scholarly journals Snowfall retrieval at X, Ka and W bands: consistency of backscattering and microphysical properties using BAECC ground-based measurements

2018 ◽  
Vol 11 (5) ◽  
pp. 3059-3079 ◽  
Author(s):  
Marta Tecla Falconi ◽  
Annakaisa von Lerber ◽  
Davide Ori ◽  
Frank Silvio Marzano ◽  
Dmitri Moisseev
Keyword(s):  
Cross Sections ◽  
Liquid Water ◽  
Microwave Radiometer ◽  
Dipole Approximation ◽  
Liquid Water Path ◽  
Microphysical Properties ◽  
Aspect Ratios ◽  
Atmospheric Radiation Measurement ◽  
Using Data ◽  
Biogenic Aerosols

Abstract. Radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths using co-located ground-based multi-frequency radar and video-disdrometer observations. Using data from four snowfall events, recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland, measurements of liquid-water-equivalent snowfall rate S are correlated to radar equivalent reflectivity factors Ze, measured by the Atmospheric Radiation Measurement (ARM) cloud radars operating at X, Ka and W frequency bands. From these combined observations, power-law Ze–S relationships are derived for all three frequencies considering the influence of riming. Using microwave radiometer observations of liquid water path, the measured precipitation is divided into lightly, moderately and heavily rimed snow. Interestingly lightly rimed snow events show a spectrally distinct signature of Ze–S with respect to moderately or heavily rimed snow cases. In order to understand the connection between snowflake microphysical and multi-frequency backscattering properties, numerical simulations are performed by using the particle size distribution provided by the in situ video disdrometer and retrieved ice particle masses. The latter are carried out by using both the T-matrix method (TMM) applied to soft-spheroid particle models with different aspect ratios and exploiting a pre-computed discrete dipole approximation (DDA) database for rimed aggregates. Based on the presented results, it is concluded that the soft-spheroid approximation can be adopted to explain the observed multi-frequency Ze–S relations if a proper spheroid aspect ratio is selected. The latter may depend on the degree of riming in snowfall. A further analysis of the backscattering simulations reveals that TMM cross sections are higher than the DDA ones for small ice particles, but lower for larger particles. The differences of computed cross sections for larger and smaller particles are compensating for each other. This may explain why the soft-spheroid approximation is satisfactory for radar reflectivity simulations under study.

scholarly journals Snowfall retrieval at X, Ka and W band: consistency of backscattering and microphysical properties using BAECC ground-based measurements

2018 ◽  
Author(s):  
Marta Tecla Falconi ◽  
Annakaisa von Lerber ◽  
Davide Ori ◽  
Frank Silvio Marzano ◽  
Dmitri Moisseev
Keyword(s):  
Cross Sections ◽  
Dipole Approximation ◽  
Microphysical Properties ◽  
Aspect Ratios ◽  
Millimeter Wavelengths ◽  
W Band ◽  
Atmospheric Radiation Measurement ◽  
Using Data ◽  
Biogenic Aerosols

Abstract. Radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths using high-quality collocated ground-based multi-frequency radar and video-disdrometer observations. Using data from four snowfall events, recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland, measurements of liquid-water-equivalent snowfall rate S are correlated to radar equivalent reflectivity factors Ze, measured by the Atmospheric Radiation Measurement (ARM) cloud radars operating at X, Ka and W frequency bands. From these coupled observations power-law Ze-S relationships are derived for all considered frequencies and distinguishing fluffy from rimed snowfall. Interestingly fluffy-snow events show a spectrally distinct signature of Ze-S with respect to rimed-snow cases. In order to understand the connection between snowflake microphysical and multi-frequency backscattering properties, numerical simulations are also performed by using the particle size distribution provided by the in-situ video-disdrometer. The latter are carried out by using both the T-matrix method (TMM) for soft-spheroids with different aspect ratios and exploiting a pre-computed discrete dipole approximation (DDA) database for complex-shape snowflakes. Based on the presented results, it is concluded that the soft-spheroid approximation can be adopted to explain the observed multi-frequency Ze-S relations if a proper spheroid aspect ratio is selected. The latter may depend on the snowfall type. A further analysis of the backscattering simulations reveals that TMM cross-sections are higher than the DDA ones for small ice particles, but lower for larger particles. These differences may explain why the soft-spheroid approximation is satisfactory for radar reflectivity simulations, the errors of computed cross-sections for larger and smaller particles compensating each other.

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

2020 ◽  
Vol 13 (3) ◽  
pp. 1485-1499 ◽  
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.

scholarly journals Ground-based remote sensing of thin clouds in the Arctic

2012 ◽  
Vol 5 (6) ◽  
pp. 8653-8699 ◽  
Author(s):  
T. J. Garrett ◽  
C. Zhao
Keyword(s):  
Water Vapor ◽  
Thermal Emission ◽  
Stratospheric Ozone ◽  
Microwave Radiometer ◽  
Single Layer ◽  
Primary Source ◽  
The Arctic ◽  
Liquid Water Path ◽  
Water Path ◽  
Microphysical Properties

Abstract. This paper describes a method for using interferometer measurements of downwelling thermal radiation to retrieve the properties of single-layer clouds. Cloud phase is determined from ratios of thermal emission in three "micro-windows" where absorption by water vapor is particularly small. Cloud microphysical and optical properties are retrieved from thermal emission in two micro-windows, constrained by the transmission through clouds of stratospheric ozone emission. Assuming a cloud does not approximate a blackbody, the estimated 95% confidence retrieval errors in effective radius, visible optical depth, number concentration, and water path are, respectively, 10%, 20%, 38% (55% for ice crystals), and 16%. Applied to data from the Atmospheric Radiation Measurement program (ARM) North Slope of Alaska – Adjacent Arctic Ocean (NSA-AAO) site near Barrow, Alaska, retrievals show general agreement with ground-based microwave radiometer measurements of liquid water path. Compared to other retrieval methods, advantages of this technique include its ability to characterize thin clouds year round, that water vapor is not a primary source of retrieval error, and that the retrievals of microphysical properties are only weakly sensitive to retrieved cloud phase. The primary limitation is the inapplicability to thicker clouds that radiate as blackbodies.

scholarly journals A new retrieval for cloud liquid water path using a ground-based microwave radiometer and measurements of cloud temperature

2001 ◽  
Vol 106 (D13) ◽  
pp. 14485-14500 ◽  
Author(s):  
James C. Liljegren ◽  
Eugene E. Clothiaux ◽  
Gerald G. Mace ◽  
Seiji Kato ◽  
Xiquan Dong
Keyword(s):  
Liquid Water ◽  
Microwave Radiometer ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Cloud Temperature ◽  
Cloud Liquid Water Path

Geometrical Thickness, Liquid Water Content, and Radiative Properties of Stratocumulus Clouds over the Western North Pacific

1995 ◽  
Vol 34 (2) ◽  
pp. 460-470 ◽  
Author(s):  
Tadahiro Hayasaka ◽  
Teruyuki Nakajima ◽  
Yasushi Fujiyoshi ◽  
Yutaka Ishizaka ◽  
Takao Takeda ◽  
...  
Keyword(s):  
Size Distribution ◽  
Liquid Water ◽  
North Pacific ◽  
Western North Pacific ◽  
Near Infrared ◽  
North Pacific Ocean ◽  
Microwave Radiometer ◽  
Radiative Properties ◽  
Liquid Water Path ◽  
Water Vapor Absorption

Abstract An algorithm was developed for retrieving cloud geometrical thickness from a measured liquid water path and equivalent width of 0.94-µm water vapor absorption band. The algorithm was applied to aircraft observations obtained by a microwave radiometer and a spectrometer in the winter of 1991 over the western North Pacific Ocean. Retrieved values of the cloud geometrical thickness are apt to be smaller than those observed by eye, especially for horizontally inhomogeneous clouds. Measured cloud albedos in the visible and near-infrared spectral region were also compared with calculated values. For homogeneous clouds there exists a single droplet size distribution that satisfies both spectral regions. However, for inhomogeneous clouds no single size distribution exists that satisfies the albedo observed in both spectral regions.

scholarly journals Comparison of MODIS and VIIRS cloud properties with ARM ground-based observations over Finland

2016 ◽  
Vol 9 (7) ◽  
pp. 3193-3203 ◽  
Author(s):  
Moa K. Sporre ◽  
Ewan J. O'Connor ◽  
Nina Håkansson ◽  
Anke Thoss ◽  
Erik Swietlicki ◽  
...  
Keyword(s):  
Infrared Imaging ◽  
Microwave Radiometer ◽  
Single Layer ◽  
Radar Data ◽  
Liquid Water Path ◽  
Cloud Parameters ◽  
Cloud Properties ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Biogenic Aerosols ◽  
Cloud Mask

Abstract. Cloud retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard the satellites Terra and Aqua and the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi-NPP satellite are evaluated using a combination of ground-based instruments providing vertical profiles of clouds. The ground-based measurements are obtained from the Atmospheric Radiation Measurement (ARM) programme mobile facility, which was deployed in Hyytiälä, Finland, between February and September 2014 for the Biogenic Aerosols – Effects on Clouds and Climate (BAECC) campaign. The satellite cloud parameters cloud top height (CTH) and liquid water path (LWP) are compared with ground-based CTH obtained from a cloud mask created using lidar and radar data and LWP acquired from a multi-channel microwave radiometer. Clouds from all altitudes in the atmosphere are investigated. The clouds are diagnosed as single or multiple layer using the ground-based cloud mask. For single-layer clouds, satellites overestimated CTH by 326 m (14 %) on average. When including multilayer clouds, satellites underestimated CTH by on average 169 m (5.8 %). MODIS collection 6 overestimated LWP by on average 13 g m−2 (11 %). Interestingly, LWP for MODIS collection 5.1 is slightly overestimated by Aqua (4.56 %) but is underestimated by Terra (14.3 %). This underestimation may be attributed to a known issue with a drift in the reflectance bands of the MODIS instrument on Terra. This evaluation indicates that the satellite cloud parameters selected show reasonable agreement with their ground-based counterparts over Finland, with minimal influence from the large solar zenith angle experienced by the satellites in this high-latitude location.

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.

scholarly journals How to estimate total differential attenuation due to hydrometeors with ground-based multi-frequency radars?

2020 ◽  
Author(s):  
Frédéric Tridon ◽  
Alessandro Battaglia ◽  
Stefan Kneifel
Keyword(s):  
Liquid Water ◽  
Microwave Radiometer ◽  
Particle Growth ◽  
Vertical Gradient ◽  
Liquid Droplets ◽  
Dual Frequency ◽  
Liquid Water Path ◽  
W Band ◽  
Frequency Ratios ◽  
Attenuation Corrected

Abstract. At millimeter wavelengths, attenuation by hydrometeors, such as liquid droplets or large snowflakes, is generally not negligible. When using multi-frequency ground-based radar measurements, it is common practice to use the Rayleigh targets at cloud top as a reference in order to derive attenuation-corrected reflectivities and meaningful dual-frequency ratios (DFR). By capitalizing on this idea, this study describes a new quality-controlled approach aiming at identifying regions of the cloud where particle growth is negligible. The core of the method is the identification of a Rayleigh plateau, i.e. a large enough region near cloud top where the vertical gradient of DFR remains small. By analyzing collocated Ka-W band radar and microwave radiometer (MWR) observations taken at two European sites under various meteorological conditions, it is shown how the resulting estimates of differential path-integrated attenuation (DeltaPIA) can be used to characterize hydrometeor properties. When the DeltaPIA is predominantly produced by cloud liquid droplets, this technique alone can provide accurate estimates of the liquid water path. When combined with MWR observations, this methodology paves the way towards profiling the cloud liquid water and/or quality flagging the MWR retrieval for rain/drizzle contamination and/or estimating the snow differential attenuation.

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