scholarly journals The impact of mineral dust on cloud formation during the Saharan dust event in April 2014 over Europe

2018 ◽  
Vol 18 (23) ◽  
pp. 17545-17572 ◽  
Author(s):  
Michael Weger ◽  
Bernd Heinold ◽  
Christa Engler ◽  
Ulrich Schumann ◽  
Axel Seifert ◽  
...  
Keyword(s):  
Cloud Cover ◽  
Mineral Dust ◽  
Dust Cloud ◽  
Ice Nucleation ◽  
Saharan Dust ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Dust Event ◽  
The Impact

Abstract. A regional modeling study on the impact of desert dust on cloud formation is presented for a major Saharan dust outbreak over Europe from 2 to 5 April 2014. The dust event coincided with an extensive and dense cirrus cloud layer, suggesting an influence of dust on atmospheric ice nucleation. Using interactive simulation with the regional dust model COSMO-MUSCAT, we investigate cloud and precipitation representation in the model and test the sensitivity of cloud parameters to dust–cloud and dust–radiation interactions of the simulated dust plume. We evaluate model results with ground-based and spaceborne remote sensing measurements of aerosol and cloud properties, as well as the in situ measurements obtained during the ML-CIRRUS aircraft campaign. A run of the model with single-moment bulk microphysics without online dust feedback considerably underestimated cirrus cloud cover over Germany in the comparison with infrared satellite imagery. This was also reflected in simulated upper-tropospheric ice water content (IWC), which accounted for only 20 % of the observed values. The interactive dust simulation with COSMO-MUSCAT, including a two-moment bulk microphysics scheme and dust–cloud as well as dust–radiation feedback, in contrast, led to significant improvements. The modeled cirrus cloud cover and IWC were by at least a factor of 2 higher in the relevant altitudes compared to the noninteractive model run. We attributed these improvements mainly to enhanced deposition freezing in response to the high mineral dust concentrations. This was corroborated further in a significant decrease in ice particle radii towards more realistic values, compared to in situ measurements from the ML-CIRRUS aircraft campaign. By testing different empirical ice nucleation parameterizations, we further demonstrate that remaining uncertainties in the ice-nucleating properties of mineral dust affect the model performance at least as significantly as including the online representation of the mineral dust distribution. Dust–radiation interactions played a secondary role for cirrus cloud formation, but contributed to a more realistic representation of precipitation by suppressing moist convection in southern Germany. In addition, a too-low specific humidity in the 7 to 10 km altitude range in the boundary conditions was identified as one of the main reasons for misrepresentation of cirrus clouds in this model study.

scholarly journals The impact of mineral dust on cloud formation during the Saharan dust event in April 2014 over Europe

2018 ◽  
Author(s):  
Michael Weger ◽  
Bernd Heinold ◽  
Ina Tegen ◽  
Christa Engler ◽  
Patric Seifert ◽  
...  
Keyword(s):  
Cloud Cover ◽  
Mineral Dust ◽  
Dust Cloud ◽  
Ice Nucleation ◽  
Saharan Dust ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Dust Event ◽  
The Impact

Abstract. A regional modeling study on the impact of desert dust on cloud formation is presented for a major Saharan dust outbreak over Europe from 2 April to 5 April 2014. The dust event coincided with an extensive and dense cirrus cloud layer, suggesting an influence of dust on atmospheric ice nucleation. Using interactive simulation with the regional dust model COSMO-MUSCAT, we investigate cloud and precipitation representation in the model and test the sensitivity of cloud parameters to dust-cloud and dust-radiation interactions of the simulated dust plume. We evaluate model results with ground-based and space-borne remote sensings of aerosol and cloud properties, as well as the in situ measurements obtained during the ML-CIRRUS aircraft campaign. A run of the model with single-moment bulk microphysics without online dust feedback considerably underestimated cirrus cloud cover over Germany in the comparison with infrared satellite imagery. This was also reflected in simulated upper-tropospheric ice water content (IWC), which accounted only for 20 % of the observed values. The interactive dust simulation with COSMO-MUSCAT, including a two-moment bulk microphysics scheme and dust-cloud as well as dust-radiation feedback, in contrast, led to significant improvements. The modeled cirrus cloud cover and IWC were by at least a factor of two higher in the relevant altitudes compared to the non-interactive model run. We attributed these improvements mainly to enhanced deposition freezing in response to the high mineral dust concentrations. This was corroborated further in a significant decrease in ice particle radii towards more realistic values, as compared to in situ measurements from the ML-CIRRUS aircraft campaign. By testing different empirical ice nucleation parameterizations, we further demonstrate that remaining uncertainties in the ice nucleating properties of mineral dust affect the model performance at least as significantly as to whether including the online representation of the mineral distribution. Dust-radiation interactions played a secondary role for cirrus cloud formation, but contributed to a more realistic representation of precipitation by suppressing moist convection in southern Germany. In addition, a too low specific humidity in the 7 to 10 km altitude range in the boundary conditions was identified as a main reason of misrepresentation of cirrus clouds in this model study.

scholarly journals Cloud-scale ice supersaturated regions spatially correlate with high water vapor heterogeneities

2013 ◽  
Vol 13 (8) ◽  
pp. 22249-22296
Author(s):  
M. Diao ◽  
M. A. Zondlo ◽  
A. J. Heymsfield ◽  
L. M. Avallone ◽  
M. E. Paige ◽  
...  
Keyword(s):  
Water Vapor ◽  
High Water ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Small Scale ◽  
Cirrus Cloud ◽  
Median Length ◽  
Upper Troposphere ◽  
Earth’S Climate

Abstract. Cirrus clouds have large yet uncertain impacts on the Earth's climate. Ice supersaturation (ISS) – where the relative humidity with respect to ice (RHi) is greater than 100% – is the prerequisite condition of ice nucleation. Here we use 1 Hz (~230 m) in situ aircraft-based observations from 87° N–67° S to analyze the spatial characteristics of ice supersaturated regions (ISSRs). The median length of 1-D horizontal ISSR segments is found to be very small (~1 km), which is two orders of magnitude smaller than previously reported. To understand the conditions of these small scale ISSRs, we compare individual ISSRs with their horizontally adjacent subsaturated surroundings and show that 99% and 73% of the ISSRs are moister and colder, respectively. When quantifying the contributions of water vapor (H2O) and temperature (T) individually, the magnitudes of the differences between the maximum RHi values inside ISSRs (RHimax) and the RHi in subsaturated surroundings are largely derived from the H2O spatial variabilities (by 88%) than from those of T (by 9%). These features hold for both ISSRs with and without ice crystals present. Similar analyses for all RHi horizontal variabilities (including ISS and non-ISS) show strong contributions from H2O variabilities at various T, H2O, pressure (P) and various horizontal scales (~1–100 km). Our results provide a new observational constraint on ISSRs on the microscale (~100 m) and point to the importance of understanding how these fine scale features originate and impact cirrus cloud formation and the RHi field in the upper troposphere (UT).

A modeling insight into the transport of large dust particles

2021 ◽  
Author(s):  
Eleni Drakaki ◽  
Alexandra Tsekeri ◽  
Vasillis Amiridis ◽  
Stavros Solomos ◽  
Antonis Gkikas ◽  
...  
Keyword(s):  
Size Distribution ◽  
Mineral Dust ◽  
Saharan Dust ◽  
Cloud Formation ◽  
Dust Particles ◽  
Negative Effects ◽  
Airborne Dust ◽  
Horizon 2020 ◽  
Research And Innovation ◽  
The Impact

<p>Mineral dust is an important component of the climate system, affecting radiation, cloud formation, biogeochemical cycles, as well as having negative effects on solar energy budget and human health. All these processes are affected from the size of the particles which is significantly underestimated by the Earth System Models. Here, we present results from a first attempt to modify the size distribution parameterizations in the GOCART-AFWA dust scheme of WRF - Chem, by including the large dust particles with diameters greater than 20 µm to describe the mineral dust cycle. The parameterization is based on Saharan dust observational datasets from FENNEC and SAMUM campaigns. We investigate the impact of the extended size distribution on the overall transported dust load and also the impact of particle settling considerations in deposition rates. The model results are compared with airborne dust measurements from AER-D campaign. In order to achieve the best agreement with the observations, an artificial force that counteracts gravity approximately by 80% for the large particles is needed, indicating the presence of one or more under-represented physical processes in the model.</p><p><strong>Acknowledgment:</strong> This research was supported by D-TECT (Grant Agreement 725698) funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme. </p>

scholarly journals Cloud-scale ice-supersaturated regions spatially correlate with high water vapor heterogeneities

2014 ◽  
Vol 14 (5) ◽  
pp. 2639-2656 ◽  
Author(s):  
M. Diao ◽  
M. A. Zondlo ◽  
A. J. Heymsfield ◽  
L. M. Avallone ◽  
M. E. Paige ◽  
...  
Keyword(s):  
Water Vapor ◽  
High Water ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Small Scale ◽  
Cirrus Cloud ◽  
Median Length ◽  
Upper Troposphere ◽  
Earth’S Climate

Abstract. Cirrus clouds have large yet uncertain impacts on Earth's climate. Ice supersaturation (ISS) – where the relative humidity with respect to ice (RHi) is greater than 100% – is the prerequisite condition of ice nucleation. Here we use 1 Hz (~230 m) in situ, aircraft-based observations from 87° N to 67° S to analyze the spatial characteristics of ice-supersaturated regions (ISSRs). The median length of 1-D horizontal ISSR segments is found to be very small (~1 km), which is 2 orders of magnitude smaller than previously reported. To understand the conditions of these small-scale ISSRs, we compare individual ISSRs with their horizontally adjacent subsaturated surroundings and show that 99% and 73% of the ISSRs are moister and colder, respectively. When quantifying the contributions of water vapor (H2O) and temperature (T) individually, the magnitudes of the differences between the maximum RHi values inside ISSRs (RHimax) and the RHi in subsaturated surroundings are largely derived from the H2O spatial variabilities (by 88%) than from those of T (by 9%). These features hold for both ISSRs with and without ice crystals present. Similar analyses for all RHi horizontal variabilities (including ISS and non-ISS) show strong contributions from H2O variabilities at various T, H2O, pressure (P) and various horizontal scales (~1–100 km). Our results provide a new observational constraint on ISSRs on the microscale (~100 m) and point to the importance of understanding how these fine-scale features originate and impact cirrus cloud formation and the RHi field in the upper troposphere (UT).

scholarly journals Ice nucleating particles over the Eastern Mediterranean measured by unmanned aircraft systems

2017 ◽  
Vol 17 (7) ◽  
pp. 4817-4835 ◽  
Author(s):  
Jann Schrod ◽  
Daniel Weber ◽  
Jaqueline Drücke ◽  
Christos Keleshis ◽  
Michael Pikridas ◽  
...  
Keyword(s):  
Transport Model ◽  
Eastern Mediterranean ◽  
Lower Troposphere ◽  
Ground Level ◽  
Ice Nucleation ◽  
Unmanned Aircraft ◽  
Unmanned Aircraft Systems ◽  
Saharan Dust ◽  
Cloud Formation ◽  
Aircraft Systems

Abstract. During an intensive field campaign on aerosol, clouds, and ice nucleation in the Eastern Mediterranean in April 2016, we measured the abundance of ice nucleating particles (INPs) in the lower troposphere from unmanned aircraft systems (UASs). Aerosol samples were collected by miniaturized electrostatic precipitators onboard the UASs at altitudes up to 2.5 km. The number of INPs in these samples, which are active in the deposition and condensation modes at temperatures from −20 to −30 °C, were analyzed immediately after collection on site using the ice nucleus counter FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment). During the 1-month campaign, we encountered a series of Saharan dust plumes that traveled at several kilometers' altitude. Here we present INP data from 42 individual flights, together with aerosol number concentrations, observations of lidar backscattering, dust concentrations derived by the dust transport model DREAM (Dust Regional Atmospheric Model), and results from scanning electron microscopy. The effect of the dust plumes is reflected by the coincidence of INPs with the particulate matter (PM), the lidar signal, and the predicted dust mass of the model. This suggests that mineral dust or a constituent related to dust was a major contributor to the ice nucleating properties of the aerosol. Peak concentrations of above 100 INPs std L−1 were measured at −30 °C. The INP concentration in elevated plumes was on average a factor of 10 higher than at ground level. Since desert dust is transported for long distances over wide areas of the globe predominantly at several kilometers' altitude, we conclude that INP measurements at ground level may be of limited significance for the situation at the level of cloud formation.

scholarly journals Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen

2012 ◽  
Vol 12 (5) ◽  
pp. 2541-2550 ◽  
Author(s):  
B. G. Pummer ◽  
H. Bauer ◽  
J. Bernardi ◽  
S. Bleicher ◽  
H. Grothe
Keyword(s):  
Radiative Forcing ◽  
Pollen Grains ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Distribution Area ◽  
Ice Cloud ◽  
Ice Nuclei ◽  
Nucleation Activity ◽  
Ice Nucleation Activity ◽  
The Impact

Abstract. The ice nucleation of bioaerosols (bacteria, pollen, spores, etc.) is a topic of growing interest, since their impact on ice cloud formation and thus on radiative forcing, an important parameter in global climate, is not yet fully understood. Here we show that pollen of different species strongly differ in their ice nucleation behaviour. The average freezing temperatures in laboratory experiments range from 240 to 255 K. As the most efficient nuclei (silver birch, Scots pine and common juniper pollen) have a distribution area up to the Northern timberline, their ice nucleation activity might be a cryoprotective mechanism. Far more intriguingly, it has turned out that water, which has been in contact with pollen and then been separated from the bodies, nucleates as good as the pollen grains themselves. The ice nuclei have to be easily-suspendable macromolecules located on the pollen. Once extracted, they can be distributed further through the atmosphere than the heavy pollen grains and so presumably augment the impact of pollen on ice cloud formation even in the upper troposphere. Our experiments lead to the conclusion that pollen ice nuclei, in contrast to bacterial and fungal ice nucleating proteins, are non-proteinaceous compounds.

Saharan Dust Records and Its Impact in the European Alps

2021 ◽  
Author(s):  
Marion Greilinger ◽  
Anne Kasper-Giebl
Keyword(s):  
Mineral Dust ◽  
Cloud Condensation Nuclei ◽  
Ice Cores ◽  
Atmospheric Particulate Matter ◽  
Saharan Dust ◽  
Cloud Formation ◽  
Dust Particles ◽  
European Alps ◽  
Airborne Dust ◽  
Dust Events

Mineral dust is one of the main natural sources of atmospheric particulate matter, with the Sahara being one of the most important source regions for the occurrence and deposition of mineral dust in Europe. The occurrence of dust events in the European Alps is documented via measurements of airborne dust and its deposits onto the glaciers. Dust events occur mainly in spring, summer, and early autumn. Dust layers are investigated in ice cores spanning the last millennium as well as in annual snow packs. They strongly affect the overall flux of dust-related compounds (e.g., calcium and magnesium), provide an alkaline input to wet deposition chemistry, and change the microbial abundance and diversity of the snow pack. Still airborne mineral dust particles can act as ice nuclei and cloud condensation nuclei, influencing the formation of cloud droplets and hence cloud formation and precipitation. Dust deposits on the snow lead to a darkening of the surface, referred to as “surface albedo reduction,” which influences the timing of the snowmelt and reduces the annual mass balance of glaciers, showing a direct link to glacier retreat as observed presently in a warming climate.

Enhanced soot particle ice nucleation ability induced by aggregate compaction

2021 ◽  
Author(s):  
Kunfeng Gao ◽  
Chong-Wen Zhou ◽  
Zamin Kanji
Keyword(s):  
Pore Size ◽  
Soot Particle ◽  
Preliminary Evidence ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Dynamic Vapor Sorption ◽  
Soot Particles ◽  
Formation Pathway ◽  
Soot Aggregate

<p>Cirrus clouds have an important influence on the climate since the ice crystal size, concentration and distribution of the clouds determine their radiation properties and effects in the atmosphere. Aviation activities in the high troposphere impact cirrus cloud formation indirectly and significantly, due to aviation contrail evolution and aviation soot particles acting as potential ice nucleating particles (INPs). Soot particles have varying ice nucleation (IN) abilities. In cirrus cloud formation conditions, pore condensation and freezing (PCF) is an important ice formation pathway for soot particles, which requires the particle to have appropriate morphology properties and mesoporous structures. In this study, the morphology and pore size of two kinds of soot were changed by a physical agitation method without any chemical modification. The IN activities of both fresh and agitated soot particles with aggregate sizes, 60, 100, 200 and 400 nm, were tested by the Horizontal Ice Nucleation Chamber (HINC) under mixed phase and cirrus cloud conditions.</p><p>In general, the IN results show clear size dependence for particles with the same agitation degree both tested soot samples at all tested temperatures (<em>T</em>) from 218 K to 243 K with a step of 5 K. In addition, all soot particles do not form ice at <em>T </em>> 235 K (homogeneous nucleation temperature, HNT) but ice nucleation was observed well below homogeneous freezing relative humidity (<em>RH</em>) for <em>T</em> < HNT, suggesting PCF as the dominating mechanism rather than deposition nucleation. Furthermore, there are significant differences between agitated and fresh soot particles for both soot samples studied. We observed that all agitated soot particles reach a higher particle activation fraction (<em>AF</em>) value at the same <em>T</em> and <em>RH</em> condition, compared to the same size fresh soot particles. Moreover, 200 and 400 nm agitated soot particles require much lower ice saturation values to reach <em>AF</em> = 0.001 than their fresh counterparts. The enhanced IN abilities of agitated soot particles are attributed to soot aggregate structure compaction thus increasing mesopore occurrence probability induced by physical agitation. Preliminary evidence obtained from the mass measurements of the single aggregates show that agitated soot particles are more dense than fresh soot particles of the same size. Furthermore, soot aggregate morphology comparisons from HR-TEM (high resolution transmission electron microscopy) images, soot-water interaction ability results from DVS (dynamic vapor sorption) tests and micro-pore size distribution results from argon desorption tests will be used to explain the soot particle IN ability promotion induced by compaction.</p>

scholarly journals The impact of Saharan dust and black carbon on albedo and long-term glacier mass balance

2015 ◽  
Vol 9 (1) ◽  
pp. 1133-1175 ◽  
Author(s):  
J. Gabbi ◽  
M. Huss ◽  
A. Bauder ◽  
F. Cao ◽  
M. Schwikowski
Keyword(s):  
Mass Balance ◽  
Black Carbon ◽  
Mineral Dust ◽  
Ice Cores ◽  
Swiss Alps ◽  
Saharan Dust ◽  
Glacier Mass Balance ◽  
Mass Balances ◽  
The Impact

Abstract. Light-absorbing impurities in snow and ice control glacier melt as shortwave radiation represents the main component of the surface energy balance. Here, we investigate the long-term effect of snow impurities, i.e. Saharan dust and black carbon (BC), on albedo and glacier mass balance. The analysis was performed over the period 1914–2014 for two sites on Claridenfirn, Swiss Alps, where an outstanding 100 year record of seasonal mass balance measurements is available. Information on atmospheric deposition of mineral dust and BC over the last century was retrieved from two firn/ice cores of high-alpine sites. A combined mass balance and snow/firn layer model was employed to assess the dust/BC-albedo feedback. Compared to pure snow conditions, the presence of Saharan dust and BC lowered the mean annual albedo by 0.04–0.06 and increased melt by 15–19% on average depending on the location on the glacier. BC clearly dominated absorption which is about three times higher than that of mineral dust. The upper site has experienced mainly positive mass balances and impurity layers were continuously buried whereas at the lower site, surface albedo was more strongly influenced by re-exposure of dust-enriched layers due to frequent years with negative mass balances.

scholarly journals BAECC: A Field Campaign to Elucidate the Impact of Biogenic Aerosols on Clouds and Climate

2016 ◽  
Vol 97 (10) ◽  
pp. 1909-1928 ◽  
Author(s):  
Tuukka Petäjä ◽  
Ewan J. O’Connor ◽  
Dmitri Moisseev ◽  
Victoria A. Sinclair ◽  
Antti J. Manninen ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Numerical Models ◽  
Cloud Formation ◽  
In Situ Observation ◽  
Forest Environment ◽  
Surface Precipitation ◽  
Biogenic Aerosols ◽  
Boreal Environment ◽  
The Impact

Abstract During Biogenic Aerosols—Effects on Clouds and Climate (BAECC), the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Program deployed the Second ARM Mobile Facility (AMF2) to Hyytiälä, Finland, for an 8-month intensive measurement campaign from February to September 2014. The primary research goal is to understand the role of biogenic aerosols in cloud formation. Hyytiälä is host to the Station for Measuring Ecosystem–Atmosphere Relations II (SMEAR II), one of the world’s most comprehensive surface in situ observation sites in a boreal forest environment. The station has been measuring atmospheric aerosols, biogenic emissions, and an extensive suite of parameters relevant to atmosphere–biosphere interactions continuously since 1996. Combining vertical profiles from AMF2 with surface-based in situ SMEAR II observations allows the processes at the surface to be directly related to processes occurring throughout the entire tropospheric column. Together with the inclusion of extensive surface precipitation measurements and intensive observation periods involving aircraft flights and novel radiosonde launches, the complementary observations provide a unique opportunity for investigating aerosol–cloud interactions and cloud-to-precipitation processes in a boreal environment. The BAECC dataset provides opportunities for evaluating and improving models of aerosol sources and transport, cloud microphysical processes, and boundary layer structures. In addition, numerical models are being used to bridge the gap between surface-based and tropospheric observations.

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