Student thesis series INES nr 499 Interpreting and composing SAGE II-III satellite data with a cloud algorithm for stratospheric aerosols Carl Svenhag 2020 Department of Physical Geography and Ecosystem Science Lund University Sölvegatan 12 S -223 62 Lund Sweden Carl Svenhag (2020). Interpreting and composing SAGE II-III satellite data with a cloud-algorithm for stratospheric aerosols. Tolkning och arrangering av SAGE II-III satellitdata med en molnalgoritm för stratosfäriska aerosoler. Master degree thesis, 30 credits in Atmospheric Science and Biochemical cycles Department of Physical Geography and Ecosystem Science, Lund University Level: Master of Science (MSc) Course duration: January 2019 until January 2020 Disclaimer This document describes work undertaken as part of a program of study at the University of Lund. All views and opinions expressed herein remain the sole responsibility of the author, and do not necessarily represent those of the institute. Interpreting and composing SAGE II-III satellite data with a cloud-algorithm for stratospheric aerosols Carl Svenhag Master thesis, 30 credits, in Atmospheric Science and Biochemical Cycles Johan Friberg Lund University Exam committee: Thomas Holst, Lund University Vaughan Phillips, Lund University Abstract Understanding and quantifying radiative effects by high air-bound particles is a significant component to further develop the climate models we use today for understanding past and future climate change (IPCC, 2013). In this study I seek to provide observations and understanding of sulphuric aerosols bound in the stratosphere from natural and possibly anthropogenic sources. Respectively draw attention to where the aerosols are located and why. The most intensive source of additional stratospheric aerosol loads stems from volcanic eruptions and in June 1991 Mt Pinatubo injected over 20 tonnes of SO2 into the troposphere and subsequently high up in the stratosphere. The climate impact of resulting Pinatubo aerosols is considered one of the largest stratospheric disruptions in the 20th century (McCormick, 1995). The study of forest fire aerosols being lunged into the stratosphere is an uncertain field which may carry more weight to our global radiative budget than previously thought. The observation of these effect is made possible through the SAGE project which have been observing light- scattering and absorption of stratospheric compounds since 1979. SAGE II (1984–2005) and SAGE III (2017-) are included in this research with a developed cloud algorithm, and these methods and results are compared to previous studies for mapping stratospheric aerosols. Keywords: Atmospheric Science, Satellite Observations, Aerosol Optical Depth, SAGE, Cloud Algorithm, Stratospheric Aerosols, Radiative Forcing. i Sammanfattning Tolkning och kvantifiering av strålningseffekter pga. atmosfäriska partiklar är en signifikant del av IPCC’s (2013) modellering av hur tidigare klimat förändrats och hur förändringar i framtiden kommer se ut. I den här studien vill vi strukturera och analysera observationer av huvudsakligen svavelpartiklar positionerade i stratosfären från naturliga och möjligtvis mänskliga källor, med hänvisning till var och varför de finns där. Vulkaniska utbrott är den största källan till naturligt höga aerosolkoncentrationer i stratosfären. Juni 1991 exploderade vulkanen Pinatubo i Indonesien och slungade kring 20 ton svaveldioxid in i atmosfären, med stor omfattning långt in i stratosfären. Effekterna av de resulterande aerosolerna från Pinatubo är uppskattat att vara en av de största klimat-inverkningarna av stratosfäriska partiklar under 1900-talet. Under väldigt stora skogsbränder kan liknande vräkningar av svavel ske upp till stratosfären, och detta är ett relativt glest studieområde men kan möjligtvis ha en viss tyngd i jordens strålningsbalans som är värd at undersöka. Iakttagelser av dessa stratosfäriska fenomen kan tillfogas med hjälp av satellitdata från SAGE II (1984–2005) och SAGE III (2017-), som observerar ljusets spridning och absorbering av olika partiklar i atmosfären. Genom att applicera och jämföra en molnalgoritm, våra resultat och tidigare studier strävar vi efter att kartlägga den stratosfäriska aerosolen för detta tidsintervall. ii Acknowledgements This project is performed to contribute to further study by Friberg et al. (2018) on the period 1984–2005 (SAGE II) and 2017–2019 (SAGE III) of stratospheric aerosol analysis and future projects made by our group at the department of nuclear physics at Lund University. From the group I would personally like to thank Johan Friberg, Bengt G. Martinsson, Moa Sporre and Oscar S. Sandvik for their cooperation and contribution to this project. All figures used in this report from external sources have been cited correspondingly with access consent. iii Acronyms and Abbreviations AOD Aerosol Optical Depth ATAL Asian Tropopause Aerosol Layer CALIPSO Cloud-Aerosol Lidar & Infrared Pathfinder Satellite Observation CCN Cloud Condensation Nuclei CDNC Cloud Droplet Number Concentration CFCs Chlorofluorocarbons CLAES Cryogenic Limb Array Etalon Spectrometer ECMWF European Centre for Medium-Range Weather Forecasts ERBS Earth Radiation Budget Satellite Ext Extinction coefficient ExTL Extratropical Transition Layer GloSSAC The Global Space based Stratospheric Aerosol Climatology HALOE Halogen Occultation Experiment ISS The International Space Station IPCC Intergovernmental Panel on Climate Change LMS Lower Most Stratosphere MERRA Modern-Era Retrospective analysis for Research and Application NH Northern Hemisphere PSC Polar Stratospheric Cloud SAGE Stratospheric Aerosol & Gas Experiment SH Southern Hemisphere TP Tropopause T.V. Thomasson and Vernier (2013) UTLS Upper Troposphere & Lower Stratosphere UV Ultra Violet WMO World Meteorological Organisation iv Contents Abstract ....................................................................................................................... i Abstract (Swedish) .................................................................................................... ii Acknowledgements .................................................................................................. iii Acronyms and Abbreviations .................................................................................. iv 1. Introduction ............................................................................................................ 1 2. Background ............................................................................................................ 3 2.1 Stratospheric Composition ................................................................................. 3 2.2 SAGE ................................................................................................................. 4 2.3 Atmospheric Optics ............................................................................................ 5 2.4 SAGE II 1993 cloud classification ....................................................................... 6 2.5 SAGE II 2013 cloud classification ....................................................................... 7 3. Aim ........................................................................................................................ 10 4. Method and Application ...................................................................................... 11 4.1 Handling and illustrating data ........................................................................... 11 4.2 Application of cloud algorithm ........................................................................... 12 4.2.1 The 1993 method of cloud removal ........................................................ 13 4.2.2 The 2013 method of cloud removal ........................................................ 14 4.3 New Combined method .................................................................................... 15 4.4 Method for polar stratospheric clouds............................................................... 16 4.5 Data extrapolation and Interpolation ................................................................. 18 5. Results .................................................................................................................. 20 5.1 Cloud mask performance on SAGE II............................................................... 20 5.2 Cloud mask performance on SAGE III ............................................................. 21 5.3 Aerosol Optical Depth....................................................................................... 23 6. Discussion ........................................................................................................... 26 7. Conclusions ......................................................................................................... 29 References ............................................................................................................... 30 Appendix .................................................................................................................. 33 1. Introduction The impact Stratospheric Aerosols have on our Earth’s climate and energy budget, can be regarded as an important but uncertain field. In particular when glancing at IPCC’s (2013) AR5 radiative forcing schematics and their respective Level of Confidence. But recognizing that aerosols in the atmosphere are having a significant impact to our weather and climate is not a newly implied discovery. A historic example was when the Laki volcano