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

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

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

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

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

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

DROP EFFECTIVE RADIUS IN MAIN CLOUD TYPES AND FRONTAL CLOUD SYSTEMS ESTIMATED BY SATELLITE OBSERVATIONS IN WARM PERIOD OF YEAR

2020 ◽  
pp. 71-82
Author(s):  
T.M Zabolotska ◽  
O.A. Kryvobok ◽  
V.M. Shpyg ◽  
A.Yu. Tsila
Keyword(s):  
Liquid Water ◽  
Effective Radius ◽  
Satellite Observations ◽  
Cloud System ◽  
Liquid Water Path ◽  
Water Path ◽  
Cloud Systems ◽  
Cloud Water Content ◽  
Precipitation Type ◽  
Upper Level

The distribution of drop effective radius on cloud upper level was defined and analyzed for main cloud forms over Ukraine during two years (2014-2015) using satellite observations. The effective radius values of isolated cumulonimbus on cloud top and its dependency on optical thickness was estimated in measurements during April-September 2014 over Kyiv area. For cumulonimbus clouds with precipitation the dependence of effective radius on the type, precipitation intensity and liquid water path was defined. The distribution of drop effective radius on cloud top in the strength frontal systems with heavy showers area over all territory of Ukraine was defined for two systems and it dependence on the cloud height and the precipitation type, their intensity and the liquid water path was estimated. For all types of clouds the size of effective radius of the droplets was 6 μm. In St and As cloud system droplets with this size of effective radius were observed in 100%, in Sc and As cloud system – 91-92%. The values of effective radius in Ns and Cb cloud system was close to 6 μm (71 and 89% respectively). Larger droplets (8 μm) in Ns were observed in 29% and in Cb in 9%. However, in Cb, accompanied by rainfalls and powerful thunderstorms, the values of effective radius were 10-15 μm (1.5%) and 25-45 μm (0.5%). In 75% of moderate precipitation cases were formed by drops with an effective radius of 6 μm and in 25% with an effective radius of 8 μm. For the heavy precipitated clouds, the drops with an effective radius of 8 μm (62%) had the highest frequency, in 33% the effective radius of 6 μm were observed. The larger droplets (≥10 μm) had a small frequency (5%). The drop effective radius for cases of heavy rainfalls was 8 μm in 75%, in 25% larger droplets were observed (10, 15 and 30 μm). More intense rainfall was accompanied by greater values of cloud water content and, accordingly, greater effective radius values. The cases with large values of microphysical parameters and precipitation were observed as streaks in frontal cloud systems.

scholarly journals Scale-by-scale analysis of probability distributions for global MODIS-AQUA cloud properties: how the large scale signature of turbulence may impact statistical analyses of clouds

2011 ◽  
Vol 11 (6) ◽  
pp. 2893-2901 ◽  
Author(s):  
M. de la Torre Juárez ◽  
A. B. Davis ◽  
E. J. Fetzer
Keyword(s):  
Liquid Water ◽  
Large Scale ◽  
Cloud Fraction ◽  
Effective Radius ◽  
Distribution Functions ◽  
Liquid Water Path ◽  
Water Path ◽  
Cloud Properties ◽  
Standard Deviations ◽  
Log Normal

Abstract. Means, standard deviations, homogeneity parameters used in models based on their ratio, and the probability distribution functions (PDFs) of cloud properties from the MODerate resolution Infrared Spectrometer (MODIS) are estimated globally as function of averaging scale varying from 5 to 500 km. The properties – cloud fraction, droplet effective radius, and liquid water path – all matter for cloud-climate uncertainty quantification and reduction efforts. Global means and standard deviations are confirmed to change with scale. For the range of scales considered, global means vary only within 3% for cloud fraction, 7% for liquid water path, and 0.2% for cloud particle effective radius. These scale dependences contribute to the uncertainties in their global budgets. Scale dependence for standard deviations and generalized flatness are compared to predictions for turbulent systems. Analytical expressions are identified that fit best to each observed PDF. While the best analytical PDF fit to each variable differs, all PDFs are well described by log-normal PDFs when the mean is normalized by the standard deviation inside each averaging domain. Importantly, log-normal distributions yield significantly better fits to the observations than gaussians at all scales. This suggests a possible approach for both sub-grid and unified stochastic modeling of these variables at all scales. The results also highlight the need to establish an adequate spatial resolution for two-stream radiative studies of cloud-climate interactions.

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

2013 ◽  
Vol 13 (1) ◽  
pp. 191-209 ◽  
Author(s):  
N. J. King ◽  
K. N. Bower ◽  
J. Crosier ◽  
I. Crawford
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Liquid Water ◽  
Droplet Size Distribution ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Water Path ◽  
High Bias ◽  
In Situ Observations

Abstract. Microphysical measurements collected during eleven profiles, by the UK BAe-146 aircraft, through marine stratocumulus as part of the Variability of the American Monsoon Systems (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) are compared to collocated overpasses of the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua and Terra satellite platforms. The full depth of the cloud is sampled in each case using a Cloud Droplet Probe (CDP) and a Two-Dimensional Stereo Probe (2DS) together sizing cloud and precipitation droplets in the diameter range 2–1260 μm. This allows the total optical depth (τc) of the cloud and effective radius (re) of the droplet size distribution to be compared to MODIS cloud retrievals of the same quantities along with the secondarily derived total liquid water path. When compared to the effective radius at cloud top, the MODIS retrieved re using the 2.1 μm wavelength channel overestimates the in situ measurements on average by 13% with the largest overestimations coinciding with the detection by the 2DS of drizzle sized droplets. We show through consideration of the full vertical profile and penetration depths of the wavelengths used in the retrieval that the expected retrieved values are less than those at cloud top thus increasing the apparent bias in re retrievals particularly when using the 1.6 and 2.1 μm channels, with the 3.7 μm channel retrievals displaying the best agreement with in situ values. Retrievals of τc also tend to overestimate in situ values which, coupled with a high bias in re retrievals, lead to an overestimation of liquid water path. There is little apparent correlation between the variation of the three near-infrared re retrievals and the vertical structure of the cloud observed in situ. Retrievals are performed using measured profiles of water vapour and temperature along with an accurate knowledge of the width of the droplet size distribution which improve agreement between in situ and retrieved values but cannot completely explain the observed biases. Additionally we show that cloud heterogeneity and three-dimensional radiative effects may high skew the mean when averaging over comparison domains but cannot explain all of the apparent high bias. An intercomparison between in situ measurements from the BAe-146 and C-130 platforms is also presented, highlighting the uncertainties associated with in situ observations.

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.

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