Aerosol optical and radiative properties during summer and winter seasons over Lahore and Karachi

Alam, Khan; Trautmann, Thomas; Blaschke, Thomas; Hussain, M.

doi:10.1016/j.atmosenv.2011.12.027

Cited by 162 publications

(118 citation statements)

References 50 publications

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“…Values at the SURF show a good general agreement, with a high correlation coefficient of 0.97. This value is similar to those obtained by Alam et al (2012) for Lahore and Karachi using SBDART model (0.99 and 0.98, respectively), and notably higher than those obtained by Bibi et al (2017) over Karachi (0.51), Lahore (0.81), Jaipur (0.66) and Kanpur (0.69). This good correlation between AERONET and libRadtran surface forcing demonstrates that the input parameters, particularly the atmospheric profiles, constitute an appropriate representation of the prevailing atmospheric conditions in our location of study.…”

Section: Aerosol Radiative Forcingsupporting

confidence: 86%

“…This wavelength dependence is more intense in winter than during the other seasons of the year, with mean values of 0.88 ± 0.08 at 440 nm and 0.80 ± 0.14 at 1020 nm. This dependence is also reported for Lahore and Karachi by Alam et al (2012), Delhi by Singh et al (2010), and four locations in the Indo-Gangetic plains by Bibi et al (2016), but only during winter, when dust is not a major contributor to the aerosol load.…”

Section: Spectral Variation Of Aod Ssa and Asysupporting

confidence: 71%

“…These values are in line with the value of 0.11 K day -1 obtained by Valenzuela et al (2017) for the same location (Évora) during one specific day. The heating rate in Évora is generally lower than values reported for stations with high atmospheric absorption such as, for example, two polluted mega-cities in Pakistan, with values higher than 1 K day -1 (Alam et al, 2012). It is also lower than the values obtained for two desert dust events analyzed by Gharibzadeh et al (2017), which showed mean values of 2.16 and 0.89 K day -1 .…”

Section: Heating Ratecontrasting

confidence: 60%

See 2 more Smart Citations

Thirteen Years of Aerosol Radiative Forcing in Southwestern Iberian Peninsula

Muñoz

Costa

Silva

et al. 2017

Aerosol Air Qual. Res.

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Notable uncertainties in the aerosol impact on the Earth's radiative budget still remain, mainly at local scales. This study aims to accurately quantify the shortwave aerosol radiative forcing (ARF) and its efficiency (ARFE) at Évora (Portugal, Southwestern Europe). This is an interesting region affected by different aerosol types and sources. Towards this goal, ARF and ARFE are calculated for Évora during thirteen years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015), which is the longest period ever analyzed for this region. For this calculation, the most updated AERONET data have been used to simulate irradiance with the libRadtran code. Thus, 1676 daily values were analyzed, obtaining a mean ARF of -7.4 W m -2 at the Earth's surface (SURF) and -1.1 W m -2 at the top of the atmosphere (TOA), indicating a cooling of the Earth-atmosphere system. The difference in ARF between TOA and SURF indicates a mean net gain of 6.3 W m -2 for the atmosphere. While no ARF seasonal pattern is observed at the TOA, a clear seasonal cycle is detected at the SURF with the most negative values occurring in summer. On the other hand, ARFE shows mean values of -62.7 W m -2 τ -1 at the SURF and -14.3 W m -2 τ -1 at the TOA. Results show that ARFE highly depends on the aerosol single scattering albedo, showing opposite behavior at the SURF and at the TOA. The large temporal variability detected in the aerosol properties in the region of study confirms the general need for long time series of measurements to achieve an accurate estimation of the ARF and ARFE.

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Section: Aerosol Radiative Forcingsupporting

confidence: 86%

Section: Spectral Variation Of Aod Ssa and Asysupporting

confidence: 71%

Section: Heating Ratecontrasting

confidence: 60%

See 1 more Smart Citation

Thirteen Years of Aerosol Radiative Forcing in Southwestern Iberian Peninsula

Muñoz

Costa

Silva

et al. 2017

Aerosol Air Qual. Res.

View full text Add to dashboard Cite

show abstract

“…Autumn marks a spot of high AOD values and spring shows a similar spatial distribution with little difference in extent. The similar seasonal variations were studied by Balakrishnaiah et al (2012) in India and Alam et al (2010Alam et al ( , 2012Alam et al ( , 2014Alam et al ( , 2015 in Pakistan. They found low AOD values in summer and high AOD values in winter season.…”

Section: Seasonal Variations In Aerosol Optical Depth (Aod)supporting

confidence: 65%

“…Most of the air masses reached Sindh from the Dasht (Iran), Hamoun Wetlands (Afghanistan), Cholistan (Pakistan), Thar (India) deserts, and also from the Arabian Sea. Alam et al (2012) found high <Alpha> values in January and low values in June that indicates the dominance of fine particles in January and coarse particles in June over urban areas of Pakistan. June is one of the months of dust storms in the region.…”

Section: Relationship Between Aod and åNgström Exponentmentioning

confidence: 94%

Spatio-Temporal Distribution of Aerosol and Cloud Properties over Sindh Using MODIS Satellite Data and a HYSPLIT Model

Sharif

Alam

Afsar

2015

Aerosol Air Qual. Res.

Self Cite

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In this study, aerosols spatial, seasonal and temporal variations over Sindh, Pakistan were analyzed which can lead to variations in the microphysics of clouds as well. All cloud optical properties were analyzed using Moderate Resolution Imaging Spectroradiometer (MODIS) data for 12 years from 2001 to 2013. We also monitored origin and movements of air masses that bring aerosol particles and may be considered as the natural source of aerosol particles in the region. For this purpose, the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to make trajectories of these air masses from their sources. Aerosol optical depth (AOD) high values were observed in summer during the monsoon period (June-August). The highest AOD values in July were recorded ranges from 0.41 to 1.46. In addition, low AOD values were found in winter season (December-February) particularly in December, ranges from 0.16 to 0.69. We then analyzed the relationship between AOD and Ångström exponent that is a good indicator of the size of an aerosol particle. We further described the relationships of AOD and four cloud parameters, namely water vapor (WV), cloud fraction (CF), cloud top temperature (CTT) and cloud top pressure (CTP) by producing regional correlation maps of their data values. The analyses showed negative correlation between AOD and Ångström exponent especially in central and western Sindh. The correlation between AOD and WV was throughout positive with high correlation values > 0.74 in whole Sindh except eastern most arid strip of the Thar Desert in the region. The correlation between AOD and CF was positive in southern Sindh and goes to negative in northern Sindh. AOD showed a positive correlation with CTP and CTT in northern Sindh and a negative correlation in southern Sindh. All these correlations were observed to be dependent on the meteorological conditions for all of the ten sites investigated.

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Quantifying the respective roles of aerosols and clouds in the strong brightening since the early 2000s over the Iberian Peninsula

et al. 2014

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The contribution of clouds and aerosols to the decadal variations of downward surface shortwave radiation (SSR) is a current controversial topic. This study proposes a method, which is based on surface-based SSR measurements, aerosol observations, and radiative transfer simulations (in cloud-free and cloud-and aerosol-free scenarios), to evaluate cloud-aerosol (CARE), cloud (CRE), and aerosol (ARE) radiative effects. This method is applied to quantify the role played by, separately, clouds and aerosols on the intense brightening of the SSR observed in the Iberian Peninsula. Clouds and Earth's Radiation Energy Budget System (CERES) and surface-based data exhibit an increase in SSR between 2003 and 2012, exceeding +10 W m À2 over this period for some areas of the peninsula. The calculations are performed for three surface-based sites: Barcelona and Valladolid (Spain), and Évora (Portugal). Ranges in monthly values of CARE, CRE, and ARE are (À80, À20), (À60, À20), and (À30, 0), respectively (in W m À2 ). The average trends for the analyzed period of CARE, CRE, and ARE are +7, +5, and +2 W m À2 per decade, respectively. Overall, three fourths of the SSR trend is explained by clouds, while the other one fourth is related to aerosol changes. The SSR trends explained by the clouds and aerosol radiative effects are in line with the observed reductions in total cloud cover and aerosol load (both at the surface and in the whole atmospheric column). Furthermore, the CRE values are compared against CERES data showing good agreement between both data series, although some discrepancies are observed in their trends.

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Aerosol optical and radiative properties during summer and winter seasons over Lahore and Karachi

Cited by 162 publications

References 50 publications

Thirteen Years of Aerosol Radiative Forcing in Southwestern Iberian Peninsula

Thirteen Years of Aerosol Radiative Forcing in Southwestern Iberian Peninsula

Spatio-Temporal Distribution of Aerosol and Cloud Properties over Sindh Using MODIS Satellite Data and a HYSPLIT Model

Quantifying the respective roles of aerosols and clouds in the strong brightening since the early 2000s over the Iberian Peninsula

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