CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; budgeting at the regional scale using a Lagrangian experimental strategy and meso-scale modeling

C Sarrat,J Elbers,P Lacarrère,A Dolman,P Ciais,E Ceschia,V Masson,C Gerbig,J Noilhan,N Jarosz

doi:10.5194/bg-6-113-2009

Abstract

Abstract. An atmospheric Lagrangian experiment for regional CO2 budgeting with aircraft measurements took place during the CarboEurope Regional Experiment Strategy campaign (CERES) in south-west France, in June 2005. The atmospheric CO2 aircraft measurements taken upstream and downstream of an active and homogeneous pine forest revealed a CO2 depletion in the same air mass, using a Lagrangian strategy. This field experiment was analyzed with a meteorological meso-scale model interactively coupled with a surface scheme, with plant assimilation, ecosystem respiration, anthropogenic CO2 emissions and sea fluxes. First, the model was carefully validated against observations made close to the surface and in the atmospheric boundary layer. Then, the carbon budget was evaluated using the numerous CERES observations, by upscaling the surface fluxes observations, and using the modeling results, in order to estimate the relative contribution of each physical process. A good agreement is found between the two methods which use the same vegetation map: the estimation of the regional CO2 surface flux by the Eulerian meso-scale model budget is close to the budget deduced from the upscaling of the observed surface fluxes, and found a budget between −9.4 and −12.1 μmol.m−2.s−1, depending on the size of the considered area. Nevertheless, the associated uncertainties are rather large for the upscaling method and reach 50%. A third method, using Lagrangian observations of CO2 estimates a regional CO2 budget a few different and more scattered, (−16.8 μmol.m−2.s−1 for the small sub-domain and −8.6 μmol.m−2.s−1 for the larger one). For this budgeting method, we estimate a mean of 31% error, mainly arising from the time of integration between the two measurements of the Lagrangian experiment. The paper describes in details the three methods to assess the regional CO2 budget and the associated errors.

Highlights

As the major greenhouse gas actor in climate change, a better knowledge of regional atmospheric CO2 budget is needed, as well as an understanding of underlying processes
Meteorological meso-scale models permit the use of higher spatial resolution, better Atmospheric Boundary Layer (ABL) and surface energy budget parametrizations, and the explicit resolution of local to regional wind circulations that are crucial for the understanding of the atmospheric CO2 variability (Perez-Landa et al, 2007)
In order to validate the simulation, the Meso-NH outputs were compared with several types of observations made during CERES, including the ABL height and structure, the CO2 surface fluxes for 6 different cover types, the CO2 concentration near the coast and in the agricultural zones

Summary

Introduction

As the major greenhouse gas actor in climate change, a better knowledge of regional atmospheric CO2 budget is needed, as well as an understanding of underlying processes. At the global and continental scale, models are able to infer the CO2 surface fluxes (Bousquet et al, 1998), but the resolution of global inversions is too coarse to get accurate information at the regional scale. Meteorological meso-scale models permit the use of higher spatial resolution, better Atmospheric Boundary Layer (ABL) and surface energy budget parametrizations, and the explicit resolution of local to regional wind circulations that are crucial for the understanding of the atmospheric CO2 variability (Perez-Landa et al, 2007). Previous studies (Sarrat et al, 2007a,b; Nicholls et al, 2004; Denning et al, 2003) showed the capacity of mesoscale models to simulate the CO2 surface fluxes as well as the atmospheric concentration gradients and their variability.

Methods

Results

Discussion

Conclusion