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| Titel |
Spatial and seasonal distribution of Arctic aerosols observed by the CALIOP satellite instrument (2006–2012) |
| VerfasserIn |
M. Pierro, L. Jaeglé, E. W. Eloranta, S. Sharma |
| 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 ; 13, no. 14 ; Nr. 13, no. 14 (2013-07-25), S.7075-7095 |
| Datensatznummer |
250018781
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| Publikation (Nr.) |
 copernicus.org/acp-13-7075-2013.pdf |
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| Zusammenfassung |
| We use retrievals of aerosol extinction from the Cloud-Aerosol Lidar with
Orthogonal Polarization (CALIOP) onboard the CALIPSO satellite to examine
the vertical, horizontal and temporal variability of tropospheric Arctic
aerosols during the period 2006–2012. We develop an empirical method that takes into
account the difference in sensitivity between daytime and nighttime
retrievals over the Arctic. Comparisons of the retrieved aerosol extinction
to in situ measurements at Barrow (Alaska) and Alert (Canada) show that
CALIOP reproduces the observed seasonal cycle and magnitude of surface
aerosols to within 25 %. In the free troposphere, we find that daytime
CALIOP retrievals will only detect the strongest aerosol haze events, as
demonstrated by a comparison to aircraft measurements obtained during NASA's
ARCTAS mission during April 2008. This leads to a systematic underestimate of
the column aerosol optical depth by a factor of 2–10. However, when the
CALIOP sensitivity threshold is applied to aircraft observations, we find
that CALIOP reproduces in situ observations to within 20% and captures the
vertical profile of extinction over the Alaskan Arctic. Comparisons with the
ground-based high spectral resolution lidar (HSRL) at Eureka, Canada, show that CALIOP and HSRL capture
the evolution of the aerosol backscatter vertical distribution from winter to
spring, but a quantitative comparison is inconclusive as the retrieved HSRL
backscatter appears to overestimate in situ observations by a factor of 2 at
all altitudes. In the High Arctic (>70° N) near the
surface (<2 km), CALIOP aerosol extinctions reach a maximum in
December–March (10–20 Mm−1), followed by a sharp decline and a
minimum in May–September (1–4 Mm−1), thus providing the first
pan-Arctic view of Arctic haze seasonality. The European and Asian Arctic
sectors display the highest wintertime extinctions, while the Atlantic sector
is the cleanest. Over the Low Arctic (60–70° N) near the surface,
CALIOP extinctions reach a maximum over land in summer due to boreal forest
fires. During summer, we find that smoke aerosols reach higher altitudes (up
to 4 km) over eastern Siberia and North America than over northern Eurasia,
where they remain mostly confined below 2 km. In the free troposphere, the
extinction maximum over the Arctic occurs in March–April at 2–5 km
altitude and April–May at 5–8 km. This is consistent with transport from
the midlatitudes associated with the annual maximum in cyclonic activity and
blocking patterns in the Northern Hemisphere. A strong gradient in aerosol
extinction is observed between 60° N and 70° N in the
summer. This is likely due to efficient stratocumulus wet scavenging at high
latitudes combined with the poleward retreat of the polar front. Interannual
variability in the middle and upper troposphere is associated with biomass
burning events (high extinctions observed by CALIOP in spring 2008 and summer
2010) and volcanic eruptions (Kasatochi in August 2008 and Sarychev in June
2009). CALIOP displays below-average extinctions observed from August 2009
through May 2010, which appear to be linked with a strongly negative Arctic
Oscillation index. |
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