Growth Rate, Seasonal, Synoptic, Diurnal Variations and Budget of Methane in the Lower Atmosphere :

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Author(s)

Abstract

We have used an AGCM (atmospheric general circulation model)-based Chemistry Transport Model (ACTM) for the simulation of methane (CH_4) in the height range of earth's surface to about 90km. The model simulations are compared with measurements at hourly, daily, monthly and interannual time scales by filtering or averaging all the timeseries appropriately. From this model-observation comparison, we conclude that the recent (1990-2006) trends in growth rate and seasonal cycle at most measurement sites can be fairly successfully modeled by using existing knowledge of CH_4 flux trends and seasonality. A large part of the interannual variability (IAV) in CH_4 growth rate is apparently controlled by IAV in atmospheric dynamics at the tropical sites and forest fires in the high latitude sites. The flux amplitudes are optimized with respect to the available hydroxyl radical (OH) distribution and model transport for successful reproduction of latitudinal and longitudinal distribution of observed CH_4 mixing ratio at the earth's surface. Estimated atmospheric CH_4 lifetime in this setup is 8.6 years. We found a small impact (less than 0.5ppb integrated over 1 year) of OH diurnal variation, due to temperature dependence of reaction rate coefficient, on CH_4 simulation compared to the transport related variability (order of ±15ppb at interannual timescales). Model-observation comparisons of seasonal cycles, synoptic variations and diurnal cycles are shown to be useful for validating regional flux distribution patterns and strengths. Our results, based on two emission scenarios, suggest reduced emissions from temperate and tropical Asia region (by 13, 5, 3 Tg-CH_4 for India, China and Indonesia, respectively), and compensating increase (by 9, 9, 3 Tg-CH_4 for Russia, United States and Canada, respectively) in the boreal Northern Hemisphere (NH) are required for improved model-observation agreement.

We have used an AGCM (atmospheric general circulation model)-based Chemistry Transport Model (ACTM) for the simulation of methane (CH_4) in the height range of earth's surface to about 90km. The model simulations are compared with measurements at hourly, daily, monthly and interannual time scales by filtering or averaging all the timeseries appropriately. From this model-observation comparison, we conclude that the recent (1990-2006) trends in growth rate and seasonal cycle at most measurement sites can be fairly successfully modeled by using existing knowledge of CH_4 flux trends and seasonality. A large part of the interannual variability (IAV) in CH_4 growth rate is apparently controlled by IAV in atmospheric dynamics at the tropical sites and forest fires in the high latitude sites. The flux amplitudes are optimized with respect to the available hydroxyl radical (OH) distribution and model transport for successful reproduction of latitudinal and longitudinal distribution of observed CH_4 mixing ratio at the earth's surface. Estimated atmospheric CH_4 lifetime in this setup is 8.6 years. We found a small impact (less than 0.5ppb integrated over 1 year) of OH diurnal variation, due to temperature dependence of reaction rate coefficient, on CH_4 simulation compared to the transport related variability (order of ±15ppb at interannual timescales). Model-observation comparisons of seasonal cycles, synoptic variations and diurnal cycles are shown to be useful for validating regional flux distribution patterns and strengths. Our results, based on two emission scenarios, suggest reduced emissions from temperate and tropical Asia region (by 13, 5, 3 Tg-CH_4 for India, China and Indonesia, respectively), and compensating increase (by 9, 9, 3 Tg-CH_4 for Russia, United States and Canada, respectively) in the boreal Northern Hemisphere (NH) are required for improved model-observation agreement.

Journal

  • Journal of the Meteorological Society of Japan. Ser. II

    Journal of the Meteorological Society of Japan. Ser. II 87(4), 635-663, 2009

    Meteorogical Society of Japan

References:  56

Codes

  • NII Article ID (NAID)
    110007359634
  • NII NACSIS-CAT ID (NCID)
    AA00702524
  • Text Lang
    ENG
  • Article Type
    ART
  • ISSN
    00261165
  • NDL Article ID
    10325701
  • NDL Source Classification
    ZM43(科学技術--地球科学--気象)
  • NDL Call No.
    Z54-J645
  • Data Source
    CJP  NDL  NII-ELS  IR  NDL-Digital 
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