1Institut Català de Ciències del Clima, Dr. Trueta 203, 08005, Barcelona, Catalonia, Spain
2Laboratori de Recerca del Clima, Parc Científic de Barcelona, Universitat de Barcelona, Baldiri i Reixach, 2, 2a planta, 08028, Barcelona, Catalonia, Spain
3Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys, 23, 08010, Barcelona, Catalonia, Spain
*now at: Environmental Research Group, King's College London, 150 Stamford Street, London, SE1 9NH, UK
Abstract. In this study the differences in the measured atmospheric CO2 mixing ratio at three aircraft profiling sites in NE Spain separated by 60 km are analyzed in regard to the variability of the surface fluxes in the regional surface influence area. First, the Regional Potential Surface Influence (RPSI) for fifty-one days in 2006 is calculated to assess the vertical, horizontal and temporal extent of the surface influence for the three sites at the regional scale (104 km2) at different altitudes of the profile (600, 1200, 2500 and 4000 meters above the sea level, m a.s.l.). Second, three flights carried out in 2006 (7 February, 24 August and 29 November) following the Crown Atmospheric Sampling (CAS) design are presented to study the relation between the measured CO2 variability and the Potential Surface Influence (PSI) and RPSI concepts. At 600 and 1200 m a.s.l. the regional signal is confined up to 50 h before the measurements whereas at higher altitudes (2500 and 4000 m a.s.l.) the regional surface influence is only recovered during spring and summer months. The RPSI from sites separated by 60 km overlap by up to 70% of the regional surface influence at 600 and 1200 m a.s.l., while the overlap decreases to 10–40% at higher altitudes (2500 and 4000 m a.s.l.). The scale of the RPSI area is suitable to understand the differences in the measured CO2 concentration in the three vertices of the CAS, as CO2 differences are attributed to local surrounding fluxes (February) or to the variability of regional surface influence as for the August and November flights. For these two flights, the variability in the regional scale influences the variability measured in the local scale. The CAS sampling design for aircraft measurements appears to be a suitable method to cope with the variability of a typical grid for inversion models as measurements are intensified within the PBL and the background concentration is measured every ~102 km.