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On the spectrum of atmospheric motions (Ludwig-Prandtl Memorial Lecture

Schumann, Ulrich (2021) On the spectrum of atmospheric motions (Ludwig-Prandtl Memorial Lecture. 91st Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM 2020/21), 15.-19. March 2021, Kassel, Germany (online).

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Abstract

Spectra of atmospheric motions describe the distribution of kinetic and potential energy as a function of scales. The spectrum of horizontal motions in the free troposphere and the lower stratosphere at horizontal scales from a few 10 m to several 1000 km has often been shown to follow a power law with logarithmic spectral slopes near -3 at large scales and near -5/3 at smaller scales. The motions are highly anisotropic. Inertial subrange turbulence occurs only occasionally. The horizontal spectrum of vertical velocity has been discussed relatively little. Vertical wind drives conversion between potential and kinetic energy, vertical fluxes, cloud formation and turbulence. This study started from measurements of velocity and temperature spectra in field campaigns investigating atmospheric dynamics over oceans and mountains with the DLR research aircraft HALO. Accurate measurements are demanding because the wind speed is often small compared to the aircraft speed. The measured spectrum of vertical velocity showed unexpected peaks at scales corresponding to the depth of the atmosphere. We discuss the Helmholtz decomposition of horizontal velocity in rotational and divergent velocity components. We then show that the horizontal spectrum of vertical velocity is kinematically connected to the spectrum of horizontal divergent motions. The observed peaks occur when the divergent motions are vertically coherent and when the horizontal spectrum of divergent velocity reaches spectral slopes larger than -2. Details can be found in a recent publication (J. Atmos. Sci., 2019, doi: 10.1175/JAS-D-19-0160.1). This lecture is dedicated to Ludwig Prandtl (1875-1953) who contributed fundamentally to fluid mechanics, including meteorology.

Item URL in elib:https://elib.dlr.de/141352/
Document Type:Conference or Workshop Item (Speech)
Title:On the spectrum of atmospheric motions (Ludwig-Prandtl Memorial Lecture
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Schumann, UlrichDLR, IPAhttps://orcid.org/0000-0001-5255-6869
Date:2021
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:kinetic energy, vertical velocity, airborne measurements, Helmholtz decomposition, turbulence
Event Title:91st Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM 2020/21)
Event Location:Kassel, Germany (online)
Event Type:international Conference
Event Dates:15.-19. March 2021
Organizer:GAMM and DGLR
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Atmospheric and climate research
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics
Deposited By: Schumann, Prof.Dr.habil. Ulrich
Deposited On:17 Mar 2021 10:16
Last Modified:17 Mar 2021 10:16

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