Identification

Title

Numerical investigation of the quasi 2 day wave in the mesosphere and lower thermosphere

Abstract

The zonal wave number 3 planetary wave with about a 2 day period is a recurrent wave feature in the mesosphere and lower thermosphere (MLT). The quasi 2 day wave (QTDW) exhibits strong seasonal variability with peak amplitudes after summer solstice. In late January and early February, satellites also discovered two strong enhancements of the QTDW in meridional wind, one peak at summer midlatitudes near 90 km and the other in the tropical lower thermosphere. For the first time, this double-peak characteristic of the QTDW meridional component is numerically investigated by the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) with the QTDW forcing prescribed at the lower model boundary and explained by the combined effect of baroclinic-barotropic instability and Rossby normal mode. Baroclinic-barotropic instability is capable of amplifying the QTDW, manifesting as Eliassen-Palm (EP) flux divergence in the summer mesosphere. Without the direct contribution from baroclinic-barotropic instability, the simulated QTDW response in a lower thermosphere temperature and horizontal wind resembles that of the (3, 0) Rossby-gravity normal mode. In the summer middle atmosphere, the wave amplitude grows substantially, like an internal wave in the regions of large refractive index. As the wave amplitude growth ceases near the mesopause, where the zonal wind reverses direction, the QTDW reaches its maximum amplitude, displaying an enhanced meridional component in the tropical lower thermosphere. Several new aspects on the QTDWs in the MLT were also revealed. Compared with a prior model run, the propagation of the QTDW can also be prohibited by a self-generated critical layer in a strong thermospheric easterly wind. In addition, a direct contribution from the migrating diurnal tide to the QTDW amplitude in the MLT is found. This is largely attributed to the change of the background zonal wind caused by the tide, thus leading to the increase of the QTDW refractive index in the summer middle atmosphere.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d7j38t77

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

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keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

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Temporal reference

Temporal extent

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End position

Dataset reference date

date type

publication

effective date

2012-03-07T00:00:00Z

Frequency of update

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Conformity

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version of format

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Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

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