Estimating methods and variability of atmospheric humidity over the Baltic Region and the Arctic
Date
2015-04-29
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Abstract
Kuna veeauru ruumiline jaotumine mõjutab otseselt sademete ja pilvede teket, keemilisi reaktsioone ning kiirguslevi atmosfääris, on see oluline nii hetkeilma kui kliima kujundaja. Veeauru, kui kõige olulisema kasvuhoonegaasi mõõtmisel on endiselt suurimaks probleemiks selle ajalise ja ruumilise muutlikkuse kirjeldamine. Kuigi õhusamba niiskussisalduse (precipitable water, PW) määramisviise on mitmeid, pole neist veel ühtki seatud etalonmeetodi staatusesse. See tekitab jätkuva vajaduse viia läbi võrdluskatseid.
Antud doktoritöö eesmärkideks oli uurida atmosfääriniiskuse pikaajalisi trende erinevatel kõrgusnivoodel Soome ja Eesti kohal alates 1980. aastatest, selgitada suvist PW ööpäevast käiku Läänemere piirkonnas, hinnata Eestis kasutusel olevate PW määramismeetodite täpsust ja valideerida viit levinuimat globaalset järelanalüüsi atmosfääriniiskuse määramisel Arktikas.
Doktoritöö tulemusena selgub, et Soome ja Eesti kohal on viimastel aastakümnetel kuni 7 km ulatuses aset leidnud soojenemine, maapinnalähedases 2 km kihis on täheldatav ka niiskussisalduse kasv. Läänemere piirkonnas saavutab PW mere ja suuremate järvede kohal maksimumi öösel ja miinimumi hilisõhtul. Võrreldes käiguga suuremate veekogude kohal, on ööpäevane käik maismaa kohal ümberpööratud – maksimum saabub hilisõhtul ja miinimum varahommikul. Õhusamba niiskussisalduse määramisel on Eestis kasutusel olevatest hindamisviisidest parim alternatiiv raadiosondile, kui ajaloolisele referentsmeetodile, GPS-meetod.
Water vapour provides the largest greenhouse effect on the Earth’s climate. Its distribution influences precipitation, clouds, chemical reactions, incoming solar radiation, outgoing heat, etc. In current meteorological practice, a significant challenge in measurements is related to estimation of its spatial and temporal distribution. However, despite of several estimation techniques for column water vapour amount or simply, precipitable water (PW), no method or model is yet identified as the most accurate or the reference one. This drives a necessity to continuously perform intercomparisons, which help to evaluate strengths and weaknesses, accuracy and biases of different methods. The aims of the thesis are to investigate long-term variability and trends in vertical humidity profiles in Estonia and Finland since 1980s, describe diurnal cycle of PW in the Baltic Region at summer, estimate the accuracy of different PW methods available in Estonia, and validate global reanalyses humidity profiles for the lowermost Arctic’s atmosphere. It is revealed that troposphere above Estonia and Finland has become warmer at all altitudes up to 7 km and more moist below the altitude of 2 km. The diurnal cycle of PW depends on whether the area of investigation is located above the Baltic Sea and larger lakes, or above the land. Humidity content above the water reaches a peak and decreases to the minimum at midnight and late evening, respectively. Above the land the peak is reached in the evening and the minimum is detected in the morning. The study suggests that besides radiosonde, as a traditional meteorological tool, the most reliable PW estimation can be made by GPS.
Water vapour provides the largest greenhouse effect on the Earth’s climate. Its distribution influences precipitation, clouds, chemical reactions, incoming solar radiation, outgoing heat, etc. In current meteorological practice, a significant challenge in measurements is related to estimation of its spatial and temporal distribution. However, despite of several estimation techniques for column water vapour amount or simply, precipitable water (PW), no method or model is yet identified as the most accurate or the reference one. This drives a necessity to continuously perform intercomparisons, which help to evaluate strengths and weaknesses, accuracy and biases of different methods. The aims of the thesis are to investigate long-term variability and trends in vertical humidity profiles in Estonia and Finland since 1980s, describe diurnal cycle of PW in the Baltic Region at summer, estimate the accuracy of different PW methods available in Estonia, and validate global reanalyses humidity profiles for the lowermost Arctic’s atmosphere. It is revealed that troposphere above Estonia and Finland has become warmer at all altitudes up to 7 km and more moist below the altitude of 2 km. The diurnal cycle of PW depends on whether the area of investigation is located above the Baltic Sea and larger lakes, or above the land. Humidity content above the water reaches a peak and decreases to the minimum at midnight and late evening, respectively. Above the land the peak is reached in the evening and the minimum is detected in the morning. The study suggests that besides radiosonde, as a traditional meteorological tool, the most reliable PW estimation can be made by GPS.
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Keywords
atmosfäär, veesisaldus, veeaur, määramismeetodid, Läänemeri, Arktika, atmosphere, water content, water vapour, fixed methods, Baltic Sea, Arctic