Parametric representation of the cloud droplet spectra for LES warm bulk microphysical schemes

O. Geoffroy; J.-L. Brenguier; F. Burnet

doi:10.5194/acp-10-4835-2010

Parametric representation of the cloud droplet spectra for LES warm bulk microphysical schemes

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-17633-2009 ◽

2009 ◽

Vol 9 (4) ◽

pp. 17633-17663 ◽

Cited By ~ 1

Author(s):

O. Geoffroy ◽

J.-L. Brenguier ◽

F. Burnet

Keyword(s):

Water Content ◽

Liquid Water ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Liquid Water Content ◽

Tuning Parameter ◽

Parametric Function ◽

Generalized Gamma ◽

Parametric Functions ◽

Generalized Gamma Function

Abstract. Parametric functions are currently used to represent droplet spectra in clouds and to develop bulk parameterizations of the microphysical processes and of their interactions with radiation. The most frequently used parametric functions are the Lognormal and the Generalized Gamma which have three and four independent parameters, respectively. In a bulk parameterization, two parameters are constrained by the total droplet number concentration and the liquid water content. In the Generalized Gamma function, one parameter is specified a priori, and the fourth one, like the third parameter of the Lognormal function, shall be tuned, for the parametric function to statistically best fit observed droplet spectra. These parametric functions are evaluated here using droplet spectra collected in non-or slightly precipitating stratocumulus and shallow cumulus. Optimum values of the tuning parameters are derived by minimizing either the absolute or the relative error for successively the first, second, fifth, and sixth moments of the droplet size distribution. A trade-off value is also proposed that minimizes both absolute and relative errors for the four moments concomitantly. Finally, a parameterization is proposed in which the tuning parameter depends on the liquid water content. This approach significantly improves the fit for the smallest and largest values of the moments.

Turbulent transport and deposition of fog droplets in the Central Namib

10.5194/egusphere-egu2020-16201 ◽

2020 ◽

Author(s):

Robert Spirig ◽

Christian Feigenwinter ◽

Roland Vogt

Keyword(s):

Water Content ◽

Sea Level ◽

Liquid Water ◽

Turbulent Transport ◽

Water Flux ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Field Measurements ◽

Liquid Water Content ◽

Fog Water

<p>Regular, nocturnal fog is a defining and seasonally varying feature in the Namib desert. Historical observations were limited to the binary measure of fog occurrence and the concurrent fog water input is quantified only since 2014 via the FogNet using Juvik fog collectors. This installation opened new avenues of research such as the efficiency of the transport mechanism, sampling and spatial variation thereof. An eddy covariance setup of a cloud droplet probe and collocated sonic(s) was installed in turns at the two FogNet stations Vogelfederberg (23.10&#176;S, 15.03&#176;E, 515 m above sea level) and Gobabeb (23.56&#176;S, 15.04&#176;E, 406 m above sea level) for 2 years in the frame of the Namib Fog Life Cycle Analysis Field Measurements (NaFoLiCA-F) project. With this setup, we gathered duration, droplet size distribution, droplet concentration, liquid water content, turbulent liquid water flux and the fog water input via the Juvik fog collector with a total of over 150 fog events. We found that fog appears suddenly and front-like as seen by an increase of droplet numbers by several magnitudes and dissolves more gradually towards the morning. All droplet classes of the resolved range of 2 to 50 &#181;m are present, but at the Vogelfederberg with around 2 to 3 times larger fog water input, the mean and median of the distribution are lower due to comparably fewer large droplets. Liquid water fluxes at both sites resulted in a net gain for the surface but the spatial discrepancy between fog water input recorded by fog collectors and the liquid water content indicates that drizzle, i.e. droplets outside the resolved range, may contribute to the larger total water deposition at Vogelfederberg.</p>

A Model Intercomparison of CCN-Limited Tenuous Clouds in the High Arctic

10.5194/acp-2017-1128 ◽

2017 ◽

Author(s):

Robin G. Stevens ◽

Katharina Loewe ◽

Christopher Dearden ◽

Antonios Dimitrelos ◽

Anna Possner ◽

...

Keyword(s):

Water Content ◽

Size Distribution ◽

Liquid Water ◽

Atmospheric Stability ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Liquid Water Content ◽

High Arctic ◽

Model Intercomparison ◽

Cloud Droplet Size Distribution

Abstract. We perform a model intercomparison of summertime high Arctic (> 80 N) clouds observed during the 2008 Arctic Summer Cloud Ocean Study (ASCOS) campaign, when observed cloud condensation nuclei (CCN) concentrations fell below 1 cm−3. Previous analyses have suggested that at these low CCN concentrations the liquid water content (LWC) and radiative properties of the clouds are determined primarily by the CCN concentrations, conditions that have previously been referred to as the tenuous cloud regime. The intercomparison includes results from three large eddy simulation models (UCLALES-SALSA, COSMO-LES, and MIMICA) and three numerical weather prediction models (COSMO-NWP, WRF, and UM-CASIM). We test the sensitivities of the model results to different treatments of cloud droplet activation, including prescribed cloud droplet number concentrations (CDNC) and diagnostic CCN activation based on either fixed aerosol concentrations or prognostic aerosol with in-cloud processing. There remains considerable diversity even in experiments with prescribed CDNCs and prescribed ice crystal number concentrations (ICNC). The sensitivity of mixed-phase Arctic cloud properties to changes in CDNC depends on the representation of the cloud droplet size distribution within each model, which impacts on autoconversion rates. Our results therefore suggest that properly estimating aerosol–cloud interactions requires an appropriate treatment of the cloud droplet size distribution within models, as well as in-situ observations of hydrometeor size distributions to constrain them. The results strongly support the hypothesis that the liquid water content of these clouds is CCN-limited. For the observed meteorological conditions, the cloud generally did not collapse when the CCN concentration was held constant at the relatively high CCN concentrations measured during the cloudy period, but the cloud thins or collapses as the CCN concentration is reduced. The CCN concentration at which collapse occurs varies substantially between models. Only one model predicts complete dissipation of the cloud due to glaciation, and this occurs only for the largest prescribed ICNC tested in this study. Global and regional models with either prescribed CDNCs or prescribed aerosol concentrations would not reproduce these dissipation events. Additionally, future increases in Arctic aerosol concentrations would be expected to decrease the frequency of occurrence of such cloud dissipation events, with implications for the radiative balance at the surface. Our results also show that cooling of the sea-ice surface following cloud dissipation increases atmospheric stability near the surface, further suppressing cloud formation. Therefore, this suggests that linkages between aerosol and clouds, as well as linkages between clouds, surface temperatures and atmospheric stability need to be considered for weather and climate predictions in this region.

A model intercomparison of CCN-limited tenuous clouds in the high Arctic

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-11041-2018 ◽

2018 ◽

Vol 18 (15) ◽

pp. 11041-11071 ◽

Cited By ~ 23

Author(s):

Robin G. Stevens ◽

Katharina Loewe ◽

Christopher Dearden ◽

Antonios Dimitrelos ◽

Anna Possner ◽

...

Keyword(s):

Water Content ◽

Size Distribution ◽

Liquid Water ◽

Atmospheric Stability ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Liquid Water Content ◽

High Arctic ◽

Model Intercomparison ◽

Cloud Droplet Size Distribution

Abstract. We perform a model intercomparison of summertime high Arctic (> 80∘ N) clouds observed during the 2008 Arctic Summer Cloud Ocean Study (ASCOS) campaign, when observed cloud condensation nuclei (CCN) concentrations fell below 1 cm−3. Previous analyses have suggested that at these low CCN concentrations the liquid water content (LWC) and radiative properties of the clouds are determined primarily by the CCN concentrations, conditions that have previously been referred to as the tenuous cloud regime. The intercomparison includes results from three large eddy simulation models (UCLALES-SALSA, COSMO-LES, and MIMICA) and three numerical weather prediction models (COSMO-NWP, WRF, and UM-CASIM). We test the sensitivities of the model results to different treatments of cloud droplet activation, including prescribed cloud droplet number concentrations (CDNCs) and diagnostic CCN activation based on either fixed aerosol concentrations or prognostic aerosol with in-cloud processing. There remains considerable diversity even in experiments with prescribed CDNCs and prescribed ice crystal number concentrations (ICNC). The sensitivity of mixed-phase Arctic cloud properties to changes in CDNC depends on the representation of the cloud droplet size distribution within each model, which impacts autoconversion rates. Our results therefore suggest that properly estimating aerosol–cloud interactions requires an appropriate treatment of the cloud droplet size distribution within models, as well as in situ observations of hydrometeor size distributions to constrain them. The results strongly support the hypothesis that the liquid water content of these clouds is CCN limited. For the observed meteorological conditions, the cloud generally did not collapse when the CCN concentration was held constant at the relatively high CCN concentrations measured during the cloudy period, but the cloud thins or collapses as the CCN concentration is reduced. The CCN concentration at which collapse occurs varies substantially between models. Only one model predicts complete dissipation of the cloud due to glaciation, and this occurs only for the largest prescribed ICNC tested in this study. Global and regional models with either prescribed CDNCs or prescribed aerosol concentrations would not reproduce these dissipation events. Additionally, future increases in Arctic aerosol concentrations would be expected to decrease the frequency of occurrence of such cloud dissipation events, with implications for the radiative balance at the surface. Our results also show that cooling of the sea-ice surface following cloud dissipation increases atmospheric stability near the surface, further suppressing cloud formation. Therefore, this suggests that linkages between aerosol and clouds, as well as linkages between clouds, surface temperatures, and atmospheric stability need to be considered for weather and climate predictions in this region.

A depolarisation lidar based method for the determination of liquid-cloud microphysical properties

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-7-9917-2014 ◽

2014 ◽

Vol 7 (9) ◽

pp. 9917-9992 ◽

Cited By ~ 1

Author(s):

D. P. Donovan ◽

H. Klein Baltink ◽

J. S. Henzing ◽

S. R. de Roode ◽

A. P. Siebesma

Keyword(s):

Water Content ◽

Multiple Scattering ◽

Liquid Water ◽

Cloud Droplet ◽

Optimal Estimation ◽

Liquid Water Content ◽

Cloud Base ◽

Base Region ◽

Large Eddy Simulation Model ◽

Inversion Procedure

Abstract. The fact that polarisation lidars measure a depolarisation signal in liquid clouds due to the occurrence of multiple-scattering is well-known. The degree of measured depolarisation depends on the lidar characteristics (e.g. wavelength and receiver field-of-view) as well as the cloud macrophysical (e.g. liquid water content) and microphysical (e.g. effective radius) properties. Efforts seeking to use depolarisation information in a quantitative manner to retrieve cloud properties have been undertaken with, arguably, limited practical success. In this work we present a retrieval procedure applicable to clouds with (quasi-)linear liquid water content (LWC) profiles and (quasi-)constant cloud droplet number density in the cloud base region. Thus limiting the applicability of the procedure allows us to reduce the cloud variables to two parameters (namely the derivative of the liquid water content with height and the extinction at a fixed distance above cloud-base). This simplification, in turn, allows us to employ a fast and robust optimal-estimation inversion using pre-computed look-up-tables produced using extensive lidar Monte-Carlo multiple-scattering simulations. In this paper, we describe the theory behind the inversion procedure and successfully apply it to simulated observations based on large-eddy simulation model output. The inversion procedure is then applied to actual depolarisation lidar data corresponding to a range of cases taken from the Cabauw measurement site in the central Netherlands. The lidar results were then used to predict the corresponding cloud-base region radar reflectivities. In non-drizzling condition, it was found that the lidar inversion results can be used to predict the observed radar reflectivities with an accuracy within the radar calibration uncertainty (2–3 dBZ). This result strongly supports the accuracy of the lidar inversion results. Results of a comparison between ground-based aerosol number concentration and lidar-derived cloud droplet number densities are also presented and discussed. The observed relationship between the two quantities is seen to be consistent with the results of previous studies based on aircraft-based in situ measurements.

Aerosol-landscape-cloud interaction: Signatures of topography effect on cloud droplet formation

10.5194/acp-2016-1015 ◽

2016 ◽

Author(s):

Sami Romakkaniemi ◽

Zubair Maalick ◽

Antti Hellsten ◽

Antti Ruuskanen ◽

Olli Väisänen ◽

...

Keyword(s):

Liquid Water ◽

Measurement Data ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Liquid Water Content ◽

Droplet Formation ◽

Cloud Base ◽

Topography Effect ◽

Boreal Environment ◽

The Hill

Abstract. Long-term in situ measurements of aerosol-cloud interactions are usually performed in measurement stations residing on hills, mountains, or high towers. In such conditions, the surface topography of the surrounding area can affect the measured cloud droplet distributions by increasing turbulence or causing orographic flows and thus the observations might not be representative for a larger scale. The objective of this work is to analyse, how the local topography affects the observations at Puijo measurement station, which is located in the 75 m high Puijo tower, which itself stands on a 150 m high hill. The analysis of the measurement data shows that the observed cloud droplet number concentration mainly depends on the CCN concentration. However, when the wind direction aligns with the direction of the steepest slope of the hill, a clear topography effect is observed. This finding was further analysed by simulating 3D flow fields around the station and by performing trajectory ensemble modelling of aerosol- and wind-dependent cloud droplet formation. The results showed that in typical conditions, with geostrophic winds of about 10 m s−1, the hill can cause updrafts of up to 1 m s−1 in the air parcels arriving at the station. This is enough to produce in-cloud supersaturations higher than typically found at the cloud base (SS of ~ 0.2 %), and thus additional cloud droplets may form inside the cloud. In the observations, this is seen in the form of a bi-modal cloud droplet size distribution. The effect is strongest with high winds across the steepest slope of the hill and with low liquid water contents, and its relative importance quickly decreases as these conditions are relaxed. We therefore conclude that, after careful screening for wind speed and liquid water content, the observations at Puijo measurement station can be considered representative for clouds in a boreal environment.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-29-2020 ◽

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.

Relationships between cloud droplet effective radius, liquid water content, and droplet concentration for warm clouds in Brazil embedded in biomass smoke

Journal of Geophysical Research Atmospheres ◽

10.1029/1998jd200119 ◽

1999 ◽

Vol 104 (D6) ◽

pp. 6145-6153 ◽

Cited By ~ 58

Author(s):

Jeffrey S. Reid ◽

Peter V. Hobbs ◽

Arthur L. Rangno ◽

Dean A. Hegg

Keyword(s):

Water Content ◽

Liquid Water ◽

Cloud Droplet ◽

Liquid Water Content ◽

Effective Radius ◽

Biomass Smoke ◽

Droplet Concentration

Stratocumulus Liquid Water Content from Dual-Wavelength Radar

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech1768.1 ◽

2005 ◽

Vol 22 (8) ◽

pp. 1207-1218 ◽

Cited By ~ 61

Author(s):

Robin J. Hogan ◽

Nicolas Gaussiat ◽

Anthony J. Illingworth

Keyword(s):

Water Content ◽

Liquid Water ◽

Wave Attenuation ◽

Droplet Size Distribution ◽

Liquid Water Content ◽

Radar Signal ◽

Cloud Base ◽

Liquid Water Path ◽

Atmospheric Radiation Measurement ◽

The Difference

Abstract A technique is described to retrieve stratocumulus liquid water content (LWC) using the differential attenuation measured by vertically pointing radars at 35 and 94 GHz. Millimeter-wave attenuation is proportional to LWC and increases with frequency, so LWC can be derived without the need to make any assumptions on the nature of the droplet size distribution. There is also no need for the radars to be well calibrated. A significant advantage over many radar techniques in stratocumulus is that the presence of drizzle drops (those with a diameter larger than around 50 μm) does not affect the retrieval, even though such drops may dominate the radar signal. It is important, however, that there are not significant numbers of drops larger than 600 μm, which scatter outside of the Rayleigh regime at 94 GHz. A lidar ceilometer is used to locate the cloud base in the presence of drizzle falling below the cloud. An accuracy of around 0.04 g m−3 is achievable with averaging over 1 min and 150 m (two range gates), but for the previously suggested frequency pair of 10 and 35 GHz, the corresponding accuracy would be considerably worse at 0.34 g m−3. First, the retrieval of LWC is simulated using aircraft-measured size spectra taken from a profile through marine stratocumulus. Results are then presented from two case studies—one using two cloud radars at Chilbolton in southern United Kingdom, and another using the Cloud Profiling Radar System at the Atmospheric Radiation Measurement site in Oklahoma. The liquid water path from the technique was found to be in good agreement with the values that were obtained from microwave radiometers, with the difference between the two being close to the accuracy of the radiometer retrieval. In the case of well-mixed stratocumulus, the profiles were close to adiabatic.

Understanding aerosol–cloud interactions through modeling the development of orographic cumulus congestus during IPHEx

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-1413-2019 ◽

2019 ◽

Vol 19 (3) ◽

pp. 1413-1437 ◽

Cited By ~ 2

Author(s):

Yajuan Duan ◽

Markus D. Petters ◽

Ana P. Barros

Keyword(s):

Water Content ◽

Liquid Water ◽

Cloud Droplet ◽

Liquid Water Content ◽

Cloud Microphysics ◽

Turbulent Dispersion ◽

Cloud Base ◽

Droplet Growth ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

Abstract. A new cloud parcel model (CPM) including activation, condensation, collision–coalescence, and lateral entrainment processes is used to investigate aerosol–cloud interactions (ACIs) in cumulus development prior to rainfall onset. The CPM was applied with surface aerosol measurements to predict the vertical structure of cloud development at early stages, and the model results were evaluated against airborne observations of cloud microphysics and thermodynamic conditions collected during the Integrated Precipitation and Hydrology Experiment (IPHEx) in the inner region of the southern Appalachian Mountains (SAM). Sensitivity analysis was conducted to examine the model response to variations in key ACI physiochemical parameters and initial conditions. The CPM sensitivities mirror those found in parcel models without entrainment and collision–coalescence, except for the evolution of the droplet spectrum and liquid water content with height. Simulated cloud droplet number concentrations (CDNCs) exhibit high sensitivity to variations in the initial aerosol concentration at cloud base, but weak sensitivity to bulk aerosol hygroscopicity. The condensation coefficient ac plays a governing role in determining the evolution of CDNC, liquid water content (LWC), and cloud droplet spectra (CDS) in time and with height. Lower values of ac lead to higher CDNCs and broader CDS above cloud base, and higher maximum supersaturation near cloud base. Analysis of model simulations reveals that competitive interference among turbulent dispersion, activation, and droplet growth processes modulates spectral width and explains the emergence of bimodal CDS and CDNC heterogeneity in aircraft measurements from different cloud regions and at different heights. Parameterization of nonlinear interactions among entrainment, condensational growth, and collision–coalescence processes is therefore necessary to simulate the vertical structures of CDNCs and CDSs in convective clouds. Comparisons of model predictions with data suggest that the representation of lateral entrainment remains challenging due to the spatial heterogeneity of the convective boundary layer and the intricate 3-D circulations in mountainous regions.