Predictive instantaneous optimal control of elastic structures during earthquakes

A predictive instantaneous optimal control (PIOC) algorithm is proposed for controlling the seismic responses of elastic structures. This algorithm compensates for the time delay that happens in practical control applications by predicting the structural response over a period that equals the time delay, and by substituting the predicted response in the instantaneous optimal control (IOC) algorithm. The unique feature of this proposed PIOC algorithm is that it is simple and at the same time compensates for the time delay very effectively. Numerical examples of single degree of freedom structures are presented to compare the performance of PIOC and IOC systems for various time delay magnitudes. Results show that a time delay always causes degradation of control efficiency, but PIOC can greatly reduce this degradation compared to IOC. The effects of the structure's natural periods and the choice of control gains on the degradation induced by the time delay are also analyzed. Results show that shorter natural periods and larger control gains are both more sensitive and more serious to the degradation of control efficiency. Finally, a practical application of PIOC is performed on a six‐story moment‐resisting steel frame. It is demonstrated that PIOC contributes significantly to maintain stability in multiple degree of freedom structures, and at the same time PIOC has a satisfactory control performance. Copyright © 2003 John Wiley & Sons, Ltd.     

Comprehensive simulation of the middle atmospheric climate: some recent results

This study discusses the results of comprehensive time-dependent, three-dimensional numerical modelling of the circulation in the middle atmosphere obtained with the GFDL SKYHI troposphere-stratosphere-mesosphere general circulation model (GCM). The climate in a long control simulation with an intermediate resolution version (3° in horizontal) is briefly reviewed. While many aspects of the simulation are quite realistic, the focus in this study is on remaining first-order problems with the modelled middle atmospheric general circulation, notably the very cold high latitude temperatures in the Southern Hemisphere (SH) winter/spring, and the virtual absence of a quasi-biennial oscillation (QBO) in the tropical stratosphere. These problems are shared by other extant GCMs. It was noted that the SH cold pole problem is somewhat ameliorated with increasing horizontal resolution in the model. This suggests that improved resolution increases the vertical momentum fluxes from the explicitly resolved gravity waves in the model, a point confirmed by detailed analysis of the spectrum of vertical eddy momentum flux in the winter SH extratropics. This result inspired a series of experiments with the 3° SKYHI model modified by adding a prescribed zonally-symmetric zonal drag on the SH winter westerlies. The form of the imposed momentum source was based on the simple assumption that the mean flow drag produced by unresolved waves has a spatial distribution similar to that of the Eliassen-Palm flux divergence associated with explicitly resolved gravity waves. It was found that an appropriately-chosen drag confined to the top six model levels (above 0.35 mb) can lead to quite realistic simulations of the SH winter flow (including even the stationary wave fields) through August, but that problems still remain in the late-winter/springtime simulation. While the imposed momentum source was largely confined to the extratropics, it produced considerable improvement in the simulation of the equatorial semiannual oscillation, with both the easterly and westerly phases being somewhat more intense than in the control simulation. A separate experiment was conducted in which the SKYHI model was simplified so that it had no topography and so that the seasonal cycle was frozen in perpetual equinox conditions. These changes result in a model that has much reduced interhemispheric asymmetry. This model spontaneously produces a long period mean flow oscillation of considerable amplitude in the tropical upper stratopause. The implication of this result for the general issue of obtaining a QBO in comprehensive GCMs is discussed.     

Spatiotemporal drought variability in northwestern Africa over the last nine centuries

Changes in precipitation patterns and the frequency and duration of drought are likely to be the feature of anthropogenic climate change that will have the most direct and most immediate consequences for human populations. The latest generation of state-of-the-art climate models project future widespread drying in the subtropics. Here, we reconstruct spatially-complete gridded Palmer drought severity index values back to A.D. 1179 over Morocco, Algeria, and Tunisia. The reconstructions provide long-term context for northwest African hydroclimatology, revealing large-scale regional droughts prior to the sixteenth century, as well as more heterogeneous patterns in sixteenth, eighteenth, and twentieth century. Over the most recent decades a shift toward dry conditions over the region is observed, which is consistent with general circulation model projections of greenhouse gas forced enhanced regional subtropical drought.     

Reconstruction of MODIS total suspended matter time series maps by DINEOF and validation with autonomous platform data

In situ measurements of total suspended matter (TSM) over the period 2003–2006, collected with two autonomous platforms from the Centre for Environment, Fisheries and Aquatic Sciences (Cefas) measuring the optical backscatter (OBS) in the southern North Sea, are used to assess the accuracy of TSM time series extracted from satellite data. Since there are gaps in the remote sensing (RS) data, due mainly to cloud cover, the Data Interpolating Empirical Orthogonal Functions (DINEOF) is used to fill in the TSM time series and build a continuous daily “recoloured” dataset. The RS datasets consist of TSM maps derived from MODIS imagery using the bio-optical model of Nechad et al. (Rem Sens Environ 114: 854–866, 2010). In this study, the DINEOF time series are compared to the in situ OBS measured in moderately to very turbid waters respectively in West Gabbard and Warp Anchorage, in the southern North Sea. The discrepancies between instantaneous RS, DINEOF-filled RS data and Cefas data are analysed in terms of TSM algorithm uncertainties, space–time variability and DINEOF reconstruction uncertainty.     

The stable aryl hydrocarbon receptor agonist potency of United Kingdom Continental Shelf (UKCS) offshore produced water effluents

The in vitro aryl hydrocarbon receptor (AhR) agonist potency of offshore produced water effluents, collected from the United Kingdom Continental Shelf, was determined using the dioxin responsive (DR)-chemically activated luciferase expression (CALUX) assay. Octadecylsilane (C18) solid phase extraction (SPE) extracts of produced water were exposed to DR-CALUX cells for 24 h in order to investigate the contribution in potency from compounds that are stable to metabolism by the CALUX cells during exposure. The stable AhR agonist potency determined over 24 h was highly variable and ranged from 1 to 430 ng TCDD TEQ_CALUX l⁻¹. These data reflect the highly variable composition of produced water discharges from different production fields. It is recommended that further work be performed to characterise the full range of stable dioxin like AhR agonists present in offshore produced water discharges using techniques such as bioassay-directed analysis.     

Equatorial Atlantic sea surface temperature variations: Research note

Abstract

Monthly mean sea surface temperature (SST) anomalies were computed for six 10°‐wide boxes stretching across the equatorial Atlantic Ocean for the period 1890–1979. These values were used to produce a time‐longitude section of the interannual SST variability along the equator. This section shows cycles of basin‐wide warming and cooling occurring with irregular periods that typically range between two and four years. The warming and cooling events in these cycles normally display some westward phase propagation. The peak magnitudes of the interannual SST anomalies are generally of the order of 1°C or less, except in the Gulf of Guinea where they can be somewhat larger.

An estimate was made of the basin‐wide equatorial SST anomaly in each month (excluding the Gulf of Guinea). This was composited around the times of the warm and cold extremes of the Pacific Southern Oscillation. This analysis revealed a detectable, but rather weak, tendency for phase locking of the interannual SST variations in the equatorial Pacific and Atlantic oceans.     

Calculation of the effect of stratospheric mean wind variations on the solar semidiurnal barometric oscillation

Abstract

A simple perturbation procedure is developed for incorporating the effects of mean zonal winds in atmospheric tidal calculations. This method is used to determine the variation of the solar semidiurnal surface pressure oscillation, S₂(p), that is expected to result from the mean wind changes during the course of the quasi‐biennial oscillation of the tropical stratosphere. The results are consistent with earlier observations of a quasi‐biennial variation in S₂(p). Some new observations of biennial variability in S₂(p) at four tropical stations are also discussed.     

Identifying coherent spatiotemporal modes in time-uncertain proxy paleoclimate records

High-resolution sedimentary paleoclimate proxy records offer the potential to expand the detection and analysis of decadal- to centennial-scale climate variability during recent millennia, particularly within regions where traditional high-resolution proxies may be short, sparse, or absent. However, time uncertainty in these records potentially limits a straightforward objective identification of broad-scale patterns of climate variability. Here, we describe a procedure for identifying common patterns of spatiotemporal variability from time uncertain sedimentary records. This approach, which we term Monte Carlo Empirical Orthogonal Function analysis, uses iterative age modeling and eigendecomposition of proxy time series to isolate common regional patterns and estimate uncertainties. As a test case, we apply this procedure to a diverse set of time-uncertain lacustrine proxy records from East Africa. We also perform a pseudoproxy experiment using climate model output to examine the ability of the method to extract shared anomalies given known signals. We discuss the advantages and disadvantages of our approach, including possible extensions of the technique.     

Influence of El Niño–Southern Oscillation on the long-term record of floods over Bangladesh

Theoretical and Applied Climatology - The present study analyzed a long-term record of major floods over Bangladesh under the influence of El Niño–Southern Oscillation (ENSO). Bangladesh...