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- ItemThe vertical aerosol type distribution above Israel – 2 years of lidar observations at the coastal city of Haifa(Katlenburg-Lindau : EGU, 2022) Heese, Birgit; Floutsi, Athena Augusta; Baars, Holger; Althausen, Dietrich; Hofer, Julian; Herzog, Alina; Mewes, Silke; Radenz, Martin; Schechner, Yoav Y.For the first time, vertically resolved long-term lidar measurements of the aerosol distribution were conducted in Haifa, Israel. The measurements were performed by a PollyXT multi-wavelength Raman and polarization lidar. The lidar was measuring continuously over a 2-year period from March 2017 to May 2019. The resulting data set is a series of manually evaluated lidar optical property profiles. To identify the aerosol types in the observed layers, a novel aerosol typing method that was developed at TROPOS is used. This method applies optimal estimation to a combination of lidar-derived intensive aerosol properties to determine the statistically most-likely contribution per aerosol component in terms of relative volume. A case study that shows several elevated aerosol layers illustrates this method and shows, for example, that coarse dust particles are observed up to 5ĝ€¯km height over Israel. From the whole data set, the seasonal distribution of the observed aerosol components over Israel is derived. Throughout all seasons, coarse spherical particles like sea salt and hygroscopically grown continental aerosol were observed. These particles originate from continental Europe and were transported over the Mediterranean Sea. Sea-salt particles were observed frequently due to the coastal site of Haifa. The highest contributions of coarse spherical particles are present in summer, autumn, and winter. During spring, mostly coarse non-spherical particles that are attributed to desert dust were observed. This is consistent with the distinct dust season in spring in Israel. An automated time-height-resolved air mass source attribution method identifies the origin of the dust in the Sahara and the Arabian deserts. Fine-mode spherical particles contribute significantly to the observed aerosol mixture during all seasons. These particles originate mainly from the industrial region at the bay of Haifa.
- ItemHigh number concentrations of transparent exopolymer particles in ambient aerosol particles and cloud water – a case study at the tropical Atlantic Ocean(Katlenburg-Lindau : EGU, 2022) van Pinxteren, Manuela; Robinson, Tiera-Brandy; Zeppenfeld, Sebastian; Gong, Xianda; Bahlmann, Enno; Fomba, Khanneh Wadinga; Triesch, Nadja; Stratmann, Frank; Wurl, Oliver; Engel, Anja; Wex, Heike; Herrmann, HartmutTransparent exopolymer particles (TEPs) exhibit the properties of gels and are ubiquitously found in the world oceans. TEPs may enter the atmosphere as part of sea-spray aerosol. Here, we report number concentrations of TEPs with a diameter >4.5 μm, hence covering a part of the supermicron particle range, in ambient aerosol and cloud water samples from the tropical Atlantic Ocean as well as in generated aerosol particles using a plunging waterfall tank that was filled with the ambient seawater. The ambient TEP concentrations ranged between 7×102 and 3×104 #TEP m-3 in the aerosol particles and correlations with sodium (Na+) and calcium (Ca2+) (R2=0.5) suggested some contribution via bubble bursting. Cloud water TEP concentrations were between 4×106 and 9×106 #TEP L-1 and, according to the measured cloud liquid water content, corresponding to equivalent air concentrations of 2-4 × 103 #TEP m-3. Based on Na+ concentrations in seawater and in the atmosphere, the enrichment factors for TEPs in the atmosphere were calculated. The tank-generated TEPs were enriched by a factor of 50 compared with seawater and, therefore, in-line with published enrichment factors for supermicron organic matter in general and TEPs specifically. TEP enrichment in the ambient atmosphere was on average 1×103 in cloud water and 9×103 in ambient aerosol particles and therefore about two orders of magnitude higher than the corresponding enrichment from the tank study. Such high enrichment of supermicron particulate organic constituents in the atmosphere is uncommon and we propose that atmospheric TEP concentrations resulted from a combination of enrichment during bubble bursting transfer from the ocean and a secondary TEP in-situ formation in atmospheric phases. Abiotic in-situ formation might have occurred from aqueous reactions of dissolved organic precursors that were present in particle and cloud water samples, whereas biotic formation involves bacteria, which were abundant in the cloud water samples. The ambient TEP number concentrations were two orders of magnitude higher than recently reported ice nucleating particle (INP) concentrations measured at the same location. As TEPs likely possess good properties to act as INPs, in future experiments it is worth studying if a certain part of TEPs contributes a fraction of the biogenic INP population.
- ItemSignificant continental source of ice-nucleating particles at the tip of Chile's southernmost Patagonia region(Katlenburg-Lindau : EGU, 2022) Gong, Xianda; Radenz, Martin; Wex, Heike; Seifert, Patric; Ataei, Farnoush; Henning, Silvia; Baars, Holger; Barja, Boris; Ansmann, Albert; Stratmann, FrankThe sources and abundance of ice-nucleating particles (INPs) that initiate cloud ice formation remain understudied, especially in the Southern Hemisphere. In this study, we present INP measurements taken close to Punta Arenas, Chile, at the southernmost tip of South America from May 2019 to March 2020, during the Dynamics, Aerosol, Cloud, And Precipitation Observations in the Pristine Environment of the Southern Ocean (DACAPO-PESO) campaign. The highest ice nucleation temperature was observed at −3◦C, and from this temperature down to ∼ −10◦C, a sharp increase of INP number concentration (NINP) was observed. Heating of the samples revealed that roughly 90 % and 80 % of INPs are proteinaceous-based biogenic particles at > −10 and −15◦C, respectively. The NINP at Punta Arenas is much higher than that in the Southern Ocean, but it is comparable with an agricultural area in Argentina and forestry environment in the US. Ice active surface site density (ns) is much higher than that for marine aerosol in the Southern Ocean, but comparable to English fertile soil dust. Parameterization based on particle number concentration in the size range larger than 500 nm (N>500 nm) from the global average (DeMott et al., 2010) overestimates the measured INP, but the parameterization representing biological particles from a forestry environment (Tobo et al., 2013) yields NINP comparable to this study. No clear seasonal variation of NINP was observed. High precipitation is one of the most important meteorological parameters to enhance the NINP in both cold and warm seasons. A comparison of data from in situ and lidar measurements showed good agreement for concentrations of large aerosol particles (> 500 nm) when assuming continental conditions for retrieval of the lidar data, suggesting that these particles were well mixed within the planetary boundary layer (PBL). This corroborates the continental origin of these particles, consistent with the results from our INP source analysis. Overall, we suggest that a high NINP of biogenic INPs originated from terrestrial sources and were added to the marine air masses during the overflow of a maximum of roughly 150 km of land before arriving at the measurement station.
- ItemShip-based measurements of ice nuclei concentrations over the Arctic, Atlantic, Pacific and Southern oceans(Katlenburg-Lindau : EGU, 2020) Welti, André; Bigg, Keith E.; DeMott, Paul J.; Gong, Xianda; Hartmann, Markus; Harvey, Mike; Henning, Silvia; Herenz, Paul; Hill, Thomas C.J.; Hornblow, Blake; Leck, Caroline; Löffler, Mareike; McCluskey, Christina S.; Rauker, Anne Marie; Schmale, Julia; Tatzelt, Christian; van Pinxteren, Manuela; Stratmann, FrankAmbient concentrations of ice-forming particles measured during ship expeditions are collected and summarised with the aim of determining the spatial distribution and variability in ice nuclei in oceanic regions. The presented data from literature and previously unpublished data from over 23 months of ship-based measurements stretch from the Arctic to the Southern Ocean and include a circumnavigation of Antarctica. In comparison to continental observations, ship-based measurements of ambient ice nuclei show 1 to 2 orders of magnitude lower mean concentrations. To quantify the geographical variability in oceanic areas, the concentration range of potential ice nuclei in different climate zones is analysed by meridionally dividing the expedition tracks into tropical, temperate and polar climate zones. We find that concentrations of ice nuclei in these meridional zones follow temperature spectra with similar slopes but vary in absolute concentration. Typically, the frequency with which specific concentrations of ice nuclei are observed at a certain temperature follows a log-normal distribution. A consequence of the log-normal distribution is that the mean concentration is higher than the most frequently measured concentration. Finally, the potential contribution of ship exhaust to the measured ice nuclei concentration on board research vessels is analysed as function of temperature. We find a sharp onset of the influence at approximately 36 C but none at warmer temperatures that could bias ship-based measurements. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
- ItemTracing the Snowball bifurcation of aquaplanets through time reveals a fundamental shift in critical-state dynamics(Göttingen : Copernicus, 2023) Feulner, Georg; Bukenberger, Mona; Petri, StefanThe instability with respect to global glaciation is a fundamental property of the climate system caused by the positive ice-albedo feedback. The atmospheric concentration of carbon dioxide (CO2) at which this Snowball bifurcation occurs changes through Earth's history, most notably because of the slowly increasing solar luminosity. Quantifying this critical CO2 concentration is not only interesting from a climate dynamics perspective but also constitutes an important prerequisite for understanding past Snowball Earth episodes, as well as the conditions for habitability on Earth and other planets. Earlier studies are limited to investigations with very simple climate models for Earth's entire history or studies of individual time slices carried out with a variety of more complex models and for different boundary conditions, making comparisons and the identification of secular changes difficult. Here, we use a coupled climate model of intermediate complexity to trace the Snowball bifurcation of an aquaplanet through Earth's history in one consistent model framework. We find that the critical CO2 concentration decreased more or less logarithmically with increasing solar luminosity until about 1 billion years ago but dropped faster in more recent times. Furthermore, there was a fundamental shift in the dynamics of the critical state about 1.2 billion years ago (unrelated to the downturn in critical CO2 values), driven by the interplay of wind-driven sea-ice dynamics and the surface energy balance: for critical states at low solar luminosities, the ice line lies in the Ferrel cell, stabilised by the poleward winds despite moderate meridional temperature gradients under strong greenhouse warming. For critical states at high solar luminosities, on the other hand, the ice line rests at the Hadley cell boundary, stabilised against the equatorward winds by steep meridional temperature gradients resulting from the increased solar energy input at lower latitudes and stronger Ekman transport in the ocean.