https://orfeo.belnet.be/handle/internal/1 2026-05-06T11:23:20Z https://orfeo.belnet.be/handle/internal/14690 Report documenting the changes in PSC parameterization and improvements of ozone hole forecasts Chabrillat, S.; Minganti, D.; Huijnen, V.; Remy, S. This report documents the ability of IFS Cy48R1, including model revisions planned for inclusion in Cy49R1, to forecast the composition of the polar lower stratosphere during ozone hole events (or more generally winter and spring seasons) using the BASCOE module for stratospheric chemistry, i.e. the IFS(CBA) configuration, and chemical reanalyses as reference. https://orfeo.belnet.be/handle/internal/14688 A rare observation from mid-latitude of a blue aurora Beaudoin, E.; Lilensten, J.; Gronoff, G.; Cessateur, G.; Bosse, L.; Barthélemy, M.; Pitout, F.; Simon Wedlund, C.; Lamy, H. Aurora observations at mid-latitudes are rare but not exceptional. The aurorae are usually seen as diffuse red illuminations of the sky above the Northern (respectively Southern) horizon (respectively in the northern and southern hemispheres) because they take place at much higher latitude and their lower parts (green, purple, blue) fall below the horizon. However, while high-latitude sightings of blue aurorae are frequent, sighting at mid-latitudes have rarely been reported. During the night of September 24–25, 2023, a series of aurorae were seen from a viewpoint at 48.3° geographic north and 1.2° geographic east (49.88°N, 84.55°E in geomagnetic coordinates). These aurorae appeared above the horizon in northern to north-eastern direction. At around 23 UT (1 LT), the aurora appeared red. Three hours later, a blue aurora was seen in the northeast direction from the observation site and photographed using a wavelength-calibrated canon 6D camera. No colors other than blue were present on the images. While the red aurora is common and its excitation mechanism understood, the origin of the blue aurora is more difficult to determine. We argue that the observed blue aurora cannot be attributed to electron or proton precipitation. The excitation of the Vegard-Kaplan and first positive bands of N2 by low energy electrons cannot account for the lack of red and green colors in the images although they cannot be fully ruled out. The resonant scattering of solar light on N2+ at ionospheric F-region heights appears to be the most likely explanation. More frequent systematic multi-instrument multi-point observations could provide additional insight into the origin of these aurorae and help understand how often N2+ is uplifted to F-region heights. For such kind of work, amateur astrophotographers could provide valuable support. https://orfeo.belnet.be/handle/internal/14687 Global atmospheric methanol emissions inferred from IASI satellite measurements and aircraft data Müller, J.-F.; Stavrakou, T.; Franco, B.; Clarisse, L.; Amelynck, C.; Schoon, N.; Verreyken, B.; Opacka, B.; Vigouroux, C.; Guenther, A.B.; Mahieu, E.; Makarova, M.; Strong, K. We employ an updated retrieval of space-based methanol (CH3OH) column measurements from the Infrared Atmospheric Sounding Interferometer (IASI) and an emission optimisation framework built on the MAGRITTE chemical transport model to assess terrestrial emissions of methanol to the atmosphere between 2008–2019. We first carry out a IASI CH3OH validation study based on concentration measurements from three airborne campaigns, using the model and the IASI averaging kernels to compute aircraft-based columns directly comparable to IASI data. IASI is found to underestimate high columns in the considered region. A linear regression gives ΩIASI = 0.46 Ωairc + 10.6 x 10 15 molec.cm -2, with ΩIASI and Ωairc the IASI and aircraft-derived columns, respectively. Inverse modelling of terrestrial methanol emissions using MAGRITTE and bias-corrected IASI columns leads to much-improved overall agreement against in situ measurement campaigns and column data at eight FTIR stations. The optimised global biogenic methanol emissions (~160Tgyr -1) are 22 %–60 % higher than previous top-down estimates, due to (1) column enhancements caused by the IASI bias-correction and (2) higher dry deposition velocities in the model over land, compared to previous model studies, based on a parametrisation constrained by extensive campaign data. The inversion results are less reliable over boreal forests due to shortcomings of both the bias-correction and the dry deposition scheme over these regions. The optimisation suggests large changes in the distribution and seasonality of emissions. Over tropical ecosystems, radiation and temperature appear to exert a stronger control on biogenic emissions than is currently accounted for in the MEGAN model. https://orfeo.belnet.be/handle/internal/14686 Validation of TROPOMI and WRF-Chem NO2 across seasons using SWING+ and surface observations over Bucharest Pasternak, A.; Müller, J.-F.; Poraicu, C.; Merlaud; A., Tack, F.; Stavrakou, T. Nitrogen oxides (NOx) are key pollutants involved in ozone and particulate matter formation, with strong spatial variability near urban sources. Accurate monitoring of tropospheric nitrogen dioxide (NO2) is essential for air quality management and relies on validated chemistry transport models and multi-scale observations. This study evaluates the WRF-Chem model v4.5.1, run at 1 km resolution over Bucharest, Romania, using in situ meteorological data and surface chemical measurements, as well as airborne NO2 columns from 17 SWING+ flights conducted between 2021 and 2022. The model successfully captures key atmospheric processes and NO2 variability across all but one observation period. Our results indicate that anthropogenic NOx emissions from CAMS-REG v7.0 are underestimated. Satisfactory agreement with observations is achieved when the emissions are scaled by a factor of 1.5. We also assess TROPOMI tropospheric NO2 columns v2.4.0 using SWING+ as reference, with WRF-Chem used as an intercomparison platform to account for differences in sampling and vertical sensitivity. TROPOMI biases range from +20 % at low concentrations (1015 molec. cm−2) to −13 % at higher levels (15 × 1015 molec. cm−2). Seasonal diagnostics indicate variability in the bias for low columns, showing a marked positive bias in fall and negative biases in other seasons, whereas the negative bias at higher columns remains stable. Additionally, we provide a detailed treatment of uncertainty estimates and contextualize our findings through a review of recent TROPOMI tropospheric NO2 validation studies.