Weakly or strongly nonlinear mesoscale dynamics close to the tropopause?

Weakly or strongly nonlinear mesoscale dynamics close to the tropopause? AbstractRecently, it has been discussed whether the mesoscale energy spectra in the upper troposphere and lower stratosphere are generated by weakly or strongly nonlinear dynamics. A necessary condition for weak nonlinearity is that , where is the vertical vorticity and f the Coriolis parameter. We first show that Ro can be estimated by integration of the rotational wave number energy spectrum, Er. Then we calculate divergence and rotational energy spectra and their ratio, , from the MOZAIC data set, and show that at least one thousand flight segments are needed to obtain converged results. We find that R < 1 in the upper troposphere, ruling out the hypothesis that the spectra are produced by inertia-gravity waves with frequencies larger than f. In the lower stratosphere R is slightly larger than unity. An analysis separating between land and ocean data shows that Ed as well as temperature spectra have somewhat larger magnitude over land compared to ocean in the upper troposphere – a signature of orographically or convectively forced gravity waves. No such effect is seen in the lower stratosphere. At mid latitudes the Rossby number is of the order of unity and at low latitudes it is larger than unity, indicating that strong nonlinearities are prevalent. We also point out that temperature spectra, when converted into potential energy spectra, have larger magnitude than predicted by the weakly nonlinear wave hypothesis. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Weakly or strongly nonlinear mesoscale dynamics close to the tropopause?

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
D.O.I.
10.1175/JAS-D-17-0063.1
Publisher site
See Article on Publisher Site

Abstract

AbstractRecently, it has been discussed whether the mesoscale energy spectra in the upper troposphere and lower stratosphere are generated by weakly or strongly nonlinear dynamics. A necessary condition for weak nonlinearity is that , where is the vertical vorticity and f the Coriolis parameter. We first show that Ro can be estimated by integration of the rotational wave number energy spectrum, Er. Then we calculate divergence and rotational energy spectra and their ratio, , from the MOZAIC data set, and show that at least one thousand flight segments are needed to obtain converged results. We find that R < 1 in the upper troposphere, ruling out the hypothesis that the spectra are produced by inertia-gravity waves with frequencies larger than f. In the lower stratosphere R is slightly larger than unity. An analysis separating between land and ocean data shows that Ed as well as temperature spectra have somewhat larger magnitude over land compared to ocean in the upper troposphere – a signature of orographically or convectively forced gravity waves. No such effect is seen in the lower stratosphere. At mid latitudes the Rossby number is of the order of unity and at low latitudes it is larger than unity, indicating that strong nonlinearities are prevalent. We also point out that temperature spectra, when converted into potential energy spectra, have larger magnitude than predicted by the weakly nonlinear wave hypothesis.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Feb 7, 2018

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