26 research outputs found
Complex refractive index and single scattering albedo of Icelandic dust in the shortwave part of the spectrum
Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by
changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the
spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering
albedo (SSA) and the complex refractive index (m=n-ik) of Icelandic dust from five major emission hotspots were retrieved between
370–950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca)
coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured
βabs and βsca increased from 0.90–0.94 at 370 nm to 0.94–0.96 at 950 nm in Icelandic dust from the
different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was
retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for
spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive
index (n(λ)) was found to be 1.60–1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was
almost constant with wavelength and was found to be around 0.004 at 370 nm and 0.002–0.003 at 950 nm. The estimated complex
refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed
in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust
are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing
towards the near-infrared. In Icelandic dust, k(λ) between 660–950 nm was 2–8 times higher than most of the dust samples sourced
in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has
not been accounted for in climate predictions.</p
Iceland is an episodic source of atmospheric ice-nucleating particles relevant for mixed-phase clouds.
Ice-nucleating particles (INPs) have the potential to remove much of the liquid water in climatically important mid- to high-latitude shallow supercooled clouds, markedly reducing their albedo. The INP sources at these latitudes are very poorly defined, but it is known that there are substantial dust sources across the high latitudes, such as Iceland. Here, we show that Icelandic dust emissions are sporadically an important source of INPs at mid to high latitudes by combining ice-nucleating active site density measurements of aircraft-collected Icelandic dust samples with a global aerosol model. Because Iceland is only one of many high-latitude dust sources, we anticipate that the combined effect of all these sources may strongly contribute to the INP population in the mid- and high-latitude northern hemisphere. This is important because these emissions are directly relevant for the cloud-phase climate feedback and because high-latitude dust emissions are expected to increase in a warmer climate
Insulation effects of Icelandic dust and volcanic ash on snow and ice
In the Arctic region, Iceland is an important source of dust due to ash production from volcanic eruptions. In addition, dust is resuspended from the surface into the atmosphere as several dust storms occur each year. During volcanic eruptions and dust storms, material is deposited on the glaciers where it influences their energy balance. The effects of deposited volcanic ash on ice and snow melt were examined using laboratory and outdoor experiments. These experiments were made during the snow melt period using two different ash grain sizes (1 phi and 3.5 phi) from the Eyjafjallajokull 2010 eruption, collected on the glacier. Different amounts of ash were deposited on snow or ice, after which the snow properties and melt were measured. The results show that a thin ash layer increases the snow and ice melt but an ash layer exceeding a certain critical thickness caused insulation. Ash with 1 phi in grain size insulated the ice below at a thickness of 9-15 mm. For the 3.5 phi grain size, the insulation thickness is 13 mm. The maximum melt occurred at a thickness of 1 mm for the 1 phi and only 1-2 mm for 3.5 phi ash. A map of dust concentrations on Vatnajokull that represents the dust deposition during the summer of 2013 is presented with concentrations ranging from 0.2 up to 16.6 g m(-2).Peer reviewe
Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes
The Nordic Centre of Excellence CRAICC (Cryosphere–Atmosphere Interactions
in a Changing Arctic Climate), funded by NordForsk in the years 2011–2016,
is the largest joint Nordic research and innovation initiative to date,
aiming to strengthen research and innovation regarding climate change issues
in the Nordic region. CRAICC gathered more than 100Â scientists from all
Nordic countries in a virtual centre with the objectives of identifying and
quantifying the major processes controlling Arctic warming and related feedback
mechanisms, outlining strategies to mitigate Arctic warming, and developing
Nordic Earth system modelling with a focus on short-lived climate
forcers (SLCFs), including natural and anthropogenic aerosols.
The outcome of CRAICC is reflected in more than 150Â peer-reviewed scientific
publications, most of which are in the CRAICC special issue of the journal
Atmospheric Chemistry and Physics. This paper presents an overview
of the main scientific topics investigated in the centre and provides the
reader with a state-of-the-art comprehensive summary of what has been achieved in
CRAICC with links to the particular publications for further detail. Faced
with a vast amount of scientific discovery, we do not claim to completely
summarize the results from CRAICC within this paper, but rather
concentrate here on the main results which are related to feedback loops in
climate change–cryosphere interactions that affect Arctic amplification.</p
Temporal and spatial variability of Icelandic dust emissions and atmospheric transport
Icelandic dust sources are known to be highly active, yet there
exist few model simulations of Icelandic dust that could be used to
assess its impacts on the environment. We here present estimates of
dust emission and transport in Iceland over 27Â years
(1990–2016) based on FLEXDUST and FLEXPART simulations and
meteorological re-analysis data. Simulations for the year 2012
based on high-resolution operational meteorological analyses are
used for model evaluation based on PM2. 5 and
PM10 observations in Iceland. For stations in Reykjavik,
we find that the spring period is well predicted by the model, while
dust events in late fall and early winter are overpredicted. Six
years of dust concentrations observed at Stórhöfði
(Heimaey) show that the model predicts concentrations of the same
order of magnitude as observations and timing of modelled and
observed dust peaks agrees well. Average annual dust emission is
4.3 ± 0.8 Tg during the 27 years of
simulation. Fifty percent of all dust from Iceland is on average
emitted in just 25Â days of the year, demonstrating the
importance of a few strong events for annual total dust
emissions. Annual dust emission as well as transport patterns
correlate only weakly to the North Atlantic Oscillation. Deposition
amounts in remote regions (Svalbard and Greenland) vary from year to
year. Only limited dust amounts reach the upper Greenland Ice Sheet,
but considerable dust amounts are deposited on Icelandic glaciers
and can impact melt rates there. Approximately 34 % of the
annual dust emission is deposited in Iceland itself. Most dust
(58 %), however, is deposited in the ocean and may strongly
influence marine ecosystems
Icelandic volcanic dust can have a significant influence on the cryosphere in Greenland and elsewhere
No abstract available.(Published: 24 July 2016)Citation: Polar Research 2016, 35, 31313,http://dx.doi.org/10.3402/polar.v35.313
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