scholarly journals The interdependence of continental warm cloud properties derived from unexploited solar background signals in ground-based lidar measurements

2014 ◽  
Vol 14 (16) ◽  
pp. 8389-8401 ◽  
Author(s):  
J. C. Chiu ◽  
J. A. Holmes ◽  
R. J. Hogan ◽  
E. J. O'Connor
Keyword(s):  
Optical Depth ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Cloud Optical Depth ◽  
Cloud Properties ◽  
Warm Cloud ◽  
Lidar Measurements ◽  
Atmospheric Radiation Measurement ◽  
Ground Based Lidar ◽  
Geometric Thickness

Abstract. We have extensively analysed the interdependence between cloud optical depth, droplet effective radius, liquid water path (LWP) and geometric thickness for stratiform warm clouds using ground-based observations. In particular, this analysis uses cloud optical depths retrieved from untapped solar background signals that are previously unwanted and need to be removed in most lidar applications. Combining these new optical depth retrievals with radar and microwave observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility in Oklahoma during 2005–2007, we have found that LWP and geometric thickness increase and follow a power-law relationship with cloud optical depth regardless of the presence of drizzle; LWP and geometric thickness in drizzling clouds can be generally 20–40% and at least 10% higher than those in non-drizzling clouds, respectively. In contrast, droplet effective radius shows a negative correlation with optical depth in drizzling clouds and a positive correlation in non-drizzling clouds, where, for large optical depths, it asymptotes to 10 μm. This asymptotic behaviour in non-drizzling clouds is found in both the droplet effective radius and optical depth, making it possible to use simple thresholds of optical depth, droplet size, or a combination of these two variables for drizzle delineation. This paper demonstrates a new way to enhance ground-based cloud observations and drizzle delineations using existing lidar networks.

scholarly journals The interdependence of continental warm cloud properties derived from unexploited solar background signal in ground-based lidar measurements

2014 ◽  
Vol 14 (7) ◽  
pp. 8963-8996
Author(s):  
J. C. Chiu ◽  
J. A. Holmes ◽  
R. J. Hogan ◽  
E. J. O'Connor
Keyword(s):  
Optical Depth ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Background Signal ◽  
Cloud Optical Depth ◽  
Cloud Properties ◽  
Lidar Measurements ◽  
Atmospheric Radiation Measurement ◽  
Ground Based Lidar ◽  
Geometric Thickness

Abstract. We have extensively analysed the interdependence between cloud optical depth, droplet effective radius, liquid water path (LWP) and geometric thickness for stratiform warm clouds using ground-based observations. In particular, this analysis uses cloud optical depths retrieved from untapped solar background signal that is previously unwanted and needs to be removed in most lidar applications. Combining these new optical depth retrievals with radar and microwave observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility in Oklahoma during 2005–2007, we have found that LWP and geometric thickness increase and follow a power-law relationship with cloud optical depth regardless of the presence of drizzle; LWP and geometric thickness in drizzling clouds can be generally 20–40% and at least 10% higher than those in non-drizzling clouds, respectively. In contrast, droplet effective radius shows a negative correlation with optical depth in drizzling clouds, while it increases with optical depth and reaches an asymptote of 10 μm in non-drizzling clouds. This asymptotic behaviour in non-drizzling clouds is found in both droplet effective radius and optical depth, making it possible to use simple thresholds of optical depth, droplet size, or a combination of these two variables for drizzle delineation. This paper demonstrates a new way to enhance ground-based cloud observations and drizzle delineations using existing lidar networks.

Design of a Shadowband Spectral Radiometer for the Retrieval of Thin Cloud Optical Depth, Liquid Water Path, and the Effective Radius

2011 ◽  
Vol 28 (11) ◽  
pp. 1458-1465 ◽  
Author(s):  
M. J. Bartholomew ◽  
R. M. Reynolds ◽  
A. M. Vogelmann ◽  
Q. Min ◽  
R. Edwards ◽  
...  
Keyword(s):  
Optical Depth ◽  
Liquid Water ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Cloud Optical Depth ◽  
Water Path ◽  
Cloud Properties ◽  
Radiative Intensity ◽  
Thin Cloud ◽  
Aerosol Properties

Abstract The design and operation of a Thin-Cloud Rotating Shadowband Radiometer (TCRSR) described here was used to measure the radiative intensity of the solar aureole and enable the simultaneous retrieval of cloud optical depth, drop effective radius, and liquid water path. The instrument consists of photodiode sensors positioned beneath two narrow metal bands that occult the sun by moving alternately from horizon to horizon. Measurements from the narrowband 415-nm channel were used to demonstrate a retrieval of the cloud properties of interest. With the proven operation of the relatively inexpensive TCRSR instrument, its usefulness for retrieving aerosol properties under cloud-free skies and for ship-based observations is discussed.

scholarly journals Application of a multiple scattering model to estimate optical depth, lidar ratio and ice crystal effective radius of cirrus clouds observed with lidar.

2018 ◽  
Vol 176 ◽  
pp. 05037
Author(s):  
Diego Gouveia ◽  
Holger Baars ◽  
Patric Seifert ◽  
Ulla Wandinger ◽  
Henrique Barbosa ◽  
...  
Keyword(s):  
Multiple Scattering ◽  
Optical Depth ◽  
Single Scattering ◽  
Effective Radius ◽  
Cirrus Clouds ◽  
Ice Crystal ◽  
Backscatter Signal ◽  
Cloud Optical Depth ◽  
Lidar Measurements ◽  
Lidar Ratio

Lidar measurements of cirrus clouds are highly influenced by multiple scattering (MS). We therefore developed an iterative approach to correct elastic backscatter lidar signals for multiple scattering to obtain best estimates of single-scattering cloud optical depth and lidar ratio as well as of the ice crystal effective radius. The approach is based on the exploration of the effect of MS on the molecular backscatter signal returned from above cloud top.

scholarly journals Spectral invariant behavior of zenith radiance around cloud edges simulated by radiative transfer

2010 ◽  
Vol 10 (6) ◽  
pp. 14557-14581
Author(s):  
J. C. Chiu ◽  
A. Marshak ◽  
Y. Knyazikhin ◽  
W. J. Wiscombe
Keyword(s):  
Radiative Transfer ◽  
Optical Depth ◽  
Cloud Optical Depth ◽  
Cloud Properties ◽  
Atmospheric Radiation Measurement ◽  
Visible Wavelengths ◽  
Thermodynamic Phase ◽  
The Relationship ◽  
Invariant Relationship ◽  
Spectral Invariant

Abstract. A previous paper discovered a surprising spectral-invariant relationship in shortwave spectrometer observations taken by the Atmospheric Radiation Measurement (ARM) program. Here, using radiative transfer simulations, we study the sensitivity of this relationship to the properties of aerosols and clouds, to the underlying surface type, and to the finite field-of-view (FOV) of the spectrometer. Overall, the relationship is mostly sensitive to cloud properties and has little sensitivity to the other factors. At visible wavelengths, the relationship primarily depends on cloud optical depth regardless of cloud thermodynamic phase and drop size. At water-absorbing wavelengths, the slope of the spectral-invariant relationship depends primarily on cloud optical depth; the intercept, by contrast, depends primarily on cloud absorption properties, suggesting a new retrieval method for cloud drop effective radius. These results suggest that the spectral-invariant relationship can be used to infer cloud properties even with insufficient or no knowledge about spectral surface albedo and aerosol properties.

scholarly journals Information content of OCO-2 oxygen A-band channels for retrieving marine liquid cloud properties

2018 ◽  
Vol 11 (3) ◽  
pp. 1515-1528 ◽  
Author(s):  
Mark Richardson ◽  
Graeme L. Stephens
Keyword(s):  
Information Content ◽  
Optical Depth ◽  
Marine Boundary Layer ◽  
Initial Conditions ◽  
High Spectral Resolution ◽  
Cloud Optical Depth ◽  
Boundary Layer Clouds ◽  
Cloud Properties ◽  
Cloud Top Pressure ◽  
Geometric Thickness

Abstract. Information content analysis is used to select channels for a marine liquid cloud retrieval using the high-spectral-resolution oxygen A-band instrument on NASA's Orbiting Carbon Observatory-2 (OCO-2). Desired retrieval properties are cloud optical depth, cloud-top pressure and cloud pressure thickness, which is the geometric thickness expressed in hectopascals. Based on information content criteria we select a micro-window of 75 of the 853 functioning OCO-2 channels spanning 763.5–764.6 nm and perform a series of synthetic retrievals with perturbed initial conditions. We estimate posterior errors from the sample standard deviations and obtain ±0.75 in optical depth and ±12.9 hPa in both cloud-top pressure and cloud pressure thickness, although removing the 10 % of samples with the highest χ2 reduces posterior error in cloud-top pressure to ±2.9 hPa and cloud pressure thickness to ±2.5 hPa. The application of this retrieval to real OCO-2 measurements is briefly discussed, along with limitations and the greatest caution is urged regarding the assumption of a single homogeneous cloud layer, which is often, but not always, a reasonable approximation for marine boundary layer clouds.

scholarly journals Spectrally-invariant behavior of zenith radiance around cloud edges simulated by radiative transfer

2010 ◽  
Vol 10 (22) ◽  
pp. 11295-11303 ◽  
Author(s):  
J. C. Chiu ◽  
A. Marshak ◽  
Y. Knyazikhin ◽  
W. J. Wiscombe
Keyword(s):  
Radiative Transfer ◽  
Optical Depth ◽  
Retrieval Method ◽  
Cloud Optical Depth ◽  
Cloud Properties ◽  
Atmospheric Radiation Measurement ◽  
Visible Wavelengths ◽  
Thermodynamic Phase ◽  
The Relationship ◽  
Invariant Relationship

Abstract. In a previous paper, we discovered a surprising spectrally-invariant relationship in shortwave spectrometer observations taken by the Atmospheric Radiation Measurement (ARM) program. The relationship suggests that the shortwave spectrum near cloud edges can be determined by a linear combination of zenith radiance spectra of the cloudy and clear regions. Here, using radiative transfer simulations, we study the sensitivity of this relationship to the properties of aerosols and clouds, to the underlying surface type, and to the finite field-of-view (FOV) of the spectrometer. Overall, the relationship is mostly sensitive to cloud properties and has little sensitivity to other factors. At visible wavelengths, the relationship primarily depends on cloud optical depth regardless of cloud phase function, thermodynamic phase and drop size. At water-absorbing wavelengths, the slope of the relationship depends primarily on cloud optical depth; the intercept, by contrast, depends primarily on cloud absorbing and scattering properties, suggesting a new retrieval method for cloud drop effective radius. These results suggest that the spectrally-invariant relationship can be used to infer cloud properties near cloud edges even with insufficient or no knowledge about spectral surface albedo and aerosol properties.

scholarly journals Aerosol properties and their influences on low warm clouds during the Two-Column Aerosol Project

2019 ◽  
Vol 19 (14) ◽  
pp. 9515-9529 ◽  
Author(s):  
Jianjun Liu ◽  
Zhanqing Li
Keyword(s):  
Optical Depth ◽  
Aerosol Particles ◽  
Large Contribution ◽  
Loading Conditions ◽  
Liquid Water Path ◽  
Air Mass ◽  
Aerosol Loading ◽  
Cloud Properties ◽  
Stable Conditions ◽  
Cloud Development

Abstract. Twelve months of measurements collected during the Two-Column Aerosol Project field campaign at Cape Cod, Massachusetts, which started in the summer of 2012, were used to investigate aerosol physical, optical, and chemical properties and their influences on the dependence of cloud development on thermodynamic (i.e., lower tropospheric stability, LTS) conditions. Relationships between aerosol loading and cloud properties under different dominant air-mass conditions and the magnitude of the first indirect effect (FIE), as well as the sensitivity of the FIE to different aerosol compositions, are examined. The seasonal variation in aerosol number concentration (Na) was not consistent with variations in aerosol optical properties (i.e., scattering coefficient, σs, and columnar aerosol optical depth). Organics were found to have a large contribution to small particle sizes. This contribution decreased during the particle growth period. Under low-aerosol-loading conditions, the liquid water path (LWP) and droplet effective radius (DER) significantly increased with increasing LTS, but, under high-aerosol-loading conditions, LWP and DER changed little, indicating that aerosols significantly weakened the dependence of cloud development on LTS. The reduction in LWP and DER from low- to high-aerosol-loading conditions was greater in stable environments, suggesting that clouds under stable conditions are more susceptible to aerosol perturbations than those under more unstable conditions. High aerosol loading weakened the increase in DER as LWP increased and strengthened the increase in cloud optical depth (COD) with increasing LWP, resulting in changes in the interdependence of cloud properties. Under both continental and marine air-mass conditions, high aerosol loading can significantly increase COD and decrease LWP and DER, narrowing their distributions. Magnitudes of the FIE estimated under continental air-mass conditions ranged from 0.07±0.03 to 0.26±0.09 with a mean value of 0.16±0.03 and showed an increasing trend as LWP increased. The calculated FIE values for aerosols with a low fraction of organics are greater than those for aerosols with a high fraction of organics. This implies that clouds over regions dominated by aerosol particles containing mostly inorganics are more susceptible to aerosol perturbations, resulting in larger climate forcing, than clouds over regions dominated by organic aerosol particles.

scholarly journals Marine liquid cloud geometric thickness retrieved from OCO-2's oxygen A-band spectrometer

2019 ◽  
Vol 12 (3) ◽  
pp. 1717-1737 ◽  
Author(s):  
Mark Richardson ◽  
Jussi Leinonen ◽  
Heather Q. Cronk ◽  
James McDuffie ◽  
Matthew D. Lebsock ◽  
...  
Keyword(s):  
Optical Depth ◽  
Single Layer ◽  
Cloud Droplet ◽  
Satellite Observation ◽  
Cloud Optical Depth ◽  
First Case ◽  
Phase Classification ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Cloud Top Pressure ◽  
Geometric Thickness

Abstract. This paper introduces the OCO2CLD-LIDAR-AUX product, which uses the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and the Orbiting Carbon Observatory-2 (OCO-2) hyperspectral A-band spectrometer. CALIPSO provides a prior cloud top pressure (Ptop) for an OCO-2-based retrieval of cloud optical depth, Ptop and cloud geometric thickness expressed in hPa. Measurements are of single-layer liquid clouds over oceans from September 2014 to December 2016 when collocated data are available. Retrieval performance is best for solar zenith angles <45∘ and when the cloud phase classification, which also uses OCO-2's weak CO2 band, is more confident. The highest quality optical depth retrievals agree with those from the Moderate Resolution Imaging Spectroradiometer (MODIS) with discrepancies smaller than the MODIS-reported uncertainty. Retrieved thicknesses are consistent with a substantially subadiabatic structure over marine stratocumulus regions, in which extinction is weighted towards the cloud top. Cloud top pressure in these clouds shows a 4 hPa bias compared with CALIPSO which we attribute mainly to the assumed vertical structure of cloud extinction after showing little sensitivity to the presence of CALIPSO-identified aerosol layers or assumed cloud droplet effective radius. This is the first case of success in obtaining internal cloud structure from hyperspectral A-band measurements and exploits otherwise unused OCO-2 data. This retrieval approach should provide additional constraints on satellite-based estimates of cloud droplet number concentration from visible imagery, which rely on parameterization of the cloud thickness.

Observed Southern Ocean Cloud Properties and Shortwave Reflection. Part I: Calculation of SW Flux from Observed Cloud Properties*

2014 ◽  
Vol 27 (23) ◽  
pp. 8836-8857 ◽  
Author(s):  
Daniel T. McCoy ◽  
Dennis L. Hartmann ◽  
Daniel P. Grosvenor
Keyword(s):  
Seasonal Variation ◽  
Solar Radiation ◽  
Southern Ocean ◽  
Water Content ◽  
Liquid Water ◽  
Effective Radius ◽  
Shortwave Radiation ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Cloud Properties

Abstract The sensitivity of the reflection of shortwave radiation over the Southern Ocean to the cloud properties there is estimated using observations from a suite of passive and active satellite instruments in combination with radiative transfer modeling. A composite cloud property observational data description is constructed that consistently incorporates mean cloud liquid water content, ice water content, liquid and ice particle radius information, vertical structure, vertical overlap, and spatial aggregation of cloud water as measured by optical depth versus cloud-top pressure histograms. The observational datasets used are Moderate Resolution Imaging Spectroradiometer (MODIS) effective radius filtered to mitigate solar zenith angle bias, the Multiangle Imaging Spectroradiometer (MISR) cloud-top height–optical depth (CTH–OD) histogram, the liquid water path from the University of Wisconsin dataset, and ice cloud properties from CloudSat. This cloud database is used to compute reflected shortwave radiation as a function of month and location over the ocean from 40° to 60°S, which compares well with observations of reflected shortwave radiation. This calculation is then used to test the sensitivity of the seasonal variation of shortwave reflection to the observed seasonal variation of cloud properties. Effective radius decreases during the summer season, which results in an increase in reflected solar radiation of 4–8 W m−2 during summer compared to what would be reflected if the effective radius remained constant at its annual-mean value. Summertime increases in low cloud fraction similarly increase the summertime reflection of solar radiation by 9–11 W m−2. In-cloud liquid water path is less in summertime, causing the reflected solar radiation to be 1–4 W m−2 less.

scholarly journals Is positive correlation between cloud droplet effective radius and aerosol optical depth over land due to retrieval artifacts or real physical processes?

2019 ◽  
Vol 19 (13) ◽  
pp. 8879-8896 ◽  
Author(s):  
Hailing Jia ◽  
Xiaoyan Ma ◽  
Johannes Quaas ◽  
Yan Yin ◽  
Tom Qiu
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Radiant Energy ◽  
Single Layer ◽  
Cloud Droplet ◽  
Energy System ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Anthropogenic Aerosol ◽  
Aerosol Cloud

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3, Clouds and the Earth's Radiant Energy System (CERES) Edition-4 L3 products, and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data are employed to systematically study aerosol–cloud correlations over three anthropogenic aerosol regions and their adjacent oceans, as well as explore the effect of retrieval artifacts and underlying physical mechanisms. This study is confined to warm phase and single-layer clouds without precipitation during the summertime (June, July, and August). Our analysis suggests that cloud effective radius (CER) is positively correlated with aerosol optical depth (AOD) over land (positive slopes), but negatively correlated with aerosol index (AI) over oceans (negative slopes) even with small ranges of liquid water path (quasi-constant). The changes in albedo at the top of the atmosphere (TOA) corresponding to aerosol-induced changes in CER also lend credence to the authenticity of this opposite aerosol–cloud correlation between land and ocean. It is noted that potential artifacts, such as the retrieval biases of both cloud (partially cloudy and 3-D-shaped clouds) and aerosol, can result in a serious overestimation of the slope of CER–AOD/AI. Our results show that collision–coalescence seems not to be the dominant cause for positive slope over land, but the increased CER caused by increased aerosol might further increase CER by initializing collision–coalescence, generating a positive feedback. By stratifying data according to the lower tropospheric stability and relative humidity near cloud top, it is found that the positive correlations more likely occur in the case of drier cloud top and stronger turbulence in clouds, while negative correlations occur in the case of moister cloud top and weaker turbulence in clouds, which implies entrainment mixing might be a possible physical interpretation for such a positive CER–AOD slope.

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