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B. R. Bean and B. A. Cahoon

Maps of the variation of absolute humidity over the United States are presented for the values exceeded 1, 50 and 99 percent of the time during the months of February and August. Cumulative distributions of absolute humidity are presented for nine climatically diverse locations for the four seasons of the year. In addition, regression equations have been derived to enable one to estimate the values of absolute humidity exceeded 1 and 99 percent of the time at any location for which average values are available.

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B. R. Bean and J. D. Horn

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B. R. Bean, C. B. Emmanuel, R. O. Gilmer, and R. E. Megavin

Abstract

During the 1972 IFYGL “alert” periods, the NOAA/RFF/DC-6 gust probe instrumented aircraft was used to record time series of wind, temperature and water vapor at heights ranging from 18 to 300 m above the surface of Lake Ontario. The time series records show great variability. This is especially the case for evaporation when, in the fall, polar continental outbreaks move across the lake. In particular, such an outbreak of cold dry air moved across the lake at 12–15 m s−1 on 9 October 1972. This resulted in a drop of the air temperature at 30 m above the take from 12 to 6°C while the evaporation rate increased to more than 1 cm day−1. This may be compared to the 0.5 cm day−1 typical evaporation rate observed in the tropics during BOMEX. Furthermore, IR lake surface temperatures show cold regions (∼5°C) along the north shore, presumably due to strong upwelling, while the center and south shore regions of the lake were of the order of 12–15°C. The turbulent flux quantities of momentum, heat and water vapor were obtained by the eddy correlation technique and their spectra were determined at severed locations over the lake surface for 3 min sampling lengths. At the aircraft speed of 92 m s−1 this represents a flight path of about 17 km. The spectra demonstrate the tendency for the peak value to march to longer wavelengths with increasing height.

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B. R. Bean, R. Gilmer, R. L. Grossman, R. McGavin, and C. Travis

Abstract

The initial analysis of the water vapor flux measurements taken onboard a NOAA DC-6 during the Barbados Oceanographic and Meteorological Experiment (BOMEX) is presented. The flux of water vapor seems to be constant in the lower subcloud layer. Day-to-day variations, as well as variations within a day are apparent in the evaporation data. Spatial variations of evaporation also seem to be present. The average value of water vapor flux for the experimental period is ∼0.5 cm day−1. Spectra of the instantaneous flux reveal significant alongwind-crosswind differences. Height variation of the wavelength of maximum spectral density for crosswind runs is confirmed. The instantaneous flux is intermittent in nature. Consideration of the cross spectra and time series signatures allows some speculation upon models which may be responsible for a major portion of the water vapor transport in the lower subcloud layer during BOMEX.

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C. B. Emmanuel, B. R. Bean, L. G. McAllister, and J. R. Pollard

Abstract

Acoustic probing of the lower atmosphere (<150 m) reveals structures that appear similar to those of instability waves produced by wind shear at the stable interface of a temperature inversion. The acoustic sounder was located in the vicinity of a meteorological tower 152 m in height. Profiles of wind velocity and temperature were taken during the acoustic sounder operation. Regions of enhanced thermal stability and wind shear produce strong echoes which the acoustic sounder maps on a height vs time facsimile record. In this paper we limit our discussion of those echo returns that have the characteristic appearance of Helmholtz waves. Richardson numbers calculated from the tower measurements over the layer thickness as determined from the acoustic sounder returns appear to he of the order of ½, while sub-strata embedded within the layer thickness exist where the Richardson number drops near the theoretically predicted critical value of ¼. In addition, measurements of the wavelengths associated with the “breaking” phenomenon conform to the theoretically predicted range of values.

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A. G. Kjelaas, D. W. Beran, W. H. Hooke, and B. R. Bean

Abstract

Three acoustic sounders, with antennas having vertically-pointed beams located at the vertices of a triangle about 300 m on a side, have been used successfully to calculate horizontal phase velocities of gravity waves in the lowest 1000 m of the atmosphere. The wave parameters obtained were compared with those obtained by an array of micrographs. The results from the two independent techniques agreed well in all cases where the waves were detected by both methods. However, the acoustic-sounder array was also able to detect gravity waves propagating in an inversion overlying the convective boundary layer that were undetected by the microbarograph array because of wave attenuation in the convective region.

Wave-associated vertical-velocity fluctuations inside the undulating structure were measured using Doppler techniques to an accuracy of about ±0.1 m sec−1. Vertical-velocity fluctuations of about ±0.5 m sec−1 were measured inside one wave with displacement amplitude of 120 m and wavelength of 5.5 km. From wave-associated vertical-velocity fluctuations, displacement amplitude and wave period, we could calculate the wind speed component along the wave propagation direction. This calculated wind speed component agreed reasonably well with the value derived independently from radiosonde measurements.

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T. P. Barnett, W. C. Patzert, S. C. Webb, and B. R. Bean

Two different satellite estimates of sea-surface temperature (SST) have been compared with observed temperature sections in the central tropical Pacific Ocean. The satellite products were found to be biased with respect to the observations by approximately 1–4°C. The bias field had a strong latitudinal and longitudinal structure. The spatial structure of this field and the large magnitude of errors in estimates of SST, if a normal situation, preclude the use of the satellite products by themselves in climatological studies of the area. However, if some means can be found to remove the bias from the satellite products then they will be marginally useful in the study of interannual variations of SST in the tropical Pacific.

The errors associated with the estimates of satellite SST are strongly linked to cloud cover and the amount of water vapor in the atmosphere, indicating present methods of correcting for these types of contamination are inadequate. The errors also depend on the number of observations that have gone into the satellite estimate of SST.

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