WP4 Advanced characterisation of NORS data products Satellite Comparison NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Validation exercise within MULTITASTE Effective location: Location that best represents the measurements For DOAS zenith pointing instruments it may be shifted a few hundreds of km towards the direction of the Sun during twilights. NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Effective location for Izaña (28ºN, 16ºW) Horizontal projection of the coordinates of the measurements sampled with DOAS at zenith, for Tenerife (Subtropics) NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Consideration for diurnal behaviour of NO2 GOME 2 SCIA OMI According to NO2 diurnal evolution and taking into account satellite overpassings , AM columns are more suitable for comparison with satellite. NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

How effective location affects the results: NO2 at Izaña 10º x 10º centered on the station, and 4º x 8º Estward of the station by 2º. The later is more representative of the DOAS measurement area if 90º am data are used. If BL below the “effective location” is polluted, then discrepancies would appear. Since Canary Archipielago is located following a latitudinal parallel, pollution has a larger influence when averaging in longitude. However, when taking a single value for the selected areas, the two scenes provide almost no difference in the NO2 VCD value (≈1%) 10º x 10º centered on the station 4º x 8º Estward of the station by 2º NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Consideration for differences on seasonal SZA due to overpassings Maximum error introduced for this effect can be up to 2.5% (summer solstice) and 4.1%(winter solstice). Since on the overpass strip NO2 variation is essentially linear, this error can be easily corrected. NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Consideration for effective location and seasonal SZA due to overpassings Morning data are at a distance of over 300 km eastward of the station, which for this latitude represents about 2.5º difference in Solar elevation Very little difference between summer and winter. The correction for this particular instrument is minimal An important issue when comparing the GB and satellite data is to consider the sza over the “effective location” and not above the station. In figure 4 it is shown how morning data are at a distance of over 300 km eastward of the station, which for this latitude represents about 2.5º difference in Solar elevation, with very little difference between summer and winter. When applying this correction, it can be seen in figure 6 that correction for this particular instrument is minimal. Overpass time in fractional day can be from 0.44 to 0.50, depending on the orbit If no correction is applied, the maximum error introduced for this effect can be up to 2.5% (summer solstice) and 4.1%(winter solstice). Since on the overpass strip NO2 variation is essentially linear, this error can be easily corrected. NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

NO2 at Izaña NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Differences between GB and satellite data: NO2 monthly means at Izaña NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Other sites Ushuaia: CADIC Coordinates: 54º49'S, 68º19'W Vicecomodoro Marambio Coordinates: 64º14'S, 56º38'W Belgrano II Coordinates: 77º52'S, 34º37'W NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Effective location for other sites: NO2 at Marambio (64º14'S, 56º38'W) NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Other sites: NO2 at Marambio First step correction: all overpassing takes place at 0.52 fractional day (middle of the strip) except solstice in which differences are supposed to be negligible. A sine fitting provides the correction factor. After applying this factor to data mean of the instruments in winter ratio are reduced from 1.17 to 0.97, and standard deviation from 0.55 to 0.40. NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Other sites: NO2 at Marambio NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Effective location for Belgrano (77º52'S, 34º37'W) NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

Effective location for Ushuaia (54º49'S, 68º19'W) NORS/NDACC UV-VIS Working Group Meeting 3-4 July 2012 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium