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Free Content Development of meteorological parameters and total ozone during the total solar eclipse of August 11, 1999

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During the total eclipse of August 11, 1999 frequent showers occurred due to a unstable stratification of the air mass. At different observation sites, meteorological effects from the eclipse (99.4% coverage at Hohenpeißenberg) and from showers were superimposed making it partly difficult to unambiguously interpret the observations. The weather radar at Hohenpeißenberg observatory provided a general overview of the distribution of clouds and precipitation in this area (200 km diameter). From the Garching site in the zone of totality (100%) temperature and wind data taken on a 50 m mast were evaluated. By selecting periods with relatively low cloud cover it was possible to approximately follow the development of the vertical temperature and wind profiles during the eclipse. The minimum temperature at Hohenpeißenberg (about 450 m above the altitude of Garching) during the eclipse was comparable to that during the previous night, the corresponding value measured at Garching remained about 2 K above the minimum observed during clear sky conditions in the previous night. Showers before, during or after the eclipse may have induced vertical exchange of air parcels. Temperatures during a shower change towards the same direction at all altitudes, thus no inversion forms. Additionally, air parcels with relatively lower concentrations of trace constituents were transported down from aloft for time periods of 10–15 minutes. These mixing processes significantly determined the temporal variations of various trace substances measured during the eclipse. Total ozone measurements at Hohenpeißenberg were performed with both DOBSON and BREWER spectrophotometers and at another site within the zone of totality by using a portable Microtops II filter instrument. Different results were obtained for both sites. These differences can be to a large extend, but not exclusively, attributed to eclipse induced shifts (limb darkening and straylight effects in the atmosphere) in the wavelength pairs used to calculate total ozone. However, there also appeared to be real fluctuations in total ozone during the reemerging phase of the sun which may be related to eclipse induced gravity waves.

Während der totalen Sonnenfinsternis am 11. August 1999 bildeten sich bei der herrschenden labilen Wetterlage in Bayern zahlreiche Schauer. Schauereffekte überlagerten sich daher an vielen Beobachtungsplätzen (99,4% Sonnenabdeckung am Hohenpeißenberg) mit Finsterniseffekten, weshalb eindeutige Interpretationen schwierig sind. Das Bildprodukt des Hohenpeißenberger Wetterradars ermöglicht einen Überblick über die Verteilung von Niederschlag und dichter Bewölkung. In Garching wurden in der Totalitätszone Temperatur und Wind an einem 50 m Mast gemessen. Durch Auswahl von Zeiten mit geringer Bewölkung ist es möglich, die ungefähre Entwicklung der Temperatur- und Windprofile zu verfolgen. Am Hohenpeißenberg etwa 450 m oberhalb von Garching erreichte das Temperaturminimum etwa die Temperatur, die auch in der vorangegangenen Nacht beobachtet wurde. In Garching dagegen blieb die Temperatur während der Finsternis deutlich oberhalb (2K) des Nachtminimums. Bei Schauern vor, während und nach der Totalität kam es zum Vertikalaustausch von Luftpaketen. Die Temperaturen am 50 m Mast änderten sich dabei gleichsinnig in allen Höhen. Gleichzeitig wiesen diese Luftpakete für 10-15 Minuten geringere Belastungen an Luftbeimengungen auf. Diese Beobachtungen sind für die Interpretation luftchemischer Messreihen während der Finsternis von Bedeutung. Messungen des Gesamtozons am Hohenpeißenberg mit BREWER-und DOBSON Spektrophotometern und in der Totalitätszone mit einem portablen Mikrotops II Filtergerät ergaben unterschiedliche Ergebnisse. Die Unterschiede können zum Teil auf finsternisbedingte Verschiebungen in den Wellenlängenpaaren (Randverdunklung der Sonne und Streueffekte in der Atmosphäre) zurückgeführt werden, die zur Berechnung des Gesamtozons benutzt werden. Es scheint aber auch realistische Fluktuationen im Gesamtozon nach der Totalität zu geben, die wahrscheinlich auf von der Finsternis ausgelösten Schwerewellen in der Atmosphäre beruhen.

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Document Type: Research Article

Publication date: 2001-05-01

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