Variations in wave direction estimated using first and second order Fourier coefficients

In most design applications such as alignment of the berthing structure and breakwater alignment, it becomes necessary to determine the direction of design wave. There are two different approaches to determine wave direction. One involves the use of first order Fourier coefficients (mean wave direction) while the other uses second order Fourier coefficients (principal wave direction). Both the average wave direction over the entire frequency range (0.03–0.58 Hz) and the direction corresponding to the peak frequency are used in practice. In the present study, comparison is made on wave directions estimated based on first and second order Fourier coefficients using data collected at four locations in the west and east coasts of India. Study shows that at all locations, the mean and principal wave directions for frequencies ranging from 0.07 to 0.25 Hz (±0.5 times peak frequency) co-vary with a correlation coefficient of 0.99 but at lower and higher frequencies, difference between the parameters is large. Average difference between the mean wave direction at peak frequency and the average over the frequency related to spectral energy more than 20% of maximum value is less, around 13°. Study shows that average difference in the sea and swell directions is around 39°.     

Comparison of Near Coastal Significant Wave Height Measurements from SARAL/AltiKa with Wave Rider Buoys in the Indian Region

Significant Wave Height (SWH) measurement data from the AltiKa Radar Altimeter (RA) for the first 13 cycles of satellite coverage are compared with the SWH from Wave Rider Buoys (WRB) located at nine stations along the Indian coast to assess the performance of the altimeter over the coastal region. AltiKa SWH observations within a 30-minute interval and 50 km distance from WRBs are found to be over estimated by 6%, the Root Mean Square Error (RMSE) is 0.36 m, the Scatter Index (SI) is 26%, and the correlation coefficient (r) is 0.91. Relaxing the distance criteria by 50 km leads to increase in RMSE and deterioration of r to 0.89. There is a marked difference in the statistics on the comparison pairs pooled separately for the buoys near west and east coasts, with the latter showing RMSE error 26% more than the former. The method of Cressman weights adopted to correct for the errors arising out of the temporal and spatial differences in altimeter and buoy data comparison pairs resulted in reduction of RMSE by 5% and 25%, respectively, for the 30-minute and 50 km criteria and 4% and 56% for the 30-minute and 100 km criteria.     

Impact of climate warming on upper layer of the Bering Sea

The impact of climate warming on the upper layer of the Bering Sea is investigated by using a high-resolution coupled global climate model. The model is forced by increasing atmospheric CO₂ at a rate of 1% per year until CO₂ reaches double its initial value (after 70 years), after which it is held constant. In response to this forcing, the upper layer of the Bering Sea warms by about 2°C in the southeastern shelf and by a little more than 1°C in the western basin. The wintertime ventilation to the permanent thermocline weakens in the western Bering Sea. After CO₂ doubling, the southeastern shelf of the Bering Sea becomes almost ice-free in March, and the stratification of the upper layer strengthens in May and June. Changes of physical condition due to the climate warming would impact the pre-condition of spring bio-productivity in the southeastern shelf.     

Stable isotope analysis of carbon and nitrogen in angrites

Angrites are a small group of ancient basaltic achondrites, notable for their unusual chemistry and extreme volatile depletion. No comprehensive study of indigenous light elements currently exists for the group. Measurement of the abundances and isotopic composition of carbon and nitrogen could provide information pertaining to the evolution of the angrite parent body. Bulk‐sample stepped combustion analyses of five angrites and a glass separate from D'Orbigny were combined with earlier data and acid dissolution experiments of carbonates found in D'Orbigny to compile an inventory of indigenous carbon and nitrogen. Indigenous carbon combusted between 700 °C and 1200 °C, with abundances of 10–140 ppm and a mass‐weighted δ¹³C of ?25 to ?20‰ with the exception of D'Orbigny (δ¹³C approximately ?5‰). Nitrogen was released at 850–1200 ºC, 1–20 ppm with a δ¹⁵N ?3‰ to +4‰; again, D'Orbigny (δ¹⁵N approximately +20 to +25‰) was an exception. We interpret these components as largely indigenous and decoupled; the carbon in graphitic or amorphous form, while the nitrogen is present as a dissolved component in the silicates. No relationship with the textural sub‐classification of angrites is apparent. We suggest that the angrite parent body contains a reservoir of reduced carbon and thus may have undergone a change in redox conditions, although the timing and mechanism for this remain unclear.     

Study of the Cosmic-Ray Modulation During the Passage of ICMEs and CIRs

We compare the cosmic-ray response to interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) during their passage in near-Earth space. We study the relative importance of various structures/features identified during the passage of the ICMEs and CIRs observed during Cycle 23 (1995?–?2009). The identified ICME structures are the shock front, the sheath, and the CME ejecta. We isolate the shock arrival time, the passage of the sheath region, the arrival of ejecta, and the end time of their passage. Similarly, we isolate the CIR arrival, the associated forward shock, the stream interface, and the reverse shock during the passage of a CIR. For the cosmic-ray intensity, we utilize the data from high counting rate neutron monitors. In addition to neutron monitor data, we utilize near-simultaneous and same time-resolution data of interplanetary plasma and field, namely the solar-wind velocity, the interplanetary magnetic field (IMF) vector, and its variance. Further, we also utilize some derived interplanetary parameters. We apply the method of the superposed-epoch analysis. As the plasma and field properties are different during the passage of different structures, both in ICMEs and CIRs, we systematically vary the epoch time in our superposed-epoch analysis one by one. In this way, we study the role and effects of each of the identified individual structures/features during the passage of the ICMEs and CIRs. Relating the properties of various structures and the corresponding variations in plasma and field parameters with changes of the cosmic-ray intensity, we identify the relative importance of the plasma/field parameters in influencing the amplitude and time profiles of the cosmic-ray intensity variations during the passage of the ICMEs and CIRs.     

Linked twist maps in hamiltonian systems

Linked twist maps of ergodic theory are modified to provide a model for chaotic orbits in ‘double bowl’ potentials in conservative systems, e.g. direct ‘exchange’ orbits in the planar restricted problem of three bodies. The maps are typically ergodic (and mixing), and provide a clue to the nature of relaxation or diffusion in chaotic Hamiltonian systems.     

Drivers of response to extreme weather warnings among marine fishermen

Extreme weather events, such as storms and cyclones, pose dire occupational hazards in marine fishing. Thus, warnings against such events can reduce risks to the life and property of fishing communities. This study is an attempt to assess the factors driving fishermen’s decision to respond to weather warnings. Mixed methods, such as exploratory fieldwork, literature review, and focus group discussions, helped in identifying the available weather warnings and hypothesizing the probable factors influencing response to the warnings in the marine fishing community in Maharashtra, India. The plausible drivers of response include perceived potential risk, credibility of the warning and its disseminators, community social capital, and other demographic characteristics. Data from a household survey, comprising 601 fishermen, is used to empirically test the hypotheses. The results suggest that trust in the source and disseminator of the warning is related to higher response rates. There is heterogeneity in the role of community social capital as a motivator to respond. Further, fishermen perceiving traditional information to be more reliable are less likely to respond frequently to the warnings. The findings of the study are relevant for designing interventions which can prompt high response rates to weather warnings from fishermen.     

Enhancing the relevance of Shared Socioeconomic Pathways for climate change impacts,adaptation and vulnerability research

This paper discusses the role and relevance of the shared socioeconomic pathways (SSPs) and the new scenarios that combine SSPs with representative concentration pathways (RCPs) for climate change impacts, adaptation, and vulnerability (IAV) research. It first provides an overview of uses of social–environmental scenarios in IAV studies and identifies the main shortcomings of earlier such scenarios. Second, the paper elaborates on two aspects of the SSPs and new scenarios that would improve their usefulness for IAV studies compared to earlier scenario sets: (i) enhancing their applicability while retaining coherence across spatial scales, and (ii) adding indicators of importance for projecting vulnerability. The paper therefore presents an agenda for future research, recommending that SSPs incorporate not only the standard variables of population and gross domestic product, but also indicators such as income distribution, spatial population, human health and governance.     

Assessing integrated assessments

Integrated assessment of global environmental change is a relatively new field that is beginning to define itself and its forms of practice. As yet, the field has not grappled directly with issues of quality control and assessment of quality, and this work is a first attempt in that direction. We argue that if integrated assessment is to be successful in the long run, then building and maintaining credibility via quality control procedures is a necessary condition for realizing its potential. We highlight a number of pitfalls in the practice of integrated assessment, and discuss their causes. We buttress our concerns using examples from both within climate change integrated assessment, and from the history of other similar endeavors. We also provide a number of suggestions that we hope will serve to alleviate some of these pitfalls. For instance, tools, methods, and assumptions from disciplines form archetypes for components in integrated assessment models, and we need to apply greater scrutiny to these archetypes. Further, tools which may be reasonable to use in particular disciplinary, geographical, or temporal contexts may be unsuited to the broader contexts inherent in integrated assessment studies of global environmental change.     

Comments on Placenticeras mintoi (Vredenburg, 1906) from the Bagh Beds (Late Cretaceous), central India with special reference to Turonian Nodular Limestone Horizon

The Late Cretaceous (Cenomanian to Coniacian) marine sediments of central India prevalently known as ‘Bagh Beds,’ have been deposited in the E-W extending Narmada Basin. The stratigraphy of these Cenomanian — Coniacian sediments has been reviewed and summarized. The Bagh Beds have been found to consist of three formations: Nimar Sandstone, Nodular Limestone and Corallian Limestone in ascending order. Main emphasis has been given to Nodular Limestone Formation (Turonian), which is the most fossiliferous horizon of the Bagh Beds. Nodular Limestone Formation has more or less alternating bands of varying thickness of nodular limestone and marl. It yielded numerous ammonoid specimens, which have been found to belong to a morphologically highly variable ammoniod taxon Placenticeras mintoi Vredenburg.