scholarly journals Microphysics and Optical Attenuation in Fog: Observations from Two Coastal Sites

2021 ◽  
Author(s):  
Qing Wang ◽  
Ryan T. Yamaguchi ◽  
John A. Kalogiros ◽  
Zachary Daniels ◽  
Denny P. Alappattu ◽  
...  
Keyword(s):  
Water Content ◽  
Droplet Size ◽  
Liquid Water ◽  
Empirical Relationship ◽  
Liquid Water Content ◽  
High Energy ◽  
Number Concentration ◽  
Future Research ◽  
Optical Attenuation ◽  
Fog Prediction

AbstractA total of 15 fog events from two field campaigns are investigated: the High Energy Laser in Fog (HELFOG) project (central California) and the Toward Improving Coastal Fog Prediction (C-FOG) project (Ferryland Newfoundland). Nearly identical sensors were used in both projects to sample fog droplet-size spectra, wind, turbulence, and thermodynamic properties near the surface. Concurrent measurements of visibility were made by the present weather detector in both experiments, with the addition of a two-ended transmissometer in the HELFOG campaign. The analyses focused first on contrasting the observed fog microphysics and the associated thermodynamics from fog events in the two locations. The optical attenuation by fog was investigated using three methods: (1) derived from Mie theory using the measured droplet-size distribution, (2) parametrized as a function of fog liquid water content, and (3) parametrized in terms of total fog droplet number concentration. The consistency of these methods was investigated. The HELFOG data result in an empirical relationship between the meteorological range and liquid water content. Validation of such relationship is problematic using the C-FOG data due to the presence of rain and other factors. The parametrization with droplet number concentration only does not provide a robust visibility calculation since it cannot represent the effects of droplet size on visibility. Finally, a preliminary analysis of the mixed fog/rain case is presented to illustrate the nature of the problem to promote future research.

Turbulent Mixing in Shallow Trade Wind Cumuli: Dependence on Cloud Life Cycle

2015 ◽  
Vol 72 (4) ◽  
pp. 1447-1465 ◽  
Author(s):  
T. Schmeissner ◽  
R. A. Shaw ◽  
J. Ditas ◽  
F. Stratmann ◽  
M. Wendisch ◽  
...  
Keyword(s):  
Water Content ◽  
Droplet Size ◽  
Liquid Water ◽  
Turbulent Mixing ◽  
Liquid Water Content ◽  
Number Concentration ◽  
Trade Wind ◽  
Observation System ◽  
Mixing Process ◽  
The Impact

Abstract Helicopter-borne observations of the impact of turbulent mixing and cloud microphysical properties in shallow trade wind cumuli are presented. The measurements were collected during the Cloud, Aerosol, Radiation and Turbulence in the Trade Wind Regime over Barbados (CARRIBA) project. Basic meteorological parameters (3D wind vector, air temperature, and relative humidity), cloud condensation nuclei concentrations, and cloud microphysical parameters (droplet number, size distribution, and liquid water content) are measured by the Airborne Cloud Turbulence Observation System (ACTOS), which is fixed by a 160-m-long rope underneath a helicopter flying with a true airspeed of approximately 20 m s−1. Clouds at different evolutionary stages were sampled. A total of 300 clouds are classified into actively growing, decelerated, and dissolving clouds. The mixing process of these cloud categories is investigated by correlating the cloud droplet number concentration and cubed droplet mean volume diameter. A significant tendency to more inhomogeneous mixing with increasing cloud lifetime is observed. Furthermore, the mixing process and its effects on droplet number concentration, droplet size, and cloud liquid water content are statistically evaluated. It is found that, in dissolving clouds, liquid water content and droplet number concentration are decreased by about 50% compared to actively growing clouds. Conversely, the droplet size remains almost constant, which can be attributed to the existence of a humid shell around the cloud that prevents cloud droplets from rapid evaporation after entrainment of premoistened air. Moreover, signs of secondary activation are found, which results in a more difficult interpretation of observed mixing diagrams.

scholarly journals Theoretical Analysis of the Entrainment–Mixing Process at Cloud Boundaries. Part I: Droplet Size Distributions and Humidity within the Interface Zone

2018 ◽  
Vol 75 (6) ◽  
pp. 2049-2064 ◽  
Author(s):  
Mark Pinsky ◽  
Alexander Khain
Keyword(s):  
Water Content ◽  
Droplet Size ◽  
Liquid Water ◽  
Liquid Water Content ◽  
Mixing Process ◽  
Governing Parameter ◽  
Interface Zone ◽  
Dry Air ◽  
Air Interface ◽  
Entrainment Mixing

Abstract The problem of a complex entrainment–mixing process is analyzed by solving a diffusion–evaporation equation for an open region in the vicinity of the cloud–dry air interface. Upon normalization the problem is reduced to a one-parametric one, the governing parameter being the potential evaporation parameter R proportional to the ratio of saturation deficit in the dry air to the available liquid water content in the cloud air. As distinct from previous multiple studies analyzing mixing within closed adiabatic volumes, we consider a principally nonstationary problem that never leads to a homogeneous equilibrium state. It is shown that at R < −1 the cloud edge shifts toward the cloud; that is, the cloud dissipates due to mixing with dry air, and the cloud volume decreases. If R > −1, the cloud edge shifts outside; that is, the mixing leads to an increase in the cloud volume. The time evolution of droplet size distribution and its moments, as well as the relative humidity within the expanding cloud–dry air interface, are calculated and analyzed. It is shown that the values of the mean volume radii rapidly decrease within the interface zone in the direction away from the cloud, indicating significant changes in the cloud edge microstructure. Scattering diagrams plotted for the cloud edge agree well with high-frequency in situ measurements, corroborating the reliability of the proposed approach. It is shown that the humidity front moves toward dry air faster than the front of liquid water content. As a result, the mixing leads to formation of a humid air shell around the cloud. The widths of the interface zone and humid shell are evaluated.

scholarly journals Modelling the relationship between liquid water content and cloud droplet number concentration observed in low clouds in the summer Arctic and its radiative effects

2020 ◽  
Vol 20 (1) ◽  
pp. 29-43
Author(s):  
Joelle Dionne ◽  
Knut von Salzen ◽  
Jason Cole ◽  
Rashed Mahmood ◽  
W. Richard Leaitch ◽  
...  
Keyword(s):  
Linear Relationship ◽  
Water Content ◽  
Liquid Water ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Number Concentration ◽  
Radiative Effect ◽  
Low Clouds ◽  
Cloud Radiative Effect ◽  
Cloud Droplet Number Concentration

Abstract. Low clouds persist in the summer Arctic with important consequences for the radiation budget. In this study, we simulate the linear relationship between liquid water content (LWC) and cloud droplet number concentration (CDNC) observed during an aircraft campaign based out of Resolute Bay, Canada, conducted as part of the Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments study in July 2014. Using a single-column model, we find that autoconversion can explain the observed linear relationship between LWC and CDNC. Of the three autoconversion schemes we examined, the scheme using continuous drizzle (Khairoutdinov and Kogan, 2000) appears to best reproduce the observed linearity in the tenuous cloud regime (Mauritsen et al., 2011), while a scheme with a threshold for rain (Liu and Daum, 2004) best reproduces the linearity at higher CDNC. An offline version of the radiative transfer model used in the Canadian Atmospheric Model version 4.3 is used to compare the radiative effects of the modelled and observed clouds. We find that there is no significant difference in the upward longwave cloud radiative effect at the top of the atmosphere from the three autoconversion schemes (p=0.05) but that all three schemes differ at p=0.05 from the calculations based on observations. In contrast, the downward longwave and shortwave cloud radiative effect at the surface for the Wood (2005b) and Khairoutdinov and Kogan (2000) schemes do not differ significantly (p=0.05) from the observation-based radiative calculations, while the Liu and Daum (2004) scheme differs significantly from the observation-based calculation for the downward shortwave but not the downward longwave fluxes.

scholarly journals Application of cloud particle sensor sondes for estimating the number concentration of cloud water droplets and liquid water content: case studies in the Arctic region

2021 ◽  
Vol 14 (7) ◽  
pp. 4971-4987
Author(s):  
Jun Inoue ◽  
Yutaka Tobo ◽  
Kazutoshi Sato ◽  
Fumikazu Taketani ◽  
Marion Maturilli
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Arctic Region ◽  
Liquid Water Content ◽  
Cloud Water ◽  
Number Concentration ◽  
The Arctic ◽  
Cloud Particle ◽  
Particle Count ◽  
The Arctic Region

Abstract. A cloud particle sensor (CPS) sonde is an observing system attached with a radiosonde sensor to observe the vertical structure of cloud properties. The signals obtained from CPS sondes are related to the phase, size, and number of cloud particles. The system offers economic advantages including human resource and simple operation costs compared with aircraft measurements and land-/satellite-based remote sensing. However, the observed information should be appropriately corrected because of several uncertainties. Here we made field experiments in the Arctic region by launching approximately 40 CPS sondes between 2018 and 2020. Using these data sets, a better practical correction method was proposed to exclude unreliable data, estimate the effective cloud water droplet radius, and determine a correction factor for the total cloud particle count. We apply this method to data obtained in October 2019 over the Arctic Ocean and March 2020 at Ny-Ålesund, Svalbard, Norway, to compare with a particle counter aboard a tethered balloon and liquid water content retrieved by a microwave radiometer. The estimated total particle count and liquid water content from the CPS sondes generally agree with those data. Although further development and validation of CPS sondes based on dedicated laboratory experiments would be required, the practical correction approach proposed here would offer better advantages in retrieving quantitative information on the vertical distribution of cloud microphysics under the condition of a lower number concentration.

scholarly journals Global statistics of liquid water content and effective number concentration of water clouds over ocean derived from combined CALIPSO and MODIS measurements

2007 ◽  
Vol 7 (12) ◽  
pp. 3353-3359 ◽  
Author(s):  
Y. Hu ◽  
M. Vaughan ◽  
C. McClain ◽  
M. Behrenfeld ◽  
H. Maring ◽  
...  
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Empirical Relation ◽  
Liquid Water Content ◽  
Number Concentration ◽  
Effective Number ◽  
Passive Sensor ◽  
Global Statistics ◽  
Lidar Observations ◽  
Depolarization Ratios

Abstract. This study presents an empirical relation that links the volume extinction coefficients of water clouds, the layer integrated depolarization ratios measured by lidar, and the effective radii of water clouds derived from collocated passive sensor observations. Based on Monte Carlo simulations of CALIPSO lidar observations, this method combines the cloud effective radius reported by MODIS with the lidar depolarization ratios measured by CALIPSO to estimate both the liquid water content and the effective number concentration of water clouds. The method is applied to collocated CALIPSO and MODIS measurements obtained during July and October of 2006, and January 2007. Global statistics of the cloud liquid water content and effective number concentration are presented.

scholarly journals Droplet Spectra Measurements with the FSSP-100. Part II: Coincidence Effects

2005 ◽  
Vol 22 (11) ◽  
pp. 1756-1761 ◽  
Author(s):  
Afrâniode Araújo Coelho ◽  
Jean-Louis Brenguier ◽  
Thierry Perrin
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Dead Time ◽  
Liquid Water Content ◽  
Number Concentration ◽  
Depth Of Field ◽  
Spectral Distortion ◽  
Empirical Procedure ◽  
Droplet Concentration ◽  
Stochastic Mode

Abstract At high droplet number concentration, measurements of the droplet number concentration, of the droplet spectrum, and of the liquid water content with the FSSP-100 are significantly affected by the coincidences of particles in the probe’s detection beam and by count losses during the dead time of the probe’s electronics. Accurate statistical procedures have been proposed in the literature for the correction of the coincidence and dead-time losses in the estimation of the droplet number concentration. There are, however, no techniques available for correction of the spectral distortion, hence of the derived liquid water content. The model of probe functioning described in Part I of this series is now used on a stochastic mode in order to simulate all possible events of coincidences and dead-time losses. Observed features, such as variations of the depth of field and beam edge acceptance ratios with the droplet concentration, are correctly reproduced by the simulator. The three most currently used techniques for the correction of the droplet concentration are then evaluated with the simulator. The distortion of the spectral shape is also examined. The simulator shows that the measured droplet mean volume diameter increases with the droplet number concentration, by up to 40% at a concentration of 1500 cm−3. An empirical procedure is finally proposed for the correction of the spectral distortion and of the derived liquid water content.

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