Identification

Title

Altitude variations of the horizontal thermospheric winds during geomagnetic storms

Abstract

It is generally assumed that viscosity smooths out vertical gradients of the horizontal thermospheric winds in the upper thermosphere, and thus observations of neutral winds at one height can be used at other altitudes in this region. In this paper we present neutral wind simulations of the May 1997 geomagnetic storm using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The model results show that during quiet periods, the assumption of a shearless vertical profile of the horizontal winds is generally valid in low and middle latitudes, although vertical shears do occur in wind profiles in the upper thermosphere in some locations at higher latitudes. During disturbed periods, large variations in the vertical profiles of the upper thermospheric winds are seen globally in the model simulations. A diagnostic analysis of the forcing processes in the neutral momentum equations shows that (1) during quiet time, there are shearing forces, most noticeably the pressure gradient and ion drag, in the upper thermosphere that result in a net momentum forcing that changes with height; this induces altitude variations in the wind profiles at high latitudes and sometime even at middle latitudes. (2) During storm time, momentum advection, which is relatively weak during the quiet time, becomes a dominant force globally. Pressure gradient forces are also significantly enhanced. Ion drag, on the other hand, can be enhanced or suppressed, depending on the location of positive or negative effects. All these forces exhibit significant altitude variations that lead to a net force that is greatly enhanced and has large vertical shears. This produces globally enhanced neutral winds that vary with height. (3) Viscosity is less important than other forcing processes during both the quiet and storm periods and thus cannot prevent shears from occurring in the vertical profiles of the horizontal winds. Viscosity has an insignificant effect on vertical shears that change with height linearly. It, however, does restrict vertical shears that vary nonlinearly with height. The effectiveness of the viscosity in restricting such shears depends on its magnitude. In our simulations, viscosity is weaker than other forcing processes and thus is a relatively slow process, so it will take a few hours for viscosity to reduce such shears.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d7cj8dp1

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

2008-02-02T00:00:00Z

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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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