Ice nucleation properties of volcanic ash from Eyjafjallajökull

Abstract

Abstract. The ice nucleation ability of volcanic ash particles collected close to the Icelandic volcano Eyjafjallajökull during its eruptions in April and May 2010 is investigated experimentally, in the immersion and deposition modes, and applied to atmospheric conditions by comparison with airborne measurements and microphysical model calculations. The number of ash particles which are active as ice nuclei (IN) is strongly temperature dependent, with a very small minority being active in the immersion mode at temperatures of 250-263 K. Average ash particles show only a moderate effect on ice nucleation, by inducing freezing at temperatures between 236 K and 240 K (i.e. approximately 3-4 K higher than temperatures required for homogeneous ice nucleation, measured with the same instrument). By scaling the results to aircraft and lidar measurements of the conditions in the ash plume days down wind of the eruption, and by applying a simple microphysical model, it was found that the IN active in the immersion mode in the range 250-263 K generally occurred in atmospheric number densities at the lower end of those required to have an impact on ice cloud formation. However, 3-4 K above the homogeneous freezing point, immersion mode IN number densities a few days down wind of the eruption were sufficiently high to have a moderate influence on ice cloud formation. The efficiency of IN in the deposition mode was found to be poor except at very cold conditions (<238 K), when they reach an efficiency similar to that of mineral dust with the onset of freezing at 10 % supersaturation with respect to ice, and with the frozen fraction nearing its maximum value at a supersaturation 20 %. In summary, these investigations suggest volcanic ash particles to have only moderate effects on atmospheric ice formation.

Deposition and immersion-mode nucleation of ice by three distinct samples of volcanic ash

“…Unlike field measurements, however, it has been suggested that all volcanic ash may have similar ice nucleation efficacy, initiating ice formation in a relatively narrow temperature range of approximately 250 to 260 K (Durant et al, 2008); however, these works are difficult to interpret quantitatively, especially in cases where the nucleation mode is unclear, frozen fractions are unavailable, or the available surface area has not been quantified. More recently, several studies have investigated the deposition-and/or immersion-mode ice nucleation properties of ash from the 2010 eruption of the Eyjafjallajökull volcano in Iceland (Steinke et al, 2011;Hoyle et al, 2011;Bingemer et al, 2012). The results of these studies, combined with previous studies on large, 250-300 µm ash particles from the 1980 Mt.…”

“…It can be seen that all three ash samples exhibit minimal temperature dependence (Koop et al, 2000). Also included are onset results from depositional ice nucleation experiments on ash from the 2010 Eyjafjallajökull eruption (Hoyle et al, 2011;Steinke et al, 2011) and a parameterization for depositional ice nucleation on KGa-1b (Sihvonen et al, 2014).…”

“…Laboratory studies probing the ice nucleation efficiency of volcanic ash have also shown it can act as heterogeneous IN (Durant et al, 2008;Hoyle et al, 2011). Unlike field measurements, however, it has been suggested that all volcanic ash may have similar ice nucleation efficacy, initiating ice formation in a relatively narrow temperature range of approximately 250 to 260 K (Durant et al, 2008); however, these works are difficult to interpret quantitatively, especially in cases where the nucleation mode is unclear, frozen fractions are unavailable, or the available surface area has not been quantified.…”

A physically constrained classical description of the homogeneous nucleation of ice in water

“…Each J hom data set was weighted equally by representing it with three data points, at the maximum, minimum, and average temperature, determined from a straight line fit to ln(J hom ) versus T. In addition, we grouped measurements from separate papers, but made with the same instrument and methodology, into single data sets (i.e., we grouped data from Duft and Leisner 58 with Rzesanke et al, 59 Stöckel et al 61 with Kabath et al, 62 as well as Hoyle et al 64 with Lüönd et al 65 ). The resulting CNT fits are shown in Figure 3, with different lines originating from employing different parameterizations of D(T).…”

“…1,56 In this study, we have selected a subset [56][57][58][59][60][61][62][63][64][65][66][67][68] of the available data sets for the purposes of constraining the new parameterization. The criteria for selection were (i) minimal and well defined uncertainties, (ii) good reproducibility within the data set, and (iii) an internal droplet pressure of about 1 bar.…”