The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the Southern Hemisphere tropics, which resembles a Southern Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models. In this study, we look to the extratropics for possible causes of the double-ITCZ problem by performing a global energetic analysis with historical simulations from a suite of global climate models and comparing with satellite observations of the Earth's energy budget. Our results show that models with more energy flux into the Southern Hemisphere atmosphere (at the top of the atmosphere and at the surface) tend to have a stronger double-ITCZ bias, consistent with recent theoretical studies that suggest that the ITCZ is drawn toward heating even outside the tropics. In particular, we find that cloud biases over the Southern Ocean explain most of the modelto-model differences in the amount of excessive precipitation in Southern Hemisphere tropics, and are suggested to be responsible for this aspect of the double-ITCZ problem in most global climate models. tropical precipitation | model biases | cloud radiative forcing | atmospheric energy transport | general circulation P recipitation is essential to life, with its variation tightly linked to water and food security. Providing the best estimate of future trends in precipitation has always been a primary goal of global climate models. For this reason, global climate models are closely scrutinized not only on their ability to simulate large-scale dynamics but also on their skill in simulating precipitation distributions at regional scales. One naturally only trusts model forecasts of precipitation if there is substantial fidelity in simulating the current precipitation climatology.Because precipitation features are related with processes occurring at a tremendous range of time and spatial scales, their simulation remains challenging. The main precipitation feature that most global climate models have difficulty capturing is the Intertropical Convergence Zone (ITCZ) in the deep tropics at around 6°N, a narrow latitude band with some of the most intense rainfall on Earth. Despite decades of work by modeling centers around the world, the double-ITCZ problem, in which excessive precipitation is produced in the Southern Hemisphere tropics resembling the stronger Northern Hemisphere ITCZ, remains the largest precipitation bias of most state-of-the-art global climate models. There has been little progress in reducing this bias over recent years (1-3) (Figs. 1 A and B and 2A).The double-ITCZ bias is most apparent in the strip 5-15°S over the central and east Pacific, and a similar feature is visible in the Indian and Atlantic Oceans in most models. Most of the proposed reasons for tropical precipitation biases involve local mechanisms within or close to the tropics, for example, warm sea surface temperature errors in the coastal upwelling region off Peru (4, 5), ofte...
Non-classical behaviour, brought about by a confinement that imposes spatial constraints on molecules, is opening avenues to novel applications. For example, carbon nanotubes, which show rapid and selective transport of small molecules across the nanotubes, have significant potential as biological or chemical separation materials for organic solvents or gaseous molecules. With polymers, when the dimensions of a confining volume are much less than the radius of gyration, a quantitative understanding of perturbations to chain dynamics due to geometric constraints remains a challenge and, with the development of nanofabrication processes, the dynamics of confined polymers have significant technological implications. Here, we describe a weak molecular-weight-dependent mobility of polymers confined within nanoscopic cylindrical pores having diameters smaller than the dimension of the chains in the bulk. On the basis of the chain configuration along the pore axis, the measured mobility of polymers in the confined geometry is much higher than the mobility of the unconfined chain. With the emergence of nanofabrication processes based on polymer flow, the unexpected enhancement in flow and reduction in intermolecular entanglements are of significant importance in the design and execution of processing strategies.
Recent studies with climate models have demonstrated the power of extratropical forcing in causing the intertropical convergence zone (ITCZ) to shift northward or southward, and paleoclimate data support the notion that there have been large shifts in the ITCZ over time. It is shown that similar notions apply to slab ocean simulations of global warming. Nine slab ocean model simulations from different modeling centers show a wide range of ITCZ shifts in response to doubling carbon dioxide concentrations, which are experienced in a rather zonally symmetric way in the tropics. Using an attribution strategy based on fundamental energetic constraints, it is shown that responses of clouds and ice in the extratropics explain much of the range of ITCZ responses. There are also some positive feedbacks within the tropics due to increasing water vapor content and high clouds in the new ITCZ location, which amplify the changes driven from the extratropics. This study shows the clear importance of simulating extratropical climate responses with fidelity, because in addition to their local importance, the impacts of these climate responses have a large nonlocal impact on rainfall in the tropics.
Methods to extract trap densities at high-permittivity ͑k͒ dielectric/III-V semiconductor interfaces and their distribution in the semiconductor band gap are compared. The conductance method, the Berglund intergral, the Castagné-Vapaille ͑high-low frequency͒, and Terman methods are applied to admittance measurements from metal oxide semiconductor capacitors ͑MOSCAPs͒ with high-k / In 0.53 Ga 0.47 As interfaces with different interface trap densities. The results are discussed in the context of the specifics of the In 0.53 Ga 0.47 As band structure. The influence of different conduction band approximations for determining the ideal capacitance-voltage ͑CV͒ characteristics and those of the MOSCAP parameters on the extracted interface trap density are investigated. The origins of discrepancies in the interface trap densities determined from the different methods are discussed. Commonly observed features in the CV characteristics of high-k / In 0.53 Ga 0.47 As interfaces are interpreted and guidelines are developed to obtain reliable estimates for interface trap densities and the degree of Fermi level ͑un͒pinning for high-k / In 0.53 Ga 0.47 As interfaces.
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