Browsing by Subject "STRATOSPHERE"

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  • Tyrrell, Nicholas L.; Karpechko, Alexey Yu.; Uotila, Petteri; Vihma, Timo (2019)
    Abstract: The warm Arctic-cold continent pattern was of record strength in October 2016, providing the opportunity to test its proposed influence on large-scale atmospheric circulation. We find a record weak polar stratospheric vortex and negative North Atlantic Oscillation in November-December 2016 and link them to increased planetary wave generation associated with cold Siberian anomalies followed by troposphere-stratosphere dynamical coupling. At the same time the warm Arctic anomalies, in particular those over the Barents-Kara Seas, do not appear to play an important role in forcing the atmospheric circulation. Long-range forecasts initialized on 1 October 2016 reproduced both the weak polar vortex and negative North Atlantic Oscillation, as well as their link with the Siberian temperatures. Our results support the stratospheric pathway for atmospheric circulation forcing associated with Siberian surface anomalies and uncover a source of skill for subseasonal forecasts from October to December. Plain Language Summary: The warm Arctic-cold continent pattern is an observed, large-scale pattern of near-surface temperatures where the Arctic is warmer than average and Siberia is colder than average. This pattern was of record strength in October 2016, providing the opportunity to test its influence on the Northern Hemisphere atmospheric circulation and the possibility of skillful long-range forecasts. It has been proposed that the warm Arctic-cold continent pattern can drive large atmospheric waves, which are able to travel from the troposphere into the stratosphere, where they weaken the strong wintertime winds that make up the stratospheric polar vortex. A weakened polar vortex can then lead to changes in the surface pressure that can affect weather patterns. We find a record weak polar stratospheric vortex in late autumn 2016 and link that to cold Siberian anomalies. At the same time the warm Arctic anomalies do not appear to play an important role in forcing the atmospheric circulation. Long-range forecasts initialized in October 2016 reproduced both the weak polar vortex and resulting surface pressure patterns. Our results support the stratospheric pathway for atmospheric circulation forcing by Siberian surface anomalies and uncover a source of skill for subseasonal forecasts in the Northern Hemisphere autumn.
  • Liu, Yang; Pellikka, Petri; Li, Hansunbai; Fang, Xiuqi (2019)
    Continuous detection of dispersion and residence of volcanic plumes in troposphere and lower stratosphere is vitally important for improving the understanding on the role of volcano eruptions in climate change. We report a 3-month continuous detection of dispersion and residence of volcanic plumes in the troposphere and stratosphere generated from the volcanic SO2 erupted by Nabro in Eritrea on June 12th, 2011 observed by the OMI sensor. The background SO2 concentration of 3 different height layers in troposphere and lower stratosphere were estimated by the 3-year-average daily concentration of monthly SO2 in 2005, 2007 and 2013, when there were no large explosive volcanic eruptions occurring. We also traced the diffusion path and the concentration of volcanic SO2 for the first 3 months after Nabro's eruption, and detected the appearance and dissipation of sulfate aerosols, which is a product converted from volcanic SO2. The results show that after Nabro erupted on June 12th, the volcanic plumes spread to middle latitudes (30 degrees N -60 degrees N) of Northern Hemisphere and loading by westerly jet. The volcanic SO2 in middle troposphere layer (TRM) and lower troposphere layer (TRL) stopped eastward spreading, and dissipated over the western Pacific Ocean on June 23rd. On June 26th, the volcanic SO2 in upper troposphere and lower stratosphere (STL) reached Mexico in Central America, and almost encircled the low latitudes and parts of middle latitudes. On June 28th, the volcanic SO2 plume showed an even distribution in STL. 37 days after the eruption, the volcanic SO2 in STL encircled the Northern Hemisphere evenly, sulfate aerosols in STL largely covered the low and middle latitudes and the daily concentration of SO2 was still higher than the background value. One month after the eruption, the global mean daily concentration of SO2 dropped to the normal value, but the daily concentration of SO2 and sulfate aerosols in low latitudes remained high, and dissipated not earlier than 3 months after the eruption of Nabro.
  • Salminen-Paatero, Susanna; Thölix, Laura E; Kivi, Rigel; Paatero, Jussi (2019)
    Radionuclides 137Cs and 90Sr and total beta activity were determined from air filters collected in Rovaniemi (Finnish Lapland) in1965–2011. Nuclear contamination sources present in the air filter samples as well as temporal changes in radionuclide concentrations were examined. Ozone observations and meteorological modeling were used in combination with radionuclide analyses to study the reasons behind the observed seasonal concentration variation. In general, the magnitude and variation in activity concentrations of 137Cs and 90Sr and total beta activity in the surface air of Rovaniemi in 1965–2011 corresponded well with values from other countries. However, the obtained results prove in practice that hardly any refractory or intermediate radionuclides from the destroyed Chernobyl reactor fuel were introduced to Finnish Lapland. The main source of 137Cs and 90Sr and total beta activity in the surface air of Rovaniemi in 1965–2011 has been intense atmospheric nuclear weapon testing in 1950s–1960s and later tests performed in 1965–1980, as well as leakages from underground nuclear tests in Semipalatinsk, 1966, and Novaya Zemlya, 1987. For 137Cs and total beta activity, the influence of Chernobyl and Fukushima accidents was detected.