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| Titel |
The dynamics of the Snowball Earth Hadley circulation for off-equatorial and seasonally varying insolation |
| VerfasserIn |
A. Voigt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2190-4979
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| Digitales Dokument |
URL |
| Erschienen |
In: Earth System Dynamics ; 4, no. 2 ; Nr. 4, no. 2 (2013-11-27), S.425-438 |
| Datensatznummer |
250084961
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| Publikation (Nr.) |
 copernicus.org/esd-4-425-2013.pdf |
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| Zusammenfassung |
| I study the Hadley circulation of a completely ice-covered Snowball Earth
through simulations with a comprehensive atmosphere general circulation
model. Because the Snowball Earth atmosphere is an example of a dry
atmosphere, these simulations allow me to test to what extent dry theories
and idealized models capture the dynamics of realistic dry Hadley circulations.
Perpetual off-equatorial as well as seasonally varying insolation is used,
extending a previous study for perpetual on-equatorial (equinox) insolation.
Vertical diffusion of momentum, representing the momentum transport of dry
convection, is fundamental to the momentum budgets of both the winter and
summer cells. In the zonal budget, it is the primary process balancing the
Coriolis force. In the meridional budget, it mixes meridional momentum
between the upper and the lower branch and thereby decelerates the
circulation. Because of the latter, the circulation intensifies by a factor
of three when vertical diffusion of momentum is suppressed. For
seasonally varying insolation, the circulation undergoes rapid transitions
from the weak summer into the strong winter regime. Consistent with previous
studies in idealized models, these transitions result from a mean-flow
feedback, because of which they are insensitive to the treatment of vertical
diffusion of momentum. Overall, the results corroborate previous findings for
perpetual on-equatorial insolation. They demonstrate that descriptions of
realistic dry Hadley circulations, in particular their strength, need
to incorporate the vertical momentum transport by dry convection, a process
that is neglected in most dry theories and idealized models. An improved
estimate of the strength of the Snowball Earth Hadley circulation will also
help to better constrain the climate of a possible Neoproterozoic Snowball
Earth and its deglaciation threshold. |
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