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| 2. |
- Blum, Ulrich, et al.
(författare)
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Simultaneous lidar observations of a polar stratospheric cloud on the east and west side of the Scandinavian mountains and microphysical box model simulations
- 2006
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Ingår i: Annales Geophysicae. ; 24, s. 3267-3277
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Tidskriftsartikel (refereegranskat)abstract
- The importance of polar stratospheric clouds (PSC) for polar ozone depletion is well established. Lidar experiments are well suited to observe and classify polar stratospheric clouds. On 5 January 2005 a PSC was observed simultaneously on the east and west sides of the Scandinavian mountains by ground-based lidars. This cloud was composed of liquid particles with a mixture of solid particles in the upper part of the cloud. Multi-colour measurements revealed that the liquid particles had a mode radius of r~300 nm, a distribution width of ~1.04 and an altitude dependent number density of N~2–20 cm−3. Simulations with a microphysical box model show that the cloud had formed about 20 h before observation. High HNO3 concentrations in the PSC of 40–50 weight percent were simulated in the altitude regions where the liquid particles were observed, while this concentration was reduced to about 10 weight percent in that part of the cloud where a mixture between solid and liquid particles was observed by the lidar. The model simulations also revealed a very narrow particle size distribution with values similar to the lidar observations. Below and above the cloud almost no HNO3 uptake was simulated. Although the PSC shows distinct wave signatures, no gravity wave activity was observed in the temperature profiles measured by the lidars and meteorological analyses support this observation. The observed cloud must have formed in a wave field above Iceland about 20 h prior to the measurements and the cloud wave pattern was advected by the background wind to Scandinavia. In this wave field above Iceland temperatures potentially dropped below the ice formation temperature, so that ice clouds may have formed which can act as condensation nuclei for the nitric acid trihydrate (NAT) particles observed at the cloud top above Esrange.
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| 3. |
- Steck, T., et al.
(författare)
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Bias determination and precision validation of ozone profiles from MIPAS-Envisat retrieved with the IMK-IAA processor
- 2007
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 7:13, s. 3639-3662
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Tidskriftsartikel (refereegranskat)abstract
- This paper characterizes vertical ozone profiles retrieved with the IMK-IAA (Institute for Meteorology and Climate Research, Karlsruhe – Instituto de Astrofisica de Andalucia) science-oriented processor from high spectral resolution data (until March 2004) measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard the environmental satellite Envisat. Bias determination and precision validation is performed on the basis of correlative measurements by ground-based lidars, Fourier transform infrared spectrometers, and microwave radiometers as well as balloon-borne ozonesondes, the balloon-borne version of MIPAS, and two satellite instruments (Halogen Occultation Experiment and Polar Ozone and Aerosol Measurement III). Percentage mean differences between MIPAS and the comparison instruments for stratospheric ozone are generally within ±10%. The precision in this altitude region is estimated at values between 5 and 10% which gives an accuracy of 15 to 20%. Below 18 km, the spread of the percentage mean differences is larger and the precision degrades to values of more than 20% depending on altitude and latitude. The main reason for the degraded precision at low altitudes is attributed to undetected thin clouds which affect MIPAS retrievals, and to the influence of uncertainties in the water vapor concentration.
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| 4. |
- Tomasi, C., et al.
(författare)
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Aerosols in polar regions : A historical overview based on optical depth and in situ observations
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112:D16, s. D16205-
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Forskningsöversikt (refereegranskat)abstract
- Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and for different time periods. They were examined to estimate ensemble average, long-term trends of the summer background aerosol optical depth AOD(500 nm) in the polar regions ( omitting the data influenced by Arctic haze and volcanic eruptions). The trend for the Arctic was estimated to be between -1.6% and -2.0% per year over 30 years, depending on location. No significant trend was observed for Antarctica. The time patterns of AOD( 500 nm) and angstrom ngstrom's parameters a and beta measured with Sun photometers during the last 20 years at various Arctic and Antarctic sites are also presented. They give a measure of the large variations of these parameters due to El Chichon, Pinatubo, and Cerro Hudson volcanic particles, Arctic haze episodes most frequent in winter and spring, and the transport of Asian dust and boreal smokes to the Arctic region. Evidence is also shown of marked differences between the aerosol optical parameters measured at coastal and high-altitude sites in Antarctica. In situ optical and chemical composition parameters of aerosol particles measured at Arctic and Antarctic sites are also examined to achieve more complete information on the multimodal size distribution shape parameters and their radiative properties. A characterization of aerosol radiative parameters is also defined by plotting the daily mean values of a as a function of AOD( 500 nm), separately for the two polar regions, allowing the identification of different clusters related to fifteen aerosol classes, for which the spectral values of complex refractive index and single scattering albedo were evaluated.
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