On the relationship between water vapor over the oceans and sea surface temperature

Monthly mean precipitable water data obtained from passive microwave radiometry were correlated with the National Meteorological Center (NMC) blended sea surface temperature data. It is shown that the monthly mean water vapor content of the atmosphere above the oceans can generally be prescribed from the sea surface temperature with a standard deviation of 0.36 g/sq cm. The form of the relationship between precipitable water and sea surface temperature in the range T(sub s) greater than 18 C also resembles that predicted from simple arguments based on the Clausius-Clapeyron relationship. The annual cycle of the globally integrated mass of Scanning Multichannel Microwave Radiometer (SMMR) water vapor is shown to differ from analyses of other water vapor data in both phase and amplitude and these differences point to a significant influence of the continents on water vapor. Regional scale analyses of water vapor demonstrate that monthly averaged water vapor data, when contrasted with the bulk sea surface temperature relationship developed in this study, reflect various known characteristics of the time mean large-scale circulation over the oceans. A water vapor parameter is introduced to highlight the effects of large-scale motion on atmospheric water vapor. Based on the magnitude of this parameter, it is shown that the effects of large-scale flow on precipitable water vapor are regionally dependent, but for the most part, the influence of circulation is generally less than about + or - 20 percent of the seasonal mean

Cirrus clouds and climate feedback: Is the sky falling and should we go tell the king

It is widely believed that thin cirrus clouds act to enhance the greenhouse effect owing to a particular combination of their optical properties. It is demonstrated how this effect is perhaps based on inadequate resolution of the physics of cirrus clouds and that the more likely impact of cirrus clouds to climate change remains somewhat elusive. These conclusions are developed within the context of a specific feedback mechanism incorporated into a simple mechanistic climate model. A specific scientific question addressed is whether or not the observed relationship between the ice water content and temperature of cirrus provides any significant feedback to the CO2 greenhouse warming. A related question also examined concerns the specific role of cloud microphysics and radiation in this feedback. This raises several pertinent issues about the understanding of cirrus clouds and their likely role in climate change as there presently exists a considerable uncertainty about the microphysics of these clouds (size and shape of ice crystals) and their radiative influences

Linear and nonlinear aspects of the tropical 30-60 day oscillation: A modeling study

The scientific problem focused on study of the tropical 30-60 day oscillation and explanation for this phenomenon is discussed. The following subject areas are covered: the scientific problem (the importance of low frequency oscillations; suggested mechanisms for developing the tropical 30-60 day oscillation); proposed research and its objective; basic approach to research; and results (satellite data analysis and retrieval development; thermodynamic model of the oscillation; the 5-level GCM)

Radiative properties of visible and subvisible Cirrus: Scattering on hexagonal ice crystals

One of the main objectives of the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) is to provide a better understanding of the physics of upper level clouds. The focus is on just one specific aspect of cirrus physics, namely on characterizing the radiative properties of single, nonspherical ice particles. The basis for further more extensive studies of the radiative transfer through upper level clouds is provided. Radiation provides a potential mechanism for strong feedback between the divergence of in-cloud radiative flux and the cloud microphysics and ultimately on the dynamics of the cloud. Some aspects of ice cloud microphysics that are relevant to the radiation calculations are described. Next, the Discrete Dipole Approximation (DDA) is introduced and some new results of scattering by irregular crystals are presented. The Anomalous Diffraction Theory (ADT) was adopted to investigate the scattering properties of even larger crystals. In this way the scattering properties of nonspherical particles were determined over a range of particle sizes

Equilibrium climate modeling with a one dimensional coupled atmosphere-ocean model

December 1987.Includes bibliographical references.Sponsored by NSF ATM-8415127

On the properties of cirrus clouds over the tropical West Pacific

June 2002.Includes bibliographical references.Sponsored by DOE/ARM DE-FG03-94ER61748.Sponsored by DOE/ARM DE-FG03-98ER62569

Physical/optical model for atmospheric aerosols with application to visibility problems, A

January 1990.Date taken from cataloging record.Includes bibliographical references.The objectives of this report are to describe a conceptually simple but accurate model for efficiently computing the optical properties of atmospheric aerosols. Aerosol characteristics such as size distribution, solubility, mixture and the atmospheric moisture effect are taken into account when computing its optical properties. The dependence of the latter on aerosol microstructure is also discussed. The optical properties of aerosols are computed by employing numerically stable algorithms for obtaining Mie solutions to coated spheres. Resulting bulk quantities such as the extinction/backscatter coefficient, the probability of scattering, and the scattering phase matrix can be incorporated into multiple scattering schemes of radiative transfer for visibility investigations and other types of studies.Research supported by National Park Service through the Cooperative Institute for Research in the Atmosphere, Grant DOC-NOAA-NA85RAH05045

Microwave remote sensing algorithms for cirrus clouds and precipitation

Sponsored by NASA NAG-5-1592S

Evaluation of International Satellite Cloud Climatology Project (ISCCP) D2 cloud amount changes and their connections to large-scale dynamics

August 2005.Includes bibliographical references (pages 88-91).The International Satellite Cloud Climatology Project (ISCCP) D2 dataset exhibits a 2.6% per decade decrease in the global all-cloud cloud amount from July 1983 through September 2001. This result is consistent with other recent findings that provide evidence that the cloud amount has decreased on a decadal-scale. Such changes in cloud amount should have an obvious impact on the climate system through changes in heating and the radiation budget of the atmosphere. However, the changes evident in the ISCCP data seem too large to be accepted without question. Because these data are used as a verification tool for the global climate modeling community, it is imperative that the nature of these changes are better understood and verified for similarities with other data sources. Otherwise, climate studies might be comparing their results with faulty information. This study represents an attempt to characterize and verify the ISCCP D2 cloud amount changes. One possible reason why the ISCCP D2 trend might be too large is the presence of artifacts in the data related to changes in the number of geosynchronous satellites in orbit. This leads to changes in the viewing angle for each pixel in the dataset and explains roughly one-third of the trend in the global cloud amount. In order to account for this phenomenon, this study focuses on the region from 90°E to 180° and 30°N to 30°S where the satellite coverage has been relatively constant. It is shown that the slope of the cloud amount change in this region is still very large. This leaves open the possibility that there is other contamination in the ISCCP data, and calls into question the validity of the large cloud amount trend. Several steps are taken to examine the nature of the cloud amount changes in this region. First of all, the changes in the ISCCP cloud amount data are characterized by three criteria: where and when the changes are occurring and the types of clouds expressing them. These patterns are examined for features that appear physically reasonable. These patterns can then be checked against patterns obtained from the NOAA Interpolated OLR and PATMOS-A cloud amount datasets. These data, from sensors mounted on polar-orbiting satellites, do not experience the viewing-angle problem of ISCCP but should still corroborate evidence of real cloud amount changes. The most unique aspect of this study is the use of reanalysis data to look for signals of climate change that are related to changes in the ISCCP cloud amount data. The average ISCCP all-cloud cloud amount for the region of interest is regressed onto wind fields, geopotential height fields, divergence fields, and other data that represent how the climate has changed over the span of the ISCCP dataset. Maps of regression coefficients represent how those fields change in response to a unit increase in cloud amount. These patterns help to identify atmospheric phenomena that are connected with variations in cloud amount in the region of interest. Furthermore, the true cloud amount trend in the region of interest can be diagnosed by making time series of how well the regression maps project onto reanalysis fields at each time step. These "proxy cloud time series" represent how the true cloud amount must be changing to effect the observable changes in the reanalysis data. Both results provide a unique way to discover whether the ISCCP D2 cloud amount changes are also evident in other data sources. It is shown that the cloud amount changes evident in the ISCCP D2 dataset are indicative of changes in the intensity and location of convection associated with the Inter-Tropical Convergence Zone (ITCZ). The spatial patterns of these changes are somewhat consistent with the NOAA Interpolated OLR and PATMOS-A cloud amount datasets. However the trends in the regionally averaged time series of these data are not significantly different from zero. This supports the conclusion that the ISCCP trend is too large. Using data from the NCEPNCAR reanalysis and the ERA-40 reanalysis, it is shown that the changes in the ISCCP D2 cloud amount time series in the region of interest are highly correlated with changes in the Walker-Hadley circulation. The patterns of these changes are consistent with the redistribution of convection indicated by each of the satellite datasets, and appear to be associated with ENSO since they are also consistent with the results of Bjerknes (1969). The reanalysis data also provide independent confirmation that the actual cloud amount in the region of interest is likely not changing in a statistically significant way during the period spanned by the ISCCP D2 dataset. Therefore, while the variability of cloud amount due to ENS0 is evidently captured by the ISCCP D2 dataset, the long-term trend in the ISCCP cloud amount is likely not physically realistic.Research was supported by NASA Research grant NNG04GB97G and in part by a one-year AMS Graduate Fellowship