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

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 90 km. 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)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(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 0.5 ppb integrated over 1 year) of OH diurnal variation, due to temperature dependence of reaction rate coe‰cient, on CH 4 simulation compared to the transport related variability (order of G15 ppb 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.

Increasing synoptic scale variability in atmospheric CO<sub>2</sub> at Hateruma Island associated with increasing East-Asian emissions

“…the interannual variation in OH (Patra et al, 2009). The σ CO 2 /σ CH 4 ratio reduces this transport effect, as noted earlier.…”

“…esrl.noaa.gov/gmd/ccgg/globalview/). The CO 2 and CH 4 time series from this site have been used successfully in studies involving data from multiple organizations (see Law et al, 2008;Patra et al, 2008Patra et al, , 2009.…”

“…The modelling period is from January 1990 to December 2006, and the first six years are a spin-up period, during which longterm transport mechanisms, such as the inter-hemispheric gradient and stratosphere-troposphere exchange, are equilibrated in the model. The capability of the ACTM to simulate CO 2 and CH 4 has been investigated elsewhere (Patra et al, , 2009). We use the CH 4 emission scenario (E2 scenario) developed in Patra et al (2009) that optimally fits the interhemispheric gradient and seasonal cycles at most sites around the globe to within 10 ppb on average.…”

“…The capability of the ACTM to simulate CO 2 and CH 4 has been investigated elsewhere (Patra et al, , 2009). We use the CH 4 emission scenario (E2 scenario) developed in Patra et al (2009) that optimally fits the interhemispheric gradient and seasonal cycles at most sites around the globe to within 10 ppb on average. For the CO 2 simulation, annually balanced terrestrial ecosystem flux (Randerson et al, 1997), oceanic exchange (Takahashi et al, 2009) and fossil fuel emissions are used simultaneously.…”

“…The observations at HAT often show pollution events influenced by continental emissions during the period from the late fall to early spring each year (Tohjima et al, 2000(Tohjima et al, , 2002Yokouchi et al, 2006). Recently, analyses of the SSVs have been found to be useful for validating regional fluxes with the help of a chemistry-transport model (Patra et al, 2009). In this paper, we examine the temporal changes in atmospheric CO 2 SSVs observed at HAT in wintertime (November-April) during 1996-2007 and investigate their relationship to the continental fossil CO 2 emissions.…”