Elevated aerosol layer over South Asia worsens the Indian droughts

Sabin, T. P.; Roy, Chaitri; Rowlinson, Matthew J.; Rap, A.; Vernier, Jean‐Paul; Sioris, Christopher E.

doi:10.1038/s41598-019-46704-9

Cited by 42 publications

(44 citation statements)

References 71 publications

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“…Our study contributes to deducing the source regions of emissions of precursors of ATAL particles at the Earth's surface and their transport pathways to the UTLS which is important to develop recommendations for regulations of anthropogenic surface emissions of ATAL precursors. In a recent study, Fadnavis et al (2019b) argue that further increasing industrial emissions in Asia will lead to a wider and thicker ATAL having the potential to amplify the severity of droughts in India. Severe droughts would have fatal consequences on agriculture on the Indian subcontinent and therefore would result in strong socio-economic impacts in one of the most densely populated parts of the world.…”

Section: Discussionmentioning

confidence: 99%

“…During El Niño, the ATAL is thicker and broader over the Indian region, resulting in a reduction of the solar flux and a surface cooling of about 1 K over North India. An elevated ATAL over South Asia exacerbates the severity of Indian droughts (Fadnavis et al, 2019b). The radiative forcing by the ATAL can further be enhanced by volcanic eruptions in the region; Fairlie et al (2014, Fig.…”

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confidence: 99%

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Strong variability of the Asian Tropopause Aerosol Layer (ATAL) in August 2016 at the Himalayan foothills

Hanumanthu¹,

Vogel²,

Müller³

et al. 2020

Preprint

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Abstract. The South Asian summer monsoon is associated with a large-scale anticyclonic circulation in the Upper Troposphere and Lower Stratosphere (UTLS), which confines the air mass inside. During boreal summer, the confinement of this air mass leads to an accumulation of aerosol between about 13 km and 18 km (360 K and 440 K potential temperature), this accumulation of aerosol constitutes the Asian Tropopause Aerosol Layer (ATAL). We present balloon-borne aerosol backscatter measurements of the ATAL performed by the Compact Optical Backscatter Aerosol Detector (COBALD) instrument in Nainital in Northern India in August 2016, and compare these with COBALD measurements in the post-monsoon time in November 2016. The measurements demonstrate a strong variability of the ATAL's altitude, vertical extent, aerosol backscatter intensity and cirrus cloud occurrence frequency. Such a variability cannot be deduced from climatological means of the ATAL as they are derived from satellite measurements. To explain this observed variability we performed a Lagrangian back-trajectory analysis using the Chemical Lagrangian Model of the Stratosphere (CLaMS). We identify the transport pathways of air parcels contributing to the ATAL over Nainital in August 2016, as well as the source regions of the air masses contributing to the composition of the ATAL. Our analysis reveals a variety of factors contributing to the observed day-to-day variability of the ATAL: continental convection, tropical cyclones (maritime convection), dynamics of the anticyclone and stratospheric intrusions. Thus, the ATAL is a mixture of air masses coming from different atmospheric height layers. In addition, contributions from the model boundary layer originate in different geographic source regions. The location of strongest updraft along the backward trajectories reveal a cluster of strong upward transport at the southern edge of the Himalayan foothills. From the top of the convective outflow level (about 13 km; 360 K) the air parcels ascend slowly to ATAL altitudes within a large-scale upward spiral driven by the diabatic heating in the anticyclonic flow of the South Asian summer monsoon at UTLS altitudes. Cases with a strong ATAL typically show boundary layer contributions from the Tibetan Plateau, the foothills of the Himalayas and other continental regions below the Asian monsoon. Weaker ATAL cases show higher contributions from the maritime boundary layer, often related to tropical cyclones, indicating a mixing of unpolluted and polluted air masses. Because of the strong growth of Asian economies, increasing anthropogenic emissions in the future are expected to enhance the thickness and intensity of the ATAL, thereby also enhancing the global stratospheric aerosol loading, which likely impacts surface climate.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Strong variability of the Asian Tropopause Aerosol Layer (ATAL) in August 2016 at the Himalayan foothills

Hanumanthu¹,

Vogel²,

Müller³

et al. 2020

Preprint

Self Cite

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“…the troposphere is significant (Fadnavis et al, 2019) in altering the incoming solar radiation. The western part of India, where dust is the primary contributor of aerosol loading, exhibits decreasing trend of DRF SFC driven by decreasing trend of dust aerosols in the last decade (Pandey et al, 2017).…”

Section: Regional Variability Of Drfmentioning

confidence: 99%

Recent trend in the global distribution of aerosol direct radiative forcing from satellite measurements

Subba

Gogoi

Pathak

et al. 2020

Atmospheric Science Letters

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Global distribution of aerosol direct radiative forcing (DRF) is estimated using Clouds and Earth's Radiant Energy System (CERES) synoptic (SYN) 1 datasets. During 2001-2017, a statistically significant change of global DRFs is revealed with a general decreasing trend (i.e., a reduced cooling effect) at the top of the atmosphere (DRF TOA~0 .017 WÁm −2 Áyear −1) and at the surface (DRF SFC~0 .033 WÁm −2 Áyear −1) with rapid change over the land compared to the global ocean. South Asia and Africa/Middle East regions depict significant increasing trend of atmospheric warming by 0.025 and 0.002 WÁm −2 Áyear −1 whereas, the rest of the regions show a decline. These regional variations significantly modulate the global mean DRF (−5.36 ± 0.04 WÁm −2 at the TOA and − 9.64 ± 0.07 WÁm −2 at the surface during the study period). The observed DRF trends are coincident with the change in the underlying aerosol properties, for example, aerosol optical depth, Ångström exponent and partly due to the increasing columnar burden of SO 2 over some of the regions. This indicates that increasing industrialization and urbanization have caused prominent change in the DRF during recent decades.

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“…The tropopause temperature (CPT and LRT) on monthly scales particularly during July and August 2015 also discussed. To quantify the changes that happened within the ASMA region, 11 years (2005ASMA region, 11 years ( -2015 This is supported by a recent study reported by Fadnavis et al (2019). They showed weaker upward motions and deficient rainfall in the 2015 monsoon due to the strong El Niño conditions.…”

Section: Discussionmentioning

confidence: 77%

“…They reported that the ASMA forms earlier and stronger in the La Niña period that leads to greater equatorward transport of O3-rich air from the extra-tropics into the northern tropics than during El Niño periods. Very recently, Fadnavis et al (2019) reported higher concentrations of aerosol layers observed in the ATAL region during the El Niño period over the northern part of South Asia. However, the above-mentioned studies are mainly focused on changes in the ASMA with respect to ENSO on seasonal scales or mature stage of monsoon (combined mean of July and August) respectively.…”

Section: Introductionmentioning

confidence: 96%

Structure, dynamics, and trace gases variability within the Asian summer monsoon anticyclone in extreme El Niño of 2015–16

Babu¹,

Ratnam²,

Basha³

et al. 2020

Preprint

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Abstract. In this work, the detailed changes in the structure, dynamics and trace gases within the Asian summer monsoon anticyclone (ASMA) during extreme El Niño of 2015–16 is delineated by using Aura Microwave Limb Sounder (MLS) measurements, COSMIC Radio Occultation (RO) temperature, and NCEP reanalysis products. We have considered the individual months of July and August 2015 for the present study. The results show that the ASMA structure was quite different in 2015 as compared to the long-term (2005–2014) mean. In July, the spatial extension of the ASMA shows larger than the long-term mean in all the regions except over northeastern Asia, where, it exhibits a strong southward shift in its position. The ASMA splits into two and western Pacific mode is evident in August. Interestingly, the subtropical westerly jet (STJ) shifted southward from its normal position over northeastern Asia as resulted mid latitude air moved southward in 2015. Intense Rossby wave breaking events along with STJ are also found in July 2015. Due to these dynamical changes in the ASMA, pronounced changes in the ASMA tracers are noticed in 2015 compared to the long-term mean. A 30 % (20 %) decrease in carbon monoxide (water vapor) at 100 hPa is observed in July over most of the ASMA region, whereas in August the drop is strongly concentrated in the edges of the ASMA. Prominent increase of O3 (> 40 %) at 100 hPa is clearly evident within the ASMA in July, whereas in August the increase is strongly located (even at 121 hPa) over the western edges of the ASMA. Further, the temperature around the tropopause shows significant positive anomalies (~ 5 K) within the ASMA in 2015. Overall, warming of the tropopause region due to the increased O3 weakens the anticyclone and further supported the weaker ASMA in 2015 reported by previous studies.

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Elevated aerosol layer over South Asia worsens the Indian droughts

Cited by 42 publications

References 71 publications

Strong variability of the Asian Tropopause Aerosol Layer (ATAL) in August 2016 at the Himalayan foothills

Strong variability of the Asian Tropopause Aerosol Layer (ATAL) in August 2016 at the Himalayan foothills

Recent trend in the global distribution of aerosol direct radiative forcing from satellite measurements

Structure, dynamics, and trace gases variability within the Asian summer monsoon anticyclone in extreme El Niño of 2015–16

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