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Air Pollution, Air Quality and Climate Change (Editorial)
Get PDFThe introduction of gases and particulate contaminants in the atmosphere due to natural or human activities causes air pollution. The concentration and toxicity of these contaminants define air quality and in the long term contribute to climate change. Both air pollution and climate change influence each other through complex interactions in the atmosphere. This issue has 9 very interesting manuscripts, touching various aspects of air pollution and air quality and their impact on climate change
Reliability of regional and global climate models to simulate precipitation extremes over India
No full textExtreme precipitation events over India have resulted in loss of human lives and damaged infrastructures, food crops, and lifelines. The inability of climate models to credibly project precipitation extremes in India has not been helpful to longer-term hazards resilience policy. However, there have been claims that finer-resolution and regional climate models may improve projections. The claims are examined as hypotheses by comparing models with observations from 1951–2005. This paper evaluates the reliability of the latest generation of general circulation models (GCMs), Coupled Model Intercomparison Project Phase 5 (CMIP5), specifically a subset of the better performing CMIP5 models (called “BEST-GCM”). The relative value of finer-resolution regional climate models (RCMs) is examined by comparing Coordinated Regional Climate Downscaling Experiment (CORDEX) South Asia RCMs (“CORDEX-RCMs”) versus the GCMs used by those RCMs to provide boundary conditions, or the host GCMs (“HOST-GCMs”). Ensemble mean of BEST-GCMs performed better for most of the extreme precipitation indices than the CORDEX-RCMs or their HOST-GCMs. Weaker performance shown by ensemble mean of CORDEX-RCMs is largely associated with their high intermodel variation. The CORDEX-RCMs occasionally exhibited slightly superior skills compared to BEST-GCMs; on the whole RCMs failed to significantly outperform GCMs. Observed trends in the extremes were not adequately captured by any of the model ensembles, while neither the GCMs nor the RCMs were determined to be adequate to inform hydrologic design
Spatial and temporal analysis of rainfall over Jharkhand, India (1901-2000)
Get PDFAfter the existence of Jharkhand state in 2000, there is no in-depth study for districts rainfall climatology, its variability and the changing pattern of rainfall using a long period of data is available for the state. About 75% of the agricultural production in Jharkhand is non-irrigated, showing the dependence of the state on monsoon rainfall. In the present study, based on monthly rainfall series of all the 24 districts of Jharkhand for the period 1901-2000 variability of rainfall during monsoon seasons and annual rainfall for Jharkhand state are presented. The study can form very useful information to the agriculture and water sectors of this state. The analysis revealed that during 1901 to 1950 state has showed good rainfall activity than during 1951 to 2000. Variation in rainfall is mostly due to varied and undulating topography almost in all the districts. The maximum abnormality (>100%) in annual and seasonal rainfall was recorded during 1971-80, 1981-90 decades. Comparison of seasonality index for 1901-50, 1951-2000 and for the entire period 1901-2000 showed that SI has increased during 1951-2000. The long term mean annual rainfall based on 100 years data varied from 1136.8 mm over Koderma to 1542.5 mm over Pakur district
International Surface Temperature Initiative global land surface databank: monthly temperature data release description and methods
No full textDescribed herein is the first version release of monthly temperature holdings of a new Global Land Surface Meteorological Databank. Organized under the auspices of the International Surface Temperature Initiative (ISTI), an international group of scientists have spent three years collating and merging data from numerous sources to create a merged holding. This release in its recommended form consists of over 30 000 individual station records, some of which extend over the past 300 years. This article describes the sources, the chosen merge methodology, and the resulting databank characteristics. Several variants of the databank have also been released that reflect the structural uncertainty in merging datasets. Variants differ in, for example, the order in which sources are considered and the degree of congruence required in station geolocation for consideration as a merged or unique record. Also described is a version control protocol that will be applied in the event of updates. Future updates are envisaged with the addition of new data sources, and with changes in processing, where public feedback is always welcomed. Major updates, when necessary, will always be accompanied by a new journal paper. This databank release forms the foundation for the construction of new global land surface air temperature analyses by the global research community and their assessment by the ISTI's benchmarking and assessment working group
Impact of meteorological parameters on the development of fine and coarse particles over Delhi
No full textMeasurements of ambient particulate matters (viz., PM10 and PM2.5) were made with an hourly sampling frequency at Indian Institute of Tropical Meteorology (IITM), New Delhi Branch (a residential area) during a period from December 2010 to November 2011. The data so generated were analyzed to understand frequency distribution of their concentrations and the impact of meteorological parameters on the distribution of particulate matters on different time scales. It is found that the particulate matters with cut off aerodynamic diameter of 10 μm (PM10) preferentially occurred in the concentration range of 301–350 μg/m3 during winter and post-monsoon, 251–300 μg/m3 during summer and 51–100 μg/m3 during monsoon season. The particulate matters with cut off aerodynamic diameter of 2.5 μm (PM2.5) preferentially occurred in the concentration range of 201–250 μg/m3 during winter and 51–100 μg/m3 during the remaining seasons. The concentration of particulate matters (PM10 and PM2.5) remained always above the National Ambient Air Quality Standards (NAAQS) except during monsoon season. Annual distribution of the concentration of particulate matters showed seasonality with maximum in winter and minimum in monsoon season. Diurnal variation of PM10 and PM2.5 showed bimodal distribution with one maximum in the forenoon and the other at around mid-night. The observed seasonality and diurnal variability in the distribution are attributed mainly to the meteorology
Spectral wave characteristics off Gangavaram, Bay of Bengal
No full textSpectral wave characteristics were studied based on waves measured for 1 year during 2010 off Gangavaram, Bay of Bengal. Maximum wave height of 5.2 m was observed on 19 May 2010 due to the influence of cyclonic storm LAILA. The wave spectrum was single-peaked during 57 of the time and the double-peaked spectrum observed was mainly swell-dominated. Low-frequency waves (0.05-0.15 Hz) were predominantly from 150° to 180°, whereas high-frequency waves (>0.15 Hz) during November-January were mainly from 90° to 120°, and during July and August from 180° to 210°. Annual average significant wave height was similar to the value (1 m) observed in the eastern Arabian Sea
Droughts of Indian summer monsoon associated with El Niño and Non-ElNino years
No full textUnderstanding the conditions of droughts are imperative for many purposes especially in planning and agricultural fields. In this paper an attempt is made to analyse rainfall distribution during droughts associated with El Niño and non-El Niño events using India Meteorological Department (IMD) daily rainfall data set having a spatial resolution of 0.25° latitude × 0.25° longitude grid. Patterns of rainfall during drought years which are not associated with El Niño have below normal rainfall over most places of Indian subcontinent, except peninsular India and eastern region. Most of the drought conditions of the Indian summer monsoon rainfall are associated with El Niño (13 of the 18 years) indicating that about 72% of the drought years are associated with the influence of Pacific Ocean. North India and most of the central Indian regions are under below normal rainfall especially over west coastal stations there the severity of drought is strong. The drought that are associated with El Nino are much intense in most parts of the subcontinent, it severely affected the entire west coastal belts, monsoon zone and eastern regions than the droughts associated with non-El Nino years. The spatial patterns of rainfall during flood years associated with La Niña events and drought years associated with El Niño reveal that the spatial structure of rainfall is highly non-linear. These results are also verified using APHRODITE rainfall data. Over central India and Western Ghats (WGs), the drought associated with El Niño gives clear indication of droughts from the early June onward, however, in the case of non-El Niño-related droughts, the indication of drought can be seen only after the first week of July. The study suggests that droughts associated with El Niño events bring severe drought conditions over WG region. However, over central India, there is no considerable difference in cumulative rainfall associated with the two types of droughts. The intraseasonal properties of rainfall are prominently different from non-El Niño to El Niño droughts. During El Niño droughts, the variance of rainfall in both the central Indian and WG regions is weaker than the droughts that are not associated with El Niñ
Modulation of the diurnal cycle of rainfall over India by intraseasonal variations of Indian summer monsoon
No full textChanges in the amplitude and phase of the diurnal cycle of rainfall due to changes in the background circulation and thermodynamics associated with the intraseasonal variability of Indian summer monsoon have important implications for weather prediction over the region. Hourly rainfall data available at 91 Indian stations for 30years of observations are examined to determine the role of intraseasonal variations of Indian summer monsoon in modulating the diurnal cycle of rainfall over four homogenous regions. Harmonic analysis of the diurnal cycle of rainfall shows predominance of principal harmonic during the break phase of monsoon. During an active phase first two harmonics contribute substantially to the total variance in central parts of the country. It is observed that peak rainfall occurs in the morning hours during both the active and break phases along the West Coast with small diurnal variation in rainfall. Two peaks in the diurnal cycle are observed during active phases over central India. This region shows delay in the occurrence of afternoon peak and rise in rainfall intensity during the break phase of recent years, while, increase in rainfall intensity at all hours during break phases is observed along the West Coast of India in recent years. Further analysis of meteorological parameters indicates that lower-level convergence during late afternoon hours, reduction in geopotential height and increase in specific humidity (850hPa) in central parts of India during morning and evening hours are in phase with the two maxima observed in the diurnal cycle of rainfall in this region. Therefore, spatial variations in daily rainfall pattern during active/break phases can be attributed to orographic effect and heterogeneous convective development in different parts of the country
Lidar profiling of aerosol scavenging parameters at a tropical station, Pune, India
No full textIn this study, we deal with observations of aerosol column content (height integration of vertical distribution of aerosol number density) that have been carried out using an Ar+ lidar for three different measurement cycles (each cycle consisting of three experimental days associated with non-rain, rain, and non-rain, respectively) of weekly spaced observations for pre-monsoon (March/April 1994), monsoon (September 1991), and post-monsoon (October 1998). Based on these observed profiles of aerosol number concentration on rainy days with respect to those on non-rainy days, vertical distributions of scavenging collection efficiencies (SCEs) are computed and discussed in this article. The SCE is found to decrease from 0.3 to 0.01 between the heights, 100 and 800 m for thunderstorm rain in April 1994, and during monsoon, it increases from 0.1 to 0.7. In the October 1998 episode, SCE was found to increase initially from 0.35 to 0.75 for heights between 40 and 200 m and thereafter decrease to 0.35 in the height interval of 200–800 m
Characterization of aerosol optical properties over the high-altitude station Hanle, in the trans-Himalayan region
No full textOptical properties of aerosols over Hanle (4500. m. amsl) in the western Himalayas were studied using skyradiometer observations during October 2007 to December 2010. Yearly mean value of aerosol optical depth (AOD) at 500. nm is 0.042. ±. 0.002, which demonstrates the pristine environment of the station. Seasonal mean AODs at 500. nm during summer, autumn, winter, and spring are 0.044. ±. 0.002, 0.031. ±. 0.001, 0.031. ±. 0.001, and 0.061. ±. 0.002, respectively. The relatively high AOD during spring, associated with an elevated aerosol layer observed from space, supports the hypothesis of middle-upper tropospheric heating during pre-monsoon period. Seasonal mean values of Angstrom exponent (α) estimated from linear regression method varied from minimum 0.65 (spring) to maximum 1.02 (autumn). Dominance of coarse mode aerosols at the site is thus evident during spring. Analysis of AOD profiles obtained from satellite data and airmass back trajectories superimposed with fire-counts data indicated the presence of desert-dust at the altitudes of 5 to 7. km. amsl during the episodes of high AOD and low α. These trajectories indicated airmasses mostly coming from different desert regions, e.g in north-west Asia and Iran in the Middle east. Further, arrival of airmasses from the densely populated and industrialized Punjab and Haryana regions from the north-west of India apparently explains the relative contribution of transported anthropogenic aerosols over the station