Identification

Title

An analysis of the momentum forcing in the high-latitude lower thermosphere

Abstract

We analyze the dynamics of the high-latitude thermsopheric wind system below 170 km for negative IMF B z by using a fully nonlinear model with a realistic distribution of the forcing. A transition of the forcing patterns and their relative contribution to the high-latitude lower thermospheric wind system occurs around 123 km under various conditions, weak or strong IMF, summer or winter. Winds around and above 123 km are sustained by the gradient-wind balance among divergent/convergent pressure gradient, Coriolis, and horizontal momentum advection (mainly centrifugal) accelerations. Below 123 km winds are maintained by the approximate balance of divergent/convergent pressure gradient, Coriolis, and Hall ion drag accelerations through modified geostrophy. The dominant contribution to the wind tendency (time rate of change) is the rotational component of the ion drag acceleration. The wind tendency above 123 km tends to resemble rotational Pedersen ion drag acceleration well, which reflects a rotated pattern of the E × B velocity. Near and below 123 km the wind tendency is also affected by the rotational component of the Hall ion drag acceleration whose pattern no longer closely resembles the pattern of the E × B velocity, and the wind pattern can differ significantly from that well above 123 km. Simulations for different strengths of the IMF and different seasons indicate that largely divergent/convergent Coriolis and horizontal momentum advection accelerations tend approximately to balance with the horizontal pressure gradient (as well as with divergent/convergent ion drag at lower altitudes) under various conditions. As the forcing increases the radius of curvature of the strong winds also tends to increase, so that the centrifugal acceleration does not increase quadratically with the maximum wind speed, and the tendency for a rough balance between the Coriolis and horizontal momentum advection accelerations in the duskside vortex above 123 km is maintained.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d7kw5g8n

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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South bounding latitude

Temporal reference

Temporal extent

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End position

Dataset reference date

date type

publication

effective date

2007-01-26T00:00:00Z

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Conformity

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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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