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We describe a technique using singular vector decomposition (SVD), that can identify the spatial patterns that best describe the temporal variability of a global satellite dataset. These patterns, and their temporal evolution, are then correlated with established climate indices. We apply this technique to datasets of cloud properties over three decades, derived from five visible/IR imagers ((A)ATSR, SLSTR-A/-B and MODIS and jointly from the IR and microwave sounders on MetOp (IASI, MHS,AMSU-A), but it can be more generically used to extract the pattern of variability of any regular gridded dataset such as different parameters from satellite products and models. The leading singular vector for these three independent global data sets, on both cloud fraction and cloud-top height, from these polar orbiting satellites covering different time periods, is found to be strongly correlated with the ENSO index. The SVD approach could potentially offer a new tool for using global satellite observations in assessing global climate model (GCM) performance. [ABSTRACT FROM AUTHOR]

We use a combination of space-borne instruments to study the unprecedented stratospheric plume after the Hunga Tonga eruption of 15 January 2022. The plume was formed of two initial clouds at 30 and 28km mostly composed of submicronic sulphate particles without ashes, washed-out within the first hours. The large amount of water vapour injected led to a fast conversion of SO2 to sulphates and induced a descent of the plume over the first three weeks by radiative cooling. While SO2 returned to background levels by the end of January, the sulphate plume persisted until June, mainly confined between 20N and 35S due to the zonal symmetry of the summer stratospheric circulation at 24-25km. As sulphate particles grew through hydration and coagulation, they sediment and separate from the ascending moisture entrained in the Brewer-Dobson circulation. Sulphate aerosol optical depths derived from the IASI infared sounder show that the aerosol plume was not simply diluted and dispersed passively but rather organized in concentrated patches. Winds from the space-borne Doppler lidar ALADIN/AEOLUS suggest that those structures, generated by shear-induced instabilities, are associated with vorticity anomalies. They likely enhance the duration and impacts of the plume. [ABSTRACT FROM AUTHOR]

Excessive numerical diffusion is one of the major limitations in the representation of long-range transport by chemistry-transport models. In the present study, we focus on excessive diffusion in the vertical direction, which has been shown to be a major issue, and we explore three possible ways to address this problem: increase vertical resolution, use an advection scheme with antidiffusive properties, and represent more accurately the vertical wind. This study is done with the CHIMERE chemistry-transport model, for the March 18, 2012 eruption of Mount Etna, which has released about 3 kt of sulphur dioxide in the atmosphere into a plume that has been observed by satellite instruments (IASI and OMI) for several days. The change from the classical Van Leer et al., (1977) scheme to the Després and Lagoutière (1999) antidiffusive scheme in the vertical direction has been shown to bring the largest improvement to model outputs in terms of preserving the thin plume emitted by the volcano. To a lesser extent, improved representation of the vertical wind field has also been shown to reduce plume dispersion. Both these changes help reducing vertical diffusion in the model as much as a brute-force approach (increasing vertical resolution). [ABSTRACT FROM AUTHOR]

We developed a new retrieval algorithm based on the Infrared Atmospheric Sounding Interferometer (IASI) observations, called AEROIASI-Sulphates, to measure vertically-resolved sulphate aerosols (SA) extinction and mass concentration profiles, with limited theoretical uncertainties (typically ~25 % total uncertainty for SA mass column estimations). The algorithm, based on a self-adapting Tikhonov-Phillips regularization method, is applied to a medium-sized-intensity eruption of Mount Etna volcano (18 March 2012). Comparisons with simultaneous and independent SO2 plume observations and simulations show that AEROIASI-Sulphates correctly identifies the volcanic plume morphology both horizontally and vertically. This method provided, for the first time, crucial information pieces to describe the gaseous-to-particulate volcanic sulphur mass balance (60 % of the injected sulphur mass is converted to particulate matter, after ~24 hours) and to estimate the regional shortwave direct radiative forcing (a regional forcing of −0.8 W/m2 is exerted in the eastern Mediterranean) for moderate volcanic eruptions. [ABSTRACT FROM AUTHOR]

We developed an optimal-estimation algorithm to simultaneously retrieve, for the first time, co-emitted volcanic gaseous SO2 and sulphate aerosols (SA) from groundbased FTIR observations. These effluents, both linked to magmatic/degassing and subsequent atmospheric evolution processes, have overlapping spectral signatures leading to mutual potential interferences when retrieving one species without considering the other.We show that significant overestimations may be introduced in SO2 retrievals if the radiative impact of co-existent SA is not accounted for, which may have impacted existing SO2 long-term series, e.g. from satellite platform. The method was applied to proximal observations at Masaya volcano, where SO2 and SA concentrations, and SA acidity were retrieved. A gas-to-particle sulphur partitioning of 400 and a strong SA acidity (sulphuric acid concentration: 65 %) where found, consistently with past in-situ observations at this volcano. This method is easily exportable to other volcanoes, to monitor magma extraction processes and the atmospheric sulphur cycle. [ABSTRACT FROM AUTHOR]

Ash clouds are a geographically far reaching hazard associated with volcanic eruptions. To minimise the risk that these pose to aircraft and to limit disruption to the aviation industry, it is important to closely monitor the emission and atmospheric dispersion of these plumes. The altitude of the plume is an important consideration and is an essential input into many models of ash cloud propagation. CO2 slicing is an established technique for obtaining the top height of meteorological clouds and previous studies have demonstrated that there is potential for this method to be used for volcanic ash. In this study, the CO2 slicing technique has been adapted for volcanic ash and applied to spectra obtained from the Infrared Atmospheric Sounding Interferometer (IASI). Simulated ash spectra are first used to select the most appropriate channels and then demonstrate that the technique has merit for determining the altitude of the ash. These results indicate a strong match between the true heights and CO2 slicing output with a root mean square error (RMSE) of less than 800 m. Following this, the technique was applied to spectra obtained with IASI during the Eyjafjallajökull and Grimsvötn eruptions in 2010 and 2011 respectively, both of which emitted ash clouds into the troposphere, and which have been extensively studied with satellite imagery. The CO2 slicing results were compared against those from an optimal estimation scheme, also developed for IASI, and a satellite borne LiDAR is used for validation. Overall, the CO2 slicing tool performs better than the optimal estimation scheme. The CO2 slicing heights returned a RMSE value of 2.2 km when compared against the LiDAR. This is lower than the RMSE for the optimal estimation scheme (2.8 km). The CO2 slicing technique is a relatively fast tool and the results suggest that this method could be used to get a first approximation of the ash cloud height, potentially for use for hazard mitigation, or as an input for other retrieval techniques or models of ash cloud propagation. [ABSTRACT FROM AUTHOR]