| 1. |
- Kirkwood, Sheila, et al.
(författare)
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Independent Calibration of Radar Reflectivities Using Radiosondes: Application To ESRAD
- 2011
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Ingår i: Proceedings of the ‘20th ESA Symposium on European Rocket and Balloon Programmes and Related Research’. ; , s. 425-429
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Konferensbidrag (refereegranskat)abstract
- A large number of empirical and theoretical studies haveshown that radar reflectivity from the atmosphere at 50MHz is proportional to the mean vertical gradient of therefractive index. Up to 30 km height the refractive indexis determined by temperature, pressure and humidityprofiles, which can readily be measured by radiosondes.In practice, humidity becomes unimportant abovethe mid-troposhere. The coefficient of proportionality betweenradar reflectivity and mean refractive index gradientshould, in principle, depend on the fine-scale structureof refractive index fluctuations. However, recent empiricalevidence shows that the coefficient varies very littlebetween widely different meteorological conditions andbetween radars in very different locations (Esrange, tropicalIndia, Antarctica). This means we can use meanprofiles of refractive index, measured by radiosondes, asan independent method to provide continuous calibrationof radar reflectivity and to cross-calibrate between differentradars without the need to interrupt operations for thekind of engineering tests which are usually used for calibration.We show how this can be applied for long-termcalibration of the 52 MHz atmospheric radar at Esrange,ESRAD.The observed invariability of the coefficient of proportionalityalso poses an intriguing question as to how it canbe explained. High-resolution sondes, constant-heightsondes, and UAV’s are suggested as suitable platformsfor further study of the radar scattering mechanisms.
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| 3. |
- Mihalikova, Maria, et al.
(författare)
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Vertical mixing in the lower troposphere by mountain waves over Arctic Scandinavia
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11, s. 31475-31493
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Tidskriftsartikel (refereegranskat)abstract
- Measurements made by ozonesondes and by a 52 MHz wind-profiling radar during February and March 1997 are studied. The radar is located at Esrange, near Kiruna in Arctic Sweden, on the eastern flank of the Scandinavian mountains. Daily ozonesondes were launched from the same site. The radar vertical and horizontal wind measurements are used to identify times when mountain waves were present. Mean vertical gradients in ozone mixing ratio in the lower troposphere are determined in conditions with mountain waves present and when they were absent. Back-trajectories were calculated so that only air-masses with their origin to the west of the mountains were included in the final averages. The vertical gradient in ozone mixing ratio is found to be about twice as steep outside wave conditions as it is during mountain waves. This suggests a very high rate of vertical mixing, with an average eddy diffusivity of order 5000 m2 s−1. This is consistent with an earlier estimate of the occurrence rate of complete mixing by wave breaking over the mountain range.
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