Showing papers by "Yutaka Kondo published in 2019"

Glacially sourced dust as a potentially significant source of ice nucleating particles

Abstract: Aeolian dusts serve as ice nucleating particles in mixed-phase clouds, and thereby alter the cloud properties and lifetime. Glacial outwash plains are thought to be a major dust source in cold, high latitudes. Due to the recent rapid and widespread retreat of glaciers, high-latitude dust emissions are projected to increase, especially in the Arctic region, which is highly sensitive to climate change. However, the potential contribution of high-latitude dusts to ice nucleation in Arctic low-level clouds is not well acknowledged. Here we show that glacial outwash sediments in Svalbard (a proxy for glacially sourced dusts) have a remarkably high ice nucleating ability under conditions relevant for mixed-phase cloud formation, as compared with typical mineral dusts. The high ice nucleating ability of the sediments is probably governed by the presence of small amounts of organic matter (<1 wt% organic carbon) rather than mineral components. In addition, our results from intensive field measurements and model simulations indicate that the concentrations of atmospheric ice nucleating particles over the Svalbard region are expected to be enhanced in the summertime under the influence of dust emissions from Svalbard and its surroundings. We suggest that high-latitude dust sources have the potential to significantly influence glaciation of Arctic low-level clouds. Dusts from glaciers may contribute significantly to ice nucleation in Arctic low-level clouds, according to analyses of glacial outwash sediments in Svalbard.

The importance of the representation of air pollution emissions for the modeled distribution and radiative effects of black carbon in the Arctic

Abstract: . Aerosol particles can contribute to the Arctic amplification (AA) by direct and indirect radiative effects. Specifically, black carbon (BC) in the atmosphere, and when deposited on snow and sea ice, has a positive warming effect on the top-of-atmosphere (TOA) radiation balance during the polar day. Current climate models, however, are still struggling to reproduce Arctic aerosol conditions. We present an evaluation study with the global aerosol-climate model ECHAM6.3-HAM2.3 to examine emission-related uncertainties in the BC distribution and the direct radiative effect of BC. The model results are comprehensively compared against the latest ground and airborne aerosol observations for the period 2005–2017, with a focus on BC. Four different setups of air pollution emissions are tested. The simulations in general match well with the observed amount and temporal variability in near-surface BC in the Arctic. Using actual daily instead of fixed biomass burning emissions is crucial for reproducing individual pollution events but has only a small influence on the seasonal cycle of BC. Compared with commonly used fixed anthropogenic emissions for the year 2000, an up-to-date inventory with transient air pollution emissions results in up to a 30 % higher annual BC burden locally. This causes a higher annual mean all-sky net direct radiative effect of BC of over 0.1 W m −2 at the top of the atmosphere over the Arctic region (60–90 ∘ N), being locally more than 0.2 W m −2 over the eastern Arctic Ocean. We estimate BC in the Arctic as leading to an annual net gain of 0.5 W m −2 averaged over the Arctic region but to a local gain of up to 0.8 W m −2 by the direct radiative effect of atmospheric BC plus the effect by the BC-in-snow albedo reduction. Long-range transport is identified as one of the main sources of uncertainties for ECHAM6.3-HAM2.3, leading to an overestimation of BC in atmospheric layers above 500 hPa, especially in summer. This is related to a misrepresentation in wet removal in one identified case at least, which was observed during the ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) summer aircraft campaign. Overall, the current model version has significantly improved since previous intercomparison studies and now performs better than the multi-model average in the Aerosol Comparisons between Observation and Models (AEROCOM) initiative in terms of the spatial and temporal distribution of Arctic BC.

Accuracy of black carbon measurements by a filter-based absorption photometer with a heated inlet

Abstract: Long-term measurements of black carbon (BC) aerosols by filter-based absorption photometers with a heated inlet (COSMOS) in different regions have been useful in elucidating spatial variati...

Reduced marine phytoplankton sulphur emissions in the Southern Ocean during the past seven glacials.

Abstract: Marine biogenic sulphur affects Earth's radiation budget and may be an indicator of primary productivity in the Southern Ocean, which is closely related to atmospheric CO2 variability through the biological pump. Previous ice-core studies in Antarctica show little climate dependence of marine biogenic sulphur emissions and hence primary productivity, contradictory to marine sediment records. Here we present new 720,000-year ice core records from Dome Fuji in East Antarctica and show that a large portion of non-sea-salt sulphate, which was traditionally used as a proxy for marine biogenic sulphate, likely originates from terrestrial dust during glacials. By correcting for this, we make a revised calculation of biogenic sulphate and find that its flux is reduced in glacial periods. Our results suggest reduced dimethylsulphide emissions in the Antarctic Zone of the Southern Ocean during glacials and provide new evidence for the coupling between climate and the Southern Ocean sulphur cycle.

Black Carbon and Inorganic Aerosols in Snowpack over the Arctic

Abstract: 1. Tokyo University of Science, 2. National Institute of Polar Research, 3. The Graduate University for Advanced Studies, 4. Meteorological Research Institute, 5. Depertment of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 6. Environmental Protection Department Ministry of the Environment, 7. Institute for Space–Earth Environmental Research (ISEE), Nagoya University, 8. Department of Space Indian Space Research Organization, 9. University of Toyama, 10. Okayama University, 11. WSL Institute for Snow and Avalanche Research, 12. former Snow and Ice Research Center, 13. Reserach Institute for Humanity and Nature, 14. Melnikov’s Permafrost Institute, 15. Institute of Low Temperature Science, Hokkaido University, 16. Civil Engineering Research Institute for Cold Region, 17. Graduate School of Environmental Science, Hokkaido University

Reduced marine biogenic sulphate flux in East Antarctica during glacial periods - Based on ion chemistry records from Dome Fuji ice core -

Abstract: Marine biogenic sulphate affects Earth’s radiation budget and may be an indicator of primary productivity in the Southern Ocean, which is closely related to atmospheric CO2 variability through the biological pump. Previous ice-core studies in Antarctica show little climate dependence of marine biogenic sulphate flux over glacial cycles, suggesting almost constant dimethylsulphide (DMS) emissions, hence primary productivity, in the Antarctic Zone of the Southern Ocean. On the other hand, marine sediment records show reduced export productions in the Antarctic Zone of the Southern Ocean during glacial periods, suggesting increased primary productivity. The disparity between ice-core and marine sediment records has been attributed to differences in marine organisms that contribute to these records. We present new 720,000-year ice core records from Dome Fuji in East Antarctica and show that a large portion of non-sea-salt sulphate, which was traditionally used as a proxy for marine biogenic sulphate, likely originates from terrestrial dust during glacial periods. By correcting for this, we make a revised calculation of marine biogenic sulphate and find that its flux is reduced in glacial periods. Our results suggest reduced dimethylsulphide emissions in the Antarctic Zone of the Southern Ocean during glacial periods and provide new evidence for the coupling between climate and the Southern Ocean sulphur cycle.