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- Author or Editor: Tetsuya Fujita x
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Abstract
Over maritime areas, meteorological satellite data generally have been used only in the study of synoptic scale systems. However, TIROS 7 pictures of summertime stratus over the northern Pacific, when rectified and combined with mesoscale radiation analyses, give valuable clues regarding the mesoscale dynamics of the lower atmosphere. Radiation data distinguish stratus from middle level cloud layers. Stratus bands, averaging 15 km. wide and oriented 16° to the left of the geostrophic wind, are thought to be related to horizontal roll vortices. Reflectance cross sections cross these bands indicate sharp variations in the thickness of the stratus.
Precisely gridded photographs show the relation of marked clear areas in the stratus to the topography of the Aleutian Islands. Only when execeding a critical size do isolated mountainous islands produce clear wakes. One island appears to be shedding a possible vortex street. A derived model for the flow of the stable air over long mountain ridges in the Alentians includes such phenomena as upstream blocking, windward slope bolster eddies, and extreme turbulent mixing on the Ice slopes causing clear areas to extend over 100 km. domnstream. Radiosonde data indicate that the mixed layer downstream is approximately the depth of the obstructing ridge.
Abstract
Over maritime areas, meteorological satellite data generally have been used only in the study of synoptic scale systems. However, TIROS 7 pictures of summertime stratus over the northern Pacific, when rectified and combined with mesoscale radiation analyses, give valuable clues regarding the mesoscale dynamics of the lower atmosphere. Radiation data distinguish stratus from middle level cloud layers. Stratus bands, averaging 15 km. wide and oriented 16° to the left of the geostrophic wind, are thought to be related to horizontal roll vortices. Reflectance cross sections cross these bands indicate sharp variations in the thickness of the stratus.
Precisely gridded photographs show the relation of marked clear areas in the stratus to the topography of the Aleutian Islands. Only when execeding a critical size do isolated mountainous islands produce clear wakes. One island appears to be shedding a possible vortex street. A derived model for the flow of the stable air over long mountain ridges in the Alentians includes such phenomena as upstream blocking, windward slope bolster eddies, and extreme turbulent mixing on the Ice slopes causing clear areas to extend over 100 km. domnstream. Radiosonde data indicate that the mixed layer downstream is approximately the depth of the obstructing ridge.
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.
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.
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.
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.
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.
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.
Abstract
An extensive aerial survey was made over a large portion of the area affected by the outbreak of tornadoes on Palm Sunday on Apr. 11, 1965. The destruction from the tornadoes extended over parts of six Midwestern States. Aerial and ground damage surveys were combined with eyewitness reports to determine the exact location and time of each tornado occurrence and its path. Radar pictures of the squall line clouds were used to verify the direction and speed of the tornado-producing clouds. Almost simultaneously with the first tornado touchdown in eastern Iowa, TIROS IX took pictures of the Midwest United States that showed a large tongue of cloud-free dry air behind the cold front. The vertical structure of the cold dome is discussed in connection with its role in the development of the tornadoes.
Two predictive parameters, namely, the best lifted index (BLI) and material differential advection (MDA) were developed and evaluated with data gathered on this outbreak of tornadoes.
The wind speed of a tornado in relation to its parent tornado cyclone is discussed in terms of an anemometer trace showing a peak gust speed of 151 mi hr–1. An indirect wind-speed estimate was also attempted by examining characteristic cycloidal marks left on the fields along the tornado paths. The ground speeds computed ranged from 166 to 180 mi hr–1 for one tornado.
Abstract
An extensive aerial survey was made over a large portion of the area affected by the outbreak of tornadoes on Palm Sunday on Apr. 11, 1965. The destruction from the tornadoes extended over parts of six Midwestern States. Aerial and ground damage surveys were combined with eyewitness reports to determine the exact location and time of each tornado occurrence and its path. Radar pictures of the squall line clouds were used to verify the direction and speed of the tornado-producing clouds. Almost simultaneously with the first tornado touchdown in eastern Iowa, TIROS IX took pictures of the Midwest United States that showed a large tongue of cloud-free dry air behind the cold front. The vertical structure of the cold dome is discussed in connection with its role in the development of the tornadoes.
Two predictive parameters, namely, the best lifted index (BLI) and material differential advection (MDA) were developed and evaluated with data gathered on this outbreak of tornadoes.
The wind speed of a tornado in relation to its parent tornado cyclone is discussed in terms of an anemometer trace showing a peak gust speed of 151 mi hr–1. An indirect wind-speed estimate was also attempted by examining characteristic cycloidal marks left on the fields along the tornado paths. The ground speeds computed ranged from 166 to 180 mi hr–1 for one tornado.
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.
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.
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.
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.
