scholarly journals Measurement report: Ice nucleating particles active ≥ −15 °C in free tropospheric air over western Europe

2021 ◽  
Author(s):  
Franz Conen ◽  
Annika Einbock ◽  
Claudia Mignani ◽  
Christoph Hüglin
Keyword(s):  
Boundary Layer ◽  
Organic Matter ◽  
Western Europe ◽  
Saharan Dust ◽  
Ice Formation ◽  
Epiphytic Bacteria ◽  
Free Troposphere ◽  
Epiphytic Microorganisms ◽  
Radon Measurements ◽  
Saharan Dust Intrusions

Abstract. Ice nucleating particles (INP) initiate ice formation in supercooled clouds, typically starting at a few km above ground. However, little is known about the concentration and composition of INP in the lower free troposphere (FT). Here, we analysed INP active at −10 °C (INP−10) and −15 °C (INP−15) collected during FT conditions at the high-altitude observatory Jungfraujoch. We relied on continuous radon measurements to distinguish FT conditions from those influenced by the planetary boundary layer. Median concentrations in the FT were 2.4 INP−10 m−3 and 9.8 INP−15 m−3, with a multiplicative standard deviation of 2.0 and 1.6, respectively. A majority of INP was deactivated after exposure to 60 °C, thus probably originated from certain epiphytic bacteria or fungi. Subsequent heating to 95 °C deactivated another 15 % to 20 % of the initial INP, likely other types of fungal INP that might be associated with soil organic matter or with decaying leaves. Very few INP−10 withstood heating to 95 °C, but on average 20 % of INP−15 in FT samples did so. This percentage doubled during Saharan dust intrusions, which had practically no influence on INP−10. Overall, the results suggest that aerosolised epiphytic microorganisms, or parts thereof, are responsible for the majority of primary ice formation in moderately supercooled clouds above western Europe.

scholarly journals Investigating the quality of modeled aerosol profiles based on combined lidar and sunphotometer data

2017 ◽  
Vol 17 (11) ◽  
pp. 7003-7023 ◽  
Author(s):  
Nikolaos Siomos ◽  
Dimitris S. Balis ◽  
Anastasia Poupkou ◽  
Natalia Liora ◽  
Spyridon Dimopoulos ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mass Concentration ◽  
Center Of Mass ◽  
Saharan Dust ◽  
Concentration Profiles ◽  
Free Troposphere ◽  
Desert Dust ◽  
Aerosol Mass Concentration ◽  
Dust Component ◽  
The Mean

Abstract. In this study we present an evaluation of the Comprehensive Air Quality Model with extensions (CAMx) for Thessaloniki using radiometric and lidar data. The aerosol mass concentration profiles of CAMx are compared against the PM2.5 and PM2. 5−10 concentration profiles retrieved by the Lidar-Radiometer Inversion Code (LIRIC). The CAMx model and the LIRIC algorithm results were compared in terms of mean mass concentration profiles, center of mass and integrated mass concentration in the boundary layer and the free troposphere. The mean mass concentration comparison resulted in profiles within the same order of magnitude and similar vertical structure for the PM2. 5 particles. The mean centers of mass values are also close, with a mean bias of 0.57 km. On the opposite side, there are larger differences for the PM2. 5−10 mode, both in the boundary layer and in the free troposphere. In order to grasp the reasons behind the discrepancies, we investigate the effect of aerosol sources that are not properly included in the model's emission inventory and in the boundary conditions such as the wildfires and the desert dust component. The identification of the cases that are affected by wildfires is performed using wind backward trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model in conjunction with satellite fire pixel data from MODerate-resolution Imaging Spectroradiometer (MODIS) Terra and Aqua global monthly fire location product MCD14ML. By removing those cases the correlation coefficient improves from 0.69 to 0.87 for the PM2. 5 integrated mass in the boundary layer and from 0.72 to 0.89 in the free troposphere. The PM2.5 center of mass fractional bias also decreases to 0.38 km. Concerning the analysis of the desert dust component, the simulations from the Dust Regional Atmospheric Model (BSC-DREAM8b) were deployed. When only the Saharan dust cases are taken into account, BSC-DREAM8b generally outperforms CAMx when compared with LIRIC, achieving a correlation of 0.91 and a mean bias of −29.1 % for the integrated mass in the free troposphere and a correlation of 0.57 for the center of mass. CAMx, on the other hand, underestimates the integrated mass in the free troposphere. Consequently, the accuracy of CAMx is limited concerning the transported Saharan dust cases. We conclude that the performance of CAMx appears to be best for the PM2.5 particles, both in the boundary layer and in the free troposphere. Sources of particles not properly taken into account by the model are confirmed to negatively affect its performance, especially for the PM2. 5−10 particles.

scholarly journals Southeast Pacific stratocumulus clouds, precipitation and boundary layer structure sampled along 20° S during VOCALS-REx

2010 ◽  
Vol 10 (21) ◽  
pp. 10639-10654 ◽  
Author(s):  
C. S. Bretherton ◽  
R. Wood ◽  
R. C. George ◽  
D. Leon ◽  
G. Allen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Vertical Structure ◽  
Layer Structure ◽  
Cloud Droplet ◽  
Free Troposphere ◽  
Liquid Water Path ◽  
Typical Structure ◽  
Southeast Pacific ◽  
Over The Top

Abstract. Multiplatform airborne, ship-based, and land-based observations from 16 October–15 November 2008 during the VOCALS Regional Experiment (REx) are used to document the typical structure of the Southeast Pacific stratocumulus-topped boundary layer and lower free troposphere on a~transect along 20° S between the coast of Northern Chile and a buoy 1500 km offshore. Strong systematic gradients in clouds, precipitation and vertical structure are modulated by synoptically and diurnally-driven variability. The boundary layer is generally capped by a strong (10–12 K), sharp inversion. In the coastal zone, the boundary layer is typically 1 km deep, fairly well mixed, and topped by thin, nondrizzling stratocumulus with accumulation-mode aerosol and cloud droplet concentrations exceeding 200 cm−3. Far offshore, the boundary layer depth is typically deeper (1600 m) and more variable, and the vertical structure is usually decoupled. The offshore stratocumulus typically have strong mesoscale organization, much higher peak liquid water paths, extensive drizzle, and cloud droplet concentrations below 100 cm−3, sometimes with embedded pockets of open cells with lower droplet concentrations. The lack of drizzle near the coast is not just a microphysical response to high droplet concentrations; smaller cloud depth and liquid water path than further offshore appear comparably important. Moist boundary layer air is heated and mixed up along the Andean slopes, then advected out over the top of the boundary layer above adjacent coastal ocean regions. Well offshore, the lower free troposphere is typically much drier. This promotes strong cloud-top radiative cooling and stronger turbulence in the clouds offshore. In conjunction with a slightly cooler free troposphere, this may promote stronger entrainment that maintains the deeper boundary layer seen offshore. Winds from ECMWF and NCEP operational analyses have an rms difference of only 1 m s−1 from collocated airborne leg-mean observations in the boundary layer and 2 m s−1 above the boundary layer. This supports the use of trajectory analysis for interpreting REx observations. Two-day back-trajectories from the 20° S transect suggest that eastward of 75° W, boundary layer (and often free-tropospheric) air has usually been exposed to South American coastal aerosol sources, while at 85° W, neither boundary-layer or free-tropospheric air has typically had such contact.

scholarly journals Multivariate statistical air mass classification for the high-alpine observatory at the Zugspitze Mountain, Germany

2019 ◽  
Vol 19 (19) ◽  
pp. 12477-12494 ◽  
Author(s):  
Armin Sigmund ◽  
Korbinian Freier ◽  
Till Rehm ◽  
Ludwig Ries ◽  
Christian Schunk ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Real Time ◽  
Statistical Approach ◽  
Free Troposphere ◽  
Time Data ◽  
Detection Scheme ◽  
Air Mass ◽  
Thermally Induced ◽  
Air Masses ◽  
Mechanistic Approach

Abstract. To assist atmospheric monitoring at high-alpine sites, a statistical approach for distinguishing between the dominant air masses was developed. This approach was based on a principal component analysis using five gas-phase and two meteorological variables. The analysis focused on the Schneefernerhaus site at Zugspitze Mountain, Germany. The investigated year was divided into 2-month periods, for which the analysis was repeated. Using the 33.3 % and 66.6 % percentiles of the first two principal components, nine air mass regimes were defined. These regimes were interpreted with respect to vertical transport and assigned to the BL (recent contact with the boundary layer), UFT/SIN (undisturbed free troposphere or stratospheric intrusion), and HYBRID (influences of both the boundary layer and the free troposphere or ambiguous) air mass classes. The input data were available for 78 % of the investigated year. BL accounted for 31 % of the cases with similar frequencies in all seasons. UFT/SIN comprised 14 % of the cases but was not found from April to July. HYBRID (55 %) mostly exhibited intermediate characteristics, whereby 17 % of the HYBRID class suggested an influence from the marine boundary layer or the lower free troposphere. The statistical approach was compared to a mechanistic approach using the ceilometer-based mixing layer height from a nearby valley site and a detection scheme for thermally induced mountain winds. Due to data gaps, only 25 % of the cases could be classified using the mechanistic approach. Both approaches agreed well, except in the rare cases of thermally induced uplift. The statistical approach is a promising step towards a real-time classification of air masses. Future work is necessary to assess the uncertainty arising from the standardization of real-time data.

scholarly journals Selective incorporation of dissolved organic matter (DOM) during sea ice formation

2013 ◽  
Vol 155 ◽  
pp. 148-157 ◽  
Author(s):  
Susann Müller ◽  
Anssi V. Vähätalo ◽  
Colin A. Stedmon ◽  
Mats A. Granskog ◽  
Louiza Norman ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Sea Ice ◽  
Ice Formation ◽  
Selective Incorporation

scholarly journals Iodine monoxide in the north subtropical free troposphere

2011 ◽  
Vol 11 (10) ◽  
pp. 27833-27860 ◽  
Author(s):  
O. Puentedura ◽  
M. Gil ◽  
A. Saiz-Lopez ◽  
T. Hay ◽  
M. Navarro-Comas ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Dust Cloud ◽  
Elevation Angle ◽  
Saharan Dust ◽  
Atmospheric Composition ◽  
Trade Wind ◽  
Spectral Signature ◽  
Free Troposphere ◽  
The North ◽  
Iodine Monoxide

Abstract. Iodine monoxide (IO) was retrieved using a new multi-axis DOAS instrument deployed at the Izaña subtropical observatory as part of the Network for the Detection of Atmospheric Composition Change (NDACC) programme. The station is located at 2370 m a.s.l., well above the trade wind inversion that limits the top of the marine boundary layer, and is hence representative of the free troposphere. We report daily observations from May to August 2010 at different viewing angles. During this period, the spectral signature of IO was unequivocally detected on every day of measurement. A mean IO differential slant column density (DSCD) of 1.2 × 1013 molecules cm−2 was observed at 5° instrument elevation angle (IEA) on clear days using a single zenith reference for the reported period, with a day-to-day variability of 12% at 1 standard deviation. At an IEA of 0°, the mean DSCD value for clear days is 2.0 × 1013 molecules cm−2, with a day-to-day variability of 14%. Based on simultaneous O4 measurements, the IO mixing ratio is estimated to be 0.18 pptv in the free troposphere at an IEA of 5°. Episodes of Saharan dust outbreaks were also observed, with large increases in the DSCDs at higher elevation angles, suggesting an enhancement of IO inside the dust cloud.

scholarly journals Saharan dust and heterogeneous ice formation: Eleven years of cloud observations at a central European EARLINET site

2010 ◽  
Vol 115 (D20) ◽  
Author(s):  
P. Seifert ◽  
A. Ansmann ◽  
I. Mattis ◽  
U. Wandinger ◽  
M. Tesche ◽  
...  
Keyword(s):  
Saharan Dust ◽  
Ice Formation ◽  
Central European

scholarly journals Improved mixing height monitoring through a combination of lidar and radon measurements

2012 ◽  
Vol 5 (5) ◽  
pp. 6835-6866 ◽  
Author(s):  
A. D. Griffiths ◽  
S. D. Parkes ◽  
S. D. Chambers ◽  
M. F. McCabe ◽  
A. G. Williams
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Radon Concentration ◽  
Quantitative Measure ◽  
Potential Method ◽  
Length Scale ◽  
Mixing Length ◽  
Mixing Height ◽  
Lidar Measurements ◽  
Radon Measurements

Abstract. Surface-based radon (222Rn) measurements can be combined with lidar backscatter to obtain a higher quality time series of mixing height within the Planetary Boundary-Layer (PBL) than is possible from lidar alone, and a more quantitative measure of mixing height than is possible from only radon. The lidar measurements benefit because even when aerosol layers are detected, reliably attributing the mixing height to the correct layer presents a challenge. By combining lidar with a mixing length scale derived from a time series of radon concentration, automated and robust attribution is possible during the morning transition. Radon measurements also provide mixing information during the night and with the addition of lidar these measurements become insensitive to night-to-night changes in radon emissions. After calibration with lidar, the radon-derived equivalent mixing height agrees with other measures of mixing on daily and hourly time scales and is a potential method for studying intermittent mixing in nocturnal boundary layers.

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