Transport of trace gases via eddy shedding from the Asian summer monsoon anticyclone and associated impacts on ozone heating rates

Roy, Chaitri; Chattopadhyay, Rajib; Sioris, Christopher E.; Rap, A.; Müller, Rolf; Kumar, K. Ravi; Krishnan, R.

doi:10.5194/acp-18-11493-2018

Cited by 31 publications

(35 citation statements)

References 47 publications

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“…The close correspondence between the monsoon air mass tracers and the "wet" phase of the water vapour tape recorder in the tropics is consistent with the idea that the ASM and NASM contribute to moistening the tropical lower stratosphere during boreal summer (e.g. Dethof et al, 1999;Bannister et al, 2004;Fu et al, 2006;James et al, 2008;Randel et al, 2012). Note that large concentrations of monsoon tracers in the tropics do not always correlate with large water vapour mixing ratios in the tropical UTLS, as water vapour content at these altitudes depends not only on the origin of the air parcel but also on its temperature history (Fueglistaler and Haynes, 2005;Nützel et al, 2019).…”

Section: Two Distinct Transport Pathwayssupporting

confidence: 80%

The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

Yan¹,

Konopka²,

Ploeger³

et al. 2019

Atmos. Chem. Phys.

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Abstract. Transport of pollutants into the stratosphere via the Asian summer monsoon (ASM) or North American summer monsoon (NASM) may affect the atmospheric composition and climate both locally and globally. We identify and study the robust characteristics of transport from the ASM and NASM regions to the stratosphere using the Lagrangian chemistry transport model CLaMS driven by both the ERA-Interim and MERRA-2 reanalyses. In particular, we quantify the relative influences of the ASM and NASM on stratospheric composition and investigate the transport pathways and efficiencies of transport of air masses originating at different altitudes in these two monsoon regions to the stratosphere. We release artificial tracers in several vertical layers from the middle troposphere to the lower stratosphere in both ASM and NASM source regions during July and August 2010–2013 and track their evolution until the following summer. We find that more air mass is transported from the ASM and NASM regions to the tropical stratosphere, and even to the southern hemispheric stratosphere, when the tracers are released clearly below the tropopause (350–360 K) than when they are released close to the tropopause (370–380 K). For tracers released close to the tropopause (370–380 K), transport is primarily into the northern hemispheric lower stratosphere. Results for different vertical layers of air origin reveal two transport pathways from the upper troposphere over the ASM and NASM regions to the tropical pipe: (i) quasi-horizontal transport to the tropics below the tropopause followed by ascent to the stratosphere via tropical upwelling, and (ii) ascent into the stratosphere inside the ASM/NASM followed by quasi-horizontal transport to the tropical lower stratosphere and further to the tropical pipe. Overall, the tropical pathway (i) is faster than the monsoon pathway (ii), particularly in the ascending branch. The abundance of air in the tropical pipe that originates in the ASM upper troposphere (350–360 K) is comparable to the abundance of air ascending directly from the tropics to the tropical pipe 10 months after (the following early summer) the release of the source tracers. The air mass contributions from the ASM to the tropical pipe are about 3 times larger than the corresponding contributions from the NASM. The transport efficiency into the tropical pipe, the air mass fraction inside this destination region normalized by the mass of the domain of origin, is greatest from the ASM region at 370–380 K. Although the contribution from the NASM to the stratosphere is less than that from either the ASM or the tropics, the transport efficiency from the NASM is comparable to that from the tropics.

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Section: Two Distinct Transport Pathwayssupporting

confidence: 80%

The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

Yan¹,

Konopka²,

Ploeger³

et al. 2019

Atmos. Chem. Phys.

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“…This layer may be due to the transport of Indian sulfate aerosols to the Arctic by the lower branch of the Brewer-Dobson circulation -the AOD in the UTLS is 0.184 × 10 4 (i.e., 1.1 %) to 4.15 × 10 −4 (i.e., 4.17 %) over India and the Arctic (seasonal details in Table 2). Past studies also indicate the transport of pollution from south Asia and east Asia to the Arctic predominantly in the UTLS (Shindell et al, 2008;Fisher et al, 2011). From multi-model simulations, Shindell et al (2008) show that seasonally varying the transport of south Asian sulfate aerosols to the Arctic maximizes in the pre-monsoon season.…”

Section: Transport Into the Upper Troposphere And Lower Stratospherementioning

confidence: 98%

The impact of recent changes in Asian anthropogenic emissions of SO<sub>2</sub> on sulfate loading in the upper troposphere and lower stratosphere and the associated radiative changes

et al. 2019

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Abstract. Convective transport plays a key role in aerosol enhancement in the upper troposphere and lower stratosphere (UTLS) over the Asian monsoon region where low-level convective instability persists throughout the year. We use the state-of-the-art ECHAM6–HAMMOZ global chemistry–climate model to investigate the seasonal transport of anthropogenic Asian sulfate aerosols and their impact on the UTLS. Sensitivity simulations for SO2 emission perturbation over India (48 % increase) and China (70 % decrease) are performed based on the Ozone Monitoring Instrument (OMI) satellite-observed trend, rising over India by ∼4.8 % per year and decreasing over China by ∼7.0 % per year during 2006–2017. The enhanced Indian emissions result in an increase in aerosol optical depth (AOD) loading in the UTLS by 0.61 to 4.17 % over India. These aerosols are transported to the Arctic during all seasons by the lower branch of the Brewer–Dobson circulation enhancing AOD by 0.017 % to 4.8 %. Interestingly, a reduction in SO2 emission over China inhibits the transport of Indian sulfate aerosols to the Arctic in summer-monsoon and post-monsoon seasons due to subsidence over northern India. The region of sulfate aerosol enhancement shows significant warming in the UTLS over northern India, south China (0.2±0.15 to 0.8±0.72 K) and the Arctic (∼1±0.62 to 1.6±1.07 K). The estimated seasonal mean direct radiative forcing at the top of the atmosphere (TOA) induced by the increase in Indian SO2 emission is −0.2 to −1.5 W m−2 over northern India. The Chinese SO2 emission reduction leads to a positive radiative forcing of ∼0.6 to 6 W m−2 over China. The decrease in vertical velocity and the associated enhanced stability of the upper troposphere in response to increased Indian SO2 emissions will likely decrease rainfall over India.

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“…The large-scale slow upwelling over the AMA is suggested to be the dominant transport process (Garny and Randel, 2016;Vogel et al, 2019). Shorter timescale processes associated with the subseasonal variability of the AMA, such as fast horizontal transport and turbulent mixing on an isentropic surface, also play important roles (Vogel et al, 2016;Pan et al, 2016;Gottschaldt et al, 2018;Fadnavis et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Characterizing quasi-biweekly variability of the Asian monsoon anticyclone using potential vorticity and large-scale geopotential height field

Amemiya

Sato

2020

Atmos. Chem. Phys.

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Abstract. The spatial pattern of subseasonal variability of the Asian monsoon anticyclone is analyzed using long-term reanalysis data, focusing on the large-scale longitudinal movement. The air inside the anticyclone is quantified by a thickness-weighted low-PV (potential vorticity) area on an isentropic surface. It is shown that the longitudinal movement of the air inside the Asian monsoon anticyclone has a timescale of 1 to 2 weeks, which is shorter than the monthly dominant timescale of the variability in the anticyclone intensity. The movement of the anticyclonic air is suggested to be largely controlled by passive advection. The typical time evolution of the variability pattern, explained by two leading empirical orthogonal function (EOF) components of 100 hPa geopotential height, shows large-scale geopotential anomalies moving westward spanning from low to middle latitudes. This corresponds well with the rapid westward movement of low-PV air known as “eddy shedding” and following the eastward retreat of the anticyclonic air. The two EOF components can also explain the bimodal longitudinal distribution of geopotential maximum location.

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Transport of trace gases via eddy shedding from the Asian summer monsoon anticyclone and associated impacts on ozone heating rates

Cited by 31 publications

References 47 publications

The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

The impact of recent changes in Asian anthropogenic emissions of SO<sub>2</sub> on sulfate loading in the upper troposphere and lower stratosphere and the associated radiative changes

Characterizing quasi-biweekly variability of the Asian monsoon anticyclone using potential vorticity and large-scale geopotential height field

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Transport of trace gases via eddy shedding from the Asian summer monsoon anticyclone and associated impacts on ozone heating rates

Cited by 31 publications

References 47 publications

The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

The impact of recent changes in Asian anthropogenic emissions of SO&lt;sub&gt;2&lt;/sub&gt; on sulfate loading in the upper troposphere and lower stratosphere and the associated radiative changes

Characterizing quasi-biweekly variability of the Asian monsoon anticyclone using potential vorticity and large-scale geopotential height field

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Product

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The impact of recent changes in Asian anthropogenic emissions of SO<sub>2</sub> on sulfate loading in the upper troposphere and lower stratosphere and the associated radiative changes