatively small (with the mean biases changed by less than 10% over most subregions). The evapotranspiration differences between modified and control land-atmosphere coupled simulations are enhanced over the northwest subregion and Tibetan Plateau compared to offline simulations due to land surface feedbacks to the atmosphere (in coupled simulations). Similarly the soil moisture differences in coupled simulations are geographically different from those in offline simulations over the eastern monsoon area. The summer precipitation differences between modified and control coupled simulations are found to be explained by the differences of both surface evapotranspiration and large-scale water vapor flux convergence which have opposite signs over the northwest subregion and Tibetan Plateau but have the same signs over other subregions. ©2014. American Geophysical Union. All Rights Reserved.
Zhang Y.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research |
Gao J.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research |
Liu L.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research |
Wang Z.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research |
And 3 more authors.
Global and Planetary Change | Year: 2013
Considerable researches during the past several decades have focused on monitoring changes in vegetation growth due to its important role in regulating the terrestrial carbon cycle and the climate system. In this study, we combined datasets of the satellite-derived Normalized Difference Vegetation Index (NDVI) and climatic factors to analyze spatio-temporal patterns of vegetation growth in 1982-2006 in the Koshi River Basin (KRB) in the middle Himalayas. In addition, the dataset from the global land surface satellite sensor from SPOT-4's Vegetation instrument in 1998-2011 was used to further verify the results of this study. At the regional scale, although a statistically significant increase in average growing season NDVI was observed (0.0008yr-1, P=0.03) during the entire study period, there existed three distinct periods with opposing trends. Growing season NDVI significantly increased in 1982-1994 (0.0019yr-1, P=0.03), and then decreased in 1994-2000 (-0.0058yr-1, P<0.001), while increased again in 2000-2006 (0.0049yr-1, P<0.001) and in 2000-2011 (0.0034yr-1, P<0.001). A sudden drop in NDVI in 1994-2000 largely contributed to these fluctuations in growing season NDVI over the KRB. Spring, summer and autumn NDVI significantly decreased in 1994-2000 (-0.0077yr-1, P<0.001; -0.0067yr-1, P<0.001; and -0.0155yr-1, P<0.001; respectively). Our further spatial analyses supported the existence of the sudden decrease in spring, summer and autumn NDVI in 1994-2000. © 2013 Elsevier B.V.