scholarly journals Estimate of the impact of absorbing aerosol over cloud on the MODIS retrievals of cloud optical thickness and effective radius using two independent retrievals of liquid water path

2009 ◽  
Vol 114 (D5) ◽  
Author(s):  
Eric M. Wilcox ◽  
Harshvardhan ◽  
Steven Platnick
Keyword(s):  
Optical Thickness ◽  
Liquid Water ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Water Path ◽  
Cloud Optical Thickness ◽  
The Impact

scholarly journals MBL drizzle properties and their impact on cloud property retrievals

2015 ◽  
Vol 8 (4) ◽  
pp. 4307-4323
Author(s):  
P. Wu ◽  
X. Dong ◽  
B. Xi
Keyword(s):  
Liquid Water ◽  
Cloud Droplet ◽  
Number Concentration ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Water Path ◽  
Cloud Property ◽  
Annual Means ◽  
Mean Differences ◽  
The Impact

Abstract. In this study, we retrieve and document drizzle properties, and investigate the impact of drizzle on cloud property retrievals from ground-based measurements at the ARM Azores site from June 2009 to December 2010. For the selected cloud and drizzle samples, the drizzle occurrence is 42.6% with a maximum of 55.8% in winter and a minimum of 35.6% in summer. The annual means of drizzle liquid water path LWPd, effective radius rd, and number concentration Nd for the rain (virga) samples are 5.48 (1.29) g m−2, 68.7 (39.5) μm, and 0.14 (0.38) cm−3. The seasonal mean LWPd values are less than 4% of the MWR-retrieved LWP values. The annual mean differences in cloud-droplet effective radius with and without drizzle are 0.12 and 0.38 μm, respectively, for the virga and rain samples. Therefore, we conclude that the impact of drizzle on cloud property retrievals is insignificant at the ARM Azores site.

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

2013 ◽  
Vol 13 (19) ◽  
pp. 9997-10003 ◽  
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.

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

2013 ◽  
Vol 13 (5) ◽  
pp. 12725-12742 ◽  
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 ◽  
Cloud Dynamics ◽  
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 Edition 4 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 > 50 g m−2, and negative (up to −4 μm) for larger Hσ. Thus, re3.8 – re2.1 differences are more likely to reflect biases associated with cloud heterogeneities rather than information about the cloud vertical structure. The consequences for MODIS LWP are also discussed.

scholarly journals Cloud-type dependencies of MODIS and AMSR-E liquid water path differences

2009 ◽  
Vol 9 (1) ◽  
pp. 3367-3399 ◽  
Author(s):  
M. de la Torre Juárez ◽  
B. H. Kahn ◽  
E. J. Fetzer
Keyword(s):  
Optical Thickness ◽  
Liquid Water ◽  
Near Infrared ◽  
Cloud Type ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Cloud Water Content ◽  
Cloud Optical Thickness ◽  
Cloud Top Temperature

Abstract. Comparisons of cloud liquid water path (LWP) retrievals are presented from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Microwave Scanning Radiometer (AMSR-E) located aboard the Aqua spacecraft. LWP differences as a function of cloud top height, cloud fraction, cloud top temperature, LWP, cloud effective radius and cloud optical thickness are quantified in most geophysical conditions. The assumption of vertically homogeneous distributions of cloud water content in the MODIS LWP retrieval yields a slightly poorer agreement than the assumption of stratified cloud liquid water. Furthermore, for a fixed cloud top pressure, the cloud top temperature can lead to sign changes in the LWP difference. In general, AMSR-E LWP is larger than MODIS for small cloud fractions, low values of LWP, and warmer cloud top temperatures. On the other hand, clouds with optical thicknesses above 20 lead to larger MODIS LWP. Using cloud optical thickness as a proxy for cloud type, deep convective clouds and stratus are shown to have the poorest agreement between AMSR-E and MODIS LWP. Particularly large differences are also found at latitudes poleward of 50°. The results of this work help characterize the scene- and cloud-dependent performance of microwave and visible/near infrared retrievals of LWP.

scholarly journals A spectral method for retrieving cloud optical thickness and effective radius from surface-based transmittance measurements

2011 ◽  
Vol 11 (1) ◽  
pp. 1053-1104 ◽  
Author(s):  
P. J. McBride ◽  
K. S. Schmidt ◽  
P. Pilewskie ◽  
A. S. Kittelman ◽  
D. E. Wolfe
Keyword(s):  
Optical Thickness ◽  
Liquid Water ◽  
Effective Radius ◽  
Spectral Shape ◽  
Dual Wavelength ◽  
Lookup Table ◽  
The Arctic ◽  
Liquid Water Path ◽  
Water Path ◽  
Slope Method

Abstract. We introduce a new multispectral method for the retrieval of optical thickness and effective radius from cloud transmittance, which is less sensitive to effective radius than cloud reflectance. Based on data from the moderate spectral resolution observations of the Solar Spectral Flux Radiometer (SSFR) and Shortwave Spectroradiometer (SWS), we use the spectral shape of transmitted radiance as a means of retrieving effective radius from cloud transmittance. The observations were taken during the International Chemistry Experiment in the Arctic Lower Troposphere and at the Southern Great Plains (SGP) site of the Atmospheric Radiation Measurement (ARM) Climate Research Facility. The spectral shape was quantified by fitting a slope to the normalized transmittance between 1565 nm and 1634 nm. The retrieval was performed by comparing the observed slope at 1565 nm and the transmittance at 515 nm with a pre-calculated library (lookup table). An estimate of the retrieval uncertainty was provided by propagating the uncertainty of the observations through the best-fit algorithm. We compare the new retrieval with an algorithm that uses transmittance at two wavelengths, a method often used with cloud reflectance. The liquid water path (LWP) is derived from the retrieved optical thickness and effective radius, assuming a cloud with effective radius varying linearly with altitude above cloud base, and compared to the retrieved liquid water path from a microwave radiometer. Retrievals from two MODIS overpasses of the SGP were also compared. The data taken from the SGP was under thicker cloud than the case used from ICEALOT, with average optical thickness of 44 and 22, respectively. For the time period with the thicker clouds, the dual-wavelength method and the slope method retrieved nearly indistinguishable results. The dual-wavelength method, however, resulted in slightly higher average relative effective radius uncertainty of 12.9 μm±12.8%, as compared to 12.8 μm±8.9% from the slope method. The thinner cloud case resulted in a significant difference between the dual-wavelength and slope algorithms with average retrieved effective radius and uncertainties of 12.5 μm±8.4% and 17.0 μm±21.0% for the slope and dual-wavelength methods, respectively. The retrieved optical thickness values for this case were nearly identical. The average derived LWP was within 12.5% and 20% of the MWR LWP for the ARM and ICEALOT data. For a homogeneous cloud case, the MODIS retrievals (optical depth, effective radius, and LWP) were within the uncertainty of the SWS retrievals. Inhomogeneous clouds resulted in lesser agreement between the MODIS and SWS retrievals.

Variational Assimilation of Cloud Liquid/Ice Water Path and Its Impact on NWP

2015 ◽  
Vol 54 (8) ◽  
pp. 1809-1825 ◽  
Author(s):  
Yaodeng Chen ◽  
Hongli Wang ◽  
Jinzhong Min ◽  
Xiang-Yu Huang ◽  
Patrick Minnis ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Liquid Water ◽  
Weather Prediction ◽  
Wrf Model ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Ice Water Path ◽  
Ice Water ◽  
The Impact

AbstractAnalysis of the cloud components in numerical weather prediction models using advanced data assimilation techniques has been a prime topic in recent years. In this research, the variational data assimilation (DA) system for the Weather Research and Forecasting (WRF) Model (WRFDA) is further developed to assimilate satellite cloud products that will produce the cloud liquid water and ice water analysis. Observation operators for the cloud liquid water path and cloud ice water path are developed and incorporated into the WRFDA system. The updated system is tested by assimilating cloud liquid water path and cloud ice water path observations from Global Geostationary Gridded Cloud Products at NASA. To assess the impact of cloud liquid/ice water path data assimilation on short-term regional numerical weather prediction (NWP), 3-hourly cycling data assimilation and forecast experiments with and without the use of the cloud liquid/ice water paths are conducted. It is shown that assimilating cloud liquid/ice water paths increases the accuracy of temperature, humidity, and wind analyses at model levels between 300 and 150 hPa after 5 cycles (15 h). It is also shown that assimilating cloud liquid/ice water paths significantly reduces forecast errors in temperature and wind at model levels between 300 and 150 hPa. The precipitation forecast skills are improved as well. One reason that leads to the improved analysis and forecast is that the 3-hourly rapid update cycle carries over the impact of cloud information from the previous cycles spun up by the WRF Model.

scholarly journals Cloud optical thickness and liquid water path. Does the <i>k</i> coefficient vary with droplet concentration?

2011 ◽  
Vol 11 (2) ◽  
pp. 5173-5215
Author(s):  
J.-L. Brenguier ◽  
F. Burnet ◽  
O. Geoffroy
Keyword(s):  
Correction Factor ◽  
Optical Thickness ◽  
Liquid Water ◽  
General Circulation ◽  
Field Experiments ◽  
General Circulation Models ◽  
Light Extinction ◽  
Liquid Water Path ◽  
Water Path ◽  
Droplet Concentration

Abstract. Cloud radiative transfer calculations in general circulation models involve a link between cloud microphysical and optical properties. Indeed, the liquid water content expresses as a function of the mean volume droplet radius, while the light extinction is a function of their mean surface radius. There is a small difference between these two parameters because of the droplet spectrum width. This issue has been addressed by introducing an empirical multiplying correction factor to the droplet concentration. Analysis of in situ sampled data, however, revealed that the correction factor decreases when the concentration increases, hence partially mitigating the aerosol indirect effect. Five field experiments are reanalyzed here, in which standard and upgraded versions of the droplet spectrometer were used to document shallow cumulus and stratocumulus topped boundary layers. They suggest that the standard probe noticeably underestimates the correction factor compared to the upgraded versions. The analysis is further refined to demonstrate that the value of the correction factor derived by averaging values calculated locally along the flight path overestimates the value derived from liquid water path and optical thickness of a cloudy column, and that there is no detectable correlation between the correction factor and the droplet concentration. It is also shown that the droplet concentration dilution by entrainment-mixing after CCN activation is significantly stronger in shallow cumuli than in stratocumulus layers. These various effects are finally combined to produce the best estimate of the correction factor to use in general circulation models.

scholarly journals Combined retrieval of Arctic liquid water cloud and surface snow properties using airborne spectral solar remote sensing

2017 ◽  
Vol 10 (9) ◽  
pp. 3215-3230 ◽  
Author(s):  
André Ehrlich ◽  
Eike Bierwirth ◽  
Larysa Istomina ◽  
Manfred Wendisch
Keyword(s):  
Remote Sensing ◽  
Grain Size ◽  
Sea Ice ◽  
Optical Thickness ◽  
Liquid Water ◽  
Retrieval Algorithm ◽  
Continuous Transition ◽  
Cloud Properties ◽  
Cloud Optical Thickness ◽  
The Impact

Abstract. The passive solar remote sensing of cloud properties over highly reflecting ground is challenging, mostly due to the low contrast between the cloud reflectivity and that of the underlying surfaces (sea ice and snow). Uncertainties in the retrieved cloud optical thickness τ and cloud droplet effective radius reff, C may arise from uncertainties in the assumed spectral surface albedo, which is mainly determined by the generally unknown effective snow grain size reff, S. Therefore, in a first step the effects of the assumed snow grain size are systematically quantified for the conventional bispectral retrieval technique of τ and reff, C for liquid water clouds. In general, the impact of uncertainties of reff, S is largest for small snow grain sizes. While the uncertainties of retrieved τ are independent of the cloud optical thickness and solar zenith angle, the bias of retrieved reff, C increases for optically thin clouds and high Sun. The largest deviations between the retrieved and true original values are found with 83 % for τ and 62 % for reff, C. In the second part of the paper a retrieval method is presented that simultaneously derives all three parameters (τ, reff, C, reff, S) and therefore accounts for changes in the snow grain size. Ratios of spectral cloud reflectivity measurements at the three wavelengths λ1 = 1040 nm (sensitive to reff, S), λ2 = 1650 nm (sensitive to τ), and λ3 = 2100 nm (sensitive to reff, C) are combined in a trispectral retrieval algorithm. In a feasibility study, spectral cloud reflectivity measurements collected by the Spectral Modular Airborne Radiation measurement sysTem (SMART) during the research campaign Vertical Distribution of Ice in Arctic Mixed-Phase Clouds (VERDI, April/May 2012) were used to test the retrieval procedure. Two cases of observations above the Canadian Beaufort Sea, one with dense snow-covered sea ice and another with a distinct snow-covered sea ice edge are analysed. The retrieved values of τ, reff, C, and reff, S show a continuous transition of cloud properties across snow-covered sea ice and open water and are consistent with estimates based on satellite data. It is shown that the uncertainties of the trispectral retrieval increase for high values of τ, and low reff, S but nevertheless allow the effective snow grain size in cloud-covered areas to be estimated.

scholarly journals Retrieval of effective radius and liquid water path from ground-based instruments: A case study at Barrow, Alaska

2007 ◽  
Vol 112 (D21) ◽  
Author(s):  
Robyn Schofield ◽  
John S. Daniel ◽  
Robert W. Portmann ◽  
H. LeRoy Miller ◽  
Susan Solomon ◽  
...  
Keyword(s):  
Liquid Water ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Water Path

scholarly journals Biases caused by the instrument bandwidth and beam width on simulated brightness temperature measurements from scanning microwave radiometers

2012 ◽  
Vol 5 (6) ◽  
pp. 8085-8130
Author(s):  
V. Meunier ◽  
U. Löhnert ◽  
P. Kollias ◽  
S. Crewell
Keyword(s):  
Water Vapor ◽  
Liquid Water ◽  
Beam Width ◽  
Liquid Water Path ◽  
Water Path ◽  
Antenna Beam ◽  
Atmospheric Propagation ◽  
W Band ◽  
The Impact ◽  
Receiver Bandwidth

Abstract. More so than the traditional fixed radiometers, the scanning radiometer requires a careful design to ensure high quality measurements. Here the impact of the radiometer characteristics (e.g. antenna beam width, receiver bandwidth) and atmospheric propagation (e.g. curvature of the earth and refractivity) on the scanning radiometer measurements are presented. A forward radiative transfer model that includes all these effects to represent the instrument measurements is used to estimate the biases as differences between the measurement with and without these characteristics for three commonly used frequency bands: K, V and W-band. The receiver channel bandwidth errors are not so important in K-band and W-band. Thus, the use of a wider bandwidth to improve detection at low signal-to-noise conditions is acceptable. The impact of the antenna beam width is higher than the receiver bandwidth, but, for V-band where they are of similar importance. Using simple regression algorithms, the effects of the bandwidth and beam width biases in liquid water path, integrated water vapor, and temperature are also examined. The largest errors in liquid water path and integrated water vapor are associated with the beam width errors.

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