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Sökning: WFRF:(Ehard Benedikt)

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1.
  • Ehard, Benedikt, et al. (författare)
  • Combination of Lidar and Model Data for Studying Deep Gravity Wave Propagation
  • 2016
  • Ingår i: Monthly Weather Review. - 0027-0644 .- 1520-0493. ; 144:1, s. 77-98
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper presents a feasible method to complement ground-based middle atmospheric Rayleigh lidar temperature observations with numerical simulations in the lower stratosphere and troposphere to study gravity waves. Validated mesoscale numerical simulations are utilized to complement the temperature below 30-km altitude. For this purpose, high-temporal-resolution output of the numerical results was interpolated on the position of the lidar in the lee of the Scandinavian mountain range. Two wintertime cases of orographically induced gravity waves are analyzed. Wave parameters are derived using a wavelet analysis of the combined dataset throughout the entire altitude range from the troposphere to the mesosphere. Although similar in the tropospheric forcings, both cases differ in vertical propagation. The combined dataset reveals stratospheric wave breaking for one case, whereas the mountain waves in the other case could propagate up to about 40-km altitude. The lidar observations reveal an interaction of the vertically propagating gravity waves with the stratopause, leading to a stratopause descent in both cases.
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2.
  • Ehard, Benedikt, et al. (författare)
  • Long-term lidar observations of wintertime gravity wave activity over northern Sweden
  • 2014
  • Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 32:11, s. 1395-1405
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents an analysis of gravity wave activity over northern Sweden as deduced from 18 years of wintertime lidar measurements at Esrange (68ºN, 21ºE). Gravity wave potential energy density (GWPED) was used to characterize the strength of gravity waves in the altitude regions 30–40km and 40–50 km. The obtained values ex- ceed previous observations reported in the literature. This is suggested to be due to Esrange’s location downwind of the Scandinavian mountain range and due to differences in the various methods that are currently used to retrieve gravity wave parameters. The analysis method restricted the identification of the dominating vertical wavelengths to a range from 2 to 13 km. No preference was found for any wavelength in this window. Monthly mean values of GW- PED show that most of the gravity waves’ energy dissipates well below the stratopause and that higher altitude regions show only small dissipation rates of GWPED. Our analy- sis does not reproduce the previously reported negative trend in gravity wave activity over Esrange. The observed inter-annual variability of GWPED is connected to the occurrence of stratospheric warmings with generally lower wintertime mean GWPED during years with major stratospheric warmings. A bimodal GWPED occurrence frequency indicates that gravitywave activity at Esrange is affected by both ubiq- uitous wave sources and orographic forcing.
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  • Resultat 1-2 av 2
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tidskriftsartikel (2)
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refereegranskat (2)
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Gumbel, Jörg (2)
Achtert, Peggy (2)
Ehard, Benedikt (2)
Khaplanov, Mikhail (1)
Wagner, Johannes (1)
Rapp, Markus (1)
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Dörnbrack, Andreas (1)
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Stockholms universitet (2)
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