The assessment of aerosol optical properties over Mohal in the northwestern Indian Himalayas using satellite and ground-based measurements and an influence of aerosol transport on aerosol radiative forcing (original) (raw)
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Meteorology and …, 2011
The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.98N, 77.128E) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500 nm, Å ngström exponent and turbidity coefficient are 0.24 ± 0.08, 1.02 ± 0.34 and 0.13 ± 0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550 nm over Mohal within the expected accuracy (Ds pk = ±0.05 ± 0.15s pk ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surfacereaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72 K day -1 , respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.
Atmospheric Research, 2011
The present study deals with the aerosol optical property which carried out during April 2006 to March 2007 in the northwestern Indian Himalaya. The study was conducted using ground based Multi-wavelength Radiometer (MWR) and Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. The daily average aerosol optical depth (AOD) at 500 nm was found to be (mean ± standard deviation) 0.24 ± 0.10. The afternoon AOD values have been noticed to be higher than the forenoon AOD values. Spectral AOD values exhibited larger day-to-day variation in finer aerosols during the observation period. The daily average value of Ångström exponent 'α' and turbidity coefficient 'β' obtained was 1.10± 0.38 and 0.12 ± 0.08 respectively. Higher value of AOD~0.39± 0.06 during summer associated with low α 0.73± 0.28 has attributed to the increase in the relative dominance of coarse size particles. In winter α~1.21± 0.32 indicating a considerable increase in fine size particles, attributed to the anthropogenic activities. The AOD spectra seem to be more wavelength dependent in winter as compared to summer. Comparison of MWR observation with MODIS observation indicates a good conformity between ground-based and satellite derived AOD. The root mean square deviation (RMSD), mean absolute bias deviation (MABD) and correlation coefficient have been found to bẽ 0.08,~0.06 and~0.77 respectively. These results suggest that the AOD retrieval through satellite can be able to characterize AOD distribution over Mohal. However, further efforts to eliminate systematic errors in the existing MODIS products are needed. During the observation period~30%, 47% and~62% air parcels drawn at 4000, 5500 and 8000 m above ground level respectively reached at Mohal which passed through or originated from The Great Sahara. The maximum AOD at 500 nm occurred on 8 May 2006. This has caused a significant reduction in surface reaching solar irradiance by~59 Wm −2 . The back trajectory analysis suggested that the highest AOD during summer is due to high degree of human interference in the form of tourism and dust transport from the country lying in the northwestern part of India.
Journal of Atmospheric …, 2012
a b s t r a c t The measurements of atmospheric aerosols, the major agents of climate forcing and respiratory problems carried out by Multi-wavelength Radiometer (MWR) at Mohal (31154 0 N, 77107 0 E, 1154 m amsl) in Kullu valley of the the Northwestern Himalayan region from April 2006 to March 2009 show that the values of the spectral aerosol optical depth (AOD) and turbidity parameter 'b' (an indicator of aerosol mass) are high in summer slightly less in monsoon, low in winter and lowest in autumn season, whereas theÅngström exponent 'a' (an indicator of relative abundance of fine to coarse particles) has an opposite trend. Average annual value of AOD at 500 nm is 0.24 7 0.01, 0.467 0.01 and 0.27 70.01 that of 'b' is 0.13 7 0.01, 0.22 7 0.02 and 0.167 0.01, while that of 'a' is 1.047 0.05, 1.16 7 0.05 and 0.81 70.06, respectively, for clear, hazy and partially clear sky days. The larger value of
Atmósfera, 2012
Las observaciones de un radiómetro de longitud de onda múltiple (MWR, por sus siglas en inglés) ubicado en tierra en el valle Kullu en la región noroccidental del Himalaya, de abril de 2007 a marzo de 2008, muestran que la profundidad óptica espectral del aerosol (AOD, por sus siglas en inglés) y el coeficiente Ångstr?m de turbidez (β) son altos durante la estación del monzón, ligeramente menores en el verano, bajos en invierno y los más bajos en otoño, para días claros, neblinosos y parcialmente claros, mientras que el exponente Ångstr?m de longitud de onda (α) tiene una tendencia opuesta. Los valores promedio anuales de AOD a 5000 nm son 0.25 ± 0.01, 0.46 ± 0.02 y 0.28 ± 0.02, para días de cielos claros, nebulosos y parcialmente claros, respectivamente. Los valores correspondientes para β son 0.13 ± 0.01, 0.22 ± 0.01 y 0.15 ± 0.01 y los de α 1.09 ± 0.04, 1.18 ± 0.03 y 0.89 ± 0.05. La α es ligeramente mayor pero la β es considerablemente más alta en los días nebulosos que en los claros, indicando que la niebla montañosa es rica en partículas gruesas. Hay una buena concordancia entre los valores MWR y los AOD satelitales de MODIS, con coeficientes de correlación anuales de 0.89, 0.70 y 0.81 para días claros, nebulosos y parcialmente claros, respectivamente. La correlación entre AOD a 500 nm y el coeficiente β con la temperatura, velocidad del viento y humedad es significativamente positivo, mientras que el del exponente α es negativo para la mayoría de los días, lo que sugiere alto AOD y turbidez pero baja concentración de partículas finas en días calientes, húmedos y con viento y viceversa. Asimismo, la correlación entre AOD a 500 nm y el coeficiente β con la dirección del viento es la mayoría de las veces negativa, mientras que la del exponente α es positiva, indicando que AOD y la turbidez disminuyen pero la concentración de partículas finas aumenta al cambiar la dirección del viento más hacia el sur de nuestro sitio. Así, durante el periodo analizado, los vientos que se dirigen hacia nuestro sitio desde las planicies indogangéticas son ricos en partículas gruesas, mientras que los vientos de la dirección sur o del desierto Thar transportan principalmente partículas finas. 200 N. L. Sharma et al.
Atmospheric Research, 2014
Optical 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 desertdust 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 northwest Asia and Iran in the Middle east. Further, arrival of airmasses from the densely populated and industrialized Punjab and Haryana regions from the northwest of India apparently explains the relative contribution of transported anthropogenic aerosols over the station.
Study of Aerosol Optical Properties Over Two Sites in the Foothills of the Central Himalayas
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Atmospheric aerosol possesses impacts on climate system and ecological environments, human health and agricultural productivity. The environment over Himalayas and Tibetan Plateau region are continuously degraded due to the transport of pollution from the foothills of the Himalayas; mostly the Indo-Gangetic Plain (IGP). Thus, analysis of aerosol optical properties over two sites; Lumbini and Kathmandu (the southern slope of central Himalayas) using AERONET’s CIMEL sun photometer were conducted in this study. Aerosol optical depth (AOD at 500 nm), angstrom exponent (α or AE), volume size distribution (VSD), single scattering albedo (SSA) and asymmetry parameter (AP) were studied for 2013–2014 and the average AOD was found to be: 0.64 ± 0.41 (Lumbini) and 0.45 ± 0.30 (Kathmandu). The average AE was found to be: 1.25 ± 0.24 and 1.26 ± 0.18 respectively for two sites. The relation between AO...
PLoS ONE, 2012
Background: The loading of atmospheric particulate matter (aerosol) in the eastern Himalaya is mainly regulated by the locally generated anthropogenic aerosols from the biomass burning and by the aerosols transported from the distance sources. These different types of aerosol loading not only affect the aerosol chemistry but also produce consequent signature on the radiative properties of aerosol. Methodology/Principal Findings: An extensive study has been made to study the seasonal variations in aerosol components of fine and coarse mode aerosols and black carbon along with the simultaneous measurements of aerosol optical depth on clear sky days over Darjeeling, a high altitude station (2200 masl) at eastern Himalayas during the year 2008. We observed a heavy loading of fine mode dust component (Ca 2+) during pre-monsoon (Apr-May) which was higher by 162% than its annual mean whereas during winter (Dec-Feb), the loading of anthropogenic aerosol components mainly from biomass burning (fine mode SO 4 22 and black carbon) were higher (76% for black carbon and 96% for fine mode SO 4 22) from their annual means. These high increases in dust aerosols during pre-monsoon and anthropogenic aerosols during winter enhanced the aerosol optical depth by 25 and 40%, respectively. We observed that for every 1% increase in anthropogenic aerosols, AOD increased by 0.55% during winter whereas for every 1% increase in dust aerosols, AOD increased by 0.46% during pre-monsoon. Conclusion/Significance: The natural dust transport process (during pre-monsoon) plays as important a role in the radiation effects as the anthropogenic biomass burning (during winter) and their differential effects (rate of increase of the AOD with that of the aerosol concentration) are also very similar. This should be taken into account in proper modeling of the atmospheric environment over eastern Himalayas.
Acta Geophysica, 2011
The measurements using a ground based multi wavelength radiometer (MWR) at Mohal (31°54′N, 77°07′E, 1154 m AMSL) in the Kullu valley of Northwestern Himalayan region show that the spectral aerosol optical depth (AOD) and turbidity coefficient, β, are high in summer, moderate in monsoon season, low in winter and lowest in autumn, while wavelength exponent, α, has an opposite trend. Average annual value of AOD at 500 nm is 0.24±0.01, 0.43±0.02, and 0.28±0.02; that of β is 0.14±0.01, 0.22±0.02, and 0.17±0.03; and that of α is 1.06±0.09, 1.16±0.10, and 0.86±0.13, respectively, for clear, hazy and partially clear sky days. The considerably greater value of β on hazy days indicates more coarse particles in mountain haze. The fractional asymmetry factor (AF) is more negative in summer and autumn months. The AOD and β have significantly positive correlation with temperature and wind speed, suggesting high AODs and turbidity on hot and windy days.
Atmospheric Chemistry and Physics, 2010
Aerosol optical properties have been analyzed through the ground-based Aerosol Robotic Network (AERONET) over the mega city Karachi during August 2006-July 2007. The aerosol optical depth (AOD) is strongly dependent on wavelength; for shorter wavelengths AOD values are higher than at longer wavelengths. The results reveal that the monthly average AOD at 500 nm ranges from 0.31 to 0.92 with an annual mean of 0.48± 0.18 and monthly averaged angstrom exponent (Alpha) ranges from 0.17 to 1.05 with an annual mean of 0.49± 0.31. The maximum monthly average AOD value of 0.92± 0.28 with the corresponding Alpha value of 0.21± 0.11 is found for July 2007, while the minimum monthly average AOD value of 0.31 ± 0.11 with the corresponding Alpha value of 0.53± 0.13 is recorded for March 2007. The volume size distribution in the coarse mode is higher in summer and lower in winter, whereas in the accumulation mode the volume size distribution is higher in winter than in other seasons due to the hygroscopic growth of aerosol particles. The single scattering albedo (SSA) during spring, autumn and summer seasons shows a slight increase with the wavelength and ranges from 0.88± 0.02 to 0.97± 0.01. The asymmetry parameter (ASY) is also wavelength dependent and varies from 0.61± 0.03 to 0.74± 0.02 during the year. The aerosol radiative forcing (ARF) for the whole observation period at the top of the atmosphere (TOA) is in the range of −7 to −35 Wm −2 (average −22± 6 Wm −2 ), at the surface from −56 to −96 Wm −2 (average −73± 12 Wm −2 ), increasing the atmospheric forcing from +38 to +61 Wm −2 (average +51± 13 Wm −2 ). The SBDART-AERONET radiative forcing at the surface and TOA agree with correlation of 0.92 and 0.82, respectively.
Journal of earth system …, 2012
Aerosol parameters are measured using a ground-based Multi-wavelength Radiometer (MWR) at Mohal (31.90 • N, 77.11 • E, 1154 m amsl) in the Kullu valley during clear sky days of a seasonal year. The study shows that the values of spectral aerosol optical depths (AODs) at 500 nm and theÅngstrom turbidity coefficient 'β' (a measure of columnar loading in atmosphere) are high (0.41 ± 0.03, 0.27 ± 0.01) in summer, moderate (0.30 ± 0.03, 0.15 ± 0.03) in monsoon, low (0.19 ± 0.02, 0.08 ± 0.01) in winter and lowest (0.18 ± 0.01, 0.07 ± 0.01) in autumn, respectively. TheÅngstrom wavelength exponent 'α' (indicator of the fraction of accumulation-mode particles to coarse-mode particles) has an opposite trend having lowest value (0.64 ± 0.06) in summer, low (0.99 ± 0.10) in monsoon, moderate (1.20 ± 0.15) in winter and highest value (1.52 ± 0.03) in autumn. The annual mean value of AOD at 500 nm, 'α' and 'β' are 0.24 ± 0.01, 1.06 ± 0.09 and 0.14 ± 0.01, respectively. The fractional asymmetry factor is more negative in summer due to enhanced tourists' arrival and also in autumn months due to the monthlong International Kullu Dussehra fair. The AOD values given by MWR and satellite-based moderate resolution imaging spectro-radiometer have good correlation of 0.76, 0.92 and 0.97 on diurnal, monthly and seasonal basis, respectively. The AODs at 500 nm as well as 'β' are found to be highly correlated, while 'α' is found to be strongly anti-correlated with temperature and wind speed suggesting high AODs and turbidity but low concentration of fine particles during hot and windy days. With wind direction, the AOD and 'β' are found to be strongly anti-correlated, while 'α' is strongly correlated.