scholarly journals Potential impact of carbonaceous aerosols on the Upper Troposphere and Lower Stratosphere (UTLS) during Asian summer monsoon in a global model simulation

2017 ◽  
Author(s):  
Suvarna Fadnavis ◽  
Gayatry Kalita ◽  
K. Ravi Kumar ◽  
Blaz Gasparini ◽  
Jui-Lin Frank Li
Keyword(s):  
Summer Monsoon ◽  
Radiative Forcing ◽  
Asian Summer Monsoon ◽  
Radiative Heating ◽  
The Tibetan Plateau ◽  
Carbonaceous Aerosols ◽  
The South ◽  
Upper Troposphere ◽  
North East ◽  
Asian Summer

Abstract. Recent satellite observations show efficient vertical transport of Asian pollutants from the surface to the upper level anticyclone by deep monsoon convection. In this paper, we examine the transport of carbonaceous aerosols including Black Carbon (BC) and Organic Carbon (OC) into the monsoon anticyclone using of ECHAM6-HAM, a global aerosol climate model. Further, we investigate impacts of enhanced (doubled) carbonaceous aerosols emissions on the UTLS from sensitivity simulations. These model simulations show that boundary layer aerosols are transported into the monsoon anticyclone by the strong monsoon convection from the Bay of Bengal, southern slopes of the Himalayas and the South China Sea. Doubling of emissions of BC and OC aerosols, each, over the South East Asia (10° S–50° N; 65° E–155° E) shows that lofted aerosols produce significant warming in the mid/upper troposphere. These aerosols lead to an increase in temperature by 1 K–3 K in the mid/upper troposphere and in radiative heating rates by 0.005 K/day near the tropopause. They alter aerosol radiative forcing at the surface by −1.4 W/m2; at the Top Of the Atmosphere (TOA) by +1.2 W/m2 and in the atmosphere by 2.7 W/m2 over the Asian summer monsoon region (20° N–40° N, 60° E–120° E). Atmospheric warming increases vertical velocities and thereby cloud ice in the upper troposphere. An anomalous warming over the Tibetan Plateau (TP) facilitate the relative strengthening of the monsoon Hadley circulation and elicit enhancement in precipitation over India and north east China.

scholarly journals Modelling the aerosol chemical composition of the tropopause over the Tibetan Plateau during the Asian summer monsoon

2019 ◽  
Author(s):  
Jianzhong Ma ◽  
Christoph Brühl ◽  
Qianshan He ◽  
Benedikt Steil ◽  
Vlassis A. Karydis ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Lower Stratosphere ◽  
Mineral Dust ◽  
Asian Summer Monsoon ◽  
The Tibetan Plateau ◽  
Aerosol Extinction ◽  
Upper Troposphere ◽  
Asian Summer

Abstract. Enhanced aerosol abundance in the upper troposphere and lower stratosphere (UTLS) associated with the Asian summer monsoon (ASM), is referred to as the Asian Tropopause Aerosol Layer (ATAL). The chemical composition, microphysical properties and climate effects of aerosols in the ATAL have been the subject of discussion over the past decade. In this work, we use the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model at a relatively fine grid resolution (about 1.1 × 1.1 degrees) to numerically simulate the emissions and chemistry of aerosols and their precursors in the UTLS within the ASM anticyclone during the years 2010–2012. We find a pronounced maximum in aerosol extinction in the UTLS over the Tibetan Plateau, which to a large extent is caused by mineral dust emitted from the northern Tibetan Plateau and slope areas, lofted to an altitude of at least 10 km, and accumulating within the anticyclonic circulation. Our simulations show that mineral dust, water soluble compounds, such as nitrate and sulfate, and associated liquid water dominate aerosol extinction in the UTLS within the ASM anticyclone. Due to shielding of high background sulfate concentrations outside the anticyclone from volcanoes, a relative minimum of aerosol extinction within the anticyclone in the lower stratosphere is simulated, being most pronounced in 2011 when the Nabro eruption occurred. In contrast to mineral dust and nitrate concentrations, sulfate increases with increasing altitude due to the larger volcano effects in the lower stratosphere compared to the upper troposphere. Our study indicates that the UTLS over the Tibetan Plateau can act as a well-defined conduit for natural and anthropogenic gases and aerosols into the stratosphere.

scholarly journals Modeling the aerosol chemical composition of the tropopause over the Tibetan Plateau during the Asian summer monsoon

2019 ◽  
Vol 19 (17) ◽  
pp. 11587-11612 ◽  
Author(s):  
Jianzhong Ma ◽  
Christoph Brühl ◽  
Qianshan He ◽  
Benedikt Steil ◽  
Vlassis A. Karydis ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Lower Stratosphere ◽  
Mineral Dust ◽  
Asian Summer Monsoon ◽  
The Tibetan Plateau ◽  
Aerosol Extinction ◽  
Upper Troposphere ◽  
Asian Summer

Abstract. Enhanced aerosol abundance in the upper troposphere and lower stratosphere (UTLS) associated with the Asian summer monsoon (ASM) is referred to as the Asian Tropopause Aerosol Layer (ATAL). The chemical composition, microphysical properties, and climate effects of aerosols in the ATAL have been the subject of discussion over the past decade. In this work, we use the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model at a relatively fine grid resolution (about 1.1×1.1∘) to numerically simulate the emissions, chemistry, and transport of aerosols and their precursors in the UTLS within the ASM anticyclone during the years 2010–2012. We find a pronounced maximum of aerosol extinction in the UTLS over the Tibetan Plateau, which to a large extent is caused by mineral dust emitted from the northern Tibetan Plateau and slope areas, lofted to an altitude of at least 10 km, and accumulating within the anticyclonic circulation. We also find that the emissions and convection of ammonia in the central main body of the Tibetan Plateau make a great contribution to the enhancement of gas-phase NH3 in the UTLS over the Tibetan Plateau and ASM anticyclone region. Our simulations show that mineral dust, water-soluble compounds, such as nitrate and sulfate, and associated liquid water dominate aerosol extinction in the UTLS within the ASM anticyclone. Due to shielding of high background sulfate concentrations outside the anticyclone from volcanoes, a relative minimum of aerosol extinction within the anticyclone in the lower stratosphere is simulated, being most pronounced in 2011, when the Nabro eruption occurred. In contrast to mineral dust and nitrate concentrations, sulfate increases with increasing altitude due to the larger volcano effects in the lower stratosphere compared to the upper troposphere. Our study indicates that the UTLS over the Tibetan Plateau can act as a well-defined conduit for natural and anthropogenic gases and aerosols into the stratosphere.

Long-term trends and transport of surface pollutants to UTLS  during the Asian summer monsoon

2021 ◽  
Author(s):  
William K.M. Lau ◽  
Kyu-Myong Kim
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Linear Trend ◽  
Monsoon Season ◽  
Radiative Heating ◽  
Aerosol Layer ◽  
Near Surface ◽  
Upper Troposphere ◽  
Asian Summer

<p>Using MERRA2 reanalyses, we have examined the long-term (2000-2019) trends and transport of surface pollutants, CO, BC and OC from surface to the upper troposphere and lower stratosphere (UTLS) during the Asian summer monsoon.    We find a strong linear trend indicating an expansion and strengthening of the Asian Monsoon Anticyclone (AMA), in conjunction with increased concentration of CO, BC and OC in the UTLS, including the Aerosol Tropopause Aerosol Layer (ATAL). </p><p>The UTLS trend in CO can be tracked to increased upward transport primarily from surface sources near 25-35<sup>o</sup>N, in association with the expansion/strengthening of the AMA, and a northward displacement of ascending branch of the monsoon meridional circulation.  In contrast, near 25-35<sup>o</sup>N, BC and OC trends show significant reduction from surface to mid-troposphere, coupled a weak increase at UTLS (above 250 -100 hPa).  The reduction in surface and tropospheric BC and OC likely reflects reduced emission due to the clean air acts in East Asia.  Additionally, heavier rainfall associated with the enhanced ascent and wet scavenging may also contribute to the strong reduction in tropospheric BC and OC.  The increase in UTLS OC/BC appears to stem from increased and extended biomass burning near surface sources located in extratropical latitudes (70-130<sup>o</sup> E, 55-70<sup>o</sup> N).  The OC/BC aerosols are transported upward by vertical mixing over the source regions, and enter the tropical UTLS through horizonal diffusive processes.   Additionally, enhanced penetrative convection in the anomalous ascent regions during the peak monsoon season may also play a role in further enhancing the monsoon ascent, lifting ambient hydrophobic OC/BC and water vapor in the mid-to-upper troposphere to higher elevations, resulting in enhanced ice-cloud fraction, increased latent and radiative heating in the UTLS/ATAL region.</p><p> </p>

scholarly journals Characterization of non-methane hydrocarbons in Asian summer monsoon outflow observed by the CARIBIC aircraft

2011 ◽  
Vol 11 (2) ◽  
pp. 503-518 ◽  
Author(s):  
A. K. Baker ◽  
T. J. Schuck ◽  
F. Slemr ◽  
P. van Velthoven ◽  
A. Zahn ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Summer Monsoon ◽  
Fossil Fuels ◽  
Asian Summer Monsoon ◽  
Trace Gases ◽  
Northern Region ◽  
Monsoon Circulation ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Asian Summer

Abstract. Between April and December 2008 the CARIBIC commercial aircraft conducted monthly measurement flights between Frankfurt, Germany and Chennai, India. These flights covered the period of the Asian summer monsoon (June–September), during which enhancements in a number of atmospheric species were observed in the upper troposphere over southwestern Asia. In addition to in situ measurements of trace gases and aerosols, whole air samples were collected during the flights, and these were subsequently analyzed for a suite of trace gases that included a number of C2–C8 non-methane hydrocarbons. Non-methane hydrocarbons are relatively short-lived compounds and the large enhancements in their mixing ratios in the upper troposphere over southwestern Asia during the monsoon, sometimes more than double their spring and fall means, provides qualitative evidence for the influence of convectively uplifted boundary layer air. The particularly large enhancements of the combustion tracers benzene and ethyne, along with the similarity of their ratios with carbon monoxide and emission ratios from the burning of household biofuels, indicate a strong influence of biofuel burning to NMHC emissions in this region. Conversely, the ratios of ethane and propane to carbon monoxide, along with the ratio between i-butane and n-butane, indicate a significant source of these compounds from the use of fossil fuels, and comparison to previous campaigns suggests that this source could be increasing. Photochemical aging patterns of NMHCs showed that the CARIBIC samples were collected in two distinctly different regions of the monsoon circulation: a southern region where air masses had been recently influenced by low level contact and a northern region, where air parcels had spent substantial time in transit in the upper troposphere before being probed. Estimates of age using ratios of individual NMHCs have ranges of 3–6 days in the south and 9–12 days in the north.

scholarly journals Trapping, chemistry and export of trace gases in the South Asian summer monsoon observed during CARIBIC flights in 2008

2015 ◽  
Vol 15 (5) ◽  
pp. 6967-7018 ◽  
Author(s):  
A. Rauthe-Schöch ◽  
A. K. Baker ◽  
T. J. Schuck ◽  
C. A. M. Brenninkmeijer ◽  
A. Zahn ◽  
...  
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Trace Gases ◽  
Particle Dispersion ◽  
Atmospheric Pollutants ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Air Masses ◽  
Asian Summer

Abstract. The CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) passenger aircraft observatory performed in situ measurements at 10–12 km altitude in the South Asian summer monsoon anticyclone between June and September 2008. These measurements enable us to investigate this atmospheric region, which so far has mostly been observed from satellites, using the broad suite of trace gases and aerosols measured by CARIBIC. Elevated levels of a range of atmospheric pollutants were recorded e.g. carbon monoxide, total reactive nitrogen oxides, aerosol particles and several volatile organic compounds. The measurements provide detailed information about the chemical composition of air in different parts of the monsoon anticyclone, particularly of ozone precursors. While covering a range of 3500 km inside the monsoon anticyclone, CARIBIC observations show remarkable consistency, i.e. with regular latitudinal patterns of trace gases during the entire monsoon period. Trajectory calculations indicate that these air masses originated mainly from South Asia and Mainland Southeast Asia. Using the CARIBIC trace gas and aerosol measurements in combination with the Lagrangian particle dispersion model FLEXPART we investigated the characteristics of monsoon outflow and the chemical evolution of air masses during transport. Estimated photochemical ages of the air were found to agree well with transport times from a source region east of 95° E. The photochemical ages of the air in the southern part of the monsoon anticyclone were consistently younger (less than 7 days) and the air masses mostly in an ozone forming chemical regime. In its northern part the air masses were older (up to 13 days) and had unclear ozone formation or destruction potential. Based on analysis of forward trajectories several receptor regions were identified. In addition to predominantly westward transport, we found evidence for efficient transport (within 10 days) to the Pacific and North America, particularly during June and September, and also of cross-tropopause exchange, which was strongest during June and July. Westward transport to Africa and further to the Mediterranean was the main pathway during July.

scholarly journals Distinct responses of Asian summer monsoon to black carbon aerosols and greenhouse gases

2020 ◽  
Author(s):  
Xiaoning Xie ◽  
Gunnar Myhre ◽  
Xiaodong Liu ◽  
Xinzhou Li ◽  
Zhengguo Shi ◽  
...  
Keyword(s):  
Greenhouse Gases ◽  
Black Carbon ◽  
Summer Monsoon ◽  
Radiative Forcing ◽  
Asian Summer Monsoon ◽  
Atmospheric Temperature ◽  
Monsoon Circulation ◽  
Low Level ◽  
Asian Summer ◽  
Upper Level

Abstract. Black carbon (BC) aerosols emitted from natural and anthropogenic sources induce positive radiative forcing and global warming, which in turn significantly affect the Asian summer monsoon (ASM). However, many aspects of the BC effect on ASM remain elusive and largely inconsistent among previous studies, which is strongly dependent on different low-level thermal feedbacks over the Asian continent and the surrounding ocean. This study examines the response of ASM to BC forcing in comparison with the effect of doubled greenhouse gases (GHGs) by analyzing the Precipitation Driver Response Model Intercomparison Project (PDRMIP) simulations under an extreme high BC level (10 times modern global BC emissions or concentrations, labeled by BC × 10) from nine global climate models (GCMs). The results show that although BC and GHGs both enhance the ASM precipitation minus evaporation (P–E) (a 13.6 % increase for BC forcing and 12.1 % for GHGs from the nine-model ensemble, respectively), there exists a much larger uncertainty in changes in ASM P–E induced by BC than by GHGs. The summer P–E is increased by 7.7 % to 15.3 % due to these two forcings over three sub-regions including East Asian, South Asian, and western North Pacific monsoon regions. Further analysis of moisture budget reveals distinct mechanisms controlling the increases in ASM P–E induced by BC and GHGs. The change in ASM P–E by BC is dominated by the dynamic effect due to the enhanced large-scale monsoon circulation, whereas the GHG-induced change is dominated by the thermodynamic effect through increasing atmospheric water vapor. Radiative forcing of BC significantly increases the upper-level atmospheric temperature over the Asian region to enhance the upper-level meridional land-sea thermal gradient (MLOTG), resulting in a northward shift of the upper-level subtropical westerly jet and an enhancement of the low-level monsoon circulation; whereas radiative forcing of GHGs significantly increases the tropical upper-level temperature, which reduces the upper-level MLOTG and suppresses the low-level monsoonal circulation. Hence, our results indicate a different mechanism of BC climate effects under the extreme high BC level, that BC forcing significantly enhances the upper-level atmospheric temperature over the Asian region, determining ASM changes, instead of low-level thermal feedbacks as indicated by previous studies.

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