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PAUL A. DAVIS

Abstract

A basic objective of this study was to evaluate the applicability of medium-resolution satellite radiation measurements to assessments of the diabatic heating and cooling within the atmosphere. Data from portions of TIROS III orbital passes in mid-July 1961 and concurrent conventional data were examined over a 4-by-4-degree grid scale. Computations, appropriate to analyzed cloud conditions for each grid block, included the outgoing long-wave flux, the infrared radiational cooling, the total radiational cooling (including solar absorption in the atmosphere), and the total potential energy. In addition, simple relative estimates were made of the latent heat released and the average boundary heat flux into the atmosphere.

Results show that, for nadir angles less than about 45 deg., the unaltered Channel 2 temperature is proportional to the computed outgoing long-wave flux and is related to the average cloudiness in each grid block. The Channel 2 temperature has a higher positive correlation with the total radiational cooling (long-wave and short-wave) in the atmosphere than with the long-wave cooling alone. The relative heating from the distributions of net radiation and precipitation are correlated in the same sense to the Channel 2 temperature, but the relative boundary heat flux is correlated in the opposite sense. Unaltered Channel 3 fluxes show a general relationship to atmospheric solar absorption rates and to a cloudiness parameter for the grid scale.

Some slight generation of eddy potential energy was suggested by the analyses of the differential diabatic cooling.

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Paul A. Davis

Abstract

The infrared flux expressions, both upward and downward at an arbitrary reference level, are presented for two computational models. In one model the stipulated cloud and terrain surfaces are nontransparent, but not necessarily black, each with an emissivity given by the departure of the apparent reflectance from unity. The second model includes a semitransparent layer that is assigned an infinitesimal thickness and an emissivity given by the departure from unity of the sum of the reflectance and the transmittance. All significant simplifications that have been adopted in the application of the models are reviewed. Results from sample computations of total infrared flux, cooling rates, and simulated high-altitude views through a “window” region of the spectrum are presented. Surface effects are noted.

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Paul A. Davis

Abstract

A ruby lidar was mounted in an aircraft to obtain measurements of cirrus and haze layers concurrently with an airborne infrared radiometer during Project BOMEX in July 1969. The capability of the lidar for detecting cirrus or haze layers and for describing directly their range and thickness provided uniquely the information essential to a meaningful analysis of radiometric data. In addition to the geometric descriptions, analyses of lidar returns were performed to determine optical parameters. The procedure for conducting these analyses required that an average profile of the clear air backscattering coefficient in the troposphere above the boundary layer be established. Samples of lidar data and derived optical parameters are shown; one illustration includes data from a dense dust layer below an altitude of 12,000 ft.

Comparison of analyses of lidar and radiometric data from cirrus clouds indicated that the infrared transmittance (10.2–11.6 μ) was directly related to the geometric thickness of the cloud. This important statistical result suggests a basis for simplified modeling of the influence of cirrus on infrared transfer.

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Paul A. Davis

Abstract

With the aid of recent climatological data and laboratory radiation data, a meridional heat budget has been formed for the atmosphere below the 25-mb level and between 2ON and 7ON latitude. The significant components and balance requirements of the budget are presented as a function of height, latitude and season. Components of the budget include infrared radiative cooling, solar heating, net latent beating, the heat flux across the lower boundary, and the rate of heat storage. Balance requirements are those demanded solely of the atmospheric motions. Each item of the budget is discussed and some comparisons with related studies are included.

Although the heat sources produced an extensive lower layer of excessive heating, except in the arctic winter region, the total atmospheric columns revealed thermal deficits almost everywhere within the model. The convergences of the large-scale eddy heat transports determined by other investigators are sufficient to balance the deficits north of 50N latitude. Heat transports by mean meridional motions must become important balancing agents in the sub-tropical latitudes of the model, especially in winter.

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William Viezee and Paul A. Davis

Abstract

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Larry L. Stowe, Paul A. Davis, and E. Paul McClain

Abstract

An algorithm for the remote sensing of global cloud cover using multispectral radiance measurements from the Advanced Very High Resolution Radiometer (AVHRR) on board National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites has been developed. The CLAVR-1 (Clouds from AVHRR-Phase I) algorithm classifies 2 × 2 pixel arrays from the Global Area Coverage (GAC) 4-km-resolution archived database into CLEAR, MIXED, and CLOUDY categories. The algorithm uses a sequence of multispectral contrast, spectral, and spatial signature threshold tests to perform the classification. The various tests and the derivation of their thresholds are presented. CLAVR-1 has evolved through experience in applying it to real-time NOAA-11 data, and retrospectively through the NOAA AVHRR Pathfinder Atmosphere project, where 16 years of data have been reprocessed into cloud, radiation budget, and aerosol climatologies. The classifications are evaluated regionally with image analysis, and it is concluded that the algorithm does well at classifying perfectly clear pixel arrays, except at high latitudes in their winter seasons. It also has difficulties with classifications over some desert and mountainous regions and when viewing regions of ocean specular reflection. Generally, the CLAVR-1 fractional cloud amounts, when computed using a statistically equivalent spatial coherence method, agree to within about 0.05–0.10 of image/analyst estimates on average. There is a tendency for CLAVR-1 to underestimate cloud amount when it is large and to overestimate it when small.

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Gang Luo, Paul A. Davis, Larry L. Stowe, and E. Paul McClain

Abstract

An automated pixel-scale algorithm has been developed to retrieve cloud type, related cloud layer(s), and the fractional coverages for all cloud layers in each AVHRR (Advanced Very High Resolution Radiometer) pixel at night. In the algorithm, cloud-contaminated pixels are separated from cloud-free pixels and grouped into three generic cloud types. Cloud layers in each cloud type are obtained through a cloud-type uniformity check, a thermal uniformity check, and a channel 4 ( 11 μm) brightness temperature histogram analysis, within a grid area. The algorithm allows for pixels to be mixed among different cloud layers of different cloud types, as well as between cloud layers and the ocean or land surface. A “neighbor-cheek” method is developed to identify the cloud layers associated with each mixed pixel and to calculate the coverages of each of the cloud layers in the pixel. Digital color images are generated based on information on the location, cloud type, cloud layer, and cloud amount of each individual pixel. Visualization comparisons show good agreement between color-coded images and the standard black and white satellite images. The results of the pixel-scale algorithm also show good agreements with the spatial coherence analysis and with National Weather Service surface and radiosonde observations. The pixel-scale algorithm has been developed for use in validation of output from CLAYR (clouds from AVHRR) project algorithms.

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Hermann E. Gerber, Paul A. Allee, Ulprich Katz, Charles I. Davis, and Lewis O. Grant

Abstract

The Goetz Aerosol Spectrometer, generally considered to possess only a fair ability in resolving size distributions of polydispersed aerosols, operates properly following a modification to the geometry of the entrance to the instrument's deposition channels. Its accuracy is demonstrated with an electron microscopic evaluation of a collecting surface deposit of a thermally produced polydispersed AgI aerosol with particle sizes ranging from 60 to 1000Å In diameter.

Thus calibrated, the instrument was utilized to investigate the activity of the same aerosol as freezing nuclei. The AgI particles on the hydrophobic chrome-plated collecting foil were nucleated by sorption at water saturation for temperatures of −15 and −20C. The results appear to reflect the influence of the Kelvin effect since the activity decreased at a faster rate than predicted by the “surface area rare” and since it showed a sharp cutoff corresponding to Fletcher's theoretical size temperature predictions for ideal sublimation nuclei.

Also, field measurements were conducted on 12,000-ft Chalk Mountain (Climax, Colo.) for the purpose of measuring the sizes of active AgI-NaI nuclei emanating from acetone ground generators located at least 6 mi upwind. The size distribution of the nuclei on seeding days proved similar to what might he expected from this generator type. On non-seeding days, the number of active nuclei decreased sharply while the peak of the size distributions shifted to larger sizes.

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Bart Geerts, David J. Raymond, Vanda Grubišić, Christopher A. Davis, Mary C. Barth, Andrew Detwiler, Petra M. Klein, Wen-Chau Lee, Paul M. Markowski, Gretchen L. Mullendore, and James A. Moore

Abstract

Recommendations are presented for in situ and remote sensing instruments and capabilities needed to advance the study of convection and turbulence in the atmosphere. These recommendations emerged from a community workshop held on 22–24 May 2017 at the National Center for Atmospheric Research and sponsored by the National Science Foundation. Four areas of research were distinguished at this workshop: i) boundary layer flows, including convective and stable boundary layers over heterogeneous land use and terrain conditions; ii) dynamics and thermodynamics of convection, including deep and shallow convection and continental and maritime convection; iii) turbulence above the boundary layer in clouds and in clear air, terrain driven and elsewhere; and iv) cloud microphysical and chemical processes in convection, including cloud electricity and lightning.

The recommendations presented herein address a series of facilities and capabilities, ranging from existing ones that continue to fulfill science needs and thus should be retained and/or incrementally improved, to urgently needed new facilities, to desired capabilities for which no adequate solutions are as yet on the horizon. A common thread among all recommendations is the need for more highly resolved sampling, both in space and in time. Significant progress is anticipated, especially through the improved availability of airborne and ground-based remote sensors to the National Science Foundation (NSF)-supported community.

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Paul W. Staten, Kevin M. Grise, Sean M. Davis, Kristopher B. Karnauskas, Darryn W. Waugh, Amanda C. Maycock, Qiang Fu, Kerry Cook, Ori Adam, Isla R. Simpson, Robert J Allen, Karen Rosenlof, Gang Chen, Caroline C. Ummenhofer, Xiao-Wei Quan, James P. Kossin, Nicholas A. Davis, and Seok-Woo Son

Abstract

Over the past 15 years, numerous studies have suggested that the sinking branches of Earth’s Hadley circulation and the associated subtropical dry zones have shifted poleward over the late twentieth century and early twenty-first century. Early estimates of this tropical widening from satellite observations and reanalyses varied from 0.25° to 3° latitude per decade, while estimates from global climate models show widening at the lower end of the observed range. In 2016, two working groups, the U.S. Climate Variability and Predictability (CLIVAR) working group on the Changing Width of the Tropical Belt and the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project, were formed to synthesize current understanding of the magnitude, causes, and impacts of the recent tropical widening evident in observations. These working groups concluded that the large rates of observed tropical widening noted by earlier studies resulted from their use of metrics that poorly capture changes in the Hadley circulation, or from the use of reanalyses that contained spurious trends. Accounting for these issues reduces the range of observed expansion rates to 0.25°–0.5° latitude decade‒1—within the range from model simulations. Models indicate that most of the recent Northern Hemisphere tropical widening is consistent with natural variability, whereas increasing greenhouse gases and decreasing stratospheric ozone likely played an important role in Southern Hemisphere widening. Whatever the cause or rate of expansion, understanding the regional impacts of tropical widening requires additional work, as different forcings can produce different regional patterns of widening.

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