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| Titel |
Variability and trends in dynamical forcing of tropical lower stratospheric temperatures |
| VerfasserIn |
S. Fueglistaler, M. Abalos, T. J. Flannaghan, P. Lin, W. J. Randel |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 24 ; Nr. 14, no. 24 (2014-12-17), S.13439-13453 |
| Datensatznummer |
250119247
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| Publikation (Nr.) |
 copernicus.org/acp-14-13439-2014.pdf |
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| Zusammenfassung |
| The contribution of dynamical forcing to variations and trends in tropical
lower stratospheric
70 hPa temperature for the period 1980–2011 is estimated based on ERA-Interim
and Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis data. The dynamical forcing is estimated from the
tropical mean residual upwelling calculated with the momentum balance equation,
and with a simple proxy based on eddy heat fluxes averaged between
25° and 75° in both hemispheres. The thermodynamic energy equation
with Newtonian cooling is used to relate the dynamical forcing to temperature.
The deseasonalised, monthly mean time series of all four calculations are
highly correlated (~ 0.85) with temperature for the period 1995–2011
when variations in radiatively active tracers are small.
All four calculations provide additional support to previously noted
prominent aspects of the
temperature evolution 1980–2011:
an anomalously strong dynamical cooling (~ −1 to −2 K)
following the Pinatubo eruption that partially offsets the warming
from enhanced aerosol, and
a few years of enhanced dynamical cooling
(~ −0.4 K) after October 2000 that contributes to
the prominent drop in water entering the stratosphere at that time.
The time series of dynamically forced temperature calculated with the same
method are more highly correlated and have more
similar trends than those from the same reanalysis but with different methods.
For 1980–2011 (without volcanic periods), the eddy heat flux calculations give a
dynamical cooling of
~ −0.1 to ~ −0.25 K decade−1
(magnitude sensitive to latitude belt considered and reanalysis),
largely due to increasing high latitude eddy heat flux trends in September
and December–January. The eddy heat flux trends also explain the seasonality
of temperature trends very well, with maximum cooling in January–February.
Trends derived from momentum balance calculations show near-zero annual mean
dynamical cooling, with weaker seasonal trends especially in December–January.
These contradictory results arising from uncertainties in data and methods are
discussed and put in context to previous analyses. |
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