Tropospheric warming over the northern Indian Ocean caused by South Asian anthropogenic aerosols: possible impact on the upper troposphere and lower stratosphere
<p>Atmospheric concentrations of South Asian anthropogenic aerosols and their transport play a key role in the regional hydrological cycle. Here, we use the ECHAM6-HAMMOZ chemistry–climate model to show the structure and implications of the transport pathways of these aerosols during spring (M...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/7179/2022/acp-22-7179-2022.pdf |
| Summary: | <p>Atmospheric concentrations of South Asian anthropogenic aerosols and their
transport play a key role in the regional hydrological cycle. Here, we use
the ECHAM6-HAMMOZ chemistry–climate model to show the structure and
implications of the transport pathways of these aerosols during spring
(March–May). Our simulations indicate that large amounts of anthropogenic
aerosols are transported from South Asia to the northern Indian Ocean and western Pacific. These aerosols are then lifted into the upper troposphere
and lower stratosphere (UTLS) by the ascending branch of the Hadley
circulation, where they enter the westerly jet. They are further transported
to the Southern Hemisphere (<span class="inline-formula">∼15</span>–30<span class="inline-formula"><sup>∘</sup></span> S)
and downward (320–340 K) via westerly ducts over the tropical Atlantic
(5<span class="inline-formula"><sup>∘</sup></span> S–5<span class="inline-formula"><sup>∘</sup></span> N, 10–40<span class="inline-formula"><sup>∘</sup></span> W) and Pacific
(5<span class="inline-formula"><sup>∘</sup></span> S–5<span class="inline-formula"><sup>∘</sup></span> N, 95–140<span class="inline-formula"><sup>∘</sup></span> E). The
carbonaceous aerosols are also transported to the Arctic, leading to local
heating (0.08–0.3 K per month, an increase by 10 %–60 %).</p>
<p>The presence of anthropogenic aerosols causes a negative radiative forcing
(RF) at the top of the atmosphere (TOA) (<span class="inline-formula">−</span>0.90 <span class="inline-formula">±</span> 0.089 W m<span class="inline-formula"><sup>−2</sup>)</span> and surface (<span class="inline-formula">−</span>5.87 <span class="inline-formula">±</span> 0.31 W m<span class="inline-formula"><sup>−2</sup>)</span> and atmospheric warming (<span class="inline-formula">+</span>4.96 <span class="inline-formula">±</span> 0.24 W m<span class="inline-formula"><sup>−2</sup>)</span>
over South Asia (60–90<span class="inline-formula"><sup>∘</sup></span> E, 8–23<span class="inline-formula"><sup>∘</sup></span> N), except over the Indo-Gangetic Plain (75–83<span class="inline-formula"><sup>∘</sup></span> E, 23–30<span class="inline-formula"><sup>∘</sup></span> N), where RF at the TOA is
positive (<span class="inline-formula">+</span>1.27 <span class="inline-formula">±</span> 0.16 W m<span class="inline-formula"><sup>−2</sup>)</span> due to large concentrations of
absorbing aerosols. The carbonaceous aerosols lead to in-atmospheric heating
along the aerosol column extending from the boundary layer to the upper
troposphere (0.1 to 0.4 K per month, increase by 4 %–60 %) and in the
lower stratosphere at 40–90<span class="inline-formula"><sup>∘</sup></span> N (0.02 to 0.3 K per month, increase by 10 %–60 %). The increase in tropospheric
heating due to aerosols results in an increase in water vapor
concentrations, which are then transported from the northern Indian
Ocean–western Pacific to the UTLS over 45–45<span class="inline-formula"><sup>∘</sup></span> N (increasing water vapor by 1 %–10 %).</p> |
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| ISSN: | 1680-7316 1680-7324 |