scholarly journals Understanding the Importance of Microphysics and Macrophysics for Warm Rain in Marine Low Clouds. Part II: Heuristic Models of Rain Formation

2009 ◽  
Vol 66 (10) ◽  
pp. 2973-2990 ◽  
Author(s):  
Robert Wood ◽  
Terence L. Kubar ◽  
Dennis L. Hartmann
Keyword(s):  
Steady State ◽  
Droplet Size ◽  
Liquid Water ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Liquid Water Content ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Warm Rain ◽  
Rain Formation

Abstract Two simple heuristic model formulations for warm rain formation are introduced and their behavior explored. The first, which is primarily aimed at representing warm rain formation in shallow convective clouds, is a continuous collection model that uses an assumed cloud droplet size distribution consistent with observations as the source of embryonic drizzle drops that are then allowed to fall through a fixed cloud, accreting cloud droplets. The second, which is applicable to steady-state precipitation formation in stratocumulus, is a simple two-moment bulk autoconversion and accretion model in which cloud liquid water is removed by drizzle formation and replenished on a externally specified time scale that reflects the efficacy of turbulent overturning that characterizes stratocumulus. The models’ behavior is shown to be broadly consistent with observations from the A-Train constellation of satellites, allowing the authors to explore reasons for changing model sensitivity to microphysical and macrophysical cloud properties. The models are consistent with one another, and with the observations, in that they demonstrate that the sensitivity of rain rate to cloud droplet concentration Nd (which here represents microphysical influence) is greatest for weakly precipitating clouds (i.e., for low cloud liquid water path and/or high Nd). For the steady-state model, microphysical sensitivity is shown to strongly decrease with the ratio of replenishment to drizzle time scales. Thus, rain from strongly drizzling and/or weakly replenished clouds shows low sensitivity to microphysics. This is essentially because most precipitation in these clouds is forming via accretion rather than autoconversion. For the continuous-collection model, as cloud liquid water content increases, the precipitation rate becomes more strongly controlled by the availability of cloud liquid water than by the initial embryo size or by the cloud droplet size. The models help to explain why warm rain in marine stratocumulus clouds is sensitive to Nd but why precipitation from thicker cumulus clouds appears to be less so.

scholarly journals Constraints on interactions between aerosols and clouds on a global scale from a combination of MODIS-CERES satellite data and climate simulations

2010 ◽  
Vol 10 (20) ◽  
pp. 9851-9861 ◽  
Author(s):  
X. Ma ◽  
K. von Salzen ◽  
J. Cole
Keyword(s):  
Liquid Water ◽  
Negative Relationship ◽  
Cloud Droplet ◽  
Global Scale ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Cloud Droplets ◽  
Cloud Liquid Water ◽  
Albedo Effect ◽  
Cloud Liquid Water Path

Abstract. Satellite-based cloud top effective radius retrieved by the CERES Science Team were combined with simulated aerosol concentrations from CCCma CanAM4 to examine relationships between aerosol and cloud that underlie the first aerosol indirect (cloud albedo) effect. Evidence of a strong negative relationship between sulphate, and organic aerosols, with cloud top effective radius was found for low clouds, indicating both aerosol types are contributing to the first indirect effect on a global scale. Furthermore, effects of aerosol on the cloud droplet effective radius are more pronounced for larger cloud liquid water paths. While CanAM4 broadly reproduces the observed relationship between sulphate aerosols and cloud droplets, it does not reproduce the dependency of cloud top droplet size on organic aerosol concentrations nor the dependency on cloud liquid water path. Simulations with a modified version of the model yield a more realistic dependency of cloud droplets on organic carbon. The robustness of the methods used in the study are investigated by repeating the analysis using aerosol simulated by the GOCART model and cloud top effective radii derived from the MODIS Science Team.

scholarly journals An intercomparison of radar-based liquid cloud microphysics retrievals and implication for model evaluation studies

2011 ◽  
Vol 4 (6) ◽  
pp. 7109-7158 ◽  
Author(s):  
D. Huang ◽  
C. Zhao ◽  
M. Dunn ◽  
X. Dong ◽  
G. G. Mace ◽  
...  
Keyword(s):  
Great Plains ◽  
Liquid Water ◽  
Model Evaluation ◽  
Evaluation Studies ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Cloud Microphysics ◽  
Effective Radius ◽  
High Altitudes ◽  
Liquid Water Path

Abstract. To assess if current radar-based liquid cloud microphysical retrievals of the Atmospheric Radiation Measurement (ARM) program can provide useful constraints for modeling studies, this paper presents intercomparison results of three cloud products at the Southern Great Plains (SGP) site: the ARM MICROBASE, University of Utah (UU), and University of North Dakota (UND) products over the nine-year period from 1998 to 2006. The probability density and spatial autocorrelation functions of the three cloud Liquid Water Content (LWC) retrievals appear to be consistent with each other, while large differences are found in the droplet effective radius retrievals. The differences in the vertical distribution of both cloud LWC and droplet effective radius retrievals are found to be alarmingly large, with the relative difference between nine-year mean cloud LWC retrievals ranging from 20% at low altitudes to 100% at high altitudes. Nevertheless, the spread in LWC retrievals is much smaller than that in cloud simulations by climate and cloud resolving models. The MICROBASE effective radius ranges from 2.0 at high altitudes to 6.0 μm at low altitudes and the UU and UND droplet effective radius is 6 μm larger. Further analysis through a suite of retrieval experiments shows that the difference between MICROBASE and UU LWC retrievals stems primarily from the partition total Liquid Water path (LWP) into supercooled and warm liquid, and from the input cloud boundaries and LWP. The large differences between MICROBASE and UU droplet effective radius retrievals are mainly due to rain/drizzle contamination and the assumptions of cloud droplet concentration used in the retrieval algorithms. The large discrepancy between different products suggests caution in model evaluation with these observational products, and calls for improved retrievals in general.

Warm Cloud Evolution, Precipitation, and Their Weak Linkage in HadGEM3: New Process-Level Diagnostics using A-Train Observations

2021 ◽  
Author(s):  
Hanii Takahashi ◽  
Alejandro Bodas-Salcedo ◽  
Graeme Stephens
Keyword(s):  
Large Scale ◽  
Cloud Droplet ◽  
Formation Processes ◽  
Evaluation Tool ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Warm Rain ◽  
Weak Linkage ◽  
The Impact ◽  
Rain Formation

AbstractThe latest configuration of the Hadley Centre Global Environmental Model version 3 (HadGEM3) contains significant changes in the formulation of warm rain processes and aerosols. We evaluate the impacts of these changes in the simulation of warm rain formation processes using A-Train observations. We introduce a new model evaluation tool, quartile-based Contoured Frequency by Optical Depth Diagrams (CFODDs), in order to fill in some blind spots that conventional CFODDs have. Results indicate that HadGEM3 has weak linkage between the size of particle radius and warm rain formation processes, and switching to the new warm rain microphysics scheme causes more difference in warm rain formation processes than switching to the new aerosol scheme through reducing overly produced drizzle mode in HadGEM3. Finally, we run an experiment in which we perturb the second aerosol indirect effect (AIE) to study the rainfall-aerosol interaction in HadGEM3. Since the large changes in the cloud droplet number concentration (CDNC) appear in the AIE experiment, a large impact in warm rain diagnostics is expected. However, regions with large fractional changes in CDNC show a muted change in precipitation, arguably because large-scale constraints act to reduce the impact of such a big change in CDNC. The adjustment in cloud liquid water path to the AIE perturbation produces a large negative shortwave forcing in the midlatitudes.

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

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.

scholarly journals Evaluating MODIS cloud retrievals with in situ observations from VOCALS-REx

2012 ◽  
Vol 12 (9) ◽  
pp. 23679-23729 ◽  
Author(s):  
N. J. King ◽  
K. N. Bower ◽  
J. Crosier ◽  
I. Crawford
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Liquid Water ◽  
Near Infrared ◽  
Droplet Size Distribution ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Water Path ◽  
High Bias

Abstract. Microphysical measurements collected during eleven profiles through marine stratocumulus as part of the Variability of the American Monsoon Systems (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) are compared to collocated overpasses of the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua and Terra satellite platforms. The full depth of the cloud is sampled in each case using a Cloud Droplet Probe (CDP) and a Two-Dimensional Stereo Probe (2DS) together sizing cloud and precipitation droplets in the diameter range 2-1260 μm. This allows the total optical depth (τc) of the cloud and effective radius (re) of the droplet size distribution to be compared to MODIS cloud retrievals of the same quantities along with the secondarily derived total liquid water path. When compared to the effective radius at cloud top, the MODIS retrieved re using the 2.1 μm wavelength channel overestimates the in situ measurements on average by 13% with the largest overestimations coinciding with the detection by the 2DS of drizzle sized droplets. We show through consideration of the full vertical profile and penetration depths of the wavelengths used in the retrieval that the expected retrieved values are less than those at cloud top thus increasing the apparent bias in re retrievals particularly when using the 1.6 and 2.1 μm channels, with the 3.7 μm channel retrievals displaying the best agreement with in situ values. Retrievals of τc also tend to overestimate in situ values which, coupled with a high bias in re retrievals, lead to an overestimation of liquid water path. There is little apparent correlation between the variation of the three near-infrared re retrievals and the vertical structure of the cloud observed in situ. Retrievals are performed using measured profiles of water vapour and temperature along with an accurate knowledge of the width of the droplet size distribution which improve agreement between in situ and retrieved values but cannot completely explain the observed biases. Additionally we show that cloud heterogeneity and three-dimensional radiative effects may high skew the mean when averaging over comparison domains but cannot explain all of the apparent high bias.

scholarly journals Cloud droplet size and liquid water path retrievals from zenith radiance measurements: examples from the Atmospheric Radiation Measurement Program and the Aerosol Robotic Network

2012 ◽  
Vol 12 (8) ◽  
pp. 19163-19208 ◽  
Author(s):  
J. C. Chiu ◽  
A. Marshak ◽  
C.-H. Huang ◽  
T. Várnai ◽  
R. J. Hogan ◽  
...  
Keyword(s):  
Droplet Size ◽  
Liquid Water ◽  
Cloud Droplet ◽  
Effective Radius ◽  
Atmospheric Radiation ◽  
Liquid Water Path ◽  
Relative Deviation ◽  
Retrieval Method ◽  
Water Path ◽  
Atmospheric Radiation Measurement

Abstract. The ground-based Atmospheric Radiation Measurement Program (ARM) and NASA Aerosol Robotic Network (AERONET) routinely monitor clouds using zenith radiances at visible and near-infrared wavelengths. Using the transmittance calculated from such measurements, we have developed a new retrieval method for cloud effective droplet size and conducted extensive tests for non-precipitating liquid water clouds. The underlying principle is to combine a water-absorbing wavelength (i.e. 1640 nm) with a non-water-absorbing wavelength for acquiring information on cloud droplet size and optical depth. For simulated stratocumulus clouds with liquid water path less than 300 g m−2 and horizontal resolution of 201 m, the retrieval method underestimates the mean effective radius by 0.8 μm, with a root-mean-squared error of 1.7 μm and a relative deviation of 13%. For actual observations with a liquid water path less than 450 g m−2 at the ARM Oklahoma site during 2007–2008, our 1.5 min-averaged retrievals are generally larger by around 1 μm than those from combined ground-based cloud radar and microwave radiometer at a 5 min temporal resolution. We also compared our retrievals to those from combined shortwave flux and microwave observations for relatively homogeneous clouds, showing that the bias between these two retrieval sets is negligible, but the error of 2.6 μm and the relative deviation of 22% are larger than those found in our simulation case. Finally, the transmittance-based cloud effective droplet radii agree to better than 11% with satellite observations and have a negative bias of 1 μm. Overall, the retrieval method provides reasonable cloud effective radius estimates, which can enhance the cloud products of both ARM and AERONET.

scholarly journals Quantitative Investigation of Radiometric Interactions between Snowfall, Snow Cover, and Cloud Liquid Water Over Land

2021 ◽  
Author(s):  
Zeinab Takbiri ◽  
Lisa Milani ◽  
Clement Guilloteau ◽  
Efi Foufoula-Georgiou
Keyword(s):  
Snow Cover ◽  
Water Content ◽  
Liquid Water ◽  
Liquid Water Content ◽  
Reanalysis Data ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Cloud Liquid Water Path ◽  
Microwave Signatures ◽  
Global Precipitation

Falling snow alters its own microwave signatures when it begins to accumulate on the ground making retrieval of precipitation challenging. This paper investigates the effects of snow-cover depth and cloud liquid water content on microwave signatures of terrestrial snowfall using reanalysis data and multi-annual measurements by the Global Precipitation Measurement (GPM) core satellite with particular emphasis on the 89 and 166 GHz channels. It is found that over snow cover shallower than 10 cm and low values of cloud liquid water path (LWP ≤125gm−2), the scattering of light snowfall (<0.5mmh−1) is detectable only at frequency 166 GHz while for higher intensities the signal can be also detected at 89 GHz. However, when snow depth exceeds ∼20 cm and the LWP is greater than ∼125gm−2 , the emission from the increased liquid water content in snowing clouds becomes the only surrogate microwave signal of snowfall that is stronger at frequency 89 GHz than 166 GHz. The results also reveal that over high latitudes above 60∘ N where the snow cover is thicker than 20 cm and LWP is lower than 125 gm−2 the microwave snowfall signal could not be detected with GPM. Our results provide quantitative insights for improving retrieval of snowfall in particular over snow-covered terrain.

scholarly journals Stratocumulus Liquid Water Content from Dual-Wavelength Radar

2005 ◽  
Vol 22 (8) ◽  
pp. 1207-1218 ◽  
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.

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 Quantitative Investigation of Radiometric Interactions between Snowfall, Snow Cover, and Cloud Liquid Water over Land

2021 ◽  
Vol 13 (13) ◽  
pp. 2641
Author(s):  
Zeinab Takbiri ◽  
Lisa Milani ◽  
Clement Guilloteau ◽  
Efi Foufoula-Georgiou
Keyword(s):  
Snow Cover ◽  
Water Content ◽  
Liquid Water ◽  
Snow Water Equivalent ◽  
A Priori ◽  
Liquid Water Content ◽  
Microwave Signal ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Microwave Signatures

Falling snow alters its own microwave signatures when it begins to accumulate on the ground, making retrieval of snowfall challenging. This paper investigates the effects of snow-cover depth and cloud liquid water content on microwave signatures of terrestrial snowfall using reanalysis data and multi-annual observations by the Global Precipitation Measurement (GPM) core satellite with particular emphasis on the 89 and 166 GHz channels. It is found that over shallow snow cover (snow water equivalent (SWE) ≤100kg m−2) and low values of cloud liquid water path (LWP 100–150 g m−2), the scattering of light snowfall (intensities ≤0.5mm h−1) is detectable only at frequency 166 GHz, while for higher snowfall rates, the signal can also be detected at 89 GHz. However, when SWE exceeds 200 kg m−2 and the LWP is greater than 100–150 g m−2, the emission from the increased liquid water content in snowing clouds becomes the only surrogate microwave signal of snowfall that is stronger at frequency 89 than 166 GHz. The results also reveal that over high latitudes above 60°N where the SWE is greater than 200 kg m−2 and LWP is lower than 100–150 g m−2, the snowfall microwave signal could not be detected with GPM without considering a priori data about SWE and LWP. Our findings provide quantitative insights for improving retrieval of snowfall in particular over snow-covered terrain.

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