Arctic Station Dirigibile Italia

Ice Nuclaetaing Particles in Artic Region (INPAR)

Call year: 2017 Status: active IADC_id: 79

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The nucleation of ice is a key element to improve our understanding of aerosol-cloud-climate interactions and represents a major source of uncertainty for weather and climate models. rnIce first forms in clouds warmer than -36 °C on particles termed ice nucleating particle(INP). INP are a small subset of the atmospheric aerosol population, and present the unique ability to induce ice formation at conditions under  which  ice  would  not  form  without  them  (heterogeneous ice nucleation).rnThe study of ice nucleation is a very active and fast moving research field, but the unexplain variability of the ice nuclei concentrations at a given temperature remains a challenge. rnThis is particulalry true in the Arctic regions, where information based on measurement data are scarce and validation of model results is a challenge. rnTo provide a realistic representation of Arctic clouds and their impact on the local and global climate, it is necessary to describe the aerosol-cloud radiative, microphysical and dynamical interactions, and, in this regard, a better parametrization of the ice nuclei content is a key determinant to improve models.rnExtensive measurements from ground-based sites and satellite remote sensing have revealed the existence of two types of ice clouds (TICs) in the Arctic during the polar night and early spring. TICs-1 are composed by non precipitating small ice crystal (< 30 ?m), while TICs-2 are characterized by a low concentration of large precipitating ice crystals (> 30 ?m)   (Keita S.A and Girard E., 2016).  As a result, the INP concentration is reduced in these regions, resulting to a lower concentration of larger ice crystals. Observations suggest that boundary layer mixed phase clouds (MPC, mixture of liquid droplets and ice crystals) are ubiquitous in the Arctic and persist for several days under a variety of meteorological conditions (Mioche et al., 2015). They occur as single or multiple stratiform layers of supercooled droplets near the cloud top from which ice crystals form and precipitate. These clouds have a large impact on the surface radiative fluxes and Arctic climate feedbacks ( Kay et al., 2012).  In particular, atmospheric aerosol can influence the persistence of MPC by changing their microphysical properties.  However there is still a lack of observations of the liquid/ice partitioning and large discrepancies exist between observations and numerical simulations (especially due to uncertainties in microphysical/dynamical processes, but also regarding the knowledge on INP sources).  Stoppelli et al. (2016) sampled particles from air at Haldde Observatory, Norway on PM10 ?lters and determined the number of INP active at moderate supercooling temperatures (? -15 ?C) by immersion freezing. They found that air masses passing over the land were enriched in INP, with concentrations twice to three times larger than those found in air masses directly coming from the Barents Sea. Therefore, Arctic aerosol- MPC related processes and characteristics need to be better understood.rnIn addition marine aerosols, produced from primary processes but also via secondary processes, has been suggested as possible source of INP in the Artic regions.rnOur knowledge on the nature of marine emissions suffers from large gaps that in turn are responsible for a large uncertainty on our future climate (Carslaw, Nature 2013). Based on the size of aerosol formed, the chemical composition contains both inorganic sea salt and organic material, with variable ratios. Marine organic species remain largely uncharacterized (Benner, 2002) and organic concentrations can vary drastically throughout the water column, both temporally and spatially (Russell et al., 2010). Concentrations of marine organic aerosols seem to be highly dependent on the biological productivity at the ocean surface, following a seasonal bloom cycle. Studies performed at Mace Head in the North Atlantic Ocean and Amsterdam Island in the Southern Indian Ocean determined that the organic concentrations as well as the organic-to-sea salt ratio were higher during the spring/summer than during winter (Sciare et al., 2009). The impact of the organic content of marine aerosol on INP number concentration is however not straight forward and no clear link between Chlorofill rich waters and INP number concentrations has been evidenced. Indeed, recent global modeling exercises suggested that marine bioaerosols could be at the origin of INP number concentrations, hence influencing the radiative and precipitation properties of clouds (Burrows et al. 2013). The same study underlines the lack of experimental data to confirm this hypothesis. To conclude, despite the growing literature, the INP activity and concentrations in the Arctic are poorly known and further works are necessary to develop our understanding. rnIn addition it is foreseen to collect precipitating ice crystals on glass slides (25x75 mm) covered with a thin layer of 2% formvar in chloroform.  The chloroform and ice crystal, placed in a dessicator,  evaporate leaving a replica of the crystals. The replica can afterwards  be observed at SEM, so crystal shapes and scavenged aerosol particles can be examined  rn(Santachiara et al., 2016).rnReferences:rn-Belosi F. et al., Atmos. Res. (2014) 145–146, 105–111. doi:10.1016/j.atmosres.2014.03.030.rn-Belosi F., et al., Atmos. Res. (2016), Ground level Ice Nuclei Particle measurements including Saharan dust events at a Po Valley rural site, accepted paper.rn-Benner  R.  Biogeochemistry  of  Dissolved  Organic  Matter, edited by: Hansell D. and Carlson, C., Academic Press, New York, 2002.rn-Bigg E.K. et al., J. Appl. Meteorol. (1963) 2, 266–269.rn-Burrows S. M. et al., Atmos. Chem. Phys. (2013) 13, 245–267. doi:10.5194/acp-13-245-2013.rn-Carslaw K.S. et al., Nature (2013) 503, 67–71. doi:10.1038/nature12674.rn-Kay J.E. et al., J. Clim. (2012) 25, 5433-5450. doi:10.1175/JCLI-D-11-00622.1.rn-Keita S.A. and Girard E., Pure Appl. Geophys. (2016) 173, 3141-3163. doi:10.1007/s00024-016-1294-z.rn-Mioche G. et al., Atmos. Chem. Phys. (2015) 15, 2445–2461. doi:10.5194/acp-15-2445-2015.rn-Russell  L.M. et al., P.  Natl.  Acad.  Sci.  USA (2010) 107,  6652–6657. doi:10.1073/pnas.0908905107.rn-Santachiara G. et al., Atmos.Res. (2010) 96,266–272. doi:10.1016/j.atmosres.2009.08.004rn-Santachiara G., et al., Atmos.Res. (2016) 167,108-117.doi: /10.1016/j.atmosres.2015.08.006.rn-Sciare J. et al., J.  Geophys.  Res. (2009) 114,  D15302. doi:10.1029/2009JD011998.rn-Stoppelli E. et al., Atmos. Chem. Phys. (2016) 16, 8341-8351. doi:10.5194/acp-16-8341-2016.rnrn

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Ice Nuclaetaing Particles in Artic Region (INPAR)