An analysis of the global atmospheric methane budget under different climates

Methane is the second most important gas after CO$_{2}$ in the atmosphere in terms of radiative forcing. It also plays an important role in tropospheric chemistry and influences the oxidation capacity of atmosphere and amount of CO, O$_{3}$ and water vapour. Various biogenic and anthropogenic sectors including gas and oil extraction, wetlands, animal ruminants emit methane in the atmosphere while it is mainly OH which displaces it. At present, the mean global methane concentration is balanced approximately at 1780 ppb after undergoing several changes over the past decades. The sources and sinks currently contribute between 450 and 510 Tg per year although the strength of each source components suffers from uncertainty. Methane is also assumed to be a key player in past climatic changes and its global abundance underwent several transitions which were recorded in the ice cores. One of the drastic changes in methane mixing ratio is observed during the last glacial-interglacial transition, as it shows an increasing trend from 350 ppb till it reaches 700 ppb at the pre-industrial Holocene. The post industrial increase in global methane concentration is also unprecedented. In this study, methane distribution at present climate as well as at Last Glacial Maximum (LGM) and pre-industrial era is simulated with a simplified global tropospheric model ECHAM MOZ. For this simulation, methane emissions from various inventories have been used. A new parameterisation method is developed to estimate wetland methane emission for present day which is later adapted for LGM and pre-industrial time. Wetlands are the largest natural source of methane, still suffers from huge uncertainties. Contrary to the other hydrological models, the present wetland parameterisation follows a simplified approach based on a handful of soilparameters from CARAIB vegetation model. This method is easily adaptable to past climate simulations. The model result for present day from ECHAM MOZ chemistry simulation has been validated with station observation data across the globe and a set of sensitivity analysis with the modified sources are carried out to optimize the global methane budget. One of the major findings from this study is the optimized wetland methane strength which falls in the lower range of IPCC AR4 report. The ECHAM MOZ transient simulation could produce the recent methane trend and inter annual variability between 1990 and 2006 reasonably well although shows an underestimation in a range of 20-40 ppb for the first eight years. This is perhaps caused due to the underestimation of the oil and gas extracted methane source used in the model. For LGM and pre-industrial period, the model, using my wetland methane source successfully reproduces the ice core methane records. Compared to previous studies, the present LGM model source strengthis weaker which raises the possibility of a less deviated sink than present. This is supported by some recent studies on the tropospheric oxidative chemistry which found less OH variability than previously assumed. The important aspect of the present study is that contrary to previous studies where sinks are often hold responsible to explain atmospheric methane variability, here the emphasis has been given to the role of changing source based on these recent findings

Jet modification in the next decade: a pedestrian outlook

In this review, intended for non-specialists and beginners, we recount the current status of the theory of jet modification in dense matter. We commence with an outline of the "traditional" observables which may be calculated without recourse to event generators. These include single and double hadron suppression, nuclear modification factor versus reaction plane etc. All of these measurements are used to justify both the required underlying physical picture of jet modification as well as the final obtained values of jet transport coefficients. This is followed by a review of the more modern observables which have arisen with the ability to reconstruct full jets, and the challenges faced therein. This is followed by a preview of upcoming theoretical developments in the field and an outlook on how the interface between these developments, phenomenological improvements, and upcoming data will allow us to quantitatively determine properties of the medium which effect the modification of hard jets.Comment: 21 pages, 10 figure

The mass hierarchy with atmospheric neutrinos at INO

We study the neutrino mass hierarchy at the magnetized Iron CALorimeter (ICAL) detector at India-based Neutrino Observatory with atmospheric neutrino events generated by the Monte Carlo event generator Nuance. We judicially choose the observables so that the possible systematic uncertainties can be reduced. The resolution as a function of both energy and zenith angle simultaneously is obtained for neutrinos and anti-neutrinos separately from thousand years un-oscillated atmospheric neutrino events at ICAL to migrate number of events from neutrino energy and zenith angle bins to muon energy and zenith angle bins. The resonance ranges in terms of directly measurable quantities like muon energy and zenith angle are found using this resolution function at different input values of $\theta_{13}$. Then, the marginalized $\chi^2$s are studied for different input values of $\theta_{13}$ with its resonance ranges taking input data in muon energy and zenith angle bins. Finally, we find that the mass hierarchy can be explored up to a lower value of $\theta_{13}\approx 5^\circ$ with confidence level $>$ 95% in this set up.Comment: some clarifications added, version accepted in PLB, 12 pages, 34 figure