Threshold exceedances and cumulative ozone exposure indices at tropical suburban site

This study provides the first analysis of threshold exceedances and cumulative ozone exposure indices from Pune, a tropical suburban site in India. We used the directives on ozone pollution in ambient air provided by the United Nations Economic Commission for Europe, and by the World Health Organization to assess the air quality from in situ measurements of surface ozone (during the years 2003-2006). We find that the exposure-plant response index (Accumulated exposure Over a Threshold of 40 ppb (AOT40)) and target values for protection of human health (8-h > 60 ppb) are regularly surpassed. This is a concern for agricultural and human health. Air-mass classification based on back-air trajectories shows that the excess of AOT40 values is quite plausibly due to long-range transport of background ozone and its precursors to the measurement site

Projected changes of rainfall seasonality and dry spells in a high greenhouse gas emissions scenario

In this diagnostic study we analyze changes of rainfall seasonality and dry spells by the end of the twenty-first century under the most extreme IPCC5 emission scenario (RCP8.5) as projected by twenty-four coupled climate models contributing to Coupled Model Intercomparison Project 5 (CMIP5). We use estimates of the centroid of the monthly rainfall distribution as an index of the rainfall timing and a threshold-independent, information theory-based quantity such as relative entropy (RE) to quantify the concentration of annual rainfall and the number of dry months and to build a monsoon dimensionless seasonality index (DSI). The RE is projected to increase, with high inter-model agreement over Mediterranean-type regions---southern Europe, northern Africa and southern Australia---and areas of South and Central America, implying an increase in the number of dry days up to 1Â month by the end of the twenty-first century. Positive RE changes are also projected over the monsoon regions of southern Africa and North America, South America. These trends are consistent with a shortening of the wet season associated with a more prolonged pre-monsoonal dry period. The extent of the global monsoon region, characterized by large DSI, is projected to remain substantially unaltered. Centroid analysis shows that most of CMIP5 projections suggest that the monsoonal annual rainfall distribution is expected to change from early to late in the course of the hydrological year by the end of the twenty-first century and particularly after year 2050. This trend is particularly evident over northern Africa, southern Africa and western Mexico, where more than 90% of the models project a delay of the rainfall centroid from a few days up to 2Â weeks. Over the remaining monsoonal regions, there is little inter-model agreement in terms of centroid changes

Features of ozone quasi-biennial oscillation in the vertical structure of tropics and subtropics

Latitude-altitude structure of ozone QBO over the tropical-subtropical stratosphere (40° S-40°N) has been explored by analyzing Microwave Limb Sounder (MLS) aboard Upper Atmospheric Research Satellite (UARS) data for the period 1992-1999 using the multifunctional regression model. The inferred ozone QBO shows two maxima located at 22 hPa and 10 hPa with coefficient of 2-3 per 10 m/s centered at the equator. The equatorial maxima are out of phase with each other. Subtropics exhibit two peak structure near 14 hPa but of opposite sign to that of equatorial maximum near 10 hPa. Over the equatorial region, positive (zonal winds westerly) coefficients overlay negative (zonal winds easterlies) coefficients which descend with time. A pattern of equatorial maximum and two subtropical minima appears in the months December to February near 10 hpa and it propagates upward with progression of seasons. Equatorial QBO is seasonally asynchronous while subtropical QBO is seasonally synchronous

Detection of surface emission hot spots, trends, and seasonal cycle from satellite-retrieved NO2 over India

Tropospheric NO2 concentrations derived from spaceborne measurements of Global Ozone Monitoring Experiment (GOME) on board ERS 2 and Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) on board Envisat, respectively, for the time period of 1996–2006 have been used to identify major NO2 emission hot spots, trends, and seasonal cycle over different regions of India. Emission hot spots are observed over the locations of thermal power plants and over major urban and industrial regions. A multifunctional regression model has been used to analyze the trends and seasonal cycle over these emission hot spots. Increasing trends of ∼1.65 ± 0.52% a−1 have been observed for NO2 over India. The fast growing industrial regions of Mumbai and Delhi show increasing trends of ∼2.1 ± 1.1 and ∼2.4 ± 1.2% a−1, respectively. Seasonal variations of tropospheric NO2 concentrations show a maximum during winter-summer (December–May) and a minimum during the monsoon seasons (June–September). The observed seasonal cycle in satellite-derived NO2 agrees well with the surface-level observations of NO

Satellite derived trends in NO2 over the major global hotspot regions during the past decade and their inter-comparison

We assessed satellite derived tropospheric NO2 distribution on a global scale and identified the major NO2 hotspot regions. Combined GOME and SCIAMACHY measurements for the period 1996-2006 have been used to compute the trends over these regions. Our analysis shows that tropospheric NO2 column amounts have increased over the newly and rapidly developing regions like China (11 ± 2.6/year), south Asia (1.76 ± 1.1/year), Middle East (2.3 ± 1/year) and South Africa (2.4 ± 2.2/year). Tropospheric NO2 column amounts show some decrease over the eastern US (-2 ± 1.5/year) and Europe (0.9 ± 2.1/year). We found that although tropospheric NO2 column amounts decreased over the major developed regions in the past decade, the present tropospheric NO2 column amounts over these regions are still significantly higher than those observed over newly and rapidly developing regions (except China). Tropospheric NO2 column amounts show some decrease over South America and Central Africa, which are major biomass burning regions in the Southern Hemisphere. © 2009 Elsevier Ltd. All rights reserved

Evaluating WRF-Chem multi-scale model in simulating aerosol radiative properties over the tropics - A case study over India

We evaluated the performance of WRF-Chem multi-scale model over the tropics, to simulate the regional distribution and optical properties of aerosols, and its effect on radiation over India for a winter month. The model is evaluated using measurements obtained from upper-air soundings, AERONET sun photometers, various satellite instruments, and pyranometers. The simulated downward shortwave flux was overestimated when the effect of aerosols and clouds, on radiation, was -2 neglected. The simulated downward shortwave radiation was 1 to 20 Wm closer to the observations when we included aerosol-cloud-radiation interaction in the simulation. The model usually underestimated particulate concentration for the few observations available. This is likely due to turbulent mixing, transport errors and the lack of dust emission/scheme and the secondary organic aerosol treatment in the model. The model efficiently captured the broad regional hotspots such as, higher aerosol optical depth over the northern parts of India, especially over the Indo-Gangetic basin and lower aerosol optical depth over southern parts of India. The regional distribution of aerosol optical depth agreed well with the AVHRR aerosol optical depth and the TOMS aerosol index pattern. The magnitude and wavelength-dependence of simulated aerosol optical depth was also similar to the AERONET observations across India. The difference in surface shortwave radiation between two simulations that included and neglected aerosol-radiation (aerosol-radiation-cloud) interactions -2 were as high as -25 (-30) Wm -2. The spatial variations of these differences were also compared with the AVHRR observation. This study suggests that the model is able to qualitatively simulate the distribution of particulates and its impact on radiation over India; however, additional measurements of particulate mass and composition are needed to fully evaluate the model performance

Precipitation in a warming world: Assessing projected hydro-climate changes in California and other Mediterranean climate regions

Abstract In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. In California, however, projections of changes in annual precipitation are inconsistent. Analysis of daily precipitation in 30 GCMs reveals patterns in projected hydrometeorology over each of the five MedClm regions globally and helps disentangle their causes. MedClim regions, except California, are expected to dry via decreased frequency of winter precipitation. Frequencies of extreme precipitation, however, are projected to increase over the two MedClim regions of the Northern Hemisphere where projected warming is strongest. The increase in heavy and extreme precipitation is particularly robust over California, where it is only partially offset by projected decreases in low-medium intensity precipitation. Over the Mediterranean Basin, however, losses from decreasing frequency of low-medium-intensity precipitation are projected to dominate gains from intensifying projected extreme precipitation. MedClim regions are projected to become more sub-tropical, i.e. made dryer via pole-ward expanding subtropical subsidence. California’s more nuanced hydrological future reflects a precarious balance between the expanding subtropical high from the south and the south-eastward extending Aleutian low from the north-west. These dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events