Varun Sheel

Seasonal and interannual variability of tropospheric ozone over an urban site in India: A study based on MOZAIC and CCM vertical profiles over Hyderabad

This study is based on the analysis of Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) data measured over Hyderabad, India during the years 2006–2008. Tropospheric profiles of O3 show clear seasonality with high and low values during the premonsoon and monsoon seasons, respectively. Analysis of back trajectory and fire count data indicates major roles for long-range transport and biomass burning in the seasonal variation of O3. Typically, lower levels of O3 in the monsoon season were due to the flow of marine air and negligible regional biomass burning, while higher levels in other seasons were due to transport of continental air. In the upper troposphere, relatively low levels of O3 during the monsoon and postmonsoon seasons were associated with deep convection. In the free troposphere, levels of O3 also show year-to-year variability as the values in the premonsoon of 2006 were higher by about 30 ppbv compared to 2008. The year-to-year variations were mainly due to transition from El Nino (2006) to La Nina (2008). The higher and lower levels of O3 were associated with strong and weak wind shears, respectively. Typically, vertical variations of O3 were anticorrelated with the lapse rate profile. The lower O3 levels were observed in the stable layers, but higher values in the midtroposphere were caused by long-range transport. In the PBL region, the mixing ratio of O3 shows strong dependencies on meteorological parameters. The Chemistry Climate Model (CCM2) reasonably reproduced the observed profiles of O3 except for the premonsoon season.

Seasonal and interannual variability of carbon monoxide based on MOZAIC observations, MACC reanalysis, and model simulations over an urban site in India

The spatial and temporal variations of carbon monoxide (CO) are analyzed over a tropical urban site, Hyderabad (17°27′N, 78°28′E) in central India. We have used vertical profiles from the Measurement of ozone and water vapor by Airbus in-service aircraft (MOZAIC) aircraft observations, Monitoring Atmospheric Composition and Climate (MACC) reanalysis, and two chemical transport model simulations (Model for Ozone And Related Tracers (MOZART) and MRI global Chemistry Climate Model (MRI-CCM2)) for the years 2006–2008. In the lower troposphere, the CO mixing ratio showed strong seasonality, with higher levels (>300 ppbv) during the winter and premonsoon seasons associated with a stable anticyclonic circulation, while lower CO values (up to 100 ppbv) were observed in the monsoon season. In the planetary boundary layer (PBL), the seasonal distribution of CO shows the impact of both local meteorology and emissions. While the PBL CO is predominantly influenced by strong winds, bringing regional background air from marine and biomass burning regions, under calm conditions CO levels are elevated by local emissions. On the other hand, in the free troposphere, seasonal variation reflects the impact of long-range transport associated with the Intertropical Convergence Zone and biomass burning. The interannual variations were mainly due to transition from El Nino to La Nina conditions. The overall modified normalized mean biases (normalization based on the observed and model mean values) with respect to the observed CO profiles were lower for the MACC reanalysis than the MOZART and MRI-CCM2 models. The CO in the PBL region was consistently underestimated by MACC reanalysis during all the seasons, while MOZART and MRI-CCM2 show both positive and negative biases depending on the season.

A study of the atmospheric photochemical loss of N2O based on trace gas measurements

Abstract Nitrous oxide (N 2 O) plays an important role in ozone chemistry as well as in greenhouse warming. It is the source of NO x radicals in the stratosphere which are the dominant catalysts for ozone depletion. Recently, doubts have been raised on the global N 2 O budget. One approach to solve this problem has been the consideration of new mechanisms for atmospheric production and destruction of N 2 O. In parallel, N 2 O sinks have been constrained from observed tracer correlations in the lower stratosphere based on aircraft measurements, which are limited up to an altitude of only 20 km. We use vertical distributions of N 2 O and other trace gases measured simultaneously from Hyderabad, India (17.5°N, 78.6°E) in 1987, 1990, 1994 and 1998 using balloon-borne cryogenic air samplers covering the altitude range of about 8–37 km to study these issues together with 2-D model simulations. The slopes of N 2 O correlations with CH 4 , CFC-12 and CFC-11 compare well with the model derived slopes, with exceptions in cases where dynamical perturbations are strong. Average N 2 O lifetimes of 85±43 and 111±38 years have been estimated using the observed slopes and two sets of reference lifetimes for the correlated tracers. This average lifetime compares well within the spread, with the lifetime estimated from the sink of N 2 O in the model, suggesting that the present estimate of the N 2 O photochemical sink incorporated in the model is adequate.

Spatio-temporal variation of biomass burning sources over South and Southeast Asia

In this study, we have investigated the seasonality and long-term trends of major biomass burning (BB) sources over South and Southeast Asia (S-SE Asia). The activities of BB and related emissions show bi-modal seasonality in S-SE Asia. From January to May period, the BB dominates in the northern hemisphere parts of S-SE Asia. From July to September, the activities shift to the southern hemisphere where the emissions from Indonesian and Malaysian islands make largest contributions. Overall, the activities of BB are lowest during October–December period in S-SE Asia. The seasonality of BB intensity and rain are just opposite in the phase over India. The climatological (1997–2008) emissions of carbon monoxide (CO), oxides of nitrogen (NOx) and non-methane hydrocarbons (NMHCs) show strong spatio-temporal variation. The trends show large inter-annual variations with highest and lowest values during years 1997 and 2000, respectively. In the southern hemisphere parts of S-SE Asia mainly in Indonesia, the intensity of biomass fires has been modulated by the large scale climatic phenomena like El Niño and Southern Oscillation (ENSO). The annual emissions of trace gases in southern hemisphere region during the El Niño years exceed to those for the normal years. The estimates for northern hemisphere region during the La Niña years were significantly higher than those for the normal years. The Model for Ozone And Related Chemical Tracers (MOZART) simulations of columnar CO and NOx tend to capture the prominent features of BB emissions in S-SE Asia. The impacts of extensive fires in Indonesia during El Niño year of 2006 compared to a normal year of 2005 were clearly seen in the MOZART-4 simulations of both CO and NOx.

Regional biomass burning trends in India: Analysis of satellite fire data

The results based on the analysis of satellite fire counts detected by the Along-Track Scanning Radiometer (ATSR) sensors over different regions of India during 1998–2009 have been presented. Generally, the activities of open biomass burning show large spatial and temporal variations in India. The highest and lowest values of monthly fire counts were detected during the periods of March–May and July–September, respectively over different regions of India. The activities of biomass burning in two central states of Madhya Pradesh and Maharashtra were the highest and together accounted for about 25–45% of total annual fire counts detected over India during the study period. However, in opposite phases, the rainfall and fire count data show strong seasonal variation. In addition to large regional and seasonal variations, the fire data also show significant year-to-year variation. The higher annual fire counts exceeding the mean of entire period by about 16% and 43% were detected during the two periods of 1998–2000 and 2007–2009, respectively. We have estimated normalized anomaly of annual fire count data which shows large positive departures from long-term mean for the years 1999, 2007, 2008 and 2009, while negative departures for the years 2002, 2003 and 2005. Consistently, the mixing ratio of carbon monoxide (CO) typical peaks during winter but extended to pre-monsoon season during extensive fire years. The annual data over the entire region of India show lesser positive trend of about 3% yr−1. The inter-annual variation of fire count over entire India follows the trend in the ENSO Precipitation Index (ESPI) but shows opposite trend to the multivariate ENSO Index (MEI).

Secondary organic aerosol over an urban environment in a semi-arid region of western India

Carbonaceous species in PM10 and PM2.5 samples, collected from an urban location at Ahmedabad in India during summer, were analyzed to study variability in water-soluble organic carbon (WSOC) and secondary organic carbon (SOC) along with atmospheric water vapor content. A significant correlation between WSOC and SOC was found indicating major contribution of soluble organic compounds by secondary organic aerosol formation. A strong inverse dependence of WSOC and SOC on atmospheric water vapor content is observed in both PM10 and PM2.5 (at <45% relative humidity, RH) during daytime; whereas data collected during monsoon season at higher RH conditions do not exhibit such relation. Aerosol liquid water content (LWC) calculated from thermodynamic equilibrium model suggests that the decrease in secondary organic aerosol (SOA) with increase in RH occurs when LWC is absent or insignificant amount. The inverse correlation in summertime indicates possible decrease in the extent of heterogeneous photochemical oxidation of precursor volatile organic compounds on mineral aerosol surface with increase in ambient water vapor. These results have implications for SOA estimations on regional scales especially in arid and semi-arid regions where significant amount of fine mineral dust is present.

Chlorine partitioning in the stratosphere based on in situ measurements

Balloon-borne cryogenic air sampler experiments have been conducted from a tropical (Hyderabad, 17.5°N) and a midlatitude (GAP, southern France, 44°N) station since 1987 in the altitude range of about 8–35 km. Air samples are analysed at the Max Planck Institute for Aeronomy (MPAE) and Physical Research Laboratory (PRL) using various gas chromatographic techniques to obtain the vertical distributions of several halogenated source gases and long-lived dynamical tracers. These observations are used to determine the stratospheric partitioning of the chlorine species into their organic and inorganic forms for the altitude range of 20 to 35 km. Distributions of inorganic chlorine indicate increase in their abundances with altitude, latitude and time. Mixing ratio correlations of organic and inorganic chlorine with N2O have been obtained which also suggest that the rate of increase in inorganic halogens component in the stratosphere is larger than the increase rate of total organic halogen. This supports previous assessments that halogen-induced ozone depletion will continue to be observed for a few more years, despite the decrease of halocarbon loading into the stratosphere since 1994.

Meson correlators at finite temperature

We evaluate equal time point to point spatial correlation functions of mesonic currents at finite temperature. For this purpose we consider the QCD vacuum structure in terms of quark antiquark condensates and their fluctuations in terms of an irreducible four point structure of the vacuum. The temperature dependence of quark condensates is modeled using chiral perturbation theory for low temperatures and lattice QCD simulations near the critical temperature.We first consider the propagation of quarks in a condensate medium at finite temperature. We then determine the correlation functions in a hot medium. Parameters such as mass, coupling constant and threshold energy are deduced from the finite temperature correlators. We find that all of them decrease close to the critical temperature.

VACUUM STRUCTURE IN QCD WITH QUARK AND GLUON CONDENSATES

We consider here the vacuum structure in QCD with both quark and gluon condensates and a variational ansatz for the ground state. The method is nonperturbative, using only equal time algebra for the field operators. We then find that a constrained energy minimization of the Hamiltonian leads to a QCD vacuum with both quark and gluon condensates for αs>αc=0.62. The pion decay constant and the charge radius of the pion seem to fix the QCD coupling constant αs as 1.28, with the bag pressure given by This approach to QCD opens up possibilities of relating the mysterious vacuum structure with common place hadronic properties in a more direct manner.

Improvement of tracer implementation in martian atmosphere using GCM over HPC cluster

The Martian atmosphere has Carbon Dioxide (CO2) as its main gas comprising of 95.4%. The second main gas is Nitrogen (N2) with 2.7%. All the other gases are in trace amounts, that is they are less than 1% in the atmosphere[6]. Even then these trace gases have a large contribution in the chemical reactions taking place in the atmosphere. These tracer gases are O2, Ozone (O3), Sulfur Dioxide (SO2), Nitrogen Oxide(NO), CO to name a few[4]. General Circulation Models (GCM) are used to simulate the general circulation of the gases in the atmosphere. There are a few GCMs available to study Martian atmosphere. We are using the GCM developed at Laboratory de Meteorologie Dynamique (LMDZ) at France[5]. The aim of this work is to implement SO2 tracer species in the LMDZ model. SO2 is the most abundant species occurring from the volcanic eruption and contributes to a few percent of the total gases released. SO2 can also be obtained by the ultra violet photons from sulphates on the Surface of Mars or dust present in the air. SO2 can be one of the effective tracers, ongoing out gassing on Mars.