The spatial and temporal distribution of Arctic aerosols as seen from the CALIPSO satellite
(2006 – 2012)
AGU Fall Meeting
Maurizio Di Pierro and Lyatt Jaeglé
Dec 3-7 2012
A13K-0331
University of Washington, Department of Atmospheric Sciences, Seattle (dipierro@uw.edu)
1. Introduction
• The Arctic is a known receptor of pollution emitted in the mid-latitudes. Anthropogenic aerosols alter
the radiative balance of the Arctic via both the aerosol direct and indirect effect. Climate simulations
indicate that sulfur emission reductions in the northern mid-latitudes can explain a substantial fraction
of the rapid Arctic warming observed during the past 3 decades (Shindell and Faluvegi, 2009).
• Long-term observations in the Arctic, however, have historically relied on a sparse network of ground
stations, with limited ability to observe the middle-upper troposphere.
• We present results on the distribution of Arctic aerosols retrieved by the Cloud and Aerosol Lidar with
Orthogonal Polarization (CALIOP) on board the CALIPSO satellite, from 2006 to 2012. We explore
the spatial and vertical distributions of Arctic aerosols, their seasonality and inter-annual variability.
 CALIPSO orbits the Earth at 98 inclination, thus has
excellent observation density over the Arctic
 The CALIOP instrument measures vertical profiles of
attenuated backscatter at 532 nm (polarized channel) and
1064 nm.
 We use Level 2 Aerosol and Cloud layer data, version
3.01, from June 2006 to May 2012, 59º-82º N. From this
data we extract the Aerosol Optical Thickness (AOT) of
each aerosol layer identified.
 Clear sky profiles and profiles above the first cloud top
are considered
 Low quality data and unphysical retrievals are discarded. Aerosol contamination by diamond dust is
removed by imposing an extinction cut-off threshold of 350 Mm-1
 The aerosol layers are finally gridded at 2º latitude by 2.5º longitude at 0.2 km vertical resolution
3. Combine day and night retrievals
•
•
In order to reconstruct the seasonal cycle of Arctic aerosol extinction it is necessary to deal with the
seasonal cycle of daylight which greatly affects CALIOP’s performance, particularly for optically thin
aerosols.
CALIOPs’ higher backscatter detection sensitivity threshold at daytime results in fewer aerosol layers
detected at daytime than at nighttime
The ratio of daytime to nighttime detection frequency is found to scale linearly with the value of the
backscatter of the detected aerosol layers
Figure caption: Left: CALIOP
detection frequency in DecemberMarch, 2006-2012, 61-71ºN. Right:
number distribution points in the β/𝑓𝑓𝑛𝑑
plane, for September-March 20062012 (when the number of daytime
and nighttime retrievals is identical).
ASIA
1. Observations from NASA ARCTAS
campaign (April 2008)
Nephelometer
extinction =
2-5 km Extinction
NAM
5-8 km Extinction
EUR
ATL
CALIOP NighttimeEquivalent
Low Arctic
(60º-70ºN)
Neph. with
CALIOP th.
Haze layers over the Brooks Range (Alaska), April 2008. Courtesy of NASA
 Over Alaska, only 25% of the data points are above
CALIOP sensitivity threshold
 CALIOP nighttime-equivalent extinction captures both
the near-surface and the 3-6 km extinction peak, with
a 30% underestimate of the column AOD
2. Monthly-mean ambient extinction at two Arctic sites:
Barrow
Barrow
Alert
Alert
 CALIOP sensitivity threshold
is applied after the extinction
is corrected for ambient RH
 CALIOP captures the
seasonal cycle at both sites,
with a bias <15%
High Arctic
(70º-82ºN)
 Strong seasonal cycle in the high Arctic  The springtime free tropospheric
consistent with Arctic Haze literature
maximum in March-April in the High
studies
Arctic, and in May in the Low Arctic
 Two annual maxima in the low Arctic
 May peak in the upper troposphere
consistent with volume concentration
matches previous observations
surface measurements at Zotino (89ºE,
(Treffeisen et al., 2006)
62ºN). (Heintzenberg et al., 2011).
Atlantic Sector (60ºW-10ºE)
Asian Sector (110ºE-140ºW)
European Sector (10º-110ºE)
North American Sector (60º-140ºW)
All Sectors
7. Inter-annual variability
Intense agricultural fires in
Russia/Kazakhstan
Kasatochi (Aleutian Islands)
volcanic eruption
Sarychev Eruption
5. Aerosol spatial distributions
Low-level pollution inflow
around the Siberian
anticyclone
The wind speed seasonal
maximum causes sea salt
aerosol over the North
Atlantic to peak in winter
Strong gradient in extinction from
60-70N due to efficient wet
scavenging by drizzle and polar
front retreat
(Stohl, 2006; Garrett et al., 2011)
Increased transport from midlatitudes causes the mid-and
upper tropospheric maximum in
spring
Biomass burning summer maximum
Boreal forest fires
This relationship is used to correct the daytime detection frequency to form the nighttime-equivalent
mean extinction via the correction factor S:
𝑊𝑑 𝑓𝑑 𝑏𝑑 𝑆 𝛽 + 𝑊𝑛 𝑓𝑛 𝑏𝑛
𝑊𝑑 +𝑊𝑛
0-2 km Extinction
CALIOP
2. CALIPSO Satellite Observations
•
6. Multi-year seasonal cycle by sector
4. Method Validation
Figure caption: 5-day averaged aerosol extinction from June 2006 to May 2012.
8. Summary
“Surface Arctic Haze”
 CALIOP captures the seasonal cycle of aerosols extinction as measured in-situ at the stations
of Barrow and Alert, as well as the vertical profile of extinction measured during the ARCTAS
aircraft campaign of April 2008.
 Arctic Haze is a Pan-Arctic phenomenon. Central Asia is the preferred point of entry of
pollution in winter.
 In the middle and upper troposphere, extinction maximizes in spring, when the frequency of
cyclonic activity and blocking anticyclones reaches an annual maximum. Extinction is highest
in the Asian sector.
 Low and High Arctic are strongly decoupled in summer, due to the poleward retreat of the
Polar Front as well as efficient wet scavenging by stratocumulus drizzle.
 Inter-annual variability is relatively small at the surface. In the free troposphere, biomass
burning anomalies and volcanic eruptions drive the variability during the period considered.
Acknowledgments:
We thank Sangeeta Sharma and Richard Leaitch from Climate Research Division, Environment Canada, Ed Eloranta for the HSRL data, as
well as NOAA for providing the Barrow data and Luke Ziemba for the ARCTAS data. This work was supported by funding from the NASA
Earth and Space Science Fellowship under award NNX11AL69H and by NASA award NNX08AQ07G.
References:
extinction = Nighttime-Equivalent aerosol mean extinction
W = number of observations
; f = detection frequency (0-1)
b = mean extinction of the detected aerosols
β = mean backscatter of the detected aerosols
S = correction factor
; Subscripts d,n : Day, Night
Figure caption: Spatial distribution of aerosol mean extinction from 2006 to 2012 by season and altitude
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