09:45 〜 10:00
[ACG37-04] Estimation of regional CH4 flux based on an ensemble of atmospheric inversions
キーワード：Greenhouse gases, Methane budget, Atmospheric inversions, Atmospheric modeling
Methane (CH4) is an important anthropogenic greenhouse gas (GHG) that also plays a significant role in air pollution chemistry in the troposphere and water vapor changes in the stratosphere. In this study, we have estimated of methane sources and sinks on regional to global scales using the Japan Agency for Marine-Earth Science and Technology’s Model for Interdisciplinary Research on Climate (MIROC, version 4.0) (referred to as MIROC4-ACTM) and atmospheric measurements from about 60 sites from 2000 to 2020, with a special focus on the 2010-2020 time period. The CH4 inversion helps to identify the key regions with emission changes, and the information of emissions from different source sectors from an extensive set of inventories has been used to attribute affecting drivers. Our inversion model system contributes to the global CH4 budget performed in the frame of the Global Carbon Project (GCP) with a set of mandatory and optional runs using various oxidant fields.
Emissions of methane from the South Asia region (India, Pakistan, Bangladesh, Nepal, Bhutan, and Sri Lanka) have increased during the last decades along with rapid economic growth, especially in the Indo-Gangetic Plain (IGP), encompassing northern regions of the Indian subcontinent. The IGP is one of the most densely populated regions with strong emissions of various tracers due to human activity. The GHG observation program in the Indian region is expanding gradually. However, the characterization of methane behavior in the northern Indian subcontinent and its long-term trends are not well understood. In order to improve flux estimation in the South Asia region weekly air sampling at Nainital (NTL; 29.36° N, 79.46° E; 1940 m a.s.l.) in northern India from 2006 and Comilla (CLA; 23.43° N, 91.18° E; 30 m a.s.l.) in Bangladesh from 2012 were included in our inversion system. The mountain site Nainital located near the Himalayan mountain range can be considered a background site representing northern Indian air partly influenced by anthropogenic activities from IGP. The Comilla site is located on the eastern edge of the IGP, where agricultural activities are believed to be the main factor in GHG emissions.
Along with the heterogeneous distributions of surface emissions the CH4 seasonal cycle over the Indian subcontinent is governed by the influence of the global monsoon divergent wind circulations. Basically, the air masses were transported from the Indian Ocean region during summer (monsoon season) and from the inland during winter. The back-trajectory analysis for NTL and CLA shows the sensitivity of the site to the adjacent regions: West Asia, East Asia, and Southeast Asia. Thus, these sites make it possible to reduce the uncertainty of methane fluxes in a large area weakly covered by observations, where many developing countries are located.
Emissions of methane from the South Asia region (India, Pakistan, Bangladesh, Nepal, Bhutan, and Sri Lanka) have increased during the last decades along with rapid economic growth, especially in the Indo-Gangetic Plain (IGP), encompassing northern regions of the Indian subcontinent. The IGP is one of the most densely populated regions with strong emissions of various tracers due to human activity. The GHG observation program in the Indian region is expanding gradually. However, the characterization of methane behavior in the northern Indian subcontinent and its long-term trends are not well understood. In order to improve flux estimation in the South Asia region weekly air sampling at Nainital (NTL; 29.36° N, 79.46° E; 1940 m a.s.l.) in northern India from 2006 and Comilla (CLA; 23.43° N, 91.18° E; 30 m a.s.l.) in Bangladesh from 2012 were included in our inversion system. The mountain site Nainital located near the Himalayan mountain range can be considered a background site representing northern Indian air partly influenced by anthropogenic activities from IGP. The Comilla site is located on the eastern edge of the IGP, where agricultural activities are believed to be the main factor in GHG emissions.
Along with the heterogeneous distributions of surface emissions the CH4 seasonal cycle over the Indian subcontinent is governed by the influence of the global monsoon divergent wind circulations. Basically, the air masses were transported from the Indian Ocean region during summer (monsoon season) and from the inland during winter. The back-trajectory analysis for NTL and CLA shows the sensitivity of the site to the adjacent regions: West Asia, East Asia, and Southeast Asia. Thus, these sites make it possible to reduce the uncertainty of methane fluxes in a large area weakly covered by observations, where many developing countries are located.