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Author: Chenxi Wang Publisher: ISBN: Category : Languages : en Pages : 180
Book Description
This dissertation focuses on the global investigation of optically thin cirrus cloud optical thickness [tau] and microphysical properties, such as, effective particle size (D_(eff)) and ice crystal habits (shapes), based on the global satellite observations and fast radiative transfer models (RTMs). In the first part, we develop two computationally efficient RTMs simulating satellite observations under cloudy-sky conditions in the visible/shortwave infrared (VIS/SWIR) and thermal inferred (IR) spectral regions, respectively. To mitigate the computational burden associated with absorption, thermal emission and multiple scattering, we generate pre-computed lookup tables (LUTs) using two rigorous models, i.e., the line-by-line radiative transfer model (LBLRTM) and the discrete ordinates radiative transfer model (DISORT). The second part introduces two methods (i.e., VIS/SWIR- and IR-based methods) to retrieve [tau] and D_(eff) from satellite observations in corresponding spectral regions of the two RTMs. We discuss the advantages and weakness of the two methods by estimating the impacts from different error sources on the retrievals through sensitivity studies. Finally, we develop a new method to infer the scattering phase functions of optically thin cirrus clouds in a water vapor absorption channel (1.38-[mu]m). We estimate the ice crystal habits and surface structures by comparing the inferred scattering phase functions and numerically simulated phase functions calculated using idealized habits. We find two critical features of the two retrieval methods: (1) the IR-based method is more sensitive to optically thin cirrus cloud, and (2) the VIS/SWIR-based method is more sensitive to the pre-assumed ice cloud microphysical parameterization schemes. We derive the optically thin cirrus cloud phase functions based on the two methods. We find that small column-like particles (e.g., solid columns and column-aggregates) and droxtals with rough surfaces are likely to reside in optically thin cirrus clouds. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151213
Author: Chenxi Wang Publisher: ISBN: Category : Languages : en Pages : 180
Book Description
This dissertation focuses on the global investigation of optically thin cirrus cloud optical thickness [tau] and microphysical properties, such as, effective particle size (D_(eff)) and ice crystal habits (shapes), based on the global satellite observations and fast radiative transfer models (RTMs). In the first part, we develop two computationally efficient RTMs simulating satellite observations under cloudy-sky conditions in the visible/shortwave infrared (VIS/SWIR) and thermal inferred (IR) spectral regions, respectively. To mitigate the computational burden associated with absorption, thermal emission and multiple scattering, we generate pre-computed lookup tables (LUTs) using two rigorous models, i.e., the line-by-line radiative transfer model (LBLRTM) and the discrete ordinates radiative transfer model (DISORT). The second part introduces two methods (i.e., VIS/SWIR- and IR-based methods) to retrieve [tau] and D_(eff) from satellite observations in corresponding spectral regions of the two RTMs. We discuss the advantages and weakness of the two methods by estimating the impacts from different error sources on the retrievals through sensitivity studies. Finally, we develop a new method to infer the scattering phase functions of optically thin cirrus clouds in a water vapor absorption channel (1.38-[mu]m). We estimate the ice crystal habits and surface structures by comparing the inferred scattering phase functions and numerically simulated phase functions calculated using idealized habits. We find two critical features of the two retrieval methods: (1) the IR-based method is more sensitive to optically thin cirrus cloud, and (2) the VIS/SWIR-based method is more sensitive to the pre-assumed ice cloud microphysical parameterization schemes. We derive the optically thin cirrus cloud phase functions based on the two methods. We find that small column-like particles (e.g., solid columns and column-aggregates) and droxtals with rough surfaces are likely to reside in optically thin cirrus clouds. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151213
Author: National Aeronautics and Space Adm Nasa Publisher: Independently Published ISBN: 9781723942761 Category : Science Languages : en Pages : 92
Book Description
The First International Satellite Cloud Climatology Regional Experiment (FIRE) program has the goal of improving our capabilities to understand, model and detect the properties of climatically-important clouds. This is being undertaken through a three-pronged effort of modeling, long-term observations and short-term intensive field studies. Through examination of satellite and other data it is apparent that stratus and cirrus cloud types have the greatest impact on climate due to their radiative effects and ubiquitous nature. As a result, the FIRE program has developed two paths of investigation, each having its own subset of research objectives and measurement programs. The work conducted under this grant was directed toward furthering our understanding of cirrus cloud systems. While it is known that cirrus are climatically important, the magnitude and even sign of the impact is unclear. Cirrus clouds affect the transfer of radiation according to their physical depth and location in the atmosphere and their microphysical composition. However, significant uncertainties still exist in how cirrus clouds form and how they are maintained, what their physical properties are and how they can be parameterized in numerical models. Better remote sensing techniques for monitoring cirrus cloud systems and improved modeling of radiative transfer through ice particles are also needed. A critical element in resolving these issues is a better understanding of cirrus cloud microphysical properties and how they vary. The focus of the research to be conducted under this grant was th data collected in situ by the University of North Dakota Citation aircraft. The goals of this research were to add to the body of knowledge of cirrus cloud microphysics, particularly at the small end of the size spectrum; and analyze the spatial variation of cirrus clouds.Poellot, Michael R. and Grainger, Cedric A.Langley Research CenterCIRRUS CLOUDS; REMOTE SENSING; CLOUD PHYSICS; MATHEMATICAL MODELS; IS
Author: David K. Lynch Publisher: Oxford University Press, USA ISBN: 0195130723 Category : Cirrus clouds Languages : en Pages : 499
Book Description
This text, devoted entirely to cirrus clouds, captures the state of knowledge of cirrus clouds and serves as a practical handbook as well.
Author: Robert S. Stone Publisher: ISBN: Category : Cloud physics Languages : en Pages : 113
Book Description
In this study, differences between narrowband near infrared (NIR) and infrared (IR) brightness temperatures are related to cloud optical depth providing a theoretical basis for determining cirrus optical properties from combined satellite images.
Author: Publisher: ISBN: Category : Languages : en Pages : 13
Book Description
To understand the radiative impact of tropical thin cirrus clouds, the frequency of occurrence and optical depths of these clouds have been derived. "Thin" cirrus clouds are defined here as being those that are not detected by the operational Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask, corresponding to an optical depth value of approximately 0.3 or smaller, but that are detectable in terms of the cirrus reflectance product based on the MODIS 1.375-micron channel. With such a definition, thin cirrus clouds were present in more than 40% of the pixels flagged as "clear sky" by the operational MODIS cloud mask algorithm. It is shown that these thin cirrus clouds are frequently observed in deep convective regions in the western Pacific. Thin cirrus optical depths were derived from the cirrus reflectance product. Regions of significant cloud fraction and large optical depths were observed in the Northern Hemisphere during the boreal spring and summer and moved southward during the boreal autumn and winter. The radiative effects of tropical thin cirrus clouds were studied on the basis of the retrieved cirrus optical depths, the atmospheric profiles derived from the Atmospheric Infrared Sounder (AIRS) observations, and a radiative transfer model in conjunction with a parameterization of ice cloud spectral optical properties. To understand how these clouds regulate the radiation field in the atmosphere, the instantaneous net fluxes at the top of the atmosphere (TOA) and at the surface were calculated. The present study shows positive and negative net forcings at the TOA and at the surface, respectively. The positive (negative) net forcing at the TOA (surface) is due to the dominance of longwave (shortwave) forcing. Both the TOA and surface forcings are in a range of 0-20 W/sq m, depending on the optical depths of thin cirrus clouds.
Author: Yong-Keun Lee Publisher: ISBN: Category : Languages : en Pages :
Book Description
This dissertation reports on three different yet related topics in light scattering computation, radiative transfer simulation, and remote sensing implementation, regarding the cloud properties and the retrieval of cloud properties from satellite-based infrared radiometric measurements. First, the errors associated with the use of circular cylinders as surrogates for hexagonal columns in computing the optical properties of pristine ice crystals at infrared (8-12 [micron]) wavelengths are investigated. It is found that the differences between the results for circular cylinders and hexagonal columns are on the order of a few percent at infrared wavelengths. Second, investigated in this dissertation are the outgoing broadband longwave and window channel radiances at the top-of-atmosphere under clear-sky conditions on the basis of the data acquired by the Cloud and the Earth's Radiant Energy System (CERES) instrument onboard the NASA Terra satellite platform. Based on the comparison of the observed broadband radiances with those obtained from rigorous radiative transfer simulations, it is found that the theoretical results tend to be larger than their measured counterparts. Extensive sensitivity studies regarding the uncertainties of various parameters were carried out. Within the considered uncertainties of various factors, the computed radiances are still larger than the observed radiances if thin cirrus clouds are excluded. Thus, a potential cause for the differences could be associated with the presence of thin cirrus clouds whose visible optical thickness is smaller than approximately 0.3. Third, presented in this dissertation is an illustration of the application of hyperspectral infrared channel observations to the retrieval of the cloud properties. Specifically, the hyperspectral measurements acquired from the Atmospheric Infrared Sounder (AIRS) aboard the NASA Aqua platform are used to infer cloud top pressure, effective cloud amount, cloud thermodynamic phase, cloud optical thickness, and the effective size of cloud particles. The AIRS-based retrievals are compared with the counterparts of the operational cloud products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). The two retrievals agree reasonably well except for the retrieved cloud effective particle size. Furthermore, the diurnal and seasonal contrasts of cloud properties are also investigated on the basis of the cloud properties retrieved from the AIRS data.
Author: Publisher: ISBN: Category : Languages : en Pages : 7
Book Description
The main work activity during this period was the refinement and GCM parameterization of the treatment of ice cloud radiative properties, developed for this project. The treatment has now been rigorously tested and improved, and can now be used with confidence in radiation transfer schemes. The ice Cloud radiation scheme has also proven useful in satellite remote sensing. The radiation scheme differs from others in the thermal infrared, where it is assumed that photon tunneling does not occur for real ice particles (tunneling can be viewed as a process by which photons outside a particle's area-cross section can still be absorbed). Single particle T-matrix and Mie calculations suggest that a particle's ability to capture energy through tunneling depends on surface morphology, with more tunneling the more circular (or less angular) a surface is. This assumption leads to retrievals of mean particle size which are similar to those observed in tropical cirrus by optical imaging probes, whereas retrieved sizes using Mie theory are about 1/3 those predicted by this scheme. The retrieval method requires channels in the 8--9 [mu]m and 11--12 [mu]m ranges. This assumption about tunneling, as well as treating size distributions in the radiation scheme as bimodal, allows retrievals over a broader range of mean particle size than previous schemes permitted, making such size retrievals applicable to most types of cirrus clouds.
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781725112667 Category : Languages : en Pages : 28
Book Description
The 8 to 13 micron spectral region is an important atmospheric window for radiometric studies of the Earth's surface and clouds. Most of the Earth-atmosphere longwave radiative loss to space occurs in this spectral region. Selective gaseous absorption in this window occurs in the 9.6 micron ozone band with the remaining absorption dominated by the water vapor continuum. Cirrus clouds have a large impact on the transmittance of this atmospheric window region; it is therefore important to understand the interaction of cirrus cloud with the radiation field for climate studies and in the interpretation of satellite radiometric measurements. The focus was to employ observations of the High-resolution Interferometer Sounder (HIS) made during First ISCCP Regional Experiment (FIRE) to improve the understanding of the radiative properties of cirrus clouds within this window region. Studies were undertaken to investigate the coupling between the microphysical properties of cirrus clouds and their spectral variation within this window region. Extensions of the HIS studies to satellite measurements, with regards to remote sensing and interpretation, were also investigated. Smith, William L. and Ackerman, Steven A. Unspecified Center NASA-CR-186365, NAS 1.26:186365 NAG1-1015...
Author: Chenxi Wang
Author: Chenxi Wang
Author: National Aeronautics and Space Adm Nasa
Author: David K. Lynch
Author: Robert S. Stone
Author: 
Author: Yong-Keun Lee
Author: 
Author: Я Зембницкий
Author: Erik R. Olson
Author: National Aeronautics and Space Administration (NASA)