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Tetsuya Fujita
and
William Bandeen

Abstract

For the purpose of evaluating the resolution of the High Resolution Infrared Radiometer (HRIR) flown on board the Nimbus I meteorological satellite, three cloud-free regions in the western United States—the Grand Canyon, Death Valley, and Sierra Nevada—were selected. Enlarged HRIR pictures and the analog frequency traces of the scan lines in the pictures were examined in an attempt to investigate the types of noise superimposed on the signals. Two types of noise which appear in periodic and oscillatory fashions were found. The latter can be eliminated by taking running-mean values at one-degree scan angle intervals. The equivalent blackbody temperatures thus obtained were analysed over these three regions, leading to the determination of the apparent temperature lapse rate inside the Grand Canyon atmosphere and of the temperature of Lake Tahoe and other lakes in the Sierra Nevadas. Death Valley was found to be about 10C warmer than the surrounding desert area 5000 ft high. An attempt was also made to produce an HRIR picture with isoneph contours similar to the iso-echo presentation of radar pictures.

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Tetsuya Fujita
,
Gisela Baralt
, and
Kiyoshi Tsuchiya

Abstract

A Barnes PRT-4 portable radiometer with a spectral response in the 8–14 μ range was used to determine the equivalent blackbody temperature of 1) the slope of Mt. Fuji, 2) Sagami Bay, and 3) the city of Tokyo. A twin-engine aircraft was used to fly over these areas at various altitudes up to 12,000 ft. Through mapping the slope temperatures of Mt. Fuji, it was learned that the rocky slope heats up under the morning sun very rapidly to 32C almost irrespective of the elevation. The distribution of measured temperatures explains the reasons for the rapid growth of cumulus clouds along the east slope in the early morning hours. The nadir angle and the height dependence of equivalent blackbody temperatures measured over Tokyo and Sagami Bay were examined. The measured temperatures were compared with those computed from the radiative transfer equation. It was found that the values over Tokyo are reproduced fairly well by the addition of a graybody smog filling the layers up to 910 mb. To express the effects of atmospheric radiation upon the reduction of the radiant emittance from the surface, a damping factor was introduced. The factor which designates the reduction of the amplitude of the surface temperature when measured from aircraft or satellites must be known to an accuracy of about 10% in order to estimate the true temperature variation or gradient from measured equivalent blackbody temperatures. Further investigation of the temperature damping is necessary to determine accurately the radiometric sea-surface temperature.

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Tetsuya T. Fujita
,
Kazuo Watanabe
, and
Tatsuo Izawa

Abstract

Because of poor coverage by synoptic stations, the tropical circulation over the eastern Pacific has not been known too well. As a result of photographic experiments, using the geosynchronous ATS-I satellite, fields of cloud motion over the eastern equatorial Pacific were mapped in detail on a number of days in September 1967. It was found that a large-scale flow from the Southern Hemisphere recurves after crossing the equator to form an anticyclone centered around 10N. Dynamical characteristics of this type of anticyclone were investigated by estimating the vorticity dissipating force from computed values of divergence and vorticity of low-cloud velocities determined from successive ATS-I pictures. The vorticity dissipating force seems to be related closely to the sea-surface temperature which would reduce the frictional coupling between the low-level atmosphere and the underlying sea surface. It was found that the anticyclone in its development stage results in a discontinuity of the intertropical band of cloudiness, before it travels westward with an active cloud band along its leading edge. Based upon evidence found through case studies, a model of an equatorial anticyclone is proposed in this paper. Numerical computations of cross-equatorial trajectories were performed by using the divergence-vorticity relationships and the vorticity dissipating force, which were obtained through numerical analyses. This paper thus presents an initial step toward the further development of tropical synoptic meteorology, which is expected during the next few years as a result of photographic experiments using the ATS-I and III.

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Tetsuya Fujita
,
Tatsuo Izawa
,
Kazuo Watanabe
, and
Ichiro Imai

Abstract

Both hurricanes and typhoons are relatively circular storms with their winds at high levels blowing mostly outward. Assuming that the outflow is characterized by central motion under the influence of the pressure-gradient forces pointing toward the storm center, the absolute angular momentum of the outflow winds and radar echoes were computed. The upward motion inside these echoes plays an important role in the upward transport of the low-level angular momentum. Detailed analysis made by using satellite, radar and aerological data revealed that the absolute angular momentum of radar echoes near the eye wall is almost one order of magnitude smaller than that of the echoes in the outer rainbands. This fact leads to a suspicion that the radial distribution of the vertical velocity inside a storm would significantly alter the pattern of the outflow winds near the storm top. A numerical model, including the radial distribution of the vertical velocity, was thus established. Computations indicated that the vertical transport of momentum by outer rainbands alters the outflow wind pattern, resulting in the formation of a ring of high-cloud-free region which separates the inner cirrus shield from the outer cirrus decks. This ring sometimes appears as a clear area on a satellite photograph.

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Tetsuya Fujita
,
Kenneth A. Styber
, and
Rodger A. Brown

Abstract

During the month of July 1960, a mesometeorological field network was established in an area of 30 by 40 mi centered around San Francisco Mountain, Arizona. Network instrumentation included 33 micro-barographs, 10 hygrothermographs, 10 Beckman-Whitley wind recorders, about 165 nonrecording rain gauges, and 165 hail gauges. Daily precipitation amounts were carefully studied in order to relate them with the characteristics of moisture inflow into the network area. An analysis of the 22 July case over the network area revealed that a very small low-pressure area formed over the heated side of the mountain slope, providing a field of convergence leading to the morning cumulus convection. AS time went on, this low dissipated and cumulonimbus convection occurred. The mesometeorological network was found to be most suitable for the investigation of cumulus to cumulonimbus convection over the San Francisco Mountain area.

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R. Cecil Gentry
,
Tetsuya T. Fujita
, and
Robert C. Sheets

Abstract

Hurricane Gladys, 17 October 1968, is studied with data collected by Aollo 7 manned spacecraft, ESSA's especially instrumented aircraft, weather search radar, the ATS-III and ESSA 7 satellites, and conventional weather networks. This is the feast time data from all of these observing tools have been used to study the structure and dynamics of a hurricane. Techniques used in computing and integrating the various types of data are described and illustrated.

A dominant feature of this immature hurricane was a large cloud which provided a major link between the low- and high-level circulations of the storm. Evidence is presented to suggest this type of cloud and its attendant circulation are features representative of tropical cyclones passing from the tropical storm to the hurricane stage.

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