A numerical response of the middle atmosphere to the 11-year solar cycle

A two-dimensional numerical model with coupled photochemistry and dynamics has been used to investigate the response of the middle atmosphere (16–116 km) to changes in solar activity over the 11-year solar cycle. Model inputs that vary with solar cycle include solar radiation, cosmic ray and auroral ionization rates and the flux of NO_x at the model's upper boundary.In this study, the results of model runs for solar cycle minimum and maximum conditions are compared. In the stratosphere, using currently accepted estimates of changes in solar radiation at wavelengths longer than 180 nm, only small responses in ozone, temperature and zonal winds are obtained. On the other hand, changes at shorter wavelengths, and the effects of particle precipitation, lead to large variations in the abundances of trace species in the thermosphere and upper mesosphere. In particular, very large abundances of NO_x are produced above 90 km by auroral particle precipitation. Considerable amounts of NO_x are transported subsequently to the stratosphere by the global mean meridional circulation. It is shown that this excess NO_x can lead to significant decreases in ozone concentrations at high latitudes and that it may explain observations of nitrate deposition in Antarctic snow.     

北吕宋岛菲律宾活动带蛇绿岩及其上覆浊积岩的放射虫研究新进展

The basement of the Philippine Mobile Belt (PMB) is mainly composed of ophiolites that are mostly overlain by Paleogene to Miocene turbidites in central Luzon. To clarify the geological development of the PMB with respect to the initial stage of the arc volcanism (eg. Yumul et al., 2003, 2008; Dimalanta and Yumul, 2003; Suzuki et al., 2011), radiolarian dating was examined in siliceous sediments associated with the ophiolites and turbidites. The samples were collected from sites identified with the Zambales and Montalban ophiolites, basic tuff phyllites in NW Din-galan, and their overlying formations.     

Extreme temperature scenarios in Mexicali,Mexico under climate change conditions

Extreme weather events can have severe consequences for the population and the environment. Therefore, in this study a temporal trend of annual temperatures was built with a time series from 1950 to 2010 for Mexicali, Mexico, and estimates of 5- to 100-year return periods are provided by modeling of summer maximum and winter minimum temperatures. A non-parametric Kendall’s tau test and the Sen’s slope estimator were used to compute trends. The generalized extreme value (GEV) distribution was applied to the approximation of block maxima and the generalized Pareto distribution (GPD) to values over a predetermined threshold. Due to the non-stationary characteristic of the series of temperature values, the temporal trend was included as a covariable in the location parameter and substantial improvements were observed, particularly with the extreme minimum temperature, compared to that obtained with the GEV with no covariable and with the GPD. A positive and significant statistically trend in both summer maximum temperature and winter minimum temperature was found. By the end of 21st century the extreme maximum temperature could be 2 to 3 °C higher than current, and the winter could be less severe, as the probabilistic model suggests increases of 7 to 9 °C in the extreme minimum temperature with respect to the base period. The foreseeable consequences on Mexicali city are discussed.     

Assessment of liquefaction potential based on peak ground motion parameters

Conventionally, evaluation of liquefaction potential of loose saturated cohesionless deposits as specified in Japanese design codes employs peak ground acceleration (PGA). However, recent large-scale earthquakes in Japan revealed that liquefaction at some sites did not occur even though large PGAs were recorded at or near these sites. As an alternative approach, an evaluation procedure based on peak ground motion parameters, i.e. incorporating both PGA and the peak ground velocity (PGV), is proposed. By performing parametric studies using one-dimensional seismic response analysis and formulating regression models, seismic-induced shear stresses within the deposit are expressed in terms of peak ground motion parameters at the surface, and these are used to calculate the factor of safety against liquefaction. Application to case histories in Japan indicates that the proposed two-parameter equation can adequately account for the occurrence and non-occurrence of liquefaction at various sites as compared to the conventional PGA-based approach. Moreover, analyses of several strong motion records at various sites show that liquefaction may occur when PGA≥150 gal and PGV≥20 kine, indicating that these values can serve as thresholds in assessing the possible occurrence of liquefaction.     

Modeling the onset of photosynthesis after the Chicxulub asteroid impact

We do a preliminary modelling of the photosynthetic rates of phytoplankton at the very beginning of the Paleogene, just after the impact of the Chicxulub asteroid, which decisively contributed to the last known mass extinction of the Phanerozoic eon. We assume the worst possible scenario from the photobiological point of view: an already clear atmosphere with no ozone, as the timescale for soot and dust settling (years) is smaller than that of the full ozone regeneration (decades). Even in these conditions we show that most phytoplankton species would have had reasonable potential for photosynthesis in all the three main optical ocean water types. This modelling could help explain why the recovery of phytoplankton was relatively rapid after the huge environmental stress of that asteroid impact. In a more general scope, it also reminds us of the great resilience of the unicellular biosphere against huge environmental perturbations.     

The lower paleolithic landscape of 'Ayoun Qedim,al‐Jafr Basin,Jordan

The 'Ayoun Qedim locality includes seven deflated Acheulian sites within and around a limestone box canyon, Juwit el Ghuweir, in the northern al‐Jafr Basin, Jordan. Survey of these sites identified dense scatters of Acheulian bifaces ( _ 1650) along with debris, cores, and reduction material from their production and maintenance. Although there is a clear Levallois component in the assemblages, reflecting a Late Acheulian occupation, strictly Middle and Upper Paleolithic sites are uncommon in this locality. Analysis of the geology and geomorphology of the northern al‐Jafr Basin indicates the area is strongly influenced by shallow subsurface groundwater flow and discharge, and Juwit el Ghuweir displays classic features of a canyon formed by groundwater seepage and sapping, except for the lack of a perennial spring within the modern canyon. The authors suggest that the extreme density of Lower Paleolithic material at 'Ayoun Qedim is associated with perennial groundwater discharge at Juwit el Ghuweir during the Middle Pleistocene and that the dearth of later Paleolithic material is attributable to the cessation of perennial spring discharge. The cause of the spring's cessation is unknown, but may have been related to local geomorphic factors, such as head migration of adjacent streams, or to more regional geomorphic factors, such as the lowering of theregional water table in the area of al‐Jafr Basin. © 2007 Wiley Periodicals, Inc.     

Wavelet analyses of neural networks based river discharge decomposition

The problem of discharge forecasting using precipitation as input is still very active in Hydrology, and has a plethora of approaches to its solution. But, when the objective is to simulate discharge values without considering the phenomenology behind the processes involved, Artificial Neural Networks, ANN give good results. However, the question of how the black box internally solve this problem remains open. In this research, the classical rainfall-runoff problem is approached considering that the total discharge is a sum of components of the hydrological system, which from the ANN perspective is translated to the sum of three signals related to the fast, middle and slow flow. Thus, the present study has two aims (a) to study the time-frequency representation of discharge by an ANN hydrologic model and (b) to study the capabilities of ANN to additively decompose total river discharge. This study adds knowledge to the open problem of the physical interpretability of black-box models, which remains very limited. The results show that total discharge is adequately simulated in the time frequency domain, although less power spectrum is evident during the rainy seasons in the ANN model, due to fast flow underestimation. The wavelet spectrum of discharge represents well the slow, middle and fast flow components of the system with transit times of 256, 12–64 and 2–12 days, respectively. Interestingly, these transit times are remarkably similar to those of the soil water reservoirs of the studied system, a small headwater catchment in the tropical Andes. This result needs further research because it opens the possibility of determining MMT on a fraction of the cost of isotopic based methods. The cross-power spectrum indicates that the error in the simulated discharge is more related to the misrepresentation of the fast and the middle flow components, despite limitations in the recharge period of the slow flow component. With respect to the representation of individual signals of the slow, middle and fast flows components, the three neurons were uncapable to individually represent such flows. However, the combination of pairs of these signals resemble the dynamics and the spectral content of the aforementioned flows signals. These results show some evidence that signal processing techniques may be used to infer information about the hydrological functioning of a basin.     

Seasonal Variability in Circulation Pattern and Residence Time of Suo-Nada

The development and evolution of the persistent counterclockwise circulation in Suo-Nada have been studied in detail using a three-dimensional numerical model. The realistic circulation has been reproduced from the monthly climatological fields of salinity, temperature along the open boundary, wind, heat flux and buoyancy input from twenty-two major rivers surrounding the basin. The seasonal variation of fresh-water discharge from the rivers proved to be the most important forcing mechanism driving the circulation. The expansion and contraction of coastal low salinity water well corresponded with the development of counterclockwise circulation from spring to summer and dissipation from autumn to winter. The circulation was found to be vertically homogenous and quasi-barotropic. However, confined along the coastal zone is an estuarine flow (i.e., oppositely directed currents in the upper and lower layers) whose horizontal dimension conforms to the period of maximum buoyancy flux from the rivers. This indicates that the flow pattern in Suo-Nada can be separated into two distinct regions where the relative dominance of estuarine circulation plays a significant role. Furthermore, the monthly water exchange capacity for autonomous purification of the basin has been evaluated from the average residence time of conservative material based on the calculated current field. It is demonstrated that the kinetic energy of the basin is directly responsible in promoting water exchange in Suo-Nada. This revised version was published online in August 2006 with corrections to the Cover Date.     

Circulation and Material Transport in Suo-Nada during Spring and Summer

An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM). The results revealed a small difference in the average residence times of materials within each season but a large seasonal variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar trend of variation between the seasonal values of average residence times. This revised version was published online in July 2006 with corrections to the Cover Date.