Search Results

You are looking at 1 - 10 of 10 items for

  • Author or Editor: Richard W. Stewart x
  • Refine by Access: All Content x
Clear All Modify Search
Richard W. Stewart

Abstract

Calculations have been completed on the structure of the ionosphere of Venus. Comparisons between these calculations and the results of the Mariner 5 and Venera 4 flights yield the following information on the structure of the Venus upper atmosphere: the ionosphere of Venus is of the F1 type; no more than 2% of the CO2 in the Venus ionosphere is dissociated; the relative abundance of N2 is ≤10%, in rough agreement with the Venus 4 limit of 7%; the exospheric temperature is 700±100K, the uncertainty in this result reflecting uncertainties in the CO2 vibrational deactivation coefficient and beating efficiency.

Full access
Richard W. Stewart

Abstract

Theoretical models of the Mars and Venus ionospheres are constructed and compared with the observed electron distributions in the upper atmospheres of these planets. It is found that a serious discrepancy exists between calculated and observed electron densities for all the Mariner flights if the presently accepted values of the solar extreme ultraviolet radiation are assumed to be the only ionization source. This result suggests the presence of a second source of ionization having an importance at least comparable to that of the ultra-violet. The proton flux that would be required to provide a source of ionization strong enough to bring the computed electron densities into agreement with observation is calculated, and a comparison of these flux values with those typical of the solar wind shows that the solar wind is a potentially important ionization source for the Mars and Venus upper atmospheres. A quantitative treatment of solar wind flow across the planetary bow shock and the subsequent ionization produced will be necessary before its actual importance can be established.

Full access
Richard W. Stewart

Abstract

Terms in the thermal conduction equation arising from infrared emissions and absorptions by atomic oxygen and carbon monoxide are investigated. The purpose of the investigation is to develop general expressions for the net emission by O and CO taking into account absorption of planetary radiation from below as well as radiation from regions of the mesosphere and thermosphere. These expressions are valid at all optical depths in the thermosphere. An expression for the net emission from a molecular band is also given.

The radiative terms are developed under the assumption of local thermodynamic equilibrium. The expressions developed for the radiative terms permit the evaluation of net heating as well as cooling in the O and CO emission lines.

The results are compared to the Bates' approximation to the radiative loss terms for a partly dissociated CO2 atmosphere which is optically thick in both O and CO. For this model it is found that, at high altitudes where the atmosphere is optically thin in O and CO, the net emission differs from the Bates' approximation by about 15% due to the effect of absorption. Near unit optical depth the net emission differs by more than an order of magnitude from the Bates' terms.

Full access
Joseph S. Hogan and Richard W. Stewart

Abstract

No abstract available.

Full access
Richard W. Stewart and Joseph S. Hogan

Abstract

No abstract available.

Full access
Richard W. Stewart and Martin I. Hoffert

Abstract

A time-dependent, one-dimensional model of the coupled chemistry and vertical mixing of the atmosphere is used to compute the distribution for many atmospheric constituents of the troposphere and stratosphere. The model treats the photochemistry of the carbon-hydrogen-oxygen-nitrogen system and is (with the exception of H2o) self-consistent in the sense of requiring no assumptions regarding minor constituent distributions.

Full access
Thomas R. Stewart, Richard W. Katz, and Allan H. Murphy

This paper reports some results of a descriptive study of the value of weather information used by fruit growers in the Yakima Valley of central Washington to decide when to protect their orchards against freezing temperatures. Specifically, the study provides data concerning the decision-making procedures of individual orchardists, the growers' use of weather information including frost (i.e., minimum temperature) forecasts, and the dimensions of the value of such forecasts.

Results from the descriptive study regarding the orchardists' information-processing and decision-making procedures are compared with the procedures included in a previous prescriptive study of the fruit-frost problem in the same geographical area (Katz et al., 1982). The prescriptive study employed a dynamic decision-making model and yielded estimates of the economic value of frost forecasts under the assumption (inter alia) that the orchardists' decisions were based solely on these forecasts. On the other hand, the descriptive study with which the current paper is primarily concerned indicates that growers use temperature and dew point observations available after the frost forecast has been issued, as well as the frost forecasts themselves, to make frost protection decisions. Furthermore, while the results of the descriptive study show that the grower makes a series of decisions to protect or not to protect during the night, the model assumed that an irreversible commitment is made early in the night. The results of an initial effort to modify the original prescriptive model in accordance with the descriptive findings to obtain more realistic estimates of the value of frost forecasts also are reported in this paper.

Some implications of this study for the further development of prescriptive models of the decision-making process in the fruit-frost context and in other weather-information-sensitive contexts are discussed.

Full access
William J. Koshak, Mike F. Stewart, Hugh J. Christian, James W. Bergstrom, John M. Hall, and Richard J. Solakiewicz

Abstract

The authors present in detail the laboratory apparatus and techniques that were used to complete a full radiometric calibration of two space-based lightning detectors: the optical transient detector (OTD) and the lightning imaging sensor (LIS) that were developed at the National Aeronautics and Space Administration Marshall Space Flight Center. These instruments are nadir-staring imagers that are optimized to detect and locate lightning from low-Earth orbit during day and night conditions. The radiometric calibration consisted of characterizing the pixel response to steady and transient optical sources, sensor field of view, and sensor spectral response. The transient optical signals produced in the calibration laboratory were used to derive estimates of sensor lightning detection efficiency.

Full access
Edward N. Rappaport, James L. Franklin, Lixion A. Avila, Stephen R. Baig, John L. Beven II, Eric S. Blake, Christopher A. Burr, Jiann-Gwo Jiing, Christopher A. Juckins, Richard D. Knabb, Christopher W. Landsea, Michelle Mainelli, Max Mayfield, Colin J. McAdie, Richard J. Pasch, Christopher Sisko, Stacy R. Stewart, and Ahsha N. Tribble

Abstract

The National Hurricane Center issues analyses, forecasts, and warnings over large parts of the North Atlantic and Pacific Oceans, and in support of many nearby countries. Advances in observational capabilities, operational numerical weather prediction, and forecaster tools and support systems over the past 15–20 yr have enabled the center to make more accurate forecasts, extend forecast lead times, and provide new products and services. Important limitations, however, persist. This paper discusses the current workings and state of the nation’s hurricane warning program, and highlights recent improvements and the enabling science and technology. It concludes with a look ahead at opportunities to address challenges.

Full access
Thomas C. Peterson, Richard R. Heim Jr., Robert Hirsch, Dale P. Kaiser, Harold Brooks, Noah S. Diffenbaugh, Randall M. Dole, Jason P. Giovannettone, Kristen Guirguis, Thomas R. Karl, Richard W. Katz, Kenneth Kunkel, Dennis Lettenmaier, Gregory J. McCabe, Christopher J. Paciorek, Karen R. Ryberg, Siegfried Schubert, Viviane B. S. Silva, Brooke C. Stewart, Aldo V. Vecchia, Gabriele Villarini, Russell S. Vose, John Walsh, Michael Wehner, David Wolock, Klaus Wolter, Connie A. Woodhouse, and Donald Wuebbles

Weather and climate extremes have been varying and changing on many different time scales. In recent decades, heat waves have generally become more frequent across the United States, while cold waves have been decreasing. While this is in keeping with expectations in a warming climate, it turns out that decadal variations in the number of U.S. heat and cold waves do not correlate well with the observed U.S. warming during the last century. Annual peak flow data reveal that river flooding trends on the century scale do not show uniform changes across the country. While flood magnitudes in the Southwest have been decreasing, flood magnitudes in the Northeast and north-central United States have been increasing. Confounding the analysis of trends in river flooding is multiyear and even multidecadal variability likely caused by both large-scale atmospheric circulation changes and basin-scale “memory” in the form of soil moisture. Droughts also have long-term trends as well as multiyear and decadal variability. Instrumental data indicate that the Dust Bowl of the 1930s and the drought in the 1950s were the most significant twentieth-century droughts in the United States, while tree ring data indicate that the megadroughts over the twelfth century exceeded anything in the twentieth century in both spatial extent and duration. The state of knowledge of the factors that cause heat waves, cold waves, floods, and drought to change is fairly good with heat waves being the best understood.

Full access