Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming. Satellite observations of aerosol optical depth ...above 15 km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, Aerosol Robotic Network, and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15 km at middle to high latitudes and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be 0.19 +/- 0.09W/sq m. This translates into an estimated global cooling of 0.05 to 0.12 C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15 km.
Ice nucleating particles (INPs) affect the radiative properties of cold clouds. Knowledge concerning their concentration above ground level and their potential sources is scarce. Here we present the ...first highly temperature resolved ice nucleation spectra of airborne samples from an aircraft campaign during late winter in 2018. Most INP spectra featured low concentration levels (<3 · 10−4 L−1 at −15°C). However, we also found INP concentrations of up to 1.8·10−2 L−1 at −15°C and freezing onsets as high as −7.5°C for samples mainly from the marine boundary layer. Shape and onset temperature of the ice nucleation spectra of those samples as well as heat sensitivity hint at biogenic INP. Colocated measurements additionally indicate a local marine influence rather than long‐range transport. Our results suggest that even in late winter above 80°N a local marine source for biogenic INP, which can efficiently nucleate ice at high temperatures, is present.
Plain Language Summary
Clouds are a key factor in the energy budget of the Arctic atmosphere. Ice nucleating particles (INPs) can modify the radiation properties and lifetime of clouds by affecting the relative abundance of liquid and frozen droplets in a cloud. Despite this important ability, knowledge about the INP concentration above ground level is limited as airborne INP measurements are very scarce in the Arctic. Here we present results from an aircraft campaign, which took place during the late winter of 2018 in latitudes above 80°N. We found INP concentrations at above −15°C, which are similar to those found in midlatitudes. These INPs also initiate freezing already at high temperatures. We found indications that the INPs are biogenic and originate from a local, marine source, rather than being transported from midlatitudes into the Arctic. Due to the presence of numerous cracks, open leads and polynyas in the sea ice in the investigation area, the ocean may provide a source for these biogenic INP in an environment, where sources on land are still shrouded in snow and ice. However, in a warming Arctic contributions from different sources might change, making the characterization of the current state important.
Key Points
Ice nucleating particles on airborne filter samples containing mainly Arctic marine boundary layer aerosol initiate freezing at −7.5°C
At −15°C, concentrations of ice nucleating particles ranged from up to 2 · 10−2 L−1 down to below 10−3 L−1
A local marine source and biogenic origin for the high‐temperature ice nucleating particles is likely
Fram Strait is the main gateway for sea ice export out of the Arctic Ocean, and therefore observations there give insight into the composition and properties of Arctic sea ice in general and how it ...varies over time. A data set of ground-based and airborne electromagnetic ice thickness measurements collected during summer between 2001 and 2012 is presented here, including long transects well into the southern part of the Transpolar Drift obtained using fixed-wing aircrafts. The primary source of the surveyed sea ice leaving Fram Strait is the Laptev Sea and its age has decreased from 3 to 2 years between 1990 and 2012. The thickness data consistently also show a general thinning of sea ice for the last decade, with a decrease in modal thickness of second year and multiyear ice, and a decrease in mean thickness and fraction of ice thicker than 3 m. Local melting in the strait was investigated in two surveys performed in the downstream direction, showing a decrease in sea ice thickness of 0.19 m degree−1 latitude south of 81° N. Further north variability in ice thickness is more related to differences in age and deformation. The thickness observations were combined with ice area export estimates to calculate summer volume fluxes of sea ice. While satellite data show that monthly ice area export had positive trends since 1980 (10.9 × 103 km2 decade−1), the summer (July and August) ice area export is low with high uncertainties. The average volume export amounts to 16.78 km3. Naturally, the volume flux estimates are limited to the period when airborne thickness surveys are available. Nevertheless, we could show that the combination of satellite data and airborne observations can be used to determine volume fluxes through Fram Strait and as such, can be used to bridge the lack of satellite-based sea ice thickness information in summer.
The intestinal flora harbors varies pathogens. Clostridium perfringens (gas gangrene), Enterococci (endocarditis), Enterobacteriaceae (sepsis), Bacteroides (abscesses) are present in the large ...intestine of every healthy person in high concentrations. These bacteria are, however, separated from the colonic wall by an impenetrable mucus layer and are tolerated by the host. This separation is disturbed in patients with inflammatory bowel disease (IBD), where bacteria adhere to the mucosa and invade epithelial cells with concomitant inflammatory response. This chronic bowel inflammation can not subside as long as the mucus barrier remains defective. The inflammatory response interferes with the state of tolerance to the intestinal bacteria and leads to characteristic changes in the biostructure of the faecal microbiota. These changes in the biostructure of faecal microbiota are specific for active Crohn's disease and ulcerative colitis (UC) and can be longitudinally monitored. The reason for the defect of the mucus barrier in IBD patients is unclear. Epidemiologic studies indicate a negative role of western lifestyle and foods and document the rise in the incidence of IBD in the industrialized countries during the 20(th) century. In parallel to this, detergents were introduced in households and emulsifiers were increasingly added to food. The cleaning effect of these on the colonic mucus has to be investigated. The present contribution summarizes new data on the biostructure of the intestinal microbiota.
During summer of 2004, about 2.7 million hectare of boreal forest burned in Alaska, the largest annual area burned on record, and another 3.1 million hectare burned in Canada. This study explores the ...impact of emissions from these fires on light absorbing aerosol concentration levels, aerosol optical depths (AOD), and albedo at the Arctic stations Barrow (Alaska), Alert (Canada), Summit (Greenland), and Zeppelin/Ny Ålesund on Spitsbergen (Norway). The Lagrangian particle dispersion model FLEXPART was run backward from these sites to identify periods that were influenced by forest fire pollution plumes. It is shown that the fires led to enhanced values of particle light absorption coefficients (σap) at all of these sites. Barrow, about 1000 km away from the fires, was affected by several fire pollution plumes, one leading to spectacularly high 3‐hour mean σap values of up to 32 Mm−1, more than the highest values measured in Arctic Haze. AOD measurements for a wavelength of 500 nm saturated but were estimated at above 4–5 units, unprecedented in the station records. Fire plumes were transported through the atmospheric column over Summit continuously for 2 months, during which all measured AOD values were enhanced, with maxima up to 0.4–0.5 units. Equivalent black carbon concentrations at the surface at Summit were up to 600 ng m−3 during two major episodes, and Alert saw at least one event with enhanced σap values. FLEXPART results show that Zeppelin was located in a relatively unaffected part of the Arctic. Nevertheless, there was a 4‐day period with daily mean σap > 0.3 Mm−1, the strongest episode of the summer half year, and enhanced AOD values. Elevated concentrations of the highly source‐specific compound levoglucosan positively confirmed that biomass burning was the source of the aerosols at Zeppelin. In summary, this paper shows that boreal forest fires can lead to elevated concentrations of light absorbing aerosols throughout the entire Arctic. Enhanced AOD values suggest a substantial impact of these plumes on radiation transmission in the Arctic atmosphere. During the passage of the largest fire plume, a pronounced drop of the albedo of the snow was observed at Summit. We suggest that this is due to the deposition of light absorbing particles on the snow, with further potentially important consequences for the Arctic radiation budget.
A consistent meteorological dataset of the Arctic site Ny-Ålesund (11.9° E, 78.9° N) spanning the 18 yr-period 1 August 1993 to 31 July 2011 is presented. Instrumentation and data handling of ...temperature, humidity, wind and pressure measurements are described in detail. Monthly mean values are shown for all years to illustrate the interannual variability of the different parameters. Climatological mean values are given for temperature, humidity and pressure. From the climatological dataset, we also present the time series of annual mean temperature and humidity, revealing a temperature increase of +1.35 K per decade and an increase in water vapor mixing ratio of +0.22 g kg−1 per decade for the given time period, respectively. With the continuation of the presented measurements, the Ny-Ålesund high resolution time series will provide a reliable source to monitor Arctic change and retrieve trends in the future. The relevant data are provided in high temporal resolution as averages over 5 (1) min before (after) 14 July 1998, respectively, placed on the PANGAEA repository (doi:10.1594/PANGAEA.793046). While 6 hourly synoptic observations in Ny-Ålesund by the Norwegian Meteorological Institute reach back to 1974 (Førland et al., 2011), the meteorological data presented here cover a shorter time period, but their high temporal resolution will be of value for atmospheric process studies on shorter time scales.
The concentrations of sulfate, black carbon (BC) and other aerosols in the Arctic are characterized by high values in late winter and spring (so-called Arctic Haze) and low values in summer. Models ...have long been struggling to capture this seasonality and especially the high concentrations associated with Arctic Haze. In this study, we evaluate sulfate and BC concentrations from eleven different models driven with the same emission inventory against a comprehensive pan-Arctic measurement data set over a time period of 2 years (2008-2009). The set of models consisted of one Lagrangian particle dispersion model, four chemistry transport models (CTMs), one atmospheric chemistry-weather forecast model and five chemistry climate models (CCMs), of which two were nudged to meteorological analyses and three were running freely. The measurement data set consisted of surface measurements of equivalent BC (eBC) from five stations (Alert, Barrow, Pallas, Tiksi and Zeppelin), elemental carbon (EC) from Station Nord and Alert and aircraft measurements of refractory BC (rBC) from six different campaigns. We find that the models generally captured the measured eBC or rBC and sulfate concentrations quite well, compared to previous comparisons. However, the aerosol seasonality at the surface is still too weak in most models. Concentrations of eBC and sulfate averaged over three surface sites are underestimated in winter/spring in all but one model (model means for January-March underestimated by 59 and 37 % for BC and sulfate, respectively), whereas concentrations in summer are overestimated in the model mean (by 88 and 44 % for July-September), but with overestimates as well as underestimates present in individual models. The most pronounced eBC underestimates, not included in the above multi-site average, are found for the station Tiksi in Siberia where the measured annual mean eBC concentration is 3 times higher than the average annual mean for all other stations. This suggests an underestimate of BC sources in Russia in the emission inventory used. Based on the campaign data, biomass burning was identified as another cause of the modeling problems. For sulfate, very large differences were found in the model ensemble, with an apparent anti-correlation between modeled surface concentrations and total atmospheric columns. There is a strong correlation between observed sulfate and eBC concentrations with consistent sulfate/eBC slopes found for all Arctic stations, indicating that the sources contributing to sulfate and BC are similar throughout the Arctic and that the aerosols are internally mixed and undergo similar removal. However, only three models reproduced this finding, whereas sulfate and BC are weakly correlated in the other models. Overall, no class of models (e.g., CTMs, CCMs) performed better than the others and differences are independent of model resolution.
Atmospheric black carbon (BC) absorbs solar radiation, and exacerbates global warming through exerting positive radiative forcing (RF). However, the contribution of BC to ongoing changes in global ...climate is under debate. Anthropogenic BC emissions, and the resulting distribution of BC concentration, are highly uncertain. In particular, long-range transport and processes affecting BC atmospheric lifetime are poorly understood. Here we discuss whether recent assessments may have overestimated present-day BC radiative forcing in remote regions. We compare vertical profiles of BC concentration from four recent aircraft measurement campaigns to simulations by 13 aerosol models participating in the AeroCom Phase II intercomparison. An atmospheric lifetime of BC of less than 5 days is shown to be essential for reproducing observations in remote ocean regions, in line with other recent studies. Adjusting model results to measurements in remote regions, and at high altitudes, leads to a 25% reduction in AeroCom Phase II median direct BC forcing, from fossil fuel and biofuel burning, over the industrial era. The sensitivity of modelled forcing to BC vertical profile and lifetime highlights an urgent need for further flight campaigns, close to sources and in remote regions, to provide improved quantification of BC effects for use in climate policy.
Naturally occurring radioactive noble gas, radon (222Rn) is a valuable tracer to study atmospheric processes and to validate global chemical transport models. However, the use of radon as a proxy in ...atmospheric and climate research is limited by the uncertainties in the magnitude and distribution of the radon flux density over the Earth's surface. Terrestrial gamma radiation is a useful proxy for generating radon flux maps. A previously reported radon flux map of Europe used terrestrial gamma radiation extracted from automated radiation monitoring networks. This approach failed to account for the influence of local artificial radiation sources around the detector, leading to under/over estimation of the reported radon flux values at different locations. We present an alternative approach based on soil radionuclides which enables us to generate accurate radon flux maps with good confidence. Firstly, we present a detailed comparison between the terrestrial gamma radiation obtained from the National Radiation Monitoring network of the Netherlands and the terrestrial gamma radiation calculated from soil radionuclides. Extending further, we generated radon flux maps of the Netherlands and Europe using our proposed approach. The modelled flux values for the Netherlands agree reasonably well with the two observed direct radon flux measurements (within 2σ level). On the European scale, we find that the observed radon flux values are higher than our modelled values and we introduce a correction factor to account for this difference. Our approach discussed in this paper enables us to develop reliable and accurate radon flux maps in countries with little or no information on radon flux values.
•Radon flux maps of the Netherlands and Europe are developed and validated.•Modelled radon flux for the Netherlands agree reasonably well with the observed.•Observed radon flux values for Europe are higher than modelled radon flux values.•A correction factor has been introduced to account for this difference.•Soils with high moisture content have a smaller radon flux than dry soils.