A comparison of ship and satellite measurements of cloud properties in the southeast Pacific stratus deck

Abstract. Here, liquid water path (LWP), cloud fraction, cloud top height, and cloud base height are retrieved by a suite of satellite instruments (the CPR aboard CloudSat, CALIOP aboard CALIPSO, and MODIS aboard Aqua) and compared to ship observations from research cruises made in 2001 and 2003–2007 into the stratus/stratocumulus deck over the southeast Pacific Ocean. It is found that CloudSat LWP is generally too high over this region and the CloudSat/CALIPSO cloud bases are too low which is to be expected from the increased sensitivity to precipitation by both the radar and lidar. This results in a relationship (LWP~h9) between CloudSat LWP and CALIPSO cloud thickness (h) that is very different from the adiabatic relationship (LWP~h2) from in situ observations. Furthermore, comparing results from a global model (CAM3.1) to ship observations reveals that, while the simulated LWP is quite reasonable, the model cloud is too thick and too low, allowing the model to have LWPs that are almost independent of h. Such differences may be reduced in future versions of both the satellite data and the model.

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A comparison of ship and satellite measurements of cloud properties with global climate model simulations in the southeast Pacific stratus deck

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-6527-2010 ◽

2010 ◽

Vol 10 (14) ◽

pp. 6527-6536 ◽

Cited By ~ 16

Author(s):

M. A. Brunke ◽

S. P. de Szoeke ◽

P. Zuidema ◽

X. Zeng

Keyword(s):

Diurnal Cycle ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Cloud Fraction ◽

Cloud Base ◽

Liquid Water Path ◽

Cloud Properties ◽

Southeast Pacific ◽

Cloud Thickness

Abstract. Here, liquid water path (LWP), cloud fraction, cloud top height, and cloud base height retrieved by a suite of A-train satellite instruments (the CPR aboard CloudSat, CALIOP aboard CALIPSO, and MODIS aboard Aqua) are compared to ship observations from research cruises made in 2001 and 2003–2007 into the stratus/stratocumulus deck over the southeast Pacific Ocean. It is found that CloudSat radar-only LWP is generally too high over this region and the CloudSat/CALIPSO cloud bases are too low. This results in a relationship (LWP~h9) between CloudSat LWP and CALIPSO cloud thickness (h) that is very different from the adiabatic relationship (LWP~h2) from in situ observations. Such biases can be reduced if LWPs suspected to be contaminated by precipitation are eliminated, as determined by the maximum radar reflectivity Zmax>−15 dBZ in the apparent lower half of the cloud, and if cloud bases are determined based upon the adiabatically-determined cloud thickness (h~LWP1/2). Furthermore, comparing results from a global model (CAM3.1) to ship observations reveals that, while the simulated LWP is quite reasonable, the model cloud is too thick and too low, allowing the model to have LWPs that are almost independent of h. This model can also obtain a reasonable diurnal cycle in LWP and cloud fraction at a location roughly in the centre of this region (20° S, 85° W) but has an opposite diurnal cycle to those observed aboard ship at a location closer to the coast (20° S, 75° W). The diurnal cycle at the latter location is slightly improved in the newest version of the model (CAM4). However, the simulated clouds remain too thick and too low, as cloud bases are usually at or near the surface.

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Improvement of airborne retrievals of cloud droplet number concentration of trade wind cumulus using a synergetic approach

Atmospheric Measurement Techniques ◽

10.5194/amt-12-1635-2019 ◽

2019 ◽

Vol 12 (3) ◽

pp. 1635-1658 ◽

Cited By ~ 3

Author(s):

Kevin Wolf ◽

André Ehrlich ◽

Marek Jacob ◽

Susanne Crewell ◽

Martin Wirth ◽

...

Keyword(s):

Remote Sensing ◽

Cloud Droplet ◽

Number Concentration ◽

Cloud Base ◽

Trade Wind ◽

Liquid Water Path ◽

Cloud Properties ◽

Research Aircraft ◽

Cloud Droplet Number Concentration

Abstract. In situ measurements of cloud droplet number concentration N are limited by the sampled cloud volume. Satellite retrievals of N suffer from inherent uncertainties, spatial averaging, and retrieval problems arising from the commonly assumed strictly adiabatic vertical profiles of cloud properties. To improve retrievals of N it is suggested in this paper to use a synergetic combination of passive and active airborne remote sensing measurement, to reduce the uncertainty of N retrievals, and to bridge the gap between in situ cloud sampling and global averaging. For this purpose, spectral solar radiation measurements above shallow trade wind cumulus were combined with passive microwave and active radar and lidar observations carried out during the second Next Generation Remote Sensing for Validation Studies (NARVAL-II) campaign with the High Altitude and Long Range Research Aircraft (HALO) in August 2016. The common technique to retrieve N is refined by including combined measurements and retrievals of cloud optical thickness τ, liquid water path (LWP), cloud droplet effective radius reff, and cloud base and top altitude. Three approaches are tested and applied to synthetic measurements and two cloud scenarios observed during NARVAL-II. Using the new combined retrieval technique, errors in N due to the adiabatic assumption have been reduced significantly.

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Climatology of Warm Boundary Layer Clouds at the ARM SGP Site and Their Comparison to Models

Journal of Climate ◽

10.1175/jcli-3231.1 ◽

2004 ◽

Vol 17 (24) ◽

pp. 4760-4782 ◽

Cited By ~ 30

Author(s):

Manajit Sengupta ◽

Eugene E. Clothiaux ◽

Thomas P. Ackerman

Keyword(s):

Liquid Water ◽

Solar Flux ◽

Cloud Base ◽

Liquid Water Path ◽

Cloud Liquid Water ◽

Water Path ◽

Cloud Forcing ◽

Cloud Liquid Water Path ◽

Ecmwf Model ◽

Cloud Thickness

Abstract A 4-yr climatology (1997–2000) of warm boundary layer cloud properties is developed for the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SGP) site. Parameters in the climatology include cloud liquid water path, cloud-base height, and surface solar flux. These parameters are retrieved from measurements produced by a dual-channel microwave radiometer, a millimeter-wave cloud radar, a micropulse lidar, a Belfort ceilometer, shortwave radiometers, and atmospheric temperature profiles amalgamated from multiple sources, including radiosondes. While no significant interannual differences are observed in the datasets, there are diurnal variations with nighttime liquid water paths consistently higher than daytime values. The summer months of June, July, and August have the lowest liquid water paths and the highest cloud-base heights. Model outputs of cloud liquid water paths from the European Centre for Medium-Range Weather Forecasts (ECMWF) model and the Eta Model for 104 model output location time series (MOLTS) stations in the environs of the SGP central facility are compared to observations. The ECMWF and MOLTS median liquid water paths are greater than 3 times the observed values. The MOLTS data show lower liquid water paths in summer, which is consistent with observations, while the ECMWF data exhibit the opposite tendency. A parameterization of normalized cloud forcing that requires only cloud liquid water path and solar zenith angle is developed from the observations. The parameterization, which has a correlation coefficient of 0.81 with the observations, provides estimates of surface solar flux that are comparable to values obtained from explicit radiative transfer calculations based on plane-parallel theory. This parameterization is used to estimate the impact on the surface solar flux of differences in the liquid water paths between models and observations. Overall, there is a low bias of 50% in modeled normalized cloud forcing resulting from the excess liquid water paths in the two models. Splitting the liquid water path into two components, cloud thickness and liquid water content, shows that the higher liquid water paths in the model outputs are primarily a result of higher liquid water contents, although cloud thickness may a play a role, especially for the ECMWF model results.

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Temporal Variability of Fair-Weather Cumulus Statistics at the ACRF SGP Site

Journal of Climate ◽

10.1175/2007jcli2266.1 ◽

2008 ◽

Vol 21 (13) ◽

pp. 3344-3358 ◽

Cited By ~ 54

Author(s):

Larry K. Berg ◽

Evgueni I. Kassianov

Keyword(s):

Great Plains ◽

Sensible Heat Flux ◽

Cloud Fraction ◽

Surface Fluxes ◽

Chord Length ◽

Cloud Base ◽

Fair Weather ◽

Cloud Properties ◽

Cloud Thickness ◽

Cloud Base Height

Abstract Continental fair-weather cumuli exhibit significant diurnal, day-to-day, and year-to-year variability. This study describes the climatology of cloud macroscale properties, over the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern Great Plains (SGP) site. The diurnal cycle of cloud fraction, cloud-base height, cloud-top height, and cloud thickness were well defined. The cloud fraction reached its maximum value near 1400 central standard time. The average cloud-base height increased throughout the day, while the average cloud thickness decreased with time. In contrast to the other cloud properties, the average cloud-chord length remained nearly constant throughout the day. The sensitivity of the cloud properties to the year-to-year variability of precipitation and day-to-day changes in the height of the lifting condensation level (zLCL) and surface fluxes were compared. The cloud-base height was found to be sensitive to both the year, zLCL, and the surface fluxes of heat and moisture; the cloud thickness was found to be more sensitive to the year than to zLCL; the cloud fraction was sensitive to both the low-level moisture and the surface sensible heat flux; and cloud-chord length was sensitive to zLCL. Distributions of the cloud-chord length over the ACRF SGP site were computed and were well fit by an exponential distribution. The contribution to the total cloud fraction by clouds of each cloud-chord length was computed, and it was found that the clouds with a chord length of about 1 km contributed most to the observed cloud fraction. This result is similar to observations made with other remote sensing instruments or in modeling studies, but it is different from aircraft observations of the contribution to the total cloud fraction by clouds of different sizes.

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The impact of horizontal heterogeneities, cloud fraction, and liquid water path on warm cloud effective radii from CERES-like Aqua MODIS retrievals

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-9997-2013 ◽

2013 ◽

Vol 13 (19) ◽

pp. 9997-10003 ◽

Cited By ~ 18

Author(s):

D. Painemal ◽

P. Minnis ◽

S. Sun-Mack

Keyword(s):

Liquid Water ◽

Vertical Structure ◽

Cloud Fraction ◽

Effective Radius ◽

Liquid Water Path ◽

Water Path ◽

Warm Cloud ◽

Southeast Pacific ◽

The Impact

Abstract. The impact of horizontal heterogeneities, liquid water path (LWP from AMSR-E), and cloud fraction (CF) on MODIS cloud effective radius (re), retrieved from the 2.1 μm (re2.1) and 3.8 μm (re3.8) channels, is investigated for warm clouds over the southeast Pacific. Values of re retrieved using the CERES algorithms are averaged at the CERES footprint resolution (∼20 km), while heterogeneities (Hσ) are calculated as the ratio between the standard deviation and mean 0.64 μm reflectance. The value of re2.1 strongly depends on CF, with magnitudes up to 5 μm larger than those for overcast scenes, whereas re3.8 remains insensitive to CF. For cloudy scenes, both re2.1 and re3.8 increase with Hσ for any given AMSR-E LWP, but re2.1 changes more than for re3.8. Additionally, re3.8–re2.1 differences are positive (<1 μm) for homogeneous scenes (Hσ < 0.2) and LWP > 45 gm−2, and negative (up to −4 μm) for larger Hσ. While re3.8–re2.1 differences in homogeneous scenes are qualitatively consistent with in situ microphysical observations over the region of study, negative differences – particularly evinced in mean regional maps – are more likely to reflect the dominant bias associated with cloud heterogeneities rather than information about the cloud vertical structure. The consequences for MODIS LWP are also discussed.

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Aircraft millimeter-wave retrievals of cloud liquid water path during VOCALS-REx

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-19581-2011 ◽

2011 ◽

Vol 11 (7) ◽

pp. 19581-19616 ◽

Cited By ~ 4

Author(s):

P. Zuidema ◽

D. Leon ◽

A. Pazmany ◽

M. Cadeddu

Keyword(s):

Water Vapor ◽

Liquid Water ◽

Liquid Water Path ◽

Cloud Liquid Water ◽

Water Path ◽

Cloud Liquid Water Path ◽

Water Vapor Path ◽

Thickness Measurements ◽

Cloud Thickness

Abstract. A unique feature of the VOCALS Regional Experiment was the inclusion of a small, inexpensive, zenith-pointing millimeter-wavelength passive radiometer on the fourteen research flights of the NCAR C-130 plane, the G-band (183 GHz) Vapor Radiometer (GVR). The radiometer permitted above-cloud retrievals of water vapor path, and cloud liquid water path retrievals at 1 Hz resolution for the sub-cloud and cloudbase aircraft legs when combined with in-situ thermodynamic data. Retrieved free-tropospheric (above-cloud) water vapor paths possessed a strong longitudinal gradient, with off-shore values of one to two mm and near-coastal values reaching one cm. Overall the free-troposphere was drier than that sampled by radiosondes in previous years. For the sub-cloud legs, the absolute (between-leg) and relative (within-leg) LWP accuracy was estimated at 20–25 and 5 g m−2 respectively for well-mixed conditions, with greater uncertainties expected for decoupled conditions. Clouds with retrieved liquid water paths between 200 to 400 g m−2 matched adiabatic values derived from coincident cloud thickness measurements exceedingly well. A significant contribution of the GVR dataset is the extended information on the thin clouds, with 66 % of the retrieved LWPs < 100 g m−2. Nevertheless, the overall LWP cloud fraction of 62 % was less than the 92 % cloud cover determined by airborne cloud lidar and radar combined.

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The first aerosol indirect effect quantified through airborne remote sensing during VOCALS-REx

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-25441-2012 ◽

2012 ◽

Vol 12 (9) ◽

pp. 25441-25485

Author(s):

D. Painemal ◽

P. Zuidema

Keyword(s):

Remote Sensing ◽

Indirect Effect ◽

Climate Models ◽

Remotely Sensed ◽

Cloud Microphysics ◽

Liquid Water Path ◽

Aerosol Indirect Effect ◽

Southeast Pacific ◽

Millimeter Wave Radiometer

Abstract. The first aerosol indirect effect (1AIE) is investigated using a combination of in situ and remotely-sensed aircraft (NCAR C-130) observations acquired during VOCALS-REx over the Southeast Pacific stratocumulus cloud regime. Satellite analyses have previously identified a high albedo susceptibitility to changes in cloud microphysics and aerosols over this region. The 1AIE was broken down into the product of two independently-estimated terms: the cloud aerosol interaction metric ACIτ =dln τ/dln Na|LWP, and the relative albedo (A) susceptibility SR-τ = dA/3dln τ|LWP, with τ and Na denoting retrieved cloud optical thickness and in-situ aerosol concentration, respectively and calculated for fixed intervals of liquid water path (LWP). ACIτ was estimated by combining in-situ Na sampled below the cloud, with τ and LWP derived from, respectively, simultaneous upward-looking broadband irradiance and narrow field-of-view millimeter-wave radiometer measurements, collected at 1 Hz during four eight-hour daytime flights by the C-130 aircraft. ACIτ values were typically large, close to the physical upper limit (0.33), increasing with LWP. The high ACIτ values were in agreement with other in-situ airborne studies in pristine marine stratocumulus and reflect the imposition of a LWP constraint and simultaneity of aerosol and cloud measurements. SR-τ increased with LWP and τ, reached a maximum SR-τ (0.086) for LWP (τ) of 58 g m−2 (13–14), decreasing slightly thereafter. The net first aerosol indirect effect thus increased over the LWP range of 30–80 g m−2. These values were consistent with satellite estimates derived from instantaneous, collocated CERES albedo and MODIS-retrieved droplet number concentrations at 50 km resolution. The consistency of the airborne and satellite estimates (for airborne remotely sensed Nd < 1100 cm−3), despite their independent approaches, differences in observational scales, and retrieval assumptions, is hypothesized to reflect the robust remote sensing conditions for these homogeneous clouds. We recommend the Southeast Pacific for a regional assessment of the first aerosol indirect effect in climate models on this basis.

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Does precipitation susceptibility vary with increasing cloud thickness in marine stratocumulus?

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-33379-2011 ◽

2011 ◽

Vol 11 (12) ◽

pp. 33379-33417 ◽

Cited By ~ 1

Author(s):

C. R. Terai ◽

R. Wood ◽

D. C. Leon ◽

P. Zuidema

Keyword(s):

Cloud Droplet ◽

Aerosol Concentration ◽

Precipitation Rate ◽

Cloud Base ◽

Liquid Water Path ◽

Marine Stratocumulus ◽

Near Surface ◽

The Mean ◽

Using Data ◽

Cloud Thickness

Abstract. The relationship between precipitation rate and accumulation mode aerosol concentration in marine stratocumulus-topped boundary layers is investigated by applying the precipitation susceptibility metric to aircraft data obtained during the VOCALS Regional Experiment. The mean precipitation rate R over a segment of the data is expressed as the product of a drizzle fraction f multiplied by a drizzle intensity I (mean rate for drizzling columns). The susceptibility Sx is then defined as the fractional decrease in precipitation variable x = {R, f, I} per fractional increase in the concentration of aerosols with dry diameter >0.1 μm, with cloud thickness h held fixed. The precipitation susceptibility SR is calculated using data from both precipitating and non-precipitating cloudy columns to quantify how aerosol concentrations affect the mean precipitation rate of all clouds of a given h range and not just the mean precipitation of clouds that are precipitating. SR systematically decreases with increasing h, and this is largely because Sf decreases with h while SI is approximately independent of h. In a general sense, Sf can be thought of as the effect of aerosols on the probability of precipitation, while SI can be thought of as the effect of aerosols on the intensity of precipitation. Since thicker clouds are likely to precipitate regardless of ambient aerosol concentration, we expect Sf to decrease with increasing h. The results are broadly insensitive to the choice of horizontal averaging scale. Similar susceptibilities are found for both cloud base and near-surface drizzle rates and when the analysis is repeated with cloud liquid water path held fixed instead of cloud thickness. Simple power law relationships relating precipitation rate to aerosol concentration or cloud droplet concentration do not capture this observed behavior.

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Response of Marine Boundary Layer Cloud Properties to Aerosol Perturbations Associated with Meteorological Conditions from the 19-Month AMF-Azores Campaign

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0364.1 ◽

2016 ◽

Vol 73 (11) ◽

pp. 4253-4268 ◽

Cited By ~ 8

Author(s):

Jianjun Liu ◽

Zhanqing Li ◽

Maureen Cribb

Keyword(s):

Boundary Layer ◽

Large Scale ◽

Marine Boundary Layer ◽

Effective Interaction ◽

Atmospheric Stability ◽

Cloud Droplet ◽

Cloud Base ◽

Liquid Water Path ◽

Cloud Properties ◽

Stable Conditions

Abstract This study investigates the response of marine boundary layer (MBL) cloud properties to aerosol loading by accounting for the contributions of large-scale dynamic and thermodynamic conditions and quantifies the first indirect effect (FIE). It makes use of 19-month measurements of aerosols, clouds, and meteorology acquired during the Atmospheric Radiation Measurement Mobile Facility field campaign over the Azores. Cloud droplet number concentrations and cloud optical depth (COD) significantly increased with increasing aerosol number concentration . Cloud droplet effective radius (DER) significantly decreased with increasing . The correlations between cloud microphysical properties [, liquid water path (LWP), and DER] and were stronger under more stable conditions. The correlations between , LWP, DER, and were stronger under ascending-motion conditions, while the correlation between COD and was stronger under descending-motion conditions. The magnitude and corresponding uncertainty of the FIE ranged from 0.060 ± 0.022 to 0.101 ± 0.006 depending on the different LWP values. Under more stable conditions, cloud-base heights were generally lower than those under less stable conditions. This enabled a more effective interaction with aerosols, resulting in a larger value for the FIE. However, the dependence of the response of cloud properties to aerosol perturbations on stability varied according to whether ground- or satellite-based DER retrievals were used. The magnitude of the FIE had a larger variation with changing LWP under ascending-motion conditions and tended to be higher under ascending-motion conditions for clouds with low LWP and under descending-motion conditions for clouds with high LWP. A contrasting dependence of FIE on atmospheric stability estimated from the surface and satellite cloud properties retrievals reported in this study underscores the importance of assessing all-level properties of clouds in aerosol–cloud interaction studies.

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The first aerosol indirect effect quantified through airborne remote sensing during VOCALS-REx

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-917-2013 ◽

2013 ◽

Vol 13 (2) ◽

pp. 917-931 ◽

Cited By ~ 27

Author(s):

D. Painemal ◽

P. Zuidema

Keyword(s):

Remote Sensing ◽

Indirect Effect ◽

Radiative Forcing ◽

Radiant Energy ◽

Remotely Sensed ◽

Cloud Microphysics ◽

Liquid Water Path ◽

Aerosol Indirect Effect ◽

Southeast Pacific

Abstract. The first aerosol indirect effect (1AIE) is investigated using a combination of in situ and remotely-sensed aircraft (NCAR C-130) observations acquired during VOCALS-REx over the southeast Pacific stratocumulus cloud regime. Satellite analyses have previously identified a high albedo susceptibitility to changes in cloud microphysics and aerosols over this region. The 1AIE was broken down into the product of two independently-estimated terms: the cloud aerosol interaction metric ACIτ =dlnτ/dlnNa|LWP , and the relative albedo (A) susceptibility SR-τ =dA/3dlnτ|LWP, with τ and Na denoting retrieved cloud optical thickness and in situ aerosol concentration respectively and calculated for fixed intervals of liquid water path (LWP). ACIτ was estimated by combining in situ Na sampled below the cloud, with τ and LWP derived from, respectively, simultaneous upward-looking broadband irradiance and narrow field-of-view millimeter-wave radiometer measurements, collected at 1 Hz during four eight-hour daytime flights by the C-130 aircraft. ACIτ values were typically large, close to the physical upper limit (0.33), with a modest increase with LWP. The high ACIτ values slightly exceed values reported from many previous in situ airborne studies in pristine marine stratocumulus and reflect the imposition of a LWP constraint and simultaneity of aerosol and cloud measurements. SR-τ increased with LWP and τ, reached a maximum SR-τ (0.086) for LWP (τ) of 58 g m−2 (~14), and decreased slightly thereafter. The 1AIE thus increased with LWP and is comparable to a radiative forcing of −3.2– −3.8 W m−2 for a 10% increase in Na, exceeding previously-reported global-range values. The aircraft-derived values are consistent with satellite estimates derived from instantaneous, collocated Clouds and the Earth's Radiant Energy System (CERES) albedo and MOderate resolution Imaging Spectroradiometer (MODIS)-retrieved droplet number concentrations at 50 km resolution. The consistency of the airborne and satellite estimates, despite their independent approaches, differences in observational scales, and retrieval assumptions, is hypothesized to reflect the ideal remote sensing conditions for these homogeneous clouds. We recommend the southeast Pacific for regional model assessments of the first aerosol indirect effect on this basis. This airborne remotely-sensed approach towards quantifying 1AIE should in theory be more robust than in situ calculations because of increased sampling. However, although the technique does not explicitly depend on a remotely-derived cloud droplet number concentration (Nd), the at-times unrealistically-high Nd values suggest more emphasis on accurate airborne radiometric measurements is needed to refine this approach.

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