Articles | Volume 9, issue 2
Geosci. Model Dev., 9, 749–764, 2016
Geosci. Model Dev., 9, 749–764, 2016

Model description paper 19 Feb 2016

Model description paper | 19 Feb 2016

Adjoint of the global Eulerian–Lagrangian coupled atmospheric transport model (A-GELCA v1.0): development and validation

Dmitry A. Belikov1,2,3, Shamil Maksyutov1, Alexey Yaremchuk4, Alexander Ganshin3,5, Thomas Kaminski6,a, Simon Blessing7, Motoki Sasakawa1, Angel J. Gomez-Pelaez8, and Alexander Starchenko3 Dmitry A. Belikov et al.
  • 1National Institute for Environmental Studies, Tsukuba, Japan
  • 2National Institute of Polar Research, Tokyo, Japan
  • 3Tomsk State University, Tomsk, Russia
  • 4N. Andreev Acoustic Institute, Moscow, Russia
  • 5Central Aerological Observatory, Dolgoprudny, Russia
  • 6The Inversion Lab, Hamburg, Germany
  • 7FastOpt GmbH, Hamburg, Germany
  • 8Izaña Atmospheric Research Center (IARC), Meteorological State Agency of Spain (AEMET), Izaña, 38311, Spain
  • apreviously at: FastOpt GmbH, Hamburg, Germany

Abstract. We present the development of the Adjoint of the Global Eulerian–Lagrangian Coupled Atmospheric (A-GELCA) model that consists of the National Institute for Environmental Studies (NIES) model as an Eulerian three-dimensional transport model (TM), and FLEXPART (FLEXible PARTicle dispersion model) as the Lagrangian Particle Dispersion Model (LPDM). The forward tangent linear and adjoint components of the Eulerian model were constructed directly from the original NIES TM code using an automatic differentiation tool known as TAF (Transformation of Algorithms in Fortran;, with additional manual pre- and post-processing aimed at improving transparency and clarity of the code and optimizing the performance of the computing, including MPI (Message Passing Interface). The Lagrangian component did not require any code modification, as LPDMs are self-adjoint and track a significant number of particles backward in time in order to calculate the sensitivity of the observations to the neighboring emission areas. The constructed Eulerian adjoint was coupled with the Lagrangian component at a time boundary in the global domain. The simulations presented in this work were performed using the A-GELCA model in forward and adjoint modes. The forward simulation shows that the coupled model improves reproduction of the seasonal cycle and short-term variability of CO2. Mean bias and standard deviation for five of the six Siberian sites considered decrease roughly by 1 ppm when using the coupled model. The adjoint of the Eulerian model was shown, through several numerical tests, to be very accurate (within machine epsilon with mismatch around to ±6 e−14) compared to direct forward sensitivity calculations. The developed adjoint of the coupled model combines the flux conservation and stability of an Eulerian discrete adjoint formulation with the flexibility, accuracy, and high resolution of a Lagrangian backward trajectory formulation. A-GELCA will be incorporated into a variational inversion system designed to optimize surface fluxes of greenhouse gases.