Simulations of large winds and wind shears induced by gravity wave breaking in the mesosphere and lower thermosphere (MLT) region
Using a fully nonlinear two-dimensional (2-D) numerical model, we simulated gravity waves (GWs) breaking and their contributions to the formation of large winds and wind shears in the mesosphere and lower thermosphere (MLT). An eddy diffusion coefficient is used in the 2-D numerical model to par...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-05-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/32/543/2014/angeo-32-543-2014.pdf |
| Summary: | Using a fully nonlinear two-dimensional (2-D) numerical model, we simulated
gravity waves (GWs) breaking and their contributions to the formation of
large winds and wind shears in the mesosphere and lower thermosphere (MLT).
An eddy diffusion coefficient is used in the 2-D numerical model to
parameterize realistic turbulent mixing. Our study shows that the momentum
deposited by breaking GWs accelerates the mean wind. The resultant large
background wind increases the GW's apparent horizontal phase velocity and
decreases the GW's intrinsic frequency and vertical wavelength. Both the
accelerated mean wind and the decreased GW vertical wavelength contribute to
the enhancement of wind shears. This, in turn, creates a background condition
that favors the occurrence of GW instability, breaking, and momentum
deposition, as well as mean wind acceleration, which further enhances the
wind shears. We find that GWs with longer vertical wavelengths and faster
horizontal phase velocity can induce larger winds, but they may not
necessarily induce larger wind shears. In addition, the background
temperature can affect the time and height of GW breaking, thus causing
accelerated mean winds and wind shears. |
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| ISSN: | 0992-7689 1432-0576 |