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| Titel |
Modeling the Frozen-In Anticyclone in the 2005 Arctic Summer Stratosphere |
| VerfasserIn |
D. R. Allen, A. R. Douglass, G. L. Manney, S. E. Strahan, J. C. Krosschell, J. V. Trueblood, J. E. Nielsen, S. Pawson, Z. Zhu |
| 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 ; 11, no. 9 ; Nr. 11, no. 9 (2011-05-13), S.4557-4576 |
| Datensatznummer |
250009720
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| Publikation (Nr.) |
 copernicus.org/acp-11-4557-2011.pdf |
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| Zusammenfassung |
| Immediately following the breakup of the 2005 Arctic spring stratospheric
vortex, a tropical air mass, characterized by low potential vorticity (PV)
and high nitrous oxide (N2O), was advected poleward and became trapped
in the easterly summer polar vortex. This feature, known as a "Frozen-In
Anticyclone (FrIAC)", was observed in Earth Observing System (EOS) Aura
Microwave Limb Sounder (MLS) data to span the potential temperature range
from ~580 to 1100 K (~25 to 40 km altitude) and to persist from
late March to late August 2005. This study compares MLS N2O
observations with simulations from the Global Modeling Initiative (GMI)
chemistry and transport model, the GEOS-5/MERRA Replay model, and the Van
Leer Icosahedral Triangular Advection (VITA) isentropic transport model to
elucidate the processes involved in the lifecycle of the FrIAC, which is
here divided into three distinct phases. During the "spin-up phase" (March
to early April), strong poleward flow resulted in a tight isolated
anticyclonic vortex at ~70–90° N, marked with elevated N2O.
GMI, Replay, and VITA all reliably simulated the spin-up of the FrIAC,
although the GMI and Replay peak N2O values were too low. The FrIAC
became trapped in the developing summer easterly flow and circulated around
the polar region during the "anticyclonic phase" (early April to the end
of May). During this phase, the FrIAC crossed directly over the pole between
7 and 14 April. The VITA and Replay simulations
transported the N2O anomaly intact during this crossing, in agreement
with MLS, but unrealistic dispersion of the anomaly occurred in the GMI
simulation due to excessive numerical mixing of the polar cap. The vortex
associated with the FrIAC was apparently resistant to the weak vertical
shear during the anticyclonic phase, and it thereby protected the embedded
N2O anomaly from stretching. The vortex decayed in late May due to
diabatic processes, leaving the N2O anomaly exposed to horizontal and
vertical wind shears during the "shearing phase" (June to August). The
observed lifetime of the FrIAC during this phase is consistent with
timescales calculated from the ambient horizontal and vertical wind shear.
Replay maintained the horizontal structure of the N2O anomaly similar
to MLS well into August. Isentropic simulations using VITA also captured the
horizontal structure of the FrIAC during this phase, but small-scale
structures maintained by VITA are problematic and show that important mixing
processes are absent from this single-level simulation. |
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