Identification

Title

Hydrodynamic planetary thermosphere model: 1. Response of the Earth's thermosphere to extreme solar EUV conditions and the significance of adiabatic cooling

Abstract

It has been suggested that the exobase temperature of early terrestrial planetary atmosphere could have reached over 10,000 K. Although such high exobase temperatures should have caused the major gases at the exobase to experience fast Jeans escape, and the entire thermosphere should have experienced hydrodynamic flow, hydrostatic equilibrium was assumed to be valid in this earlier model. In this paper we develop a multicomponent hydrodynamic thermosphere model to self-consistently study the Earth's thermosphere under extreme solar EUV conditions. The model is validated against observations and other models for the present Earth's thermosphere. Simulations show that if forced in hydrostatic equilibrium and maintaining the current composition, the Earth's thermosphere could experience a fast transition to an atmospheric blowoff state when exposed to solar EUV radiation stronger than certain critical flux. When hydrodynamic flow and its associated adiabatic cooling are included, atmospheric blowoff is prevented and Earth's exobase temperature decreases with increasing solar EUV beyond the critical solar EUV flux. Simulations show that the transition of the thermosphere from the hydrostatic equilibrium regime to the hydrodynamic regime occurs when the exobase temperature reaches 7000 to 8000 K if atomic O and N dominate the upper thermosphere. The fast variations of the bulk motion velocities under different exobase temperatures suggest that the adiabatic cooling effect could have kept the exobase temperature lower than âˆź1000 K if light gases such as atomic hydrogen were the dominant species in the Earth's thermosphere. We propose that hydrodynamic flow and associated adiabatic cooling should exist in the thermospheres of a broad range of early and/or close-in terrestrial type planets and that the adiabatic cooling effect must be included in the energy balance in order to correctly estimate their thermospheric structures and their evolutionary paths.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d7wq053v

codeSpace

Dataset language

eng

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code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

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Text

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title

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reference date

date type

publication

effective date

2016-01-01T00:00:00Z

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East bounding longitude

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date type

publication

effective date

2008-05-31T00:00:00Z

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An edited version of this article was published by the American Geophysical Union. Copyright 2008 AGU.

Limitations on public access

None

Responsible organisations

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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

Metadata on metadata

Metadata point of contact

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

Metadata date

2023-08-18T18:44:11.343411

Metadata language

eng; USA