Liquid Water Cloud Measurements Using the Raman Lidar Technique: Current Understanding and Future Research Needs

Abstract This paper describes recent work in the Raman lidar liquid water cloud measurement technique. The range-resolved spectral measurements at the National Aeronautics and Space Administration Goddard Space Flight Center indicate that the Raman backscattering spectra measured in and below low clouds agree well with theoretical spectra for vapor and liquid water. The calibration coefficients of the liquid water measurement for the Raman lidar at the Atmospheric Radiation Measurement Program Southern Great Plains site of the U.S. Department of Energy were determined by comparison with the liquid water path (LWP) obtained with Atmospheric Emitted Radiance Interferometer (AERI) and the liquid water content (LWC) obtained with the millimeter wavelength cloud radar and water vapor radiometer (MMCR–WVR) together. These comparisons were used to estimate the Raman liquid water cross-sectional value. The results indicate a bias consistent with an effective liquid water Raman cross-sectional value that is 28%–46% lower than published, which may be explained by the fact that the difference in the detectors' sensitivity has not been accounted for. The LWP of a thin altostratus cloud showed good qualitative agreement between lidar retrievals and AERI. However, the overall ensemble of comparisons of LWP showed considerable scatter, possibly because of the different fields of view of the instruments, the 350-m distance between the instruments, and the horizontal inhomogeneity of the clouds. The LWC profiles for a thick stratus cloud showed agreement between lidar retrievals and MMCR–WVR between the cloud base and 150 m above that where the optical depth was less than 3. Areas requiring further research in this technique are discussed.

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

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-4-7109-2011 ◽

2011 ◽

Vol 4 (6) ◽

pp. 7109-7158 ◽

Cited By ~ 1

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.

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Estimation of liquid water path below the melting layer in stratiform precipitation systems using radar measurements during MC3E

Atmospheric Measurement Techniques ◽

10.5194/amt-12-3743-2019 ◽

2019 ◽

Vol 12 (7) ◽

pp. 3743-3759 ◽

Cited By ~ 2

Author(s):

Jingjing Tian ◽

Xiquan Dong ◽

Baike Xi ◽

Christopher R. Williams ◽

Peng Wu

Keyword(s):

Liquid Water ◽

Department Of Energy ◽

Cloud Base ◽

Retrieval Algorithm ◽

Doppler Velocity ◽

Liquid Water Path ◽

Water Path ◽

Melting Layer ◽

Stratiform Precipitation ◽

Cloud Particles

Abstract. In this study, the liquid water path (LWP) below the melting layer in stratiform precipitation systems is retrieved, which is a combination of rain liquid water path (RLWP) and cloud liquid water path (CLWP). The retrieval algorithm uses measurements from the vertically pointing radars (VPRs) at 35 and 3 GHz operated by the US Department of Energy Atmospheric Radiation Measurement (ARM) and National Oceanic and Atmospheric Administration (NOAA) during the field campaign Midlatitude Continental Convective Clouds Experiment (MC3E). The measured radar reflectivity and mean Doppler velocity from both VPRs and spectrum width from the 35 GHz radar are utilized. With the aid of the cloud base detected by a ceilometer, the LWP in the liquid layer is retrieved under two different situations: (I) no cloud exists below the melting base, and (II) cloud exists below the melting base. In (I), LWP is primarily contributed from raindrops only, i.e., RLWP, which is estimated by analyzing the Doppler velocity differences between two VPRs. In (II), cloud particles and raindrops coexist below the melting base. The CLWP is estimated using a modified attenuation-based algorithm. Two stratiform precipitation cases (20 and 11 May 2011) during MC3E are illustrated for two situations, respectively. With a total of 13 h of samples during MC3E, statistical results show that the occurrence of cloud particles below the melting base is low (9 %); however, the mean CLWP value can be up to 0.56 kg m−2, which is much larger than the RLWP (0.10 kg m−2). When only raindrops exist below the melting base, the average RLWP value is larger (0.32 kg m−2) than the with-cloud situation. The overall mean LWP below the melting base is 0.34 kg m−2 for stratiform systems during MC3E.

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Parameterizing cloud top effective radii from satellite retrieved values, accounting for vertical photon transport: quantification and correction of the resulting bias in droplet concentration and liquid water path retrievals

Atmospheric Measurement Techniques ◽

10.5194/amt-11-4273-2018 ◽

2018 ◽

Vol 11 (7) ◽

pp. 4273-4289 ◽

Cited By ~ 7

Author(s):

Daniel P. Grosvenor ◽

Odran Sourdeval ◽

Robert Wood

Keyword(s):

Penetration Depth ◽

Optical Depth ◽

Liquid Water ◽

Liquid Water Content ◽

Cloud Base ◽

Percentage Error ◽

Time Variability ◽

Liquid Water Path ◽

Water Path ◽

Droplet Concentration

Abstract. Droplet concentration (Nd) and liquid water path (LWP) retrievals from passive satellite retrievals of cloud optical depth (τ) and effective radius (re) usually assume the model of an idealized cloud in which the liquid water content (LWC) increases linearly between cloud base and cloud top (i.e. at a fixed fraction of the adiabatic LWC). Generally it is assumed that the retrieved re value is that at the top of the cloud. In reality, barring re retrieval biases due to cloud heterogeneity, the retrieved re is representative of smaller values that occur lower down in the cloud due to the vertical penetration of photons at the shortwave-infrared wavelengths used to retrieve re. This inconsistency will cause an overestimate of Nd and an underestimate of LWP (referred to here as the “penetration depth bias”), which this paper quantifies via a parameterization of the cloud top re as a function of the retrieved re and τ. Here we estimate the relative re underestimate for a range of idealized modelled adiabatic clouds using bispectral retrievals and plane-parallel radiative transfer. We find a tight relationship between gre=recloud top/reretrieved and τ and that a 1-D relationship approximates the modelled data well. Using this relationship we find that gre values and hence Nd and LWP biases are higher for the 2.1 µm channel re retrieval (re2.1) compared to the 3.7 µm one (re3.7). The theoretical bias in the retrieved Nd is very large for optically thin clouds, but rapidly reduces as cloud thickness increases. However, it remains above 20 % for τ<19.8 and τ<7.7 for re2.1 and re3.7, respectively. We also provide a parameterization of penetration depth in terms of the optical depth below cloud top (dτ) for which the retrieved re is likely to be representative. The magnitude of the Nd and LWP biases for climatological data sets is estimated globally using 1 year of daily MODIS (MODerate Imaging Spectroradiometer) data. Screening criteria are applied that are consistent with those required to help ensure accurate Nd and LWP retrievals. The results show that the SE Atlantic, SE Pacific and Californian stratocumulus regions produce fairly large overestimates due to the penetration depth bias with mean biases of 32–35 % for re2.1 and 15–17 % for re3.7. For the other stratocumulus regions examined the errors are smaller (24–28 % for re2.1 and 10–12 % for re3.7). Significant time variability in the percentage errors is also found with regional mean standard deviations of 19–37 % of the regional mean percentage error for re2.1 and 32–56 % for re3.7. This shows that it is important to apply a daily correction to Nd for the penetration depth error rather than a time–mean correction when examining daily data. We also examine the seasonal variation of the bias and find that the biases in the SE Atlantic, SE Pacific and Californian stratocumulus regions exhibit the most seasonality, with the largest errors occurring in the December, January and February (DJF) season. LWP biases are smaller in magnitude than those for Nd (−8 to −11 % for re2.1 and −3.6 to −6.1 % for re3.7). In reality, and especially for more heterogeneous clouds, the vertical penetration error will be combined with a number of other errors that affect both the re and τ, which are potentially larger and may compensate or enhance the bias due to vertical penetration depth. Therefore caution is required when applying the bias corrections; we suggest that they are only used for more homogeneous clouds.

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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.

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Precipitation effects of giant cloud condensation nuclei artificially introduced into stratocumulus clouds

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-47-2015 ◽

2015 ◽

Vol 15 (1) ◽

pp. 47-76 ◽

Cited By ~ 1

Author(s):

E. Jung ◽

B. A. Albrecht ◽

H. H. Jonsson ◽

Y.-C. Chen ◽

J. H. Seinfeld ◽

...

Keyword(s):

Liquid Water ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Fold Increase ◽

Liquid Water Content ◽

Cloud Base ◽

Condensation Nuclei ◽

Liquid Water Path ◽

Base Level ◽

Stratocumulus Clouds

Abstract. To study the effect of giant cloud condensation nuclei (GCCN) on precipitation processes in stratocumulus clouds, 1–10 μm diameter salt particles (salt powder) were released from an aircraft while flying near cloud top on 3 August 2011 off the central coast of California. The seeded area was subsequently sampled from the aircraft that was equipped with aerosol, cloud, and precipitation probes and an upward-facing cloud radar. During post-seeding sampling, made 30–60 min after seeding, the mean cloud droplet size increased, the droplet number concentration decreased, and large drop (e.g., diameter larger than 10 μm) concentration increased. Average drizzle rates increased from about 0.05 to 0.20 mm h−1, and liquid water path decreased from about 52 to 43 g m−2. Strong radar returns associated with drizzle were observed on the post-seeding cloud-base level-leg flights and were accompanied by a substantial depletion of the cloud liquid water content. The changes were large enough to suggest that the salt particles with concentrations estimated to be 10−2 to 10−4 cm−3 resulted in a four-fold increase in the cloud base rainfall rate and depletion of the cloud water due to rainout. In contrast, a case is shown where the cloud was already precipitating (on 10 August) and the effect of adding GCCN to the cloud was insignificant.

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Estimation of Liquid Water Path in Stratiform Precipitation Systems using Radar Measurements during MC3E

10.5194/amt-2018-388 ◽

2019 ◽

Author(s):

Jingjing Tian ◽

Xiquan Dong ◽

Baike Xi ◽

Christopher R. Williams ◽

Peng Wu

Keyword(s):

Liquid Layer ◽

Liquid Water ◽

Department Of Energy ◽

Cloud Base ◽

Retrieval Algorithm ◽

Doppler Velocity ◽

Liquid Water Path ◽

Water Path ◽

Stratiform Precipitation ◽

Cloud Particles

Abstract. In this study, the liquid water path (LWP) in stratiform precipitation systems is retrieved, which is a combination of rain liquid water path (RLWP) and cloud liquid water path (CLWP). The retrieval algorithm uses measurements from the vertically pointing radars (VPRs) at 35 GHz and 3 GHz operated by the U.S Department of Energy Atmospheric Radiation Measurement (ARM) and National Oceanic and Atmospheric Administration (NOAA) during the field campaign Midlatitude Continental Convective Clouds Experiment (MC3E). The measured radar reflectivity and mean Doppler velocity from both VPRs and spectrum width from the 35 GHz radar are utilized. With the aid of the cloud base detected by ceilometer, the LWP in the liquid layer is retrieved under two different situations: (I) no cloud exists below the melting base, and (II) cloud exists below the melting base. In (I), LWP is primarily contributed from raindrops only, i.e., RLWP, which is estimated by analyzing the Doppler velocity differences between two VPRs. In (II), cloud particles and raindrops coexist in the liquid layer. The CLWP is estimated using a modified attenuation-based algorithm. Two stratiform precipitation cases (20 May 2011 and 11 May 2011) during MC3E are illustrated for two situations, respectively. With a total of 14 hours of samples during MC3E, statistical results show that the occurrence of cloud particles below the melting base is low (8 %), however, the mean CLWP value can be up to 0.87 kg m−2, which is much larger than the RLWP (0.22 kg m−2). When only raindrops exist below the melting base, the averaged RLWP value is larger (0.33 kg m−2) than the with cloud situation. The overall mean LWP below the melting base is 0.39 kg m−2 for stratiform systems during MC3E.

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Precipitation effects of giant cloud condensation nuclei artificially introduced into stratocumulus clouds

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-5645-2015 ◽

2015 ◽

Vol 15 (10) ◽

pp. 5645-5658 ◽

Cited By ~ 13

Author(s):

E. Jung ◽

B. A. Albrecht ◽

H. H. Jonsson ◽

Y.-C. Chen ◽

J. H. Seinfeld ◽

...

Keyword(s):

Liquid Water ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Fold Increase ◽

Liquid Water Content ◽

Cloud Base ◽

Condensation Nuclei ◽

Liquid Water Path ◽

Base Level ◽

Stratocumulus Clouds

Abstract. To study the effect of giant cloud condensation nuclei (GCCN) on precipitation processes in stratocumulus clouds, 1–10 μm diameter salt particles (salt powder) were released from an aircraft while flying near the cloud top on 3 August 2011 off the central coast of California. The seeded area was subsequently sampled from the aircraft that was equipped with aerosol, cloud, and precipitation probes and an upward-facing cloud radar. During post-seeding sampling, made 30–60 min after seeding, the mean cloud droplet size increased, the droplet number concentration decreased, and large drop (e.g., diameter larger than 10 μm) concentration increased. Average drizzle rates increased from about 0.05 to 0.20 mm h−1, and the liquid water path decreased from about 52 to 43 g m−2. Strong radar returns associated with drizzle were observed on the post-seeding cloud-base level-leg flights and were accompanied by a substantial depletion of the cloud liquid water content. The changes were large enough to suggest that the salt particles with concentrations estimated to be 10−2 to 10-4 cm−3 resulted in a four-fold increase in the cloud-base rainfall rate and depletion of the cloud water due to rainout. In contrast, a case is shown where the cloud was already precipitating (on 10 August) and the effect of adding GCCN to the cloud was insignificant.

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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.

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Ground-based observations of cloud and drizzle liquid water path in stratocumulus clouds

Atmospheric Measurement Techniques ◽

10.5194/amt-13-1485-2020 ◽

2020 ◽

Vol 13 (3) ◽

pp. 1485-1499 ◽

Cited By ~ 1

Author(s):

Maria P. Cadeddu ◽

Virendra P. Ghate ◽

Mario Mech

Keyword(s):

Liquid Water ◽

Microwave Radiometer ◽

Precipitable Water ◽

Cloud Base ◽

Radiative Cooling ◽

Liquid Water Path ◽

Cell Systems ◽

Water Path ◽

Closed Cell ◽

Stratocumulus Clouds

Abstract. The partition of cloud and drizzle water path in precipitating clouds plays a key role in determining the cloud lifetime and its evolution. A technique to quantify cloud and drizzle water path by combining measurements from a three-channel microwave radiometer (23.8, 30, and 90 GHz) with those from a vertically pointing Doppler cloud radar and a ceilometer is presented. The technique is showcased using 1 d of observations to derive precipitable water vapor, liquid water path, cloud water path, drizzle water path below the cloud base, and drizzle water path above the cloud base in precipitating stratocumulus clouds. The resulting cloud and drizzle water path within the cloud are in good qualitative agreement with the information extracted from the radar Doppler spectra. The technique is then applied to 10 d each of precipitating closed and open cellular marine stratocumuli. In the closed-cell systems only ∼20 % of the available drizzle in the cloud falls below the cloud base, compared to ∼40 % in the open-cell systems. In closed-cell systems precipitation is associated with radiative cooling at the cloud top <-100Wm-2 and a liquid water path >200 g m−2. However, drizzle in the cloud begins to exist at weak radiative cooling and liquid water path >∼150 g m−2. Our results collectively demonstrate that neglecting scattering effects for frequencies at and above 90 GHz leads to overestimation of the total liquid water path of about 10 %–15 %, while their inclusion paves the path for retrieving drizzle properties within the cloud.

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Observed Boundary Layer Controls on Shallow Cumulus at the ARM Southern Great Plains Site

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-17-0244.1 ◽

2018 ◽

Vol 75 (7) ◽

pp. 2235-2255 ◽

Cited By ~ 15

Author(s):

Neil P. Lareau ◽

Yunyan Zhang ◽

Stephen A. Klein

Keyword(s):

Boundary Layer ◽

Great Plains ◽

Vertical Velocity ◽

Mass Flux ◽

Cloud Base ◽

Liquid Water Path ◽

Southern Great Plains ◽

Clear Sky ◽

Shallow Cumulus ◽

In Situ Sensors

Abstract The boundary layer controls on shallow cumulus (ShCu) convection are examined using a suite of remote and in situ sensors at ARM Southern Great Plains (SGP). A key instrument in the study is a Doppler lidar that measures vertical velocity in the CBL and along cloud base. Using a sample of 138 ShCu days, the composite structure of the ShCu CBL is examined, revealing increased vertical velocity (VV) variance during periods of medium cloud cover and higher VV skewness on ShCu days than on clear-sky days. The subcloud circulations of 1791 individual cumuli are also examined. From these data, we show that cloud-base updrafts, normalized by convective velocity, vary as a function of updraft width normalized by CBL depth. It is also found that 63% of clouds have positive cloud-base mass flux and are linked to coherent updrafts extending over the depth of the CBL. In contrast, negative mass flux clouds lack coherent subcloud updrafts. Both sets of clouds possess narrow downdrafts extending from the cloud edges into the subcloud layer. These downdrafts are also present adjacent to cloud-free updrafts, suggesting they are mechanical in origin. The cloud-base updraft data are subsequently combined with observations of convective inhibition to form dimensionless “cloud inhibition” (CI) parameters. Updraft fraction and liquid water path are shown to vary inversely with CI, a finding consistent with CIN-based closures used in convective parameterizations. However, we also demonstrate a limited link between CBL vertical velocity variance and cloud-base updrafts, suggesting that additional factors, including updraft width, are necessary predictors for cloud-base updrafts.

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