V. Aaltonen

Aerosols in polar regions: A historical overview based on optical depth and in situ observations

Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and ...

Observational signature of the direct radiative effect by natural boreal forest aerosols and its relation to the corresponding first indirect effect

By using a screened set of long-term aerosol measurement data, the contribution of natural boreal forest aerosols to the direct radiative effect (DRE) was observed at a remote continental site in n ...

Where does the optically detectable aerosol in the European Arctic come from

In this paper, we pose the question where the source regions of the aerosol, which occurs in the European Arctic, are located. Long-term aerosol optical depth (AOD) data from Ny-Ålesund and Sodankylä as well as short-term data from a campaign on a Russian drifting station were analysed by air backtrajectories, analysis of the general circulation pattern and a correlation to chemical composition from in-situ measurements. Surprisingly, our data clearly shows that direct transport of pollutants from Europe does not play an important role. Instead, Arctic haze in Ny-Ålesund has been found for air masses from the Eastern Arctic, while events with increased AOD but chemically more diverse composition have been found for air from Siberia or the central Arctic. Moreover, the AOD in Ny-Ålesund does not depend on the North Atlantic Oscillation (NAO). Hence, either the pollution pathways of aerosol are more complex or aerosol is significantly altered by clouds.

SNORTEX (Snow Reflectance Transition Experiment): Remote sensing measurement of the dynamic properties of the boreal snow-forest in support to climate and weather forecast: Report of IOP-2008

Large discrepancies are observed between snow albedo in Numerical Weather Prediction (NWP) models and from satellite observations in the case of high vegetation. Knowledge of the Bidirectional Reflectance Distribution Function (BRDF) of snow-forest system is required to solve the problem. The 3-years SNORTEX (Snow Reflectance Transition Experiment) campaign acquires from 2008 in situ measurements of snow and forest properties in support to the development of modelling tools and to validate coarse resolution satellite products (POLDER, MODIS, MERIS, METOP). The measurement scheme and some first example results are presented from the Intensive Observing Period (IOP) of 2008, which can be decomposed into airborne and ground operations. Multi-temporal BRDF at a metric resolution were acquired from OSIRIS (airPOLDER) onboard a helicopter and from ground with FigiFiGo spectrogoniometer. The same helicopter embarked a pair of UV sensors, pyranometers and a wide-optics camera. Ground component includes exhaustive snow measurements.

Primary sources control the variability of aerosol optical properties in the Antarctic Peninsula

Abstract Aerosol particle optical properties were measured continuously between years 2013–2015 at the Marambio station in the Antarctic Peninsula. Annual cycles of particle scattering and absorption were studied and explained using measured particle chemical composition and the analysis of air mass transport patterns. The particle scattering was found elevated during the winter but the absorption did not show any clear annual cycle. The aerosol single scattering albedo at nm was on average 0.96 0.10, with a median of 0.99. Aerosol scattering Ångström exponent increased during summer, indicating an increasing fraction of fine mode particles. The aerosol was mainly composed of sea salt, sulphate and crustal soil minerals, and most of the particle mass were in the coarse mode. Both the particle absorption and scattering were increased during high wind speeds. This was explained by the dominance of the primary marine sea-spray and wind-blown soil dust sources. In contrast, the back-trajectory analysis suggested that long-range transport has only a minor role as a source of absorbing aerosol at the peninsula.

Measurement of snow cover based on external radiation

Publisher Summary The measurement of SWE based on the attenuation of gamma radiation offers several advantages compared to snow cover coring and subsequent weighing. The present method takes into consideration the melted water that is not trapped into the corer. It also integrates SWE from a larger area compared to point data obtained with a corer. The method also provides continuous data. All these factors lead to improved prognoses of melt water amount that helps the planning of flood protection measures and facilitates optimized hydroelectric power production. In addition, during summer season the measurement of external dose rate can provide data on the evapotranspiration of water from the soil. In this case, too, the method is continuous and automatic unlike the traditional method of measuring the water level in an open vessel. The traditional method also ignores the effect of plant transpiration. The present method thus gives a better view of the soil moisture content that can improve the accuracy of forest fire risk assessments.

Aerosol optical properties in Finland during Russian forest fires in 2010

Effects of the pollution plume originating from the Russian forest fires in summer 2010 on the aerosol properties in Finland were analyzed. Main properties were AOD and AE measured with Cimel and PFR sun photometers at five stations. In addition, scattering and absorption coefficient, aerosol particle number concentration and meteorological parameters were measured on the surface air. AATSR and MODIS AOD data were used to get a picture about the regional distribution of the plume. Two clear extreme periods of the AOD were observed. On 30th July, the maximum AOD was detected in Sodankyla, being 0.9 at 550 nm. A more impressive episode was between the 6th and 8th of August, when the extreme AOD of 1.5 was measured in Kuopio. In-situ observations suggest that the major part of the aerosol was residing in the well mixed layer coupled with the surface.