The impact of the Atlantic Multi-decadal Oscillation (AMO) on the ENSO amplitude was investigated through observational analyses. During the past 90 years the interdecadal variability of ENSO intensity is significantly correlated with the AMO. ENSO variability was strengthened (weakened) during a negative (positive) AMO phase. An ocean mixed layer heat budget analysis reveals that the thermocline feedback is the main process regulating AMO negative phase dependent ENSO growth characteristic. A further examination indicates that a strengthened atmospheric response to unit SST anomaly, an enhanced thermocline response to unit wind stress forcing and a strengthened subsurface temperature response to unit thermocline variation all contribute to the enhanced thermocline feedback during the negative phase of AMO. Such changes are attributed to the increase of background moisture, the weakening of mean subtropical cell (STC) and increase of upper ocean vertical temperature gradient respectively.
Attention has been paid for the levels, sources and health risks of atmospheric aliphatic and polycyclic aromatic hydrocarbons
(n-alkanes and PAHs) in remote areas, however, few studies have focused on those in the Tibetan Plateau. In this study, 18 pairs
of atmospheric samples were obtained during the period from August 2006 to July 2007 in Lhasa, the capital city of Tibet.
Both gas-phase and particulate-phase n-alkanes and PAHs were measured. Concentrations of n-alkanes (gas + particulate phase, 99.1–480.9 ng/m3) and PAHs (gas + particulate phase, 11.4–72.5 ng/m3) in Lhasa are lower than those in many cities. The sources of n-alkanes related to biological and petroleum sources were 67 and 33%, respectively. According to the results of diagnostic
ratios and principal component analysis, emission of traffic vehicles was one of the important PAH sources, and sources of
benzo(a)pyrene was likely attributed to incense burning. Good simulations were obtained by traffic soot-based model for fluoranthene,
pyrene and benzo(a)anthracene, while, wood soot-based model fitted the experimental results of benzo(a)pyrene better. This
meant atmospheric fate of PAHs was mainly influenced by the adsorptive partitioning that occurred during traffic and incense
burning procedures. In addition, the benzo[a]pyrene-equivalent carcinogenic power (BaPE) in the present study (0.1–1.6 ng/m3) is lower than those in other cities and also the air quality standard of China, suggesting that atmospheric PAHs caused
low health risks. 相似文献
Soil respiration is essential for the understanding of carbon sequestration of forest plantations. Soil respiration of poplar plantations at three developmental stages was investigated in 2007 and 2008. The results showed that mean soil respiration rate was 5.74, 5.10 and 4.71 μmol CO2 m−2 s−1 for stands of 2-, 7- and 12-year-old, respectively, during the growing season. Soil temperature decreased with increasing plantation age and canopy cover. As plantation matured, fine root biomass also declined. Multiple regression analysis suggested that soil temperature in the upper layer could explain 73-77% of the variation in soil respiration and fine root biomass in the upper layer could explain further 5-8%. The seasonal dynamics of soil respiration was mainly controlled by soil temperature rhythm and fine root growth since soil water availability remained adequate due to monthly irrigation. Spatial variability of soil respiration varied considerably among three age classes, with the coefficient of variation of 28.8%, 22.4% and 19.6% for stands of 2-, 7- and 12-year-old, respectively. The results highlight the importance of the development stage in soil carbon budget over a rotation, since both temporal and spatial variation in soil respiration displayed significant differences at different developmental stages. 相似文献