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Estimation of past atmospheric carbon dioxide levels using tree-ring cellulose 13C
No full textWe study the applicability of the Farquhar model for carbon isotopic discrimination (change in carbon iso-topic composition from air CO2 to tree-ring cellulose) in C3 plants to trees growing in the field. Two new carbon isotope datasets from Himalayan conifers with published data from another eight sites across the world show disparate trends in the plot of carbon iso-tope discrimination versus atmospheric carbon dioxide concentration, in contrast to the model prediction of absence of any trend. This is because the model assumes that the tree adjusts its stomatal conductance for water-use efficiency to maintain a constant ratio of carbon dioxide concentrations inside and outside the leaf and treats the diffusive and biochemical fraction-ation factors as constants. By introducing a simple lin-ear dependence of these fractionation factors with ambient temperature and humidity, we have enhanced the applicability of the model to naturally growing trees. Further, despite the disparate trends exhibited by the 10 trees, we show using the inverse modelling that it is possible to derive a unique record of past atmospheric CO2 concentrations using tree cellulose δ13C data. The reconstructions also replicate the summer pCO2 gradient from tropics to mid-latitudes. We also discuss the merits and demerits of the model, and compare the model-derived pCO2 with that of the ice core-based records from Law Dome
Deposition ice nuclei observations over the Indian region during CAIPEEX
No full textA thermal gradient diffusion chamber (TGDC) designed to process the ice nuclei (IN) sample is illustrated with unique airborne observations. IN samples collected during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) have been analyzed using the TGDC. The TGDC is able to activate the IN by deposition mode over ice supersaturation of 6-24 and at a temperature range of -18.5 to -13.5C. These samples correspond to first observations at several vertical levels including the cloud layer and over several geographically distinct locations in India during the monsoon season. Vertical profile of IN concentration shows that at a given level, there is large spatial and temporal variation in IN concentration. Maximum IN concentrations are observed below 3km at all ice supersaturation. Highest IN concentrations are noted over inland continental regions. Spatial variation in IN concentration was observed in the range 0 to 5L-1 with an average of 1.12L-1 at highest ice supersaturation (20-25) interval. Large variation in IN concentration at a single temperature is also observed. Our observation shows that there is a significant increase in IN concentrations with supersaturation over ice. Elemental chemical analysis of the collected aerosol samples by Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectrometry (EDX) showed that copper, silica, aluminium and zinc are the most abundant elements
Chemical composition of snow-water and scavenging ratios over costal Antarctica
No full textSnow samples and aerosol samples were collected at coastal Antarctica near Larsemann Hills and Maitri, during the 29th Indian Antarctic Expedition carried out during Dec., 2009 to March 2010. The main objective of this study was to characterize the chemical composition of fresh and surface snow at coastal Antarctica and to determine the scavenging ratios using composition of snow and aerosol samples. The pH of surface and fresh snow were 6.03 and 5.64 respectively. The surface snow samples were collected along a 127-km transect from the seaward edge of the ice shelf to the Antarctic plateau and analyzed for the presence of the major inorganic components SO4 2-, NO3 -, Cl-, NH4 +, Na+, K+, Ca2+ and Mg2+. It was observed that Na+ and Cl- were the most abundantly occurring ions at Antarctica. Considerable amount of SO4 2- was also found in the both fresh and surface snow which may be attributed to the long range transport from Northern Hemisphere as well as to the oxidation of DMS produced by marine phytoplankton. A higher percentage of the ions in fresh snow may be because of trapping of the particulate matter in it. The sea-salt components i.e., Na+, Cl- and Mg2+ decreased with increasing distance from the coast. The acidic components were neutralized mainly by NH4 + and Ca2 +. The scavenging ratio was maximum for Na+ and minimum for NO3 -, indicating that the scavenging efficiency was higher for coarse size particles and lower for fine size particles. In addition, we have attempted to find out the possible sources of the observed chemical species in snow-water
Effects of environmental conditions on inducing charge structures of thunderstorms over Eastern India
Get PDFIt is well known that environmental conditions like convective instability, aerosol loading, and availability of moisture content affect the polarity of charge structures of thunderstorms. The electrical characteristics of thunderstorms observed during the pre-monsoon season of year 2009, over Eastern India were studied to identify the effects of different environmental conditions on charge structures of thunderstorms occurring over this region. Electric field and Maxwell current data suggest that at least one of these thunderstorms had an inverted charge structure. Doppler RADAR, radiosonde, and Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) data have been used to compare the microphysical and dynamical characteristics of these thunderstorms. The thermo dynamical structure observed by radiosonde during the day on which an inverted polarity thunderstorm was observed showed very high CAPE in the mixed-phase region compared to other thunderstorm days. Furthermore, the AOD peaked 1 day before this thunderstorm. The back trajectories of winds also suggest that the aerosols might have been transported from a desert region on that day. It has been proposed that the large ice nuclei concentration can produce dominant positive charge in the lower portion of the mixed-phase region by maintaining ice saturation
Estimated crop yield losses due to surface ozone exposure and economic damage in India
Get PDFIn this study, we estimate yield losses and economic damage of two major crops (winter wheat and rabi rice) due to surface ozone (O3) exposure using hourly O3 concentrations for the period 2002-2007 in India. This study estimates crop yield losses according to two indices of O3 exposure: 7-h seasonal daytime (0900-1600 hours) mean measured O3 concentration (M7) and AOT40 (accumulation exposure of O3 concentration over a threshold of 40 parts per billion by volume during daylight hours (0700-1800 hours), established by field studies. Our results indicate that relative yield loss from 5 to 11 (6-30 ) for winter wheat and 3-6 (9-16 ) for rabi rice using M7 (AOT40) index of the mean total winter wheat 81 million metric tons (Mt) and rabi rice 12 Mt production per year for the period 2002-2007. The estimated mean crop production loss (CPL) for winter wheat are from 9 to 29 Mt, account for economic cost loss was from 1,222 to 4,091 million US annually. Similarly, the mean CPL for rabi rice are from 0.64 to 2.1 Mt, worth 86-276 million US. Our calculated winter wheat and rabi rice losses agree well with previous results, providing the further evidence that large crop yield losses occurring in India due to current O3 concentration and further elevated O3 concentration in future may pose threat to food security
Prediction and monitoring of monsoon intraseasonal oscillations over Indian monsoon region in an ensemble prediction system using CFSv2
No full textAn ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using National Centers for Environmental Prediction Climate Forecast System model version 2 at T126 horizontal resolution. The EPS is formulated by generating 11 member ensembles through the perturbation of atmospheric initial conditions. The hindcast experiments were conducted at every 5-day interval for 45 days lead time starting from 16th May to 28th September during 2001–2012. The general simulation of ISM characteristics and the ERP skill of the proposed EPS at pentad mean scale are evaluated in the present study. Though the EPS underestimates both the mean and variability of ISM rainfall, it simulates the northward propagation of MISO reasonably well. It is found that the signal-to-noise ratio of the forecasted rainfall becomes unity by about 18 days. The potential predictability error of the forecasted rainfall saturates by about 25 days. Though useful deterministic forecasts could be generated up to 2nd pentad lead, significant correlations are found even up to 4th pentad lead. The skill in predicting large-scale MISO, which is assessed by comparing the predicted and observed MISO indices, is found to be ~17 days. It is noted that the prediction skill of actual rainfall is closely related to the prediction of large-scale MISO amplitude as well as the initial conditions related to the different phases of MISO. An analysis of categorical prediction skills reveals that break is more skillfully predicted, followed by active and then normal. The categorical probability skill scores suggest that useful probabilistic forecasts could be generated even up to 4th pentad lea
Trends and projections of temperature, precipitation, and snow cover during snow cover-observed period over southwestern Iran
No full textIn the present study, tendencies in temperature, precipitation, and snow cover area over the southwestern part of Iran have been assessed. The research mainly focused on snow cover-observed period which included the months of December, January, February, March, and April in the area. This research has been divided into two parts. First part consists of an analysis of the trends in temperature, precipitation, and snow cover area during the above months. Trends in these parameters were tested by linear regression, and significance was determined by t test. Mann-Kendall rank test (MK test) was also employed to confirm the results of linear regression. Sequential Mann-Kendall test (SQ-MK test) was applied for change point detection in the series. For snow cover analysis, remote sensing images from National Oceanic and Atmospheric Administration (NOAA) satellite with advanced very high resolution radiometer (AVHRR) sensor for the period 1987–2007 were used. The second part of the research involved future projections based on four models under B1 and A1B emission scenarios. The models used were centre national de recherches meteorologiques (CNRM), European Center Hamburg model (ECHAM), Model for Interdisciplinary Research on Climate (MIROCH) and United Kingdom Meteorological Office (UKMOC) under the Intergovernmental Panel on Climate Change (IPCC) AR4
Interannual Climate Variabilities of the Tropical Indian Ocean and Coral Isotopic Records
No full textIsotopic analysis of corals is known to be a useful
tool to study the interannual variability of the tropical
ocean and its interaction with the atmosphere. Oxygen
isotopic records of corals from the Indian Ocean have been
shown to respond to the interannual variability, such as,
monsoon and dipolar characteristics of the Indian Ocean.
These variabilities also get modulated by the Pacific Ocean
climate, i.e. ENSO. Modeling work based on observational
data and coral based proxy records have been used to
study these processes. A comparative analysis of these two
methods has been presented revealing the agreement and
disagreement between the two approaches
Trends in Peroxyacetyl Nitrate (PAN) in the upper troposphere and lower stratosphere over Southern Asia during the summer monsoon season: regional impacts
Get PDFWe analyze temporal trends of peroxyacetyl nitrate (PAN) retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) during 2002–2011 in the altitude range 8–23 km over the Asian summer monsoon (ASM) region. The greatest enhancements of PAN mixing ratios in the upper troposphere and lower stratosphere (UTLS) are seen during the summer monsoon season from June to September. During the monsoon season, the mole fractions of PAN show statistically significant (at 2σ) positive trends from 0.2 ± 0.05 to 4.6 ± 3.1 ppt yr−1 (except between 12 and 14 km) which is higher than the annual mean trends of 0.1 ± 0.05 to 2.7 ± 0.8 ppt yr−1. These rising concentrations point to increasing NOx (= NO + NO2) and volatile organic compound (VOC) emissions from developing nations in Asia, notably India and China.
We analyze the influence of monsoon convection on the distribution of PAN in UTLS with simulations using the global chemistry–climate model ECHAM5-HAMMOZ. During the monsoon, transport into the UTLS over the Asian region primarily occurs from two convective zones, one the South China Sea and the other over the southern flank of the Himalayas. India and China host NOx-limited regimes for ozone photochemical production, and thus we use the model to evaluate the contributions from enhanced NOx emissions to the changes in PAN, HNO3 and O3 concentrations in the UTLS. From a set of sensitivity experiments with emission changes in particular regions, it can be concluded that Chinese emissions have a greater impact on the concentrations of these species than Indian emissions. According to SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) NO2 retrievals NOx emissions increases over India have been about half of those over China between 2002 and 2011
Investigation on the consequential features of Southwest Monsoon-2007 Onset and Super cyclone "Gonu" using Satellite, Model and Ground-based data
Get PDFOnset features of the Summer monsoon-2007 were analyzed using data from five different sources, namely,the Tropical Rainfall Measuring Mission (TRMM) 3-hourly rainfall, National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) wind reanalysis data set, NOAA Outgoing Longwave Radiation (OLR), cloud imageries from the meteosat satellite,cloud base height and
cloud occurrence frequency from a ground-based Vaisala Laser Ceilometer at Thiruvananthapuram. On the day of onset, 33 mm of rainfall was registered by TRMM satellite over south Kerala region with 80% cloud frequency and an averaged cloud base height of 2 km. On the next day, the formation of ‘Gonu’ super cyclone as a consequence of the convergence of monsoon onset surge in the Arabian Sea has caused the dissipation of cloud bands in the Arabian Sea and in the Bay of Bengal, except over the region of the
system. This caused a lull situation for about ten days after the India Meteorological Department (IMD)
declared monsoon onset. In fact, the remarkable characteristics of onset, such as deepening of westerlies
and strengthening of low level jet streams were observed only after two weeks of IMD declared monsoon onset. Another unique behavior of 2007 monsoon onset was that the Arabian Sea branch of monsoon onset surge has advanced faster than the Bay of Bengal branch in the early stage