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Atmospheric Profiling Using the Lidar Technique 166 CONTRIBUTIONS ATMOSPHERIC PROFILING USING THE LIDAR TECHNIQUE MARIA FILIOGLOU FINNISH METEOROLOGICAL INSTITUTE CONTRIBUTIONS No. 166 ATMOSPHERIC PROFILING USING THE LIDAR TECHNIQUE Maria Filioglou Finnish Meteorological Institute Atmospheric Research Centre of Eastern Finland Kuopio, Finland 2020 Academic dissertation To be presented by the permission of the Faculty of Science and Forestry for public examination through video connection at the University of Eastern Finland, Kuopio, on June 17, 2020, at 12 o’clock noon ISBN 978-952-336-109-6 (paperback) ISBN 978-952-336-110-2 (pdf) ISSN 0782-6117 Edita Prima Oy Helsinki 2020 Author’s address: Finnish Meteorological Institute Atmospheric Research Centre of Eastern Finland 70211 KUOPIO, FINLAND email: [email protected] Supervisors: Docent Mika Komppula, Ph.D. Finnish Meteorological Institute Atmospheric Research Centre of Eastern Finland 70211 KUOPIO, FINLAND email: [email protected] Lecturer Eleni Giannakaki, Ph.D. Department of Environmental Physics and Meteorology, University of Athens, Athens GR15784 ATHENS, GREECE email: [email protected] Docent Tero Mielonen, Ph.D. Finnish Meteorological Institute Atmospheric Research Centre of Eastern Finland 70211 KUOPIO, FINLAND email: [email protected] Professor Kari Lehtinen, Ph.D. University of Eastern Finland Department of Applied Physics 70211 KUOPIO, FINLAND email: [email protected] Reviewers: Research scientist Francisco Navas‐Guzmán, Ph.D. Federal Office of Meteorology and Climatology MeteoSwiss, Atmospheric Data Division CH-1530 PAYERNE, SWITZERLAND email: [email protected] Research scientist Anca Nemuc, Ph.D. National Institute of Research and Development for Optoelectronics, INOE 2000 077125 MAGURELE, ROMANIA email: [email protected] Opponent: Research scientist Franco Marenco, Ph.D. Met Office EX1 3PB EXETER, UNITED KINGDOM email: [email protected] Published by Finnish Meteorological Institute Series title, number, and report code of publication Erik Palménin aukio 1, P.O. Box 503 Finnish Meteorological Institute Contributions, 166, FIN-00101 Helsinki, Finland FMI-CONT-166 Date: May 2020 Author(s) Maria Filioglou Title Atmospheric profiling using the lidar technique Abstract Atmospheric aerosol particles absorb and scatter solar radiation, altering directly the radiation balance. Indi- rectly, these particles have a complex interplay in cloud formation, affecting cloud reflectivity and cloud lifetime. Apart from the climatic effects, atmospheric particles pose negative health effects and they reduce visibility with adverse effects in road traffic and aviation safety. To improve the understanding of the aerosol effect on climate four different studies have been conducted. The main instrument utilized to retrieve vertical profiles of the aerosols was a multi-wavelength PollyXT lidar. The hygroscopic effect of the aerosol particles in the retrieved optical properties which is relevant to cloud studies can be assessed using the water vapor capabilities of the lidar. Lidar water vapor retrieval requires initial cali- bration. An evaluation of the different lidar water vapor signal calibration techniques was performed to quantify the uncertainty in the retrieved water vapor profiles. Moreover, two measurement campaigns were held in Finland and the United Arab Emirates in order to characterize the properties of understudied aerosol types (pollen and Arabian dust). Lastly, the effectiveness of the different aerosol types to the formation of ice, water, or mixed- phase clouds in the Arctic was determined using a synergy of a spaceborne lidar (CALIOP) and a cloud radar (CloudSat). The study on water vapor showed that accurate water vapor retrievals are subject to the calibration factor. Operational on-site radiosondes are the best option, but robust retrievals are possible using data from the nearest radiosonde site or modelled data. Satellite-derived water vapor profiles performed the poorest, yet they could serve as an option in the absence of better information. The analysis of the pollen observations showed that the classification of various pollen types is possible, although challenging. Characterization requires shape infor- mation from at minimum two linear particle depolarization wavelengths, as well as external information such as airmass backward trajectories to ensure that other non-spherical aerosol particles such as dust are not present over the measurement site. Regarding the Arabian dust optical properties, it was found that this aerosol type exhibits different optical properties, specifically concerning the lidar ratios, than the dust originating from the Saharan region. Consequently, the universal lidar ratio of 55 sr currently used in lidar-based applications may lead to biases for dust originating from the Arabian Peninsula. The Arctic study on aerosol-cloud interactions showed that higher aerosol load was associated with higher occurrence of mixed-phase clouds. On the contrary, moderate association was found with varying the aerosol type. Nevertheless, meteorology outweighed the aer- osol load importance over less stable atmospheric conditions, for example, over open ocean. Publishing unit Finnish Meteorological Institute, Atmospheric Research Centre of Eastern Finland Classification (UDC) Keywords 528.8.042, 528.8.044.6, 532.243, 551.521.3 Remote sensing, aerosols, clouds, 551.501.86, 52-64, 54-138 satellite, measurements ISSN and series title 0782-6117 Finnish Meteorological Institute Contributions ISBN Language Pages 978-952-336-109-6 (paperback) English 158 978-952-336-110-2 (pdf) Julkaisija Ilmatieteen laitos Julkaisun sarja, numero ja raporttikoodi Erik Palménin aukio 1 Finnish Meteorological Institute Contributions, 166, PL 503, 00101 Helsinki FMI-CONT-166 Päiväys Toukokuu 2020 Tekijä(t) Maria Filioglou Nimeke Ilmakehän luotaaminen lidar-tekniikalla Tiivistelmä Tässä väitöskirjassa tutkittiin ilmakehän pienhiukkasten ominaisuuksia ja niiden vaikutusta pilviin hyödyntä- mällä useiden kaukokartoitusmenetelmien synergiaa. Tutkimuksessa käytettiin pääasiassa PollyXT–lidar-mitta- laitetta. Tutkimus jakautui kolmeen kokonaisuuteen: 1) Arvioitiin eri kalibrointimenetelmien aiheuttamaa epävar- muutta lidar-mittauksiin pohjautuvissa vesihöyryprofiileissa. 2) Määritettiin Suomessa ja Yhdistyneissä arabiemii- rikunnissa tehtyjen mittausten avulla siitepölyn ja aavikkopölyn optiset ominaisuudet. 3) Selvitettiin miten erilaiset pienhiukkastyypit vaikuttavat erityyppisten pilvien muodostumiseen Arktisella alueella hyödyntämällä satelliitti- pohjaisia lidar- (CALIOP) ja tutkahavaintoja (CloudSat). Vesihöyrytutkimus osoitti, että tarkat lidar-havainnot vesihöyrystä vaativat tarkan kalibroinnin muiden mittaus- ten avulla. Parhaaseen tulokseen päästään käyttämällä radioluotauksia samalta asemalta mutta niiden puuttu- essa voidaan käyttää myös radioluotauksia lähiseudulta tai mallinnettuja vesihyöryprofiileja. Heikoin tulos saatiin satelliittihavaintoja käyttämällä, mutta niistäkin on apua parempien tietolähteiden puuttuessa. Siitepölymittaukset osoittavat, että siitepölytyyppien tunnistaminen lidar-mittausten avulla saatavien optisten ominaisuuksien perus- teella on mahdollista, vaikkakin haastavaa. Tyyppien tunnistamiseksi mittauksista täytyy saada tietoa hiukkasten muodosta, koosta sekä kyvystä absorboida valoa. Lisäksi pitää varmistaa, että havaintoja eivät ole häirinneet muut ei-pallomaiset hiukkaset, kuten aavikkopöly, käyttämällä tietoa ilmamassojen kulkureiteistä. Mittaukset Ara- bian niemimaan aavikkopölystä paljastivat, että sen optiset ominaisuudet poikkeavat Saharan pölystä, etenkin lidarsuhteen osalta. Täten lidar-mittausten analyyseissa usein käytetty lidarsuhde aavikkopölylle ei vastaa Ara- bian niemimaan aavikkopölyä. Tutkimus pienhiukkasten ja pilvien vuorovaikutuksesta Arktisella alueella osoitti, että pienhiukkasten määrän kasvaessa pilvet, jotka sisältävät sekä vettä että jäätä, lisääntyvät. Pienhiukkastyy- pin vaikutus pilviin oli huomattavasti pienempi. Sen sijaan ilmakehän ollessa epävakaa, esimerkiksi avomeren päällä, pilvien ominaisuudet riippuivat enemmän ilmakehän virtauksista kuin pienhiukkasten pitoisuudesta tai tyypistä. Julkaisijayksikkö Ilmatieteen laitos, Itä-Suomen ilmatieteellinen tutkimuskeskus Luokitus (UDK) Asiasanat 528.8.042, 528.8.044.6, 532.243, 551.521.3 Kaukokartoitus, aerosolit, pilvet, satelliitit, 551.501.86, 52-64, 54-138 mittausmenetelmät ISSN and series title 0782-6117 Finnish Meteorological Institute Contribution ISBN Kieli Sivumäärä 978-952-336-109-6 (nidottu) Englanti 158 978-952-336-110-2 (pdf) Acknowledgements The work presented in this dissertation has been carried out at the Atmospheric Research Centre of Eastern Finland in Kuopio at the Finnish Meteorological Institute. I am grateful to research Professor Sami Romakkaniemi for the opportunity to work in Kuopio and for all the consultation and encouragement given throughout this the- sis. I could not imagine any better support all these years. I also express my gratitude to my four supervisors: Doc. Mika Komppula for giv- ing me the opportunity to work in challenging yet interesting research projects and field campaigns all around the world. Thank you for trusting me to find my own solutions. Doc. Eleni Giannakaki for the very relevant comments that pushed me to try harder; Doc. Tero Mielonen for always having the time to discuss my concerns and research-related issues, despite the myriad times I’ve knocked his office door! It must not have been always very pleasant,
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