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| Titel |
Springtime atmospheric transport controls Arctic summer sea-ice extent |
| VerfasserIn |
Marie Kapsch, Rune Graversen, Michael Tjernström |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079109
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| Zusammenfassung |
| The sea-ice extent in the Arctic has been steadily decreasing during the satellite remote
sensing era, 1979 to present, with the highest rate of retreat found in September.
Contributing factors causing the ice retreat are among others: changes in surface
air temperature (SAT; Lindsay and Zhang, 2005), ice circulation in response to
winds/pressure patterns (Overland et al., 2008) and ocean currents (Comiso et al., 2008), as
well as changes in radiative fluxes (e.g. due to changes in cloud cover; Francis and
Hunter, 2006; Maksimovich and Vihma, 2012) and ocean conditions. However, large
interannual variability is superimposed onto the declining trend - the ice extent by the
end of the summer varies by several million square kilometer between successive
years (Serreze et al., 2007). But what are the processes causing the year-to-year ice
variability?
A comparison of years with an anomalously large September sea-ice extent (HIYs - high
ice years) with years showing an anomalously small ice extent (LIYs - low ice years) reveals
that the ice variability is most pronounced in the Arctic Ocean north of Siberia
(which became almost entirely ice free in September of 2007 and 2012). Significant
ice-concentration anomalies of up to 30% are observed for LIYs and HIYs in this area.
Focusing on this area we find that the greenhouse effect associated with clouds and
water-vapor in spring is crucial for the development of the sea ice during the subsequent
months. In years where the end-of-summer sea-ice extent is well below normal, a
significantly enhanced transport of humid air is evident during spring into the region where
the ice retreat is encountered. The anomalous convergence of humidity increases the
cloudiness, resulting in an enhancement of the greenhouse effect. As a result, downward
longwave radiation at the surface is larger than usual. In mid May, when the ice anomaly
begins to appear and the surface albedo therefore becomes anomalously low, the
net shortwave radiation anomaly becomes positive. The net shortwave radiation
contributes during the rest of the melting season to an enhanced energy flux towards the
surface.
These findings lead to the conclusion that enhanced longwave radiation associated with
positive humidity and cloud anomalies during spring plays a significant role in initiating the
summer ice melt, whereas shortwave-radiation anomalies act as an amplifying feedback once
the melt has started.
References:
Lindsay, R. and J. Zhang. The thinning of Arctic Sea Ice, 19882003: Have We Passed a
Tipping Point?. J. Clim. 18, 48794894 (2005).
Overland, J. E., M. Wang and S. Salo. The recent Arctic warm period. Tellus 60A,
589-597 (2008).
Comiso, J. C., C. L. Parkinson, R. Gersten and L. Stock. Accelerated Decline in the
Arctic sea ice cover. Geophys. Res. Lett. 35, L01703 (2008).
Francis, J. A. and E. Hunter. New Insight Into the Disappearing Arctic Sea Ice. EOS T.
Am. Geophys. Un. 87, 509511 (2006).
Maksimovich, E. and T. Vihma. The effect of heat fluxes on interannual variability in the
spring onset of snow melt in the central Arctic Ocean. J. Geophys. Res. 117, C07012
(2012).
Serreze, M. C., M. M. Holland and J. Stroeve. Perspectives on the Arctic’s Shrinking
Sea-Ice Cover. Science 315, 1533-1536 (2007). |
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