scholarly journals Water droplet calibration of a cloud droplet probe and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC

2010 ◽  
Vol 3 (4) ◽  
pp. 3133-3177 ◽  
Author(s):  
S. Lance ◽  
C. A. Brock ◽  
D. Rogers ◽  
J. A. Gordon
Keyword(s):  
Droplet Size ◽  
Optical Design ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Water Droplets ◽  
Sample Area ◽  
Pass Through ◽  
Short Time ◽  
Mixed Phase Clouds

Abstract. Laboratory calibrations of the Cloud Droplet Probe (CDP) sample area and droplet sizing are performed using water droplets of known size, generated at a known rate. However, comparison with an independent measure of liquid water content (LWC) during in-flight operation suggests much greater biases in the droplet size and/or droplet concentration measured by the CDP than would be expected based on the laboratory calibrations. Since the bias in CDP-LWC is strongly concentration dependent, we hypothesize that this discrepancy is a result of coincidence, when two or more droplets pass through the CDP laser beam within a very short time. The coincidence error, most frequently resulting from the passage of one droplet outside and one inside the instrument sample area at the same time, is evaluated in terms of an "extended sample area" (SAE), the area in which individual droplets can affect the sizing detector without necessarily registering on the qualifier. The SAE is calibrated with standardized water droplets, and used in a Monte-Carlo simulation to estimate the effect of coincidence on the measured droplet size distributions. The simulations show that extended coincidence errors are important for the CDP at droplet concentrations even as low as 200 cm−3, and these errors are necessary to explain the trend between calculated and measured LWC observed in liquid and mixed-phase clouds during the Aerosol, Radiation and Cloud Processes Affecting Arctic Climate (ARCPAC) study. We estimate from the simulations that 60% oversizing error and 50% undercounting error can occur at droplet concentrations exceeding 500 cm−3. Modification of the optical design of the CDP is currently being explored in an effort to reduce this coincidence bias.

scholarly journals Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC

2010 ◽  
Vol 3 (6) ◽  
pp. 1683-1706 ◽  
Author(s):  
S. Lance ◽  
C. A. Brock ◽  
D. Rogers ◽  
J. A. Gordon
Keyword(s):  
Laser Beam ◽  
Droplet Size ◽  
Liquid Water ◽  
Water Droplet ◽  
Optical Design ◽  
Cloud Droplet ◽  
Mixed Phase ◽  
Water Droplets ◽  
Sample Area ◽  
Mixed Phase Clouds

Abstract. Laboratory calibrations of the Cloud Droplet Probe (CDP) sample area and droplet sizing are performed using water droplets of known size, generated at a known rate. Although calibrations with PSL and glass beads were consistent with theoretical instrument response, liquid water droplet calibrations were not, and necessitated a 2 μm shift in the manufacturer's calibration. We show that much of this response shift may be attributable to a misalignment of the optics relative to the axis of the laser beam. Comparison with an independent measure of liquid water content (LWC) during in-flight operation suggests much greater biases in the droplet size and/or droplet concentration measured by the CDP than would be expected based on the laboratory calibrations. Since the bias in CDP-LWC is strongly concentration dependent, we hypothesize that this discrepancy is a result of coincidence, when two or more droplets pass through the CDP laser beam within a very short time. The coincidence error, most frequently resulting from the passage of one droplet outside and one inside the instrument sample area at the same time, is evaluated in terms of an "extended sample area" (SAE), the area in which individual droplets can affect the sizing detector without necessarily registering on the qualifier. SAE is calibrated with standardized water droplets, and used in a Monte-Carlo simulation to estimate the effect of coincidence on the measured droplet size distributions. The simulations show that extended coincidence errors are important for the CDP at droplet concentrations even as low as 200 cm−3, and these errors are necessary to explain the trend between calculated and measured LWC observed in liquid and mixed-phase clouds during the Aerosol, Radiation and Cloud Processes Affecting Arctic Climate (ARCPAC) study. We estimate from the simulations that 60% oversizing error and 50% undercounting error can occur at droplet concentrations exceeding 400 cm−3. Modification of the optical design of the CDP is currently being explored in an effort to reduce this coincidence bias.

scholarly journals Effects of Wegener-Bergeron-Findeisen Process on Global Black Carbon Distribution

2016 ◽  
Author(s):  
Ling Qi ◽  
Qinbin Li ◽  
Cenlin He ◽  
Xin Wang ◽  
Jianping Huang
Keyword(s):  
Transport Model ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
The Arctic ◽  
Deposition Flux ◽  
Chemical Transport Model ◽  
Washout Ratio ◽  
Lower Temperature ◽  
Mixed Phase Clouds ◽  
Scavenging Efficiency

Abstract. We systematically investigate the effects of Wegener-Bergeron-Findeisen (WBF) on BC scavenging efficiency, surface BCair, deposition flux, concentration in snow (BCsnow, ng g−1), and washout ratio using a global 3D chemical transport model (GEOS-Chem). We differentiate riming- versus WBF-dominated in-cloud scavenging based on liquid water content (LWC) and temperature. Specifically, we relate WBF to either temperature or ice mass fraction (IMF) in mixed-phase clouds. We find that at Jungfraujoch, Switzerland and Abisko, Sweden, where WBF dominates, the discrepancies of simulated BC scavenging efficiency and washout ratio are significantly reduced (from a factor of 3 to 10 % and from a factor of 4–5 to a factor of two). However, at Zeppelin, Norway, where riming dominates, simulation of BC scavenging efficiency, BCair, and washout ratio become worse (relative to observations) when WBF is included. There is thus an urgent need for extensive observations to distinguish and characterize riming- versus WBF-dominated aerosol scavenging in mixed-phase clouds and the associated BC scavenging efficiency. We find the reduction resulting from WBF to global BC scavenging efficiency varies substantially, from 8 % in the tropics to 76 % in the Arctic. The resulting annual mean BCair increases by up to 156 % at high altitudes and at northern high latitudes because of lower temperature and higher IMF. Overall, WBF halves the model-observation discrepancy (from −65 % to −30 %) of BCair across North America, Europe, China and the Arctic. Globally WBF increases BC burden from 0.22 to 0.29–0.35 mg m−2 yr−1, which partially explains the gap between observed and previous model simulated BC burdens over land. In addition, WBF significantly increases BC lifetime from 5.7 days to ~8 days. Additionally, WBF results in a significant redistribution of BC deposition in source and remote regions. Specifically, it lowers BC wet deposition (by 37–63 % at northern mid-latitudes and by 21–29 % in the Arctic) while increases dry deposition (by 3–16 % at mid-latitudes and by 81–159 % in the Arctic). The resulting total BC deposition is lower at mid-latitudes (by 12–34 %) but higher in the Arctic (by 2–29 %). We find that WBF decreases BCsnow at mid-latitudes (by ~15 %) but increases it in the Arctic (by 26 %) while improving model comparisons with observations. In addition, WBF dramatically reduces the model-observation discrepancy of washout ratios in winter (from a factor of 16 to 4). The remaining discrepancies in BCair, BCsnow and BC washout ratios suggest that in-cloud removal in mixed-phased clouds is likely still excessive over land.

scholarly journals Small Cloud Particle Shapes in Mixed-Phase Clouds

2013 ◽  
Vol 52 (5) ◽  
pp. 1277-1293 ◽  
Author(s):  
Greg M. McFarquhar ◽  
Junshik Um ◽  
Robert Jackson
Keyword(s):  
Water Content ◽  
Detection Threshold ◽  
Liquid Water Content ◽  
Area Ratio ◽  
Mixed Phase ◽  
Liquid Droplets ◽  
Cloud Particle ◽  
Particle Images ◽  
Mixed Phase Clouds ◽  
Particle Shapes

AbstractThe shapes of cloud particles with maximum dimensions Dmax between 35 and 60 μm in mixed-phase clouds were studied using high-resolution particle images collected by a cloud particle imager (CPI) during the Mixed-Phase Arctic Cloud Experiment (M-PACE) and the Indirect and Semi-Direct Aerosol Campaign (ISDAC). The area ratio α, the projected area of a particle divided by the area of a circle with diameter Dmax, quantified particle shape. The differing optical characteristics of CPIs used in M-PACE and ISDAC had no effect on derived α provided that Dmax > 35 μm and CPI focus > 45. The fraction of particles with 35 < Dmax < 60 μm with α > 0.8 increased with the ratio of liquid water content (LWC) to total water content (TWC). The average αmean of small particles in each 10-s interval in mixed-phase clouds was correlated with LWC/TWC with a correlation coefficient of 0.60 for M-PACE and 0.43 for ISDAC. The stronger correlation seen during M-PACE was most likely associated with the presence of more liquid droplets that were larger than the CPI detection threshold contributing to αmean; the modal effective radius was larger (11 vs 6 μm), and drops with D > 35 μm had concentrations during M-PACE that were 6 times as large as those of ISDAC. This study hence suggests that area ratio can be used to identify the phase of particles with 35 < Dmax < 60 μm and questions the assumption used in previous studies that all particles in this size range are supercooled droplets.

scholarly journals Comparing model and measured ice crystal concentrations in orographic clouds during the INUPIAQ campaign

2015 ◽  
Vol 15 (18) ◽  
pp. 25647-25694 ◽  
Author(s):  
R. J. Farrington ◽  
P. J. Connolly ◽  
G. Lloyd ◽  
K. N. Bower ◽  
M. J. Flynn ◽  
...  
Keyword(s):  
Wrf Model ◽  
Surface Flux ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Field Campaign ◽  
Orographic Clouds ◽  
Ice Multiplication ◽  
Ice Production ◽  
Surface Ice ◽  
Mixed Phase Clouds

Abstract. This paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in-situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Forecasting model (WRF) simulations over real terrain surrounding Jungfraujoch. During the 2014 winter field campaign, between the 20 January and 28 February, the model simulations regularly underpredicted the observed ice number concentration by 103 L−1. Previous literature has proposed several processes for the high ice number concentrations in orographic clouds, including an increased ice nuclei (IN) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing IN concentrations in the model prevents the simulation of the mixed-phase clouds that were witnessed during the INUPIAQ campaign at Jungfraujoch. Additionally, the inclusion of secondary ice production upwind of Jungfraujoch into the WRF simulations cannot consistently produce enough ice splinters to match the observed concentrations. A surface flux of hoar crystals was included in the WRF model, which simulated ice concentrations comparable to the measured ice number concentrations, without depleting the liquid water content (LWC) simulated in the model. Our simulations therefore suggest that high ice concentrations observed in mixed-phase clouds at Jungfraujoch are caused by a flux of surface hoar crystals into the orographic clouds.

scholarly journals Laboratory and in-flight evaluation of measurement uncertainties from a commercial Cloud Droplet Probe (CDP)

2018 ◽  
Vol 11 (6) ◽  
pp. 3645-3659 ◽  
Author(s):  
Spencer Faber ◽  
Jeffrey R. French ◽  
Robert Jackson
Keyword(s):  
Collection Efficiency ◽  
Droplet Diameter ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Hot Wire ◽  
Weighted Mean ◽  
Wire Probe ◽  
Sample Area ◽  
Droplet Concentration ◽  
Cloud Points

Abstract. Laboratory and in-flight evaluations of uncertainties of measurements from a Cloud Droplet Probe (CDP) are presented. A description of a water-droplet-generating device, similar to those used in previous studies, is provided along with validation of droplet sizing and positioning. Seven experiments with droplet diameters of 9, 17, 24, 29, 34, 38, and 46 µm tested sizing and counting performance across a 10 µm resolution grid throughout the sample area of a CDP. Results indicate errors in sizing that depend on both droplet diameter and position within the sample area through which a droplet transited. The CDP undersized 9µm droplets by 1–4 µm. Droplets with diameters of 17 and 24 µm were sized to within 2 µm, which is the nominal CDP bin width for droplets of that size. The majority of droplets larger than 17 µm were oversized by 2–4 µm, while a small percentage were severely undersized, by as much as 30 µm. This combination led to an artificial broadening and skewing of the spectra such that mean diameters from a near-monodisperse distribution compared well (within a few percent), while the median diameters were oversized by 5–15 %. This has implications on how users should calibrate their probes. Errors in higher-order moments were generally less than 10 %. Comparisons of liquid water content (LWC) calculated from the CDP and that measured from a Nevzorov hot-wire probe were conducted for 17 917 1 Hz in-cloud points. Although some differences were noted based on volume-weighted mean diameter and total droplet concentration, the CDP-estimated LWC exceeded that measured by the Nevzorov by approximately 20 %, more than twice the expected difference based on results of the laboratory tests and considerations of Nevzorov collection efficiency.

scholarly journals Comparing model and measured ice crystal concentrations in orographic clouds during the INUPIAQ campaign

2016 ◽  
Vol 16 (8) ◽  
pp. 4945-4966 ◽  
Author(s):  
Robert J. Farrington ◽  
Paul J. Connolly ◽  
Gary Lloyd ◽  
Keith N. Bower ◽  
Michael J. Flynn ◽  
...  
Keyword(s):  
Wrf Model ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Ice Crystal ◽  
Field Campaign ◽  
Orographic Clouds ◽  
Ice Multiplication ◽  
Ice Production ◽  
Surface Ice ◽  
Mixed Phase Clouds

Abstract. This paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Forecasting model (WRF) simulations over real terrain surrounding Jungfraujoch. During the 2014 winter field campaign, between 20 January and 28 February, the model simulations regularly underpredicted the observed ice number concentration by 103 L−1. Previous literature has proposed several processes for the high ice number concentrations in orographic clouds, including an increased ice nucleating particle (INP) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing INP concentrations in the model prevents the simulation of the mixed-phase clouds that were witnessed during the INUPIAQ campaign at Jungfraujoch. Additionally, the inclusion of secondary ice production upwind of Jungfraujoch into the WRF simulations cannot consistently produce enough ice splinters to match the observed concentrations. A flux of surface hoar crystals was included in the WRF model, which simulated ice concentrations comparable to the measured ice number concentrations, without depleting the liquid water content (LWC) simulated in the model. Our simulations therefore suggest that high ice concentrations observed in mixed-phase clouds at Jungfraujoch are caused by a flux of surface hoar crystals into the orographic clouds.

scholarly journals Evaluating the capabilities and uncertainties of droplet measurements for the fog droplet spectrometer (FM-100)

2012 ◽  
Vol 5 (3) ◽  
pp. 3333-3393 ◽  
Author(s):  
J. K. Spiegel ◽  
P. Zieger ◽  
N. Bukowiecki ◽  
E. Hammer ◽  
E. Weingartner ◽  
...  
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Stochastic Approach ◽  
Liquid Water Content ◽  
Mie Scattering ◽  
Size Distributions ◽  
Literature Study ◽  
Size Spectra

Abstract. Droplet size spectra measurements are crucial to obtain a quantitative microphysical description of clouds and fog. However, cloud droplet size measurements are subject to various uncertainties. This work focuses on the evaluation of two key measurement uncertainties arising during cloud droplet size measurements with a conventional droplet size spectrometer (FM-100): first, we addressed the precision with which droplets can be sized with the FM-100 on the basis of Mie theory. We deduced error assumptions and proposed how to correct measured size distributions for these errors by redistributing the measured droplet size distribution using a stochastic approach. Second, based on a literature study, we derived corrections for particle losses during sampling with the FM-100. We applied both corrections to cloud droplet size spectra measured at the high alpine site Jungfraujoch for a temperature range from 0 °C to 11 °C. We show that Mie scattering led to spikes in the droplet size distributions using the default sizing procedure, while the stochastic approach reproduced the ambient size distribution adequately. A detailed analysis of the FM-100 sampling efficiency revealed that particle losses were typically below 10% for droplet diameters up to 10 μm. For larger droplets, particle losses can increase up to 90% for the largest droplets of 50 μm at ambient windspeeds below 4.4 m s−1 and even to >90% for larger angles between the instrument orientation and the wind vector (sampling angle) at higher wind speeds. Comparisons of the FM-100 to other reference instruments revealed that the total liquid water content (LWC) measured by the FM-100 was more sensitive to particle losses than to re-sizing based on Mie scattering, while the total number concentration was only marginally influenced by particle losses. As a consequence, for further LWC measurements with the FM-100 we strongly recommend to consider (1) the error arising due to Mie scattering, and (2) the particle losses, especially for larger droplets depending on the set-up and wind conditions.

scholarly journals Intercomparison of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds

2010 ◽  
Vol 10 (17) ◽  
pp. 8173-8196 ◽  
Author(s):  
A. Muhlbauer ◽  
T. Hashino ◽  
L. Xue ◽  
A. Teller ◽  
U. Lohmann ◽  
...  
Keyword(s):  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Small Scale ◽  
Orographic Precipitation ◽  
Model Intercomparison ◽  
Droplet Coalescence ◽  
Aerosol Cloud ◽  
Aerosol Effect ◽  
Mixed Phase Clouds

Abstract. Anthropogenic aerosols serve as a source of both cloud condensation nuclei (CCN) and ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentrations is hypothesized to retard the cloud droplet coalescence and the riming in mixed-phase clouds, thereby decreasing orographic precipitation. This study presents results from a model intercomparison of 2-D simulations of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds. The sensitivity of orographic precipitation to changes in the aerosol number concentrations is analysed and compared for various dynamical and thermodynamical situations. Furthermore, the sensitivities of microphysical processes such as coalescence, aggregation, riming and diffusional growth to changes in the aerosol number concentrations are evaluated and compared. The participating numerical models are the model from the Consortium for Small-Scale Modeling (COSMO) with bulk microphysics, the Weather Research and Forecasting (WRF) model with bin microphysics and the University of Wisconsin modeling system (UWNMS) with a spectral ice habit prediction microphysics scheme. All models are operated on a cloud-resolving scale with 2 km horizontal grid spacing. The results of the model intercomparison suggest that the sensitivity of orographic precipitation to aerosol modifications varies greatly from case to case and from model to model. Neither a precipitation decrease nor a precipitation increase is found robustly in all simulations. Qualitative robust results can only be found for a subset of the simulations but even then quantitative agreement is scarce. Estimates of the aerosol effect on orographic precipitation are found to range from −19% to 0% depending on the simulated case and the model. Similarly, riming is shown to decrease in some cases and models whereas it increases in others, which implies that a decrease in riming with increasing aerosol load is not a robust result. Furthermore, it is found that neither a decrease in cloud droplet coalescence nor a decrease in riming necessarily implies a decrease in precipitation due to compensation effects by other microphysical pathways. The simulations suggest that mixed-phase conditions play an important role in buffering the effect of aerosol perturbations on cloud microphysics and reducing the overall susceptibility of clouds and precipitation to changes in the aerosol number concentrations. As a consequence the aerosol effect on precipitation is suggested to be less pronounced or even inverted in regions with high terrain (e.g., the Alps or Rocky Mountains) or in regions where mixed-phase microphysics is important for the climatology of orographic precipitation.

Constraining Precipitation Susceptibility of Warm-, Ice-, and Mixed-Phase Clouds with Microphysical Equations

2016 ◽  
Vol 73 (12) ◽  
pp. 5003-5023 ◽  
Author(s):  
Franziska Glassmeier ◽  
Ulrike Lohmann
Keyword(s):  
Initial Perturbation ◽  
Cloud Droplet ◽  
Mixed Phase ◽  
Rate Equations ◽  
Ice Crystal ◽  
Diffusional Growth ◽  
Microphysics Scheme ◽  
Aerosol Cloud Interactions ◽  
Opposing Effects ◽  
Mixed Phase Clouds

Abstract The strength of the effective anthropogenic climate forcing from aerosol–cloud interactions is related to the susceptibility of precipitation to aerosol effects. Precipitation susceptibility d lnP/d lnN has been proposed as a metric to quantify the effect of aerosol-induced changes in cloud droplet number N on warm precipitation rate P. Based on the microphysical rate equations of the Seifert and Beheng two-moment bulk microphysics scheme, susceptibilities of warm-, mixed-, and ice-phase precipitation and cirrus sedimentation to cloud droplet and ice crystal number are estimated. The estimation accounts for microphysical adjustments to the initial perturbation in N. For warm rain, d lnP/d lnN &lt; −2aut/(aut + acc) is found, which depends on the rates of autoconversion (aut) and accretion (acc). Cirrus sedimentation susceptibility corresponds to the exponent of crystal sedimentation velocity with a value of −0.2. For mixed-phase clouds, several microphysical contributions that explain low precipitation susceptibilities are identified: (i) Because of the larger hydrometeor sizes involved, mixed-phase collection processes are less sensitive to changes in hydrometeor size than autoconversion. (ii) Only a subset of precipitation formation processes is sensitive to droplet or crystal number. (iii) Effects on collection processes and diffusional growth compensate. (iv) Adjustments in cloud liquid and ice amount compensate the effect of changes in ice crystal and cloud droplet number. (v) Aerosol perturbations that simultaneously affect ice crystal and droplet number have opposing effects.

scholarly journals In-situ Observation of Riming in Mixed-Phase Clouds using the PHIPS probe

2021 ◽  
Author(s):  
Fritz Waitz ◽  
Martin Schnaiter ◽  
Thomas Leisner ◽  
Emma Järvinen
Keyword(s):  
Liquid Water ◽  
Prediction Models ◽  
Supercooled Liquid ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Ice Crystals ◽  
The Arctic ◽  
In Situ Observation ◽  
Cloud Particle ◽  
Mixed Phase Clouds

Abstract. Mixed-phase clouds consist of both supercooled liquid water droplets and solid ice crystals. Despite having a significant impact on Earth‘s climate, mixed-phase clouds are poorly understood and not well represented in climate prediction models. One piece of the puzzle is understanding and parameterizing riming of mixed-phase cloud ice crystals, which is one of the main growth mechanisms of ice crystals via the accretion of small, supercooled droplets. Especially the extent of riming on ice crystals smaller than 500 μm is often overlooked in studies – mainly because observations are scarce. Here, we investigated riming in mixed-phase clouds during three airborne campaigns in the Arctic, the Southern Ocean and US east coast. Riming was observed from stereo-microscopic cloud particle images recorded with the Particle Habit Imaging and Polar Scattering (PHIPS) probe. We show that riming is most prevalent at temperatures around −7 °C, where, on average, 43 % of the investigated particles in a size range from 100 ≤ D ≤ 700 μm showed evidence of riming. We discuss the occurrence and properties of rimed ice particles and show correlation of the occurrence and the amount of riming with ambient meteorological parameters. We show that riming fraction increases with ice particle size (< 20 % for D ≤ 200 μm, 35–40 % for D ≥ 400 μm) and liquid water content (25 % for LWC ≤ 0.05 g m−3, up to 60 % for LWC = 0.5 g m−3). We investigate the ageing of rimed particles and the difference between "normal" and "epitaxial" riming based on a case study.

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