Showing papers by "Kenneth Sassen published in 2002"
TL;DR: CloudSat as discussed by the authors is a satellite experiment designed to measure the vertical structure of clouds from space, and once launched, CloudSat will orbit in formation as part of a constellation of satellites (the A-Train) that includes NASA's Aqua and Aura satellites, a NASA-CNES lidar satellite (CALIPSO), and a CNES satellite carrying a polarimeter (PARASOL).
Abstract: CloudSat is a satellite experiment designed to measure the vertical structure of clouds from space. The expected launch of CloudSat is planned for 2004, and once launched, CloudSat will orbit in formation as part of a constellation of satellites (the A-Train) that includes NASA's Aqua and Aura satellites, a NASA–CNES lidar satellite (CALIPSO), and a CNES satellite carrying a polarimeter (PARASOL). A unique feature that CloudSat brings to this constellation is the ability to fly a precise orbit enabling the fields of view of the CloudSat radar to be overlapped with the CALIPSO lidar footprint and the other measurements of the constellation. The precision and near simultaneity of this overlap creates a unique multisatellite observing system for studying the atmospheric processes essential to the hydrological cycle. The vertical profiles of cloud properties provided by CloudSat on the global scale fill a critical gap in the investigation of feedback mechanisms linking clouds to climate. Measuring these profi...
1,929 citations
TL;DR: In this paper, the polarization lidar data presented for illustration here suggest that the dust particles, which are indicated to be especially active ice nuclei, can affect the formation and phase of clouds, and hence alter their radiative properties at least as far away as the eastern Great Basin of the US.
Abstract: [1] Aerosols lofted to high altitudes by springtime Asian dust storms advect across the Pacific Ocean and, as recognized in recent years, regularly reach the western US. As part of our long-term cirrus cloud research program using remote sensing measurements, we have observed unusually warm cirrus ice clouds associated with transported Asian dust aerosols. The polarization lidar data presented for illustration here suggest that the dust particles, which are indicated to be especially active ice nuclei, can affect the formation and phase of clouds, and hence alter their radiative properties at least as far away as the eastern Great Basin of the US.
178 citations
TL;DR: In this paper, a retrieval algorithm is described to estimate vertical profiles of cirrus-cloud ice water content (IWC) and general effective size Dge from combined lidar and radar measurements.
Abstract: A retrieval algorithm is described to estimate vertical profiles of cirrus-cloud ice water content (IWC) and general effective size Dge from combined lidar and radar measurements. In the algorithm, the lidar extinction coefficient σ is parameterized as σ = IWC[a0 + (a1/Dge)] and water equivalent radar reflectivity factor Ze is parameterized as Ze = C′(IWC/ρi)Dbge, where a0, a1, C′, and b are constants based on the assumption of a modified gamma size distribution and hexagonal ice crystals. A comparison of retrieved results from a cirrus-cloud case study with aircraft in situ measurements indicates that the algorithm can provide reliable cirrus cloud microphysical properties. A technique to estimate ice water path and layer-mean Dge is also developed using the optical depth and mean radar reflectivity factor of the cloud layer.
139 citations
TL;DR: In this article, the authors applied the lidar-radar algorithm to ∼1000 h of Raman lidar and millimeter wave cloud radar (MMCR) data collected at the Atmospheric Radiation Measurement program Southern Great Plains Clouds and Radiation Testbed site in Oklahoma during the period from November 1996 to November 2000.
Abstract: The lidar–radar algorithm described in Part I of this set of papers is applied to ∼1000 h of Raman lidar and millimeter wave cloud radar (MMCR) data collected at the Atmospheric Radiation Measurement program Southern Great Plains Clouds and Radiation Testbed site in Oklahoma during the period from November 1996 to November 2000. The resulting statistics of cirrus microphysical and radiative properties show that most cirrus clouds are optically thin (mean optical depth of 0.58 with a standard deviation of 0.67) with low ice water path (mean 12.19 g m−2 with a standard deviation of 19.0). The seasonal changes of cirrus properties are relatively small except for the general effective radius (Dge). Strong temperature dependencies of ice water content, Dge, and extinction coefficients are found in the dataset, which are well described by second-order polynomial functions. The temperature and thickness dependencies of the cirrus properties are studied in detail, providing information useful in the vali...
104 citations
TL;DR: In this article, the gamma-weighted radiative transfer (GWRT) scheme was used to compensate for the solar albedo bias in the domain-averaged cloud optical depth.
Abstract: High ice cloud horizontal inhomogeneity is examined using optical depth retrievals from four midlatitude datasets. Three datasets include ice cloud microphysical profiles derived from millimeter cloud radar at the Southern Great Plains Atmospheric Radiation Measurement site in Oklahoma. A fourth dataset combines lidar and midinfrared radiometry (LIRAD), and is from the Facility for Atmospheric Remote Sensing at the University of Utah, Salt Lake City, Utah. Plane-parallel homogeneous (PPH) calculations of domain-averaged solar albedo for these four datasets are compared to independent column approximation (ICA) results. A solar albedo bias up to 25% is found over a low reflective surface at a high solar zenith angle. A spherical solar albedo bias as high as 11% is shown. The gamma-weighted radiative transfer (GWRT) scheme is shown to be an effective correction for the solar albedo bias suitable for GCM applications. The GWRT result was, in all cases, within 1‐2 Wm 22 of the ICA outgoing solar flux. The GWRT requires a parameterization of the standard deviation of cloud optical depth. It is suggested that the domain-averaged cloud optical depth and ice water path together can be used in a parameterization to account for 80% of the standard deviation in optical depth.
58 citations
TL;DR: In this article, a series of cirrus cloud simulations performed using a model with explicit cloud microphysics is applied to testing ice water content retrieval algorithms based on millimeter-wave radar reflectivity measurements.
Abstract: A series of cirrus cloud simulations performed using a model with explicit cloud microphysics is applied to testing ice water content retrieval algorithms based on millimeter-wave radar reflectivity measurements. The simulated ice particle size spectra over a 12-h growth/dissipation life cycle are converted to equivalent radar reflectivity factors Ze and visible optical extinction coefficients σ, which are used as a test dataset to intercompare the results of various algorithms. This approach shows that radar Ze-only approaches suffer from significant problems related to basic temperature-dependent cirrus cloud processes, although most algorithms work well under limited conditions (presumably similar to those of the empirical datasets from which each was derived). However, when lidar or radiometric measurements of σ or cloud optical depth are used to constrain the radar data, excellent agreement with the modeled contents can be achieved under the conditions simulated. Implications for the satelli...
49 citations
18 Apr 2002
28 citations
TL;DR: In this article, a remote sensing methodology involving the retrieval of three-dimensional ice water content and ice crystal mean size of cirrus clouds based on a unification of satellite and ground-based cloud profiling radar observations is presented.
Abstract: [1] We have innovated a remote sensing methodology involving the retrieval of three-dimensional ice water content and ice crystal mean size of cirrus clouds based on a unification of satellite and ground-based cloud profiling radar observations. This methodology has been applied to AVHRR/NOAA satellite data and mm-wave cloud radar data obtained from the DOE's ARM program in northern Oklahoma. The three-dimensional cloud parameter fields thus constructed are assessed with ice crystal size distributions independently derived from measurements by optical probes on board the University of North Dakota Citation. The retrieved three-dimensional ice water contents and mean effective ice crystal sizes involving an impressive cirrus cloud occurring on April 18, 1997, are shown to be comparable to those derived from the analysis of collocated and coincident in situ aircraft measurements.
12 citations
3 citations
01 Jan 2002
TL;DR: In this article, a remote sensing methodology involving the retrieval of three-dimensional ice water content and ice crystal mean size of cirrus clouds based on a unification of satellite and ground-based cloud profiling radar observations is presented.
Abstract: [1] We have innovated a remote sensing methodology involving the retrieval of three-dimensional ice water content and ice crystal mean size of cirrus clouds based on a unification of satellite and ground-based cloud profiling radar observations. This methodology has been applied to AVHRR/NOAA satellite data and mm-wave cloud radar data obtained from the DOE's ARM program in northern Oklahoma. The three-dimensional cloud parameter fields thus constructed are assessed with ice crystal size distributions independently derived from measurements by optical probes on board the University of North Dakota Citation. The retrieved three-dimensional ice water contents and mean effective ice crystal sizes involving an impressive cirrus cloud occurring on April 18, 1997, are shown to be comparable to those derived from the analysis of collocated and coincident in situ aircraft measurements.