Numerical modelling of water spray barriers for dispersing dense gases

A depth-integrated numerical model is used to calculate the behavior of heavy and cold gas clouds subjected to the diluting influence of a water spray curtain. The model includes the physics of a cold cloud heated by the ground which entrains moist air. Entrainment velocities are influenced by cloud stratification. Laboratory water-curtain trials are predicted accurately. The model reveals the influence of curtain placement, width of spray, spray strength and thermal effects on the efficacy of the water curtain to mitigate potential hazards.Professor, Civil Engineering.Research Associate, Civil Engineering.     

The stratospheric quasi-biennial oscillation observed in the semidiurnal ground pressure data

Ground pressure observations made at Macao (22^○N, 113^○E) from 1953 to 1991 are analyzed and compared with the stratospheric quasi-biennial oscillation (QBO) data obtained during the same interval. The periods of the two phenomena and their time evolution are found to be close to each other. Furthermore, the time series of the stratospheric winds and the S2(p) QBO signature are highly correlated, thus confirming earlier analysis. On this basis, pressure measurements obtained at Batavia (now Djakarta: 6^○S, 107^○E) from 1870 to 1944 are used to trace back the QBO phenomenon before the advent of systematic stratospheric balloon measurements. The inferred period, which varies between 25 and 32 months, suggests that the QBO has been present in the atmosphere at least since 1870.     

Ground-based remote sensing of the atmospheric boundary layer: 25 years of progress

The role of ground-based remote sensors in boundary-layer research is reviewed, emphasizing the contributions of radars, sodars, and lidars. The review begins with a brief comparison of the state of remote sensors in boundary-layer research 25 years ago with its present-day status. Next, a summary of the current capabilities of remote sensors for boundary-layer studies demonstrates that for boundary-layer depth and for profiles of many mean quantities, remote sensors offer some of the most accurate measurements available. Similar accuracies are in general not found for most turbulence parameters. Important contributions of remote sensors to our understanding of the structure and dynamics of various boundary-layer phenomena or processes are then discussed, including the sea breeze, convergence boundaries, dispersion, and boundary-layer cloud systems. The review concludes with a discussion of the likely future role of remote sensors in boundary-layer research.     

Solar wind density model from km-wave type III bursts

Solar radio bursts were observed with a 4-channel radiometer and polarization analyser at wavelenghts around 12 m. The time and frequency resolutions were 10 ms and 100 kHz respectively. Observations on the duration, time profile and frequency splitting are described.     

Building comparable global change vulnerability assessments: The vulnerability scoping diagram

Advancing vulnerability science depends in part on identifying common themes from multiple, independent vulnerability assessments. Such insights are difficult to produce when the assessments use dissimilar, often qualitative, measures. The Vulnerability Scoping Diagram is presented to facilitate the comparison of assessments with dissimilar measures. The diagram is illustrated with recent research on drought vulnerabilities, showing that common insights into vulnerability may emerge if independent research teams use a common structure for organizing information about exposure, sensitivity and adaptive capacity—even if the underlying measures differ between assessments. Broadly adopting this technique, which is grounded in the “Eight Steps” methodological protocol [Schröter, D., Polsky, C., Patt, A., 2005. Assessing vulnerabilities to the effects of global change: an eight step approach. Mitigation and Adaptation Strategies for Global Change 10(4), 573–595], will enable a vulnerability meta-analysis, the lessons from which may permit places to identify helpful adaptation or mitigation options without first having to conduct their own vulnerability assessments.     

Phthalate ester plasticizers,DDT, DDE and polychlorinated biphenyls in biota from the Gulf of Mexico

The levels of phthalate ester plasticizers, DDT, DDE and polychlorinated biphenyls (PCBs) were determined in the tissues of 18 species of marine organisms from the northwestern Gulf of Mexico. Low levels of the most widely used phthalate, di-(2-ethylhexyl) phthalate, were found in the majority of the samples; no other phthalates were detected. DDT, DDE and PCBs were found in all samples, but at somewhat lower levels than those found in our 1971 survey. A decrease in p,p′-DDT/p,p′-DDE ratios relative to 1971 was also noted.     

Assessment of SARAL/AltiKa Wave Height Measurements Relative to Buoy,Jason-2, and Cryosat-2 Data

SARAL/AltiKa GDR-T are analyzed to assess the quality of the significant wave height (SWH) measurements. SARAL along-track SWH plots reveal cases of erroneous data, more or less isolated, not detected by the quality flags. The anomalies are often correlated with strong attenuation of the Ka-band backscatter coefficient, sensitive to clouds and rain. A quality test based on the 1 Hz standard deviation is proposed to detect such anomalies. From buoy comparison, it is shown that SARAL SWH is more accurate than Jason-2, particularly at low SWH, and globally does not require any correction. Results are better with open ocean than with coastal buoys. The scatter and the number of outliers are much larger for coastal buoys. SARAL is then compared with Jason-2 and Cryosat-2. The altimeter data are extracted from the global altimeter SWH Ifremer data base, including specific corrections to calibrate the various altimeters. The comparison confirms the high quality of SARAL SWH. The 1 Hz standard deviation is much less than for Jason-2 and Cryosat-2, particularly at low SWH. Furthermore, results show that the corrections applied to Jason-2 and to Cryosat-2, in the data base, are efficient, improving the global agreement between the three altimeters.     

Inference of Solar Magnetic Field Parameters from Data with Limited Wavelength Sampling

We investigate the diagnostic potential of polarimetric measurements with filtergraph instruments. Numerical simulations are used to explore the possibility of inferring the magnetic field vector, its filling factor, and the thermodynamics of model atmospheres when only a few wavelength measurements are available. These simulations assume the magnetic Sun to be represented by Milne–Eddington atmospheres. The results indicate that two wavelength measurements are insufficient to reliably determine the magnetic parameters, regardless of whether magnetograph techniques or least-squares fitting inversions are used. However, as few as four measurements analyzed with the inversion technique provide enough information to retrieve the intrinsic magnetic field with an accuracy better than 10% in most cases.     

A quasi-geostrophic diagnosis of the zonal flow associated with cut-off lows over South Africa and surrounding oceans

Climate Dynamics - The zonal flow associated with cut-off lows (COLs) comprises two jet streaks of different spatial extents. The smaller scale jet streak, located north of the COLs, forms as a...