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Robert W. Fett

Abstract

A study of the movement of orographic cloud plumes from one island to another in the Svalbard-Novaya Zemlya region of the Barents Sea revealed a close association with similar movements of arctic fronts. Strong northerly winds behind arctic fronts, moving southward from over the ice into the Barents Sea, cause a rapid movement of the leading edge of the marginal ice zone (MIZ) in a similar southward direction, opening up many leads and polynyas in the process. This paper shows examples illustrating the effect as documented by Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA) Advanced Very High-Resolution Radiometer (AVHRR) high-resolution picture transmission (HRPT) satellite data. It is worth noting that, despite clear satellite evidence of the movement of two strong arctic fronts into the Barents Sea over a 4-day period, neither American nor Norwegian operational surface analyses were drawn especially well to reflect these events. The study emphasizes the need for forecasters to have ready access to near real-time, high-resolution, satellite imagery over the region on a frequent basis in order to forecast properly the movement of fronts and associated movement of the ice edge toward open waters to the south.

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MAJOR ROBERT W. FETT

Abstract

Three ESSA II views and a Nimbus II view of tropical cyclone Judy illustrate an important general characteristic of tropical cyclone development. This is the tendency of the apparent center of circulation, as seen in satellite photographs, to move from the edge of major overcast, cloudiness in the weaker stages to a more central position as the storm intensifies, and to become almost symmetrical to the main cloud shield in the most, intense stages. As the storm decreases in intensity the center of circulation again assumes an asymmetric relationship to the major overcast cloud area. Some aspects of the physical plausibility of this relationship are briefly discussed.

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ROBERT W. FETT

Abstract

Satellite photographs of hurricanes reveal the complete storm in relationship to its environment. In many instances “outer convective bands” or “pre-hurricane squall lnes” appear to partially “ring” the storm. These bands are usually separated from the rim of the high cloud shield by a relatively clear channel, visible and distinct for long distances along the circumference. This channel may be formed through the action of a major subsiding branch of the hurricane's circulation. Many photographs also reveal extensive areas of convective, cirrus-producing cloudiness in the wake of the storm. This cloudiness appears to be intimately associated with that of the hurricane, and strongly influenced by outflow effects. Time cross-section analyses of hurricanes Carla and Anna suggest peripheral subsidence. The area of possible subsidence, in both instances, occurred under an upper shear line, where air diverging in the outflow layer from the hurricane converged with air emanating from the subtropical High. A jet stream, in the case of hurricane Carla, appeared in the region of the subsident annular zone, at the edge of the high cloud shield. This high speed current curved anticyclonically along the northern quadrants of the storm—then, on being directed southward, split into two main branches. The eastern branch curved cyclonically into a trailing vortex, apparent as a cold Low at 200 mb. The western branch continued southward, in alignment with the curvature of cloud streaks forming the cirrus “tail” of hurricane Carla. These features appear to be typical of many hurricanes in certain stages of development. Model considerations, employing these features, with a discussion of ramifications, are suggested in this paper.

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ROBERT W. FETT

Abstract

Typhoon Billie exhibited mesoscale warm-core characteristics and developed winds of typhoon intensity without ever forming a wall cloud around the eye. Clouds that swirled into the storm center were flattened cumulus and stratocumulus with cloud tops at 4,000 to 5,000 ft. It was clear of all higher cloudiness in the area of the eye. The storm center lay on the northern edge of major overcast cloudiness and its appearance was similar to that of an intense Stage C tropical cyclone. Satellite pictures together with conventional analyses and information gathered by the author as a pilot on reconnaissance missions into the storm indicate that Billie intensified to typhoon strength as a result of mesoscale changes in the area of the eye. It is suggested that Billie represents a type of typhoon whose maximum wind speeds are limited because of failure to develop an encircling wall cloud.

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ROBERT W. FETT

Abstract

In a survey of examples of formative tropical cyclones viewed by the TIROS satellite, and a comparison of many of these views with surface, upper-air, and time and space-section analyses, it is found that, the upper-level structure of the formative cyclone of moderate intensity is grossly similar to that of the storm at maturity. Common features in most examples studied include: (1) an upper-level trough or shear line which preceded the low-level trough and which moved with the storm system; and (2) an upper-level ridge or anticyclone which was generally superimposed over the convective area east of the lower-level trough or vortex. As has been found with the mature storm, strong subsidence occurred under the upper trough and coincided with a cloudiness minimum area in advance of the major convective cloudiness and west of the trough axis. Upward vertical motion with heavy convective activity was suggested under the upper-level ridge or anticyclone to the rear of the lower-level trough. Several examples depict these features and demonstrate changes that occurred as the storms passed individual stations. The TIROS photos were invaluable in this study as a source of additional data for confirming the distribution and type of cloudiness, for implying flow patterns at upper and lower levels, and for providing the basis for reasonable estimates of the stage of development of the entire system. It is concluded that an easterly wave model incorporating an upper-level trough and ridge or anticyclone as integral features of the moving system is one which describes most, adequately the majority of observations concerning formative tropical cyclones of moderate intensity and is one which is especially satisfying in terms of fulfilling the various theoretical and physical considerations.

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ROBERT W. FETT

Abstract

A case study of the early development of typhoon Marie (October 1966) revealed that this storm formed and intensified within the zone of the ITC. Satellite photographs, including infrared read-out during the night-time hours were obtained over the area of formation successively every 12 hr. with only one missing observation. 700- and 200-mb. streamline analyses are presented in relationship to these observations which include reconnaissance data obtained by the author as a pilot on flights into the storm. The development of Marie suggests a sequence of events which may be applicable to the development of other storms, particularly those occurring in early spring or the fall of the year. Four separate stages of development are shown covering the period prior to generation of vortical centers to that time when near typhoon intensity was attained.

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Robert W. Fett and Samson Brand

Abstract

A method to predict 24 h movement of tropical cyclones using consecutive daily satellite views is described. The method is based on the observation that changes in the location of major structural features of the storm are correlated with changes in the direction of movement of the storm centers. Major structural features appear to retain the same relative location with respect to the direction of movement of the storm center. The rotation of features noted in comparing satellite views over a 24 h period is frequently found to approximate in sense and value the further deflection the storm will take in its track during the following 24 h. A test evaluation of the method was conducted by seven individuals using 31 separate data sets of satellite data. For the purposes of the test only direction of movement forecasts were made and storm center displacement was neglected. The results on a post-analysis, non-real-time, basis compared favorably with official 24 h forecasts.

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Robert W. Fett and Stephen D. Bury

Abstract

Examples of island barrier effects appearing in visual and infrared Defense Meteorological Satellite Program (DMSP) data are shown and documented with selected conventional and research aircraft data. Effects discussed include lee and corner, atmospheric and sea state changes, induced by trade-wind flow over island barriers under low-level temperature inversion conditions. The use of DMSP satellite infrared data in detecting atmospheric temperature and humidity changes in the vicinity of island barriers and of the visual sensor of DMSP in detecting changes in aerosol particle size distributions is introduced as an analytic technique with important potential for other types of weather analysis. In this study, the usefulness of DMSP infrared data in distinguishing blocked from non-blocked or partially blocked flow over an island is demonstrated.

To aid in diagnosis of relevant phenomena, a two-dimensional (xz) numerical model is applied to the task of simulating air flow over a nonblocked, flat heated island and predicting changes in downstream parameters. Included in the model’s physics are the diffusion, transport, growth and deposition of sea salt aerosol. The model is initialized based on data gathered by a research aircraft during the Hawaii Mesoscale Energy and Climate Project (HAMEC) during flights around the island of Hawaii in June 1980. Model results are compared to selected aircraft data and discussed in relationship to satellite observations.

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Robert W. Fett and Kevin M. Rabe

Abstract

Island barrier effects on the state of the sea in the lee of islands have been studied by means of a numerical wave prediction model and by examination of data from sensors of the Defense Meteorological Satellite Program (DMSP), the Synchronous Meteorological Satellite (SMS), and the Earth Resources Technology Satellite (ERTS). Visual indications of calm areas in the lee of the Lesser Antilles, evidenced by a marked reduction in the satellite-observed sunglint at selected sun angles, are verified by the results from the numerical wave model; other lee reflective patterns correspond to areas of changed sea state. These results indicate that a reduction in the swell height, alteration of the period, and reorientation of the swell direction, in many instances long distances to the island's lee, are responsible for the satellite-observed reflective patterns noted. The additional phenomena of bow waves and wind-induced oceanographic eddies are also examined, and some evidence of their occurrence and detection is presented.

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Robert W. Fett and Ronald G. Isaacs

Abstract

Visible, Very High Resolution (VHR) and Light Fine (LF) data from the Defense Meteorological Satellite Program (DMSP) frequently exhibit areas of light-toned gray shades termed “anomalous gray shades” which appear most notable over the ocean but also over land areas, where contrast is suitable. These gray shades are distinctly different in appearance from visible, highly reflective cloud formations, and they are often particularly well delineated in DMSP VHR or LF data and either appear weakly or do not appear at all in near-simultaneous data from other satellite systems. This paper identifies low-level aerosols, such as haze, diffuse cloud particles or light fog, as one of the major causes of anomalous gray shades and shows examples with available documentation.

Since the DMSP VHR and LF sensor response curves are drastically different from those of other U.S. operational meteorological satellite systems, it was assumed that wavelength dependence on absorption and scattering effects was involved in the enhanced capability of the DMSP sensors to render anomalous gray shades visible.

A simple radiative transfer model is adopted to test the effect of haze on emergent radiation intensity as a function of wavelength and as measured by a meteorological satellite. These results are compared to previously obtained experimental measurements of particulate matter optical thickness as a function of wavelength under varying atmospheric conditions ranging from foggy or hazy to essentially clear. The results confirm that near-infrared wavelengths, except in narrow band regions where appreciable water vapor absorption occurs, provide much greater contrast between hazy and clear conditions that do shorter wavelengths in the visible portion of the spectrum. Since the DMSP VHR and LF sensors have their peak response in the near infrared, this appears to be an important factor in accounting for the sensitivity of these sensors in delineating hazy areas more adequately than other sensors from other systems which yield a peak response at shorter wavelengths.

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