09:00 〜 09:15
[AAS07-01] Long-term summer methane variability in West Siberia
キーワード：西シベリア、メタン、湿地、タワー観測
Introduction
The Siberian cryosphere is significantly affected by climate change and includes emission and sink regions for greenhouse gases, which are important for their global budget and future projections. As for methane (CH4), the most extensive wetlands in the world exist in this region, and their response to climate change is expected to impact global atmospheric CH4 concentrations significantly. However, in the world's greenhouse gas monitoring network, there is a lack of observational data regarding the vast area of Siberia. The National Institute for Environmental Studies (NIES) began airborne atmospheric observations of greenhouse gases in Siberia in 1992 as a part of the international cooperation between Japan and Russia. Then NIES began continuous observations using a tower in 2001.
The atmospheric CH4 concentration has been reported to have increased again on a global scale since 2007, and the rate of increase in 2020 and 2021 was the highest ever recorded, and the cause of this increase is under debate.
Sites and Observation Systems
The JR-STATION (Japan-Russia Siberian Tall Tower Inland Observation Network), which has a maximum of nine (currently six) tower observation sites in Siberia, conducts simultaneous multi-point observations (Figure 1) [1]. The ambient air sampled from the inlets positioned at different heights of a tower is dehumidified, and the carbon dioxide (CO2) concentration is measured by NDIR and the CH4 concentration by an improved SnO2 semiconductor sensor. To save standard gas consumption, the system uses a high-pressure cylinder filled with in-situ air, which is measured hourly to compensate for the drift of each sensor. Air intake is performed mainly from two heights, and measurements are made for three minutes per hour from each height after prior flushing the flow paths when switching sampling lines.
Methane Anomaly Variations during Summer
The equipment is designed for automated, unmanned continuous measurements, but for various reasons, the number of data from year to year is highly skewed, and there are not many cases of uninterrupted observation of CH4 concentrations throughout the year. In addition, the observation sites are located in the vicinity of seasonally dependent sources [1], making it difficult to interpret the change in simple annual averages. Therefore, by calculating the difference (anomaly) from the global mean CH4 trend value [2], we examined the interannual characteristics of CH4 concentrations in West Siberia. Since it is known that the concentration in West Siberia increases even during the summer season due to significant emissions from wetlands, we focused on fluctuations in summer (July to September). Since diurnal variations associated with changes in mixed layer top are apparent, we used only data obtained between 13:00 and 17:00 local time when temporal variations are stable to capture as broad a region of information as possible. The site near wetlands (DEM) showed a significant increase in 2016 but not in 2021 (no data available for 2020). At the mixed taiga and wetland site (KRS), a clear increase from 2006 to 2007 was apparent, with similar increases in 2016, 2020, and 2021; in 2007, growth in CH4 emissions from wetlands due to increased precipitation around KRS was suggested [3], but in 2016 and 2020 no abundant precipitation around that tower was observed. Satellite data showed a rise in CO concentrations over a wide area of West Siberia in early August 2021, indicating the transport of biomass burning air masses. Methane concentrations observed at KRS and DEM during the same period showed large fluctuations, suggesting that the impact of CH4 of biomass burning origin was widespread over a wide area of West Siberia.
[1] Sasakawa et al., 2010, Tellus 62B, 403-416.
[2] Ed Dlugokencky, NOAA/GML (gml.noaa.gov/ccgg/trends_ch4/)
[3] Sasakawa et al., 2012, Tellus 64B, 17514.
The Siberian cryosphere is significantly affected by climate change and includes emission and sink regions for greenhouse gases, which are important for their global budget and future projections. As for methane (CH4), the most extensive wetlands in the world exist in this region, and their response to climate change is expected to impact global atmospheric CH4 concentrations significantly. However, in the world's greenhouse gas monitoring network, there is a lack of observational data regarding the vast area of Siberia. The National Institute for Environmental Studies (NIES) began airborne atmospheric observations of greenhouse gases in Siberia in 1992 as a part of the international cooperation between Japan and Russia. Then NIES began continuous observations using a tower in 2001.
The atmospheric CH4 concentration has been reported to have increased again on a global scale since 2007, and the rate of increase in 2020 and 2021 was the highest ever recorded, and the cause of this increase is under debate.
Sites and Observation Systems
The JR-STATION (Japan-Russia Siberian Tall Tower Inland Observation Network), which has a maximum of nine (currently six) tower observation sites in Siberia, conducts simultaneous multi-point observations (Figure 1) [1]. The ambient air sampled from the inlets positioned at different heights of a tower is dehumidified, and the carbon dioxide (CO2) concentration is measured by NDIR and the CH4 concentration by an improved SnO2 semiconductor sensor. To save standard gas consumption, the system uses a high-pressure cylinder filled with in-situ air, which is measured hourly to compensate for the drift of each sensor. Air intake is performed mainly from two heights, and measurements are made for three minutes per hour from each height after prior flushing the flow paths when switching sampling lines.
Methane Anomaly Variations during Summer
The equipment is designed for automated, unmanned continuous measurements, but for various reasons, the number of data from year to year is highly skewed, and there are not many cases of uninterrupted observation of CH4 concentrations throughout the year. In addition, the observation sites are located in the vicinity of seasonally dependent sources [1], making it difficult to interpret the change in simple annual averages. Therefore, by calculating the difference (anomaly) from the global mean CH4 trend value [2], we examined the interannual characteristics of CH4 concentrations in West Siberia. Since it is known that the concentration in West Siberia increases even during the summer season due to significant emissions from wetlands, we focused on fluctuations in summer (July to September). Since diurnal variations associated with changes in mixed layer top are apparent, we used only data obtained between 13:00 and 17:00 local time when temporal variations are stable to capture as broad a region of information as possible. The site near wetlands (DEM) showed a significant increase in 2016 but not in 2021 (no data available for 2020). At the mixed taiga and wetland site (KRS), a clear increase from 2006 to 2007 was apparent, with similar increases in 2016, 2020, and 2021; in 2007, growth in CH4 emissions from wetlands due to increased precipitation around KRS was suggested [3], but in 2016 and 2020 no abundant precipitation around that tower was observed. Satellite data showed a rise in CO concentrations over a wide area of West Siberia in early August 2021, indicating the transport of biomass burning air masses. Methane concentrations observed at KRS and DEM during the same period showed large fluctuations, suggesting that the impact of CH4 of biomass burning origin was widespread over a wide area of West Siberia.
[1] Sasakawa et al., 2010, Tellus 62B, 403-416.
[2] Ed Dlugokencky, NOAA/GML (gml.noaa.gov/ccgg/trends_ch4/)
[3] Sasakawa et al., 2012, Tellus 64B, 17514.