Interannual variability in the shortwave aerosol direct radiative forcing over the oceanic areas around the Indian subcontinent during dry season

2006 ◽  
Author(s):  
Sandhya K. Nair ◽  
K. Rajeev ◽  
K. Parameswaran
Keyword(s):  
Interannual Variability ◽  
Radiative Forcing ◽  
Indian Subcontinent ◽  
Dry Season ◽  
Direct Radiative Forcing

scholarly journals Snow-darkening versus direct radiative effects of mineral dust aerosol on the Indian summer monsoon onset: role of temperature change over dust sources

2019 ◽  
Vol 19 (3) ◽  
pp. 1605-1622 ◽  
Author(s):  
Zhengguo Shi ◽  
Xiaoning Xie ◽  
Xinzhou Li ◽  
Liu Yang ◽  
Xiaoxun Xie ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Central Asia ◽  
Black Carbon ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Radiative Forcing ◽  
Indian Monsoon ◽  
Indian Subcontinent ◽  
Direct Radiative Forcing

Abstract. Atmospheric absorptive aerosols exert complicated effects on the climate system, two of which are through their direct radiative forcing and snow-darkening forcing. Compared to black carbon, the snow-darkening effect of dust on climate has been scarcely explored till now. When depositing in snow, dust can reduce the albedo of snow by darkening it and increasing the snowmelt. In this study, the snow-darkening effect of dust, as well as the direct radiative effect, on the Indian summer monsoon are evaluated by atmospheric general circulation model experiments. The results show that the snow-darkening and direct radiative forcing of dust both have significant impacts on the onset of the Indian monsoon, but they are distinctly opposite. The snow-darkening effect of dust weakens the Indian monsoon precipitation during May and June, opposite to black carbon. The surface temperature over central Asia and the western Tibetan Plateau becomes warmer due to the dust-induced decrease in snow cover, which leads to a local low-level cyclonic anomaly as well as an anticyclonic anomaly over the Indian subcontinent and Arabian Sea. This circulation pattern allows air currents penetrating into the Indian subcontinent more from central Asia but less from the Indian Ocean. In contrast, the direct radiative forcing of dust warms the low troposphere over the Arabian Peninsula, which intensifies moisture convergence and precipitation over the Indian monsoon region. The upper tropospheric atmospheric circulation over Asia is also sensitive to both effects. Compared to previous studies which emphasized the temperature over the Tibetan Plateau, our results further highlight an important role of surface/low tropospheric temperature changes over dust source areas, which can also significantly modify the response of summer monsoon. Thus, links between the climatic impact of dust and complicated thermal conditions over Asia are of importance and need to be clarified accurately.

scholarly journals Anthropogenic aerosol radiative forcing in Asia derived from regional models with atmospheric and aerosol data assimilation

2010 ◽  
Vol 10 (13) ◽  
pp. 6007-6024 ◽  
Author(s):  
C. E. Chung ◽  
V. Ramanathan ◽  
G. Carmichael ◽  
S. Kulkarni ◽  
Y. Tang ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Radiative Forcing ◽  
Dry Season ◽  
Heating Rates ◽  
Wet Season ◽  
Aerosol Chemistry ◽  
Anthropogenic Aerosol ◽  
Anthropogenic Forcing ◽  
Aerosol Radiative Forcing ◽  
Aerosol Forcing

Abstract. An estimate of monthly 3-D aerosol solar heating rates and surface solar fluxes in Asia from 2001 to 2004 is described here. This product stems from an Asian aerosol assimilation project, in which a) the PNNL regional model bounded by the NCEP reanalyses was used to provide meteorology, b) MODIS and AERONET data were integrated for aerosol observations, c) the Iowa aerosol/chemistry model STEM-2K1 used the PNNL meteorology and assimilated aerosol observations, and d) 3-D (X-Y-Z) aerosol simulations from the STEM-2K1 were used in the Scripps Monte-Carlo Aerosol Cloud Radiation (MACR) model to produce total and anthropogenic aerosol direct solar forcing for average cloudy skies. The MACR model and STEM-2K1 both used the PNNL model resolution of 0.45°×0.4° in the horizontal and of 23 layers in the troposphere. The 2001–2004 averaged anthropogenic all-sky aerosol forcing is −1.3 Wm−2 (TOA), +7.3 Wm−2 (atmosphere) and −8.6 Wm−2 (surface) averaged in Asia (60–138° E and Equator–45° N). In the absence of AERONET SSA assimilation, absorbing aerosol concentration (especially BC aerosol) is much smaller, giving −2.3 Wm−2 (TOA), +4.5 Wm−2 (atmosphere) and −6.8 Wm−2 (surface), averaged in Asia. In the vertical, monthly forcing is mainly concentrated below 600 hPa with maximum around 800 hPa. Seasonally, low-level forcing is far larger in dry season than in wet season in South Asia, whereas the wet season forcing exceeds the dry season forcing in East Asia. The anthropogenic forcing in the present study is similar to that in Chung et al. (2005) in overall magnitude but the former offers fine-scale features and simulated vertical profiles. The interannual variability of the computed anthropogenic forcing is significant and extremely large over major emission outflow areas. Given the interannual variability, the present study's estimate is within the implicated range of the 1999 INDOEX result.

scholarly journals Anthropogenic aerosol radiative forcing in Asia derived from regional models with atmospheric and aerosol data assimilation

2010 ◽  
Vol 10 (1) ◽  
pp. 821-862 ◽  
Author(s):  
C. E. Chung ◽  
V. Ramanathan ◽  
G. Carmichael ◽  
S. Kulkarni ◽  
Y. Tang ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Radiative Forcing ◽  
Dry Season ◽  
Heating Rates ◽  
Wet Season ◽  
Aerosol Chemistry ◽  
Anthropogenic Aerosol ◽  
Anthropogenic Forcing ◽  
Aerosol Radiative Forcing ◽  
Aerosol Forcing

Abstract. A high-resolution estimate of monthly 3-D aerosol solar heating rates and surface solar fluxes in Asia from 2001 to 2004 is described here. This product stems from an Asian aerosol assimilation project, in which a) the PNNL regional model bounded by the NCEP reanalyses was used to provide meteorology, b) MODIS and AERONET data were integrated for aerosol observations, c) the Iowa aerosol/chemistry model STEM-2K1 used the PNNL meteorology and assimilated aerosol observations, and d) 3-D (X-Y-Z) aerosol simulations from the STEM-2K1 were used in the Scripps Monte-Carlo Aerosol Cloud Radiation (MACR) model to produce total and anthropogenic aerosol direct solar forcing for average cloudy skies. The MACR model and STEM both used the PNNL model resolution of 0.45°×0.4° in the horizontal and of 23 layers in the troposphere. The 2001–2004 averaged anthropogenic all-sky aerosol forcing is -1.3 W m-2 (TOA), +7.3 W m-2 (atmosphere) and -8.6 W m-2 (surface) averaged in Asia (60–138° E and Eq. -45° N). In the absence of AERONET SSA assimilation, absorbing aerosol concentration (especially BC aerosol) is much smaller, giving -2.3 W m-2 (TOA), +4.5 W m-2 (atmosphere) and -6.8 W mm-2 (surface), averaged in Asia. In the vertical, monthly forcing is mainly concentrated below 600 hPa with maxima around 800 hPa. Seasonally, low-level forcing is far larger in dry season than in wet season in South Asia, whereas the wet season forcing exceeds the dry season forcing in East Asia. The anthropogenic forcing in the present study is similar to that in Chung et al. (2005) in overall magnitude but the former offers fine-scale features and simulated vertical profiles. The interannual variability of the computed anthropogenic forcing is significant and extremely large over major emission outflow areas. Given the interannual variability, the present study's estimate is within the implicated range of the 1999 INDOEX result. However, NCAR/CCSM3's anthropogenic aerosol forcing is much smaller than the present study's estimate at the surface, and is outside of what the INDOEX findings can support.

scholarly journals Snow-darkening versus direct radiative effects of mineral dust aerosol on the Indian summer monsoon: role of the Tibetan Plateau

2018 ◽  
Author(s):  
Zhengguo Shi ◽  
Xiaoning Xie ◽  
Xinzhou Li ◽  
Liu Yang ◽  
Xiaoxun Xie ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Central Asia ◽  
Snow Cover ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Radiative Forcing ◽  
Indian Monsoon ◽  
Indian Subcontinent ◽  
Direct Radiative Forcing

Abstract. Mineral dust aerosol exerts complicated effects on the climate system and two of which are through their direct radiative forcing and snow-darkening forcing. Especially, the snow-darkening effect of dust on climate have been scarcely explored till now. When depositing in snow, dust can reduce the albedo of snow by darkening it and increase the snow melt. In this study, the snow-darkening effect of dust, as well as the direct radiative effect, on the Indian summer monsoon are evaluated by atmospheric general circulation model experiments, with a special focus on the role of Tibetan Plateau. The results show that, the snow-darkening and direct radiative forcing of dust have both significant impacts on the onset of Indian monsoon but they are distinctly opposite. The snow-darkening effect weakens the Indian monsoon precipitation during May and June while the direct radiative forcing intensifies it. The surface temperature over western Tibetan Plateau and Central Asia becomes warmer due to the dust-induced decrease in snow cover, which leads to a local low-level cyclonic anomaly as well as an anticyclonic anomaly over Indian subcontinent and Arabian Sea. This circulation pattern allows air current penetrating into Indian subcontinent more from Central Asia but less from Indian Ocean. In contrast, the direct radiative forcing of dust cools Tibetan Plateau and adjacent areas but warms Arabian Peninsular, which intensifies the moisture convergence and upward motion over Indian monsoon region. The upper tropospheric atmospheric circulation over Asia is also sensitive to both effects. Our results highlight a potential role of snow-albedo feedback in the effects of dust, which significantly amplifies the response of temperature over Tibetan Plateau. Thus, links between the climatic impact of dust, Tibetan Plateau thermal condition and surface snow cover are of importance and require to be clarified accurately.

scholarly journals Estimates of direct radiative forcing due to aerosols from the MERRA-2 reanalysis over the Amazon region

2018 ◽  
Author(s):  
Brunna Penna ◽  
Dirceu Herdies ◽  
Simone Costa
Keyword(s):  
Radiative Forcing ◽  
Reanalysis Data ◽  
Amazon Region ◽  
Reference State ◽  
Aerosol Radiative Forcing ◽  
Aerosol Loading ◽  
Direct Radiative Forcing ◽  
Direct Forcing ◽  
The Difference ◽  
Natural Aerosols

Abstract. Sixteen years of analysis of clear-sky direct aerosol radiative forcing is presented for the Amazon region, with calculations of AERONET network, MODIS sensor and MERRA-2 reanalysis data. The results showed that MERRA-2 reanalysis is an excellent tool for calculating and providing the spatial distribution of aerosol direct radiative forcing. In addition, the difference between considering the reference state of the atmosphere without aerosol loading and with natural aerosol to obtain the aerosol direct radiative forcing is discussed. During the dry season, the monthly average direct forcing at the top of atmosphere varied from −9.60 to −4.20 Wm−2, and at the surface, it varied from −29.81 to −9.24 Wm−2, according to MERRA-2 reanalysis data and the reference state of atmosphere without aerosol loading. Already with the state of reference being the natural aerosols, the average direct forcing at the top of atmosphere varied from −5.15 to −1.18 Wm−2, and at the surface, it varied from −21.28 to −5.25 Wm−2; this difference was associated with the absorption of aerosols.

scholarly journals Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming

2007 ◽  
Vol 20 (8) ◽  
pp. 1445-1467 ◽  
Author(s):  
Masaru Yoshioka ◽  
Natalie M. Mahowald ◽  
Andrew J. Conley ◽  
William D. Collins ◽  
David W. Fillmore ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Africa ◽  
Radiative Forcing ◽  
Sea Surface ◽  
Desert Dust ◽  
Direct Radiative Forcing ◽  
Sahel Region ◽  
Precipitation Reduction ◽  
Sahel Precipitation

Abstract The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.

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