Journal of Earth System Science ( IF 1.9 ) Pub Date : 2020-10-15 , DOI: 10.1007/s12040-020-01478-x M Krishnapriya , Rabindra K Nayak , Shaik Allahudeen , A Bhuvanachandra , V K Dadhwal , C S Jha , M V R Sheshasai , S K Sasmal , K V S R Prasad
Abstract
In this study, investigation of the seasonal cycle of the tropospheric CO2 concentration over India was carried out using the GEOS-Chem atmospheric transport model, Greenhouse gas Observation SATellite (GOSAT) retrievals, and in-situ measurements. The model simulation is highly coherent with the satellite and in-situ datasets, and it shows a distinct seasonal cycle of the tropospheric CO2 tendency over India with a negative phase (decreasing concentration) during April–August and a positive phase (increasing concentration) during September–March. The model diagnostics were analyzed to estimate budgets of the surface layer CO2, up to 650 hPa pressure level, for the two-phases of the seasonal cycle. A mean tendency, equivalent to −0.70 ppmv month−1, observed during April–August, which results from the loss of CO2 content in the surface layer through horizontal advection (−2.25 ppmv month−1) and vertical diffusion (−0.20 ppmv month−1), that dominates the gain from vertical advection (1.53 ppmv month−1). The negative contribution of horizontal advection in this period comes from the transport of CO2 depleted air-parcels over the oceanic region to India by the southwest monsoon winds and the positive contributions of vertical advection comes from upwelling of CO2 enriched air-parcels. The mean tendency, equivalent to 1.01 ppmv month−1, during September–March results from the gain through vertical advection (0.78 ppmv month−1) and horizontal advection (0.37 ppmv month−1) and a small contribution of vertical diffusion (−0.15 ppmv month−1). In this period, positive contribution of horizontal advection is due to the transport of CO2 enriched air-parcels from the southeast Asian region to India by north-east monsoon winds. At the annual scale, CO2 content of the surface layer over India has a net gain of 0.75 GtC that comes from 14.31 GtC through vertical advection that exceeds the loss due to horizontal advection (−11.10 GtC) and vertical diffusion processes (−2.46 GtC). This net gain is almost 85% higher than the input of 0.4 GtC through surface fluxes, which composed of 0.61 GtC anthropogenic emission and −0.21 GtC net terrestrial ecosystem exchanges. Additional sensitivity experiment was carried out to elucidate the semi-annual features of the seasonal cycle of CO2 for north India, in contrast to the annual characteristics of the seasonal cycle for south India in relation to the GOSAT observation.
Highlights
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Greenhouse gas Observation SATellite (GOSAT) L3B and L4B retrievals and in situ flux tower measurements were analysed to describe seasonal cycle of tropospheric CO2 over India; and GEOS-Chem atmospheric transport model diagnostics were used to examine the causes of the variability.
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The seasonal cycle over north India is composed of mixed signature of annual and semi-annual frequencies while south India experiences dominance of annual oscillation. However, the surface layer CO2 seasonal tendency has a major negative phase during April–August and a positive phase during September–March.
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The net negative tendency during April–August results from the loss of CO2 from the surface layer through horizontal advection and vertical diffusion processes that dominates the gain from vertical advection; while the net positive tendency during September–March results from the gain through vertical advection and horizontal advection and a small negative contribution from vertical diffusion.
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At annual scale, the surface layer over India experiences net positive gain of CO2 concentration, which is 85% more than the net input from the surface fluxes, and is mostly contributed by large-scale transport processes.
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Sensitivity experiments were carried out to elucidate the semi-annual features of the seasonal cycle of CO2 over north India in relation to the GOSAT observation. It turns out that the secondary trough during October–December on the background of net positive tendency during September–March results from the drawdown of CO2 by the terrestrial ecosystem uptake.
中文翻译：
基于模式模拟，卫星反演和原位观测的印度对流层CO 2的季节变化
摘要
在这项研究中，使用GEOS-Chem大气传输模型，温室气体观测卫星（GOSAT）检索和原位测量对印度对流层CO 2浓度的季节性周期进行了调查。该模型模拟与卫星和原位数据集高度一致，它显示了印度对流层CO 2趋势的明显季节性周期，4月至8月为负相（浓度降低），而正相（浓度增加）。在9月至3月期间。对模型诊断程序进行了分析，以估算表面层CO 2的预算，在季节性周期的两个阶段，最高压力为650 hPa。的平均倾向，相当于-0.70 ppmv的月-1，4 - 8月期间观察到的，来自CO的损失，结果2含量在表面层通过水平平流（-2.25 ppmv的月-1）和垂直扩散（-0.20 ppmv的个月-1），占主导地位的垂直对流（1.53 ppmv月-1）。在此期间，水平对流的负贡献来自西南季风风将海洋中消耗完的CO 2气团通过西南季风向印度输送，垂直对流的积极贡献来自CO 2的上升丰富的飞机包裹。9月至3月的平均趋势等于1.01 ppmv month -1，是由于垂直对流（0.78 ppmv month -1）和水平对流（0.37 ppmv month -1）的增益以及垂直扩散的少量贡献（-0.15）引起的ppmv月-1）。在此期间，水平对流的积极作用是由于东北季风风将富含CO 2的航空包裹从东南亚地区运送到印度。在年度规模上，CO 2印度上空表层的含量具有0.75 GtC的净增益，该净增益来自通过垂直对流的14.31 GtC，超过了水平对流（−11.10 GtC）和垂直扩散过程（−2.46 GtC）造成的损耗。该净增益比通过表面通量输入的0.4 GtC高出近85％，该通量由0.61 GtC人为排放量和-0.21 GtC净陆地生态系统交换组成。进行了额外的敏感性实验，以阐明印度北部CO 2季节性周期的半年度特征，与印度南部与GOSAT观测有关的季节性周期的年度特征相反。
强调
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分析了温室气体观测卫星（GOSAT）的L3B和L4B取回量以及原位通量塔测量值，以描述印度对流层CO 2的季节性周期；并使用GEOS-Chem大气传输模型诊断程序检查了变化的原因。
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印度北部的季节周期由年和半年度频率的混合信号组成，而印度南部则经历年度振荡的主导。然而，表层CO 2的季节性趋势在4-8月期间有一个主要的负相位，而在9-3月之间则是一个正相位。
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4月至8月的净负趋势是由于水平对流和垂直扩散过程导致表层CO 2的损失所致，而该过程主导了垂直对流的增加。而9月至3月的净正趋势来自垂直对流和水平对流的增益，垂直扩散对负的贡献很小。
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在年尺度上，印度上空的表层经历了净的CO 2浓度正增长，这比地表通量的净输入增加了85％，这主要是由大规模的运输过程造成的。
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进行了敏感性实验，以阐明印度北部与GOSAT观测有关的CO 2季节性周期的半年度特征。事实证明，在9月至3月出现净正趋势的背景下，10月至12月的次要谷底是由于陆地生态系统的吸收而使CO 2下降。
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