Aerosol remote sensing in polar regions

Abstract

Multi-year sets of ground-based sun-photometer measurements conducted at 12 Arctic sites and 9 Antarctic sites were examined to determine daily mean values of aerosol optical thickness () at visible and near-infrared wavelengths, from which best-fit values of Ångström"s exponent  were calculated. Analysing these data, the monthly mean values of (0.50 µm) and  and the relative frequency histograms of the daily mean values of both parameters were determined for winterspring and summer-autumn in the Arctic and for austral summer in Antarctica. The Arctic and Antarctic covariance plots of the seasonal median values of  versus (0.50 µm) showed: (i) a considerable increase in (0.50 µm) for the Arctic aerosol from summer to winter-spring, without marked changes in ; and (ii) a marked increase in (0.50 µm) passing from the Antarctic Plateau to coastal sites, whereas  decreased considerably due to the larger fraction of sea-salt aerosol. Good agreement was found when comparing ground-based sun-photometer measurements of () and  at Arctic and Antarctic coastal sites with Microtops measurements conducted during numerous AERONET/MAN cruises from 2006 to 2013 in three Arctic Ocean sectors and in coastal and offshore regions of the Southern Atlantic, Pacific, and Indian Oceans, and the Antarctic Peninsula. Lidar measurements were also examined to characterise vertical profiles of the aerosol backscattering coefficient measured throughout the year at Ny-Ålesund. Satellite-based MODIS, MISR, and AATSR retrievals of () over large parts of the oceanic polar regions during spring and summer were in close agreement with ship-borne and coastal ground-based sun-photometer measurements. An overview of the chemical composition of fine and accumulation/coarse mode particles is also presented, based on in-situ measurements at Arctic and Antarctic sites. Fourteen log-normal aerosol number size-distributions were defined to represent the average features of fine and accumulation/coarse mode particles for Arctic haze, summer background aerosol, Asian dust and boreal forest fire smoke, and for various background austral summer aerosol types at coastal 4 and high-altitude Antarctic sites. The main columnar aerosol optical characteristics were determined for all particle modes, based on in-situ measurements of the scattering and absorption coefficients. Diurnally averaged direct aerosol-induced radiative forcing and efficiency were calculated for a set of multimodal aerosol extinction models, using various Bidirectional Reflectance Distribution Function models over vegetation-covered, oceanic and snow-covered surfaces. These gave a reliable measure of the pronounced effects of aerosols on the radiation balance of the surface-atmosphere system over polar regions.

The new sun-sky-lunar Cimel CE318-T multiband photometer – a comprehensive performance evaluation

“…The use of active remote measurements such as advanced ground-based lidars systems prevents the last two handicaps of sun photometry, providing daytime and night-time information about the atmospheric vertical structure. As a result, this technique has proven to be very effective in the characterization of aerosols in high-latitude regions (Baibakov et al, 2015;Tomasi et al, 2015;Hoffmann et al, 2009). Lidars allow us to determine vertical profiles of aerosol optical properties and estimate some microphysical properties (only using multiwavelength Raman Lidars), but some physical or mathematical constraints are necessary in the inversion algorithm.…”

Seasonal Variations of the Relative Optical Air Mass Function for Background Aerosol and Thin Cirrus Clouds at Arctic and Antarctic Sites

“…(1) The mean profile of ka(z) derived from monthly or multi-monthly average Bbs(0.532 m) profiles measured at Ny-Ålesund with the AWI (Alfred Wegener Institute, Germany) KARL (Koldewey-Aerosol-Raman Lidar) lidar-system (described by Hoffmann et al [33]) in January, April, June−July and October−December of 2013 (see also [1]). …”

“…Regular sun-photometer measurements are currently conducted at numerous Arctic and Antarctic sites to determine the spectral values of aerosol optical thickness τa(λ) at visible and near-infrared wavelengths [1]. These measurements are conducted using different sun-photometer models such as the Cimel CE-318 of the Aerosol Robotic Network (AERONET) network [2], the Prede POM-01L and POM-02L sun/sky-radiometers of the SKYNET network [3], the hand-held Microtops sun-photometers of the Maritime Aerosol Network (MAN) [4], the EKO MS-110 model [5] used by the Japan Meteorological Agency (Tokyo, Japan) at Syowa (Antarctica), and various sun-photometer models employed by the POLAR-AOD partners [6,7].…”

2014 iAREA campaign on aerosol in Spitsbergen – Part 1: Study of physical and chemical properties

“…The maximum occurs during winterespring season where a three decade long term mean values of Aerosol Optical Depth (AOD) for 500 nm in NyeÅlesund reach maximum equal to 0.07e0.09 and Ångstrom exponent (AE) being between 1.3 and 1.5 (Tomasi et al, 2015). Further investigation of Tomasi et al (2012) indicates fine mode of wateresoluble and seaesalt as well as seaesalt coarse mode to have the largest impact on aerosol optical properties.…”

“…The annual load of aerosols in Arctic varies over seasons altering the values of single scattering properties (Tomasi et al, 2015). The maximum occurs during winterespring season where a three decade long term mean values of Aerosol Optical Depth (AOD) for 500 nm in NyeÅlesund reach maximum equal to 0.07e0.09 and Ångstrom exponent (AE) being between 1.3 and 1.5 (Tomasi et al, 2015).…”