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William L. Donn

Abstract

Nearly all the microseism storms generated by extra-tropical cyclones in the western North Atlantic during the fall and winter seasons of 1948–49 and 1949–50 have been studied, together with some storms that occurred during the 1950–51 fall-winter. Seismograms from a number of east-coast stations and Bermuda were examined for each storm.

Each of the microseism storms has been correlated with a particular marine atmospheric disturbance. The period of the microseisms appears to be a function of the depth of water in the generating area, and the regularity of the microseisms appears to be a function of the uniformity of depth in the generating area. Consequently, the position and nature of marine disturbances often can be estimated from the nature of the recorded microseisms.

All the evidence on origin tends to negate ocean swell, standing waves produced by interference of ocean swell, and surf as mechanisms producing the observed microseisms. The study suggests atmospheric pulsations, resulting from turbulence or instability, to be at the root of microseism origin.

Anomalies of propagation of hurricane microseims suggest the existence of a zone or surface of discontinuity along at least a portion of the outer margin of the east-coast continental shelf.

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William L. Donn

The storm tides at six coastal stations along northeastern United States produced by eight coastal storms from 1952 to 1956 are compared with significant storm parameters. Tentative forecast graphs of tide versus wind velocity have been developed which indicate that operational usefulness can be achieved by the methods described. The storm tide appears to be a very local phenomenon, dependent primarily upon wind velocity. The problem of storm-tide lag is also examined.

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William L. Donn

Abstract

Case histories of six microseism storms generated by marine cold fronts are given. Seismograms from the New York City and Palisades stations of Columbia University and from Weston College Observatory were utilized together with 6-hourly synoptic North Atlantic surface charts. Definite correlations are made between stages of microseism activity and frontal positions over water. Microseism period is shown to vary with both distance of and water depth beneath cold fronts, with the latter apparently of greater significance. The observations tend to negate or minimize the importance of surf or any form of swell in producing the microseisms considered, and suggest atmospheric pulsations or turbulence to be a significant cause.

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William L. Donn

Abstract

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William L. Donn
and
William T. McGuinness

Abstract

An IGY tsunami recorder at Texas Tower No. 4 off New York has detected ocean waves of periods from 4 to 10 min which have amplitudes up to 100 times greater than atmospheric pressure oscillations which occurred simultaneously. The latter are shown to be pressure perturbations generated by internal surface waves on a frontal discontinuity aloft. These waves appeared to have travelled out from the coast with a velocity about the same as that for free gravity waves in the water. The long ocean waves are explained as originating from resonant coupling between the atmospheric waves and the gravity waves produced by the traveling pressure perturbations.

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Stanley David Gedzelman
and
William L. Donn

Abstract

Relations between the behavior of atmospheric gravity waves and the meteorological conditions during the approach of coastal cyclones at Palisades, New York (near New York City) are investigated. It is shown that the temperature and wind conditions favoring the development of the largest amplitude waves are most likely to occur when coastal cyclones strike. This wave record can be used to distinguish between those storms which do and those which do not produce precipitation at New York City. The wave record is also shown to provide a monitor for some of the finer scale features of the storm structures such as the shallow pockets of cold air that often form to the cast of the Appalachian Mountains. Finally, climatological aspects of the gravity-wave behavior for coastal cyclones are investigated and it is shown that there is frequently an abrupt increase in wave amplitudes some 6–12 h prior to the onset of precipitation and an abrupt decrease in wave amplitudes at about the time precipitation ends.

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William L. Donn
and
David Rind

Abstract

The relatively low frequency of the sonic boom generated by the Concorde SST permits propagation in the form of infrasound to long range with small attenuation. Signal characteristics at long range are a function of atmospheric propagation parameters. When the relationship of propagation to signal is understood, then propagation conditions can be determined by inversion with good accuracy. We show here how signal recorded at Palisades, New York, from the Dulles-bound SST reveals direction and speed of stratospheric wind variations diurnally and seasonally and also gives details of at least local circulation change at times of stratospheric warmings.

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David Rind
and
William L. Donn

Abstract

This is a further study of the use of natural infrasound in the atmosphere to monitor tidal circulation in the lower thermosphere. The height of this circulation is determined with the use of a reference atmospheric model, which is then used to calibrate infrasound/microseism ratios in terms of height. Also, we show from continuous observation over six years at 41°N, 74°W that the winter semidiurnal tide is present at least 62% of the time and the diurnal, at least 42% of the time.

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William L. Donn
and
Maurice Ewing

Abstract

Atmospheric waves from the Soviet nuclear test of 30 October 1961 axe described for nine stations having wide global distribution. The records are characterized by waves which begin with the highest amplitudes and which show normal dispersion. These appear to be superimposed on a lower amplitude, long period train of waves which show inverse dispersion. As shown on dispersion curves of group velocity against period, a maximum of group velocity is indicated by the Airy phase formed through the merging of the two dispersive trains. A more prolonged train of waves of nearly uniform period is attributed to higher modes. The direct waves from the epicenter to the stations give dispersion curves that indicate significant variation in atmospheric structure along different azimuths and probably along different segments of the same azimuth. The curves for waves which have travelled more than once around the earth represent better sampling of world-wide atmospheric conditions and give better agreement with preliminary theoretical models. The average speed of the first arrivals is 324 m per sec, comparing well with the maximum obtained for the Krakatoa eruption.

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David H. Rind
and
William L. Donn

Abstract

Observations of natural infrasound produce a continual record of the sound velocity, a function of wind and temperature, at the reflection level in the upper atmosphere. Under normal conditions in winter the reflection level, for sound generated by ocean waves to the east of Palisades, N. Y., is in the lower thermosphere. During the circulation changes associated with stratospheric warmings, winds near the stratopause may become east or north, allowing infrasound to be reflected from this level. We are then provided with a continuous record of sound velocity near the stratopause. The methods which are used to distinguish between stratosphere and thermospheric sound reflection are discussed, and circulation changes for each year are cataloged.

During the warming event sound velocities in the stratosphere are shown to vary radically, with fluctuations of up to 60 m s−1 in a few hours time period. These short time period variations, observable only because of the continuous nature of infrasound recording, are greater than expected and indeed constitute a significant fraction of the total wind and temperature variation associated with the event at our latitude. As such they imply significant energy variations on shorter time scales than those usually considered important in stratospheric dynamics. Some possible explanations for these observations are given.

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