GMD Geoscientific Model Development GMD 1991-9603 Copernicus GmbH Göttingen, Germany 10.5194/gmd-4-207-2011 Mass-conserving tracer transport modelling on a reduced latitude-longitude grid with NIES-TM Belikov D. 1 Maksyutov S. 1 Miyasaka T. 2 Saeki T. 1 Zhuravlev R. 3 Kiryushov B. 3 National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan Fujitsu FIP Corporation, Tokyo, Japan Central Aerological Observatory, Dolgoprudny, Russia 22 03 2011 4 1 207 222 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.geosci-model-dev.net/4/207/2011/gmd-4-207-2011.html The full text article is available as a PDF file from http://www.geosci-model-dev.net/4/207/2011/gmd-4-207-2011.pdf

The need to perform long-term simulations with reasonable accuracy has led to the development of mass-conservative and efficient numerical methods for solving the transport equation in forward and inverse models. We designed and implemented a flux-form (Eulerian) tracer transport algorithm in the National Institute for Environmental Studies Transport Model (NIES TM), which is used for simulating diurnal and synoptic-scale variations of tropospheric long-lived constituents, as well as their seasonal and inter-annual variability. Implementation of the flux-form method requires the mass conservative wind fields. However, the model is off-line and is driven by datasets from a global atmospheric model or data assimilation system, in which vertically integrated mass changes are not in balance with the surface pressure tendency and mass conservation is not achieved. To rectify the mass-imbalance, a flux-correction method is employed. To avoid a singularity near the poles, caused by the small grid size arising from the meridional convergence problem, the proposed model uses a reduced latitude–longitude grid scheme, in which the grid size is doubled several times approaching the poles. This approach overcomes the Courant condition in the Polar Regions, maintains a reasonably high integration time-step, and ensures adequate model performance during simulations. To assess the model performance, we performed global transport simulations for SF<sub>6</sub>, <sup>222</sup>Rn, and CO<sub>2</sub>. The results were compared with observations available from the World Data Centre for Greenhouse Gases, GLOBALVIEW, and the Hateruma monitoring station, Japan. Overall, the results show that the proposed flux-form version of NIES TM can produce tropospheric tracer transport more realistically than previously possible. The reasons for this improvement are discussed.

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