2006年重庆大旱的历史透视

对过去1千年重庆干旱记录分析表明:2006年在重庆及其周边地区所发生的“特大干旱”事件在历史上曾经多次出现,并非历史仅见。这样极端气候事件的发生仅仅是气候波动中一个正常的自然现象,无论是干旱的持续时间、严重程度,还是发生的范围都可能并未超出气候波动的正常幅度。

Graft chain propagation rate coefficients of acrylic acid in melt graft copolymerization with linear low density polyethylene

Graft chain propagation rate coefficients (k(p.g)) for grafting AA onto linear low density polyethylene (LLDPE) in the melt in ESR tubes have been measured via Fourier transform infrared (FTIR) spectroscopy and electron spin resonance (ESR) spectroscopy in the temperature range from 130 to 170 degrees C. To exclude the effect of homopolymerization on the grafting. the LLDPE was pre-irradiated in the air by electron beam to generate the peroxides and then treated with iodide solution to eliminating one kind of peroxides, hydroperoxide. The monomer conversion is determined by FTIR and the chain propagation free-radical concentration is deduced from the double integration of the well-resolved ESR spectra, consisting nine lines in the melt. The temperature dependence of k(p.g) is expressed:The magnitude of k(p.g) from FTIR and ESR analysis is in good agreement with the theoretical data deduced from ethylene-AA copolymerization, suggesting this method could reliably and directly provide the propagation rate coefficient. The comparison of k(p.g) with the data extrapolated from solution polymerization at modest temperature indicates that the extrapolated data might not be entirely fitting to discuss the kinetics behavior in the melt.

Kinetics study on melt grafting copolymerization of LLDPE with acid monomers using reactive extrusion method

Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetics studies on reactive extrusion were carried out for the difficulties as expected. In this work, the macromolecular peroxide-induced grafting of acrylic acid and methyl methacrylate onto linear low density polyethylene by reactive extrusion was chosen as the model system for the kinetics study; the samples were taken out from the barrel at five ports along screw axis and analyzed by FTIR, H-1 NMR, and ESR. For the first time, the time-evolution of reaction rate, the reaction order, and the activation energy of graft copolymerization and homopolymerization in the twin screw extruder were directly obtained. On the basis of these results, the general reaction mechanism was tentatively proposed. It was demonstrated that an amount of chain propagation free radicals could keep alive for several minutes even the peroxides completely decomposed and the addition of monomer to polymeric radicals was the rate-controlled step for the graft copolymerization.

The Obduction of Equatorial 13 degrees C Water in the Pacific Identified by a Simulated Passive Tracer

The obduction of equatorial 13 degrees C Water in the Pacific is investigated using a simulated passive tracer of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO). The result shows that the 13 degrees C Water initialized in the region 8 degrees N-8 degrees S, 130 degrees-90 degrees W enters the surface mixed layer in the eastern tropical Pacific, mainly through upwelling near the equator, in the Costa Rica Dome, and along the coast of Peru. Approximately two-thirds of this obduction occurs within 10 years after the 13 degrees C Water being initialized, with the upper portion of the water mass reaching the surface mixed layer in only about a month. The obduction of the 13 degrees C Water helps to maintain a cool sea surface temperature year-round, equivalent to a surface heat flux of about -6.0 W m(-2) averaged over the eastern tropical Pacific (15 degrees S-15 degrees N, 130 degrees W-eastern boundary) for the period of integration (1993-2006). During El Nino years, when the thermocline deepens as a consequence of the easterly wind weakening, the obduction of the 13 degrees C Water is suppressed, and the reduced vertical entrainment generates a warming anomaly of up to 10 W m(-2) in the eastern tropical Pacific and in particular along the coast of Peru, providing explanations for the warming of sea surface temperature that cannot be accounted for by local winds alone. The situation is reversed during La Nina years.

Characteristics of water exchange in the Luzon Strait during September 2006

The Luzon Strait is the only deep channel that connects the South China Sea (SCS) with the Pacific. The transport through the Luzon Strait is an important process influencing the circulation, heat and water budgets of the SCS. Early observations have suggested that water enters the SCS in winter but water inflow or outflow in summer is quite controversial. On the basis of hydrographic measurements from CTD along 120 degrees E in the Luzon Strait during the period from September 18 to 20 in 2006, the characteristics of temperature, salinity and density distributions are analyzed. The velocity and volume transport through the Luzon Strait are calculated using the method of dynamic calculation. The major observed results show that water exchanges are mainly from the Pacific to the South China Sea in the upper layer, and the flow is relatively weak and eastward in the deeper layer. The net volume transport of the Luzon Strait during the observation period is westward, amounts to about 3.25 Sv. This result is consistent with historical observations.