The influence of Indian Ocean Dipole (IOD) on biogeochemistry of carbon in the Arabian Sea during 1997–1998

Data on ocean color chlorophylla (Chl a) obtained using Sea-viewing Wide Field of view Sensor (SeaWiFS), sea surface temperature (SST) by Advanced Very High Resolution Radiometer (AVHRR), and sea surface height (SSH) by TOPEX/POSEIDON were analyzed to examine the influence of Indian Ocean Dipole (IOD) on the physical and biogeochemical processes with special reference to phytoplankton primary production and air-sea fluxes of carbon dioxide in the Arabian Sea. Positive SST anomalies (SSTA) were found in the Arabian Sea (0.4 to 1.8°C) with higher values in the southwestern Arabian Sea that decreased towards north. The SSH anomalies (SSHA) and turbulent kinetic energy anomalies (TKEA) suggest decreased mixing during the IOD compared to the normal period. Chlorophylla displayed significant negative correlations with SSTA and SSHA in the Arabian Sea. Consistently, Chla showed negative anomalies (low Chl a) during the IOD period which could be due to reduced inputs of nutrients. The photic zone integrated primary production decreased by 30% during the IOD period compared to the normal whereas pCO₂ levels were higher (by 10–20μatm). However, sea to air fluxes were lower by 10% during the IOD period due to prevailing weaker winds. Primary production seems to be the key process controlling the surface pCO₂ levels in the Arabian Sea. In future, the influence of IOD on ecosystem structure, export production and bacterial respiration rates are to be probed throughin situ time-series observations.     

Physics of the Omori law: Inferences from interevent time distributions and pore pressure diffusion modeling

Empirical laws and statistics of earthquakes are valuable as a basis for a better understanding of the earthquake cycle. In this paper we focus on the postseismic phase and the physics of aftershock sequences. Using interevent time distributions for a catalogue of Icelandic seismicity, we infer that the parameter C₂ in the Omori law, often considered to represent incomplete detection of aftershocks, is at least in part related to the physics of the earthquake process. We investigate the role of postseismic pore pressure diffusion after two Icelandic earthquakes on the rate of aftershocks and what we can infer about the physical meaning of C₂ from the diffusion process. Using the Mohr–Coulomb failure criterion we obtain a rate of triggered points in our diffusion model that agrees with the modified Omori law, with a value of C₂ that is consistent with data. Our pore pressure diffusion model suggests that C₂ is related to the process of reducing high pore pressure gradients existing across a fault zone at short times after a main shock.     

A New Method for the Determination of Area-Averaged Turbulent Surface Fluxes from Low-Level Flights Using Inverse Models

The low-level flight method (LLF) has been combined with linear inverse models (IM) resulting in an LLF+IM method for the determination of area-averaged turbulent surface fluxes. With this combination, the vertical divergences of the turbulent latent and sensible heat fluxes were calculated from horizontal flights. The statistical errors of the derived turbulent surface fluxes were significantly reduced. The LLF+IM method was tested both in numerical and field experiments. Large-eddy simulations (LES) were performed to compare ‘true’ flux profiles with ‘measurements’ of simulated flights in an idealised convective boundary layer. Small differences between the ‘true’ and the ‘measured’ fluxes were found, but the vertical flux divergences were correctly calculated by the LLF+IM method. The LLF+IM method was then applied to data collected during two flights with the Helipod, a turbulence probe carried by a helicopter, and with the research aircraft Do 128 in the LITFASS-98 field campaign. The derived surface fluxes were compared with results from eddy-covariance surface stations and with large-aperture scintillometer data. The comparison showed that the LLF+IM method worked well for the sensible heat flux at 77 and 200 m flight levels, and also for the latent heat flux at the lowest level. The model quality control indicated failures for the latent heat flux at the 200 m level (and higher), which were probably due to large moisture fluctuations that could not be modelled using linear assumptions. Finally the LLF+IM method was applied to more than twenty low-level flights from the LITFASS-2003 experiment. Comparison with aggregated surface flux data revealed good agreement for the sensible heat flux but larger discrepancies and a higher statistical uncertainty for the latent heat flux     

Modeling endogenous learning and imperfect competition effects in climate change economics

In this two-part paper we evaluate the effect of “endogenizing” technological learning and strategic behavior of agents in economic models used to assess climate change policies. In the first part we show the potential impact of R&D policies or demonstration and deployment (D&D) programs in the context of stringent stabilization scenarios. In the second part we show how game-theoretic methods can be implemented in climate change economic models to take into account three types of strategic interactions: (i) the market power of the countries benefiting from very low abatement costs on international markets for CO₂ emissions, (ii) the strategic behavior of governments in the domestic allocation of CO₂ emissions quotas, and (iii) the non-cooperative behavior of countries and regions in the burden sharing of CO₂ concentration stabilization. The two topics of endogenous learning and game-theoretic approach to economic modeling are two manifestations of the need to take into account the strategic behavior of agents in the evaluation of climate change policies. In the first case an R&D policy or a demonstration and deployment (D&D) program are put in place in order to attain a cost reduction through the learning effect; in the second case the agents (countries) reply optimally to the actions decided by the other agents by exploiting their strategic advantages. Simulations based on integrated assessment models illustrate the approaches. These studies have been conducted under the Swiss NCCR-Climate program.     

Risk minimization in water quality control problems of a river system

Methodologies are presented for minimization of risk in a river water quality management problem. A risk minimization model is developed to minimize the risk of low water quality along a river in the face of conflict among various stake holders. The model consists of three parts: a water quality simulation model, a risk evaluation model with uncertainty analysis and an optimization model. Sensitivity analysis, First Order Reliability Analysis (FORA) and Monte–Carlo simulations are performed to evaluate the fuzzy risk of low water quality. Fuzzy multiobjective programming is used to formulate the multiobjective model. Probabilistic Global Search Laussane (PGSL), a global search algorithm developed recently, is used for solving the resulting non-linear optimization problem. The algorithm is based on the assumption that better sets of points are more likely to be found in the neighborhood of good sets of points, therefore intensifying the search in the regions that contain good solutions. Another model is developed for risk minimization, which deals with only the moments of the generated probability density functions of the water quality indicators. Suitable skewness values of water quality indicators, which lead to low fuzzy risk are identified. Results of the models are compared with the results of a deterministic fuzzy waste load allocation model (FWLAM), when methodologies are applied to the case study of Tunga–Bhadra river system in southern India, with a steady state BOD–DO model. The fractional removal levels resulting from the risk minimization model are slightly higher, but result in a significant reduction in risk of low water quality.     

Spatial patterns in thunderstorm rainfall events and their coupling with watershed hydrological response

Weather radar systems provide detailed information on spatial rainfall patterns known to play a significant role in runoff generation processes. In the current study, we present an innovative approach to exploit spatial rainfall information of air mass thunderstorms and link it with a watershed hydrological model. Observed radar data are decomposed into sets of rain cells conceptualized as circular Gaussian elements and the associated rain cell parameters, namely, location, maximal intensity and decay factor, are input into a hydrological model. Rain cells were retrieved from radar data for several thunderstorms over southern Arizona. Spatial characteristics of the resulting rain fields were evaluated using data from a dense rain gauge network. For an extreme case study in a semi-arid watershed, rain cells were derived and fed as input into a hydrological model to compute runoff response. A major factor in this event was found to be a single intense rain cell (out of the five cells decomposed from the storm). The path of this cell near watershed tributaries and toward the outlet enhanced generation of high flow. Furthermore, sensitivity analysis to cell characteristics indicated that peak discharge could be a factor of two higher if the cell was initiated just a few kilometers aside.     

A Hertz contact model with non‐linear damping for pounding simulation

This paper investigates the cogency of various impact models in capturing the seismic pounding response of adjacent structures. The analytical models considered include the contact force‐based linear spring, Kelvin and Hertz models, and the restitution‐based stereomechanical approach. In addition, a contact model based on the Hertz law and using a non‐linear hysteresis damper (Hertzdamp model) is also introduced for pounding simulation. Simple analytical approaches are presented to determine the impact stiffness parameters of the various contact models. Parameter studies are performed using two degree‐of‐freedom linear oscillators to determine the effects of impact modelling strategy, system period ratio, peak ground acceleration (PGA) and energy loss during impact on the system responses. A suite of 27 ground motion records from 13 different earthquakes is used in the analysis. The results indicate that the system displacements from the stereomechanical, Kelvin and Hertzdamp models are similar for a given coefficient of restitution, despite using different impact methodologies. Pounding increases the responses of the stiffer system, especially for highly out‐of‐phase systems. Energy loss during impact is more significant at higher levels of PGA. Based on the findings, the Hertz model provides adequate results at low PGA levels, and the Hertzdamp model is recommended at moderate and high PGA levels. Copyright © 2006 John Wiley & Sons, Ltd.     

全球变化与中国东北样带(NECT)

全球变化陆地样带是从机理上理解陆地生态系统对全球变化的响应 ,预测全球变化对陆地生态系统的可能影响 ,实现预警、调节和减小全球变化不良影响 ,科学地规划和管理陆地生态系统的有效研究平台。在介绍国际全球变化陆地样带提出的背景与选定标准、中国东北样带的位置与特征的基础上 ,较系统地总结了近年来中国东北样带的研究进展 :建立了用于模型发展和比较的不同时间和空间尺度的中国东北样带数据集 ,从机理上初步探讨了全球变化对于森林、草甸草原和典型草原的可能影响 ,发展了用于古植被气候重建的植物种与表土花粉类型的定量关系模型、多尺度耦合的羊草草原生态系统动态模型和基于林窗原理的森林生态系统动态模型 ,并对全球变化对中国东北样带的影响进行了初步评估 ,进而针对我国作为发展中国家 ,财力有限的特点 ,提出未来中国东北样带研究拟充分利用我国特殊的生态环境与区域特色 ,围绕“生态过程与生态安全及其对全球变化的响应与反馈”这一关键科学问题 ,做出一些在国际上既有显示度 ,又服务于我国社会经济可持续发展的研究成果。     

Evaluating Models Of The Neutral, Barotropic Planetary Boundary Layer Using Integral Measures: Part Ii. Modelling Observed Conditions

The steady-state, horizontally homogeneous, neutral, barotropiccase forms the foundation of our theoretical understanding of the planetary boundary layer (PBL).While simple analytical models and first-order closure models simulate atmospheric observationsof this case well, more sophisticated models, in general, do not. In this paperwe examine how well three higher-order closure models, E - - l, E - l, and LRR - l,which have been especially modified for PBL applications, perform in predicting the behaviour of thecross-isobaric angle ₀, the geostrophic drag coefficient C_g, and the integral of the dissipationrate over the boundary layer, as a function of the surface Rossby number Ro. For comparison we alsoexamine the performance of three first-order closure mixing-length models, two proposed byA. K. Blackadar and one by H. H. Lettau, and the performance of the standard model forsecond-order closure and a modification of it designed to reduce the overprediction of turbulence inthe upper part of the boundary layer.