Search Results

You are looking at 1 - 10 of 20 items for

  • Author or Editor: William P. Elliott x
  • Refine by Access: All Content x
Clear All Modify Search
William P. Elliott

Abstract

No Abstract Available

Full access
William P. Elliott

Abstract

No abstract available.

Full access
William P. Elliott

Abstract

Hole closing by diffusion of water vapor and droplets is treated as a problem in classical diffusion theory with constant mixing coefficients. The results, for reasonable estimates of the variables involved, lead to closure times in the one-half to one hour range. However, the estimates of the appropriate diffusion coefficients are quite rough and it may be useful to employ cloud-dissipation techniques to estimate this variable.

Further calculations show that to maintain a given area free of clouds for the maximum time possible, a hole whose width is 75–80% of the distance between the smallest useful hole and the maximum possible hole should be opened.

Full access
William P. Elliott

Abstract

An equation for the daytime lapse rate of temperature as a function of z/L is derived assuming the lapse rate varies as z−⅔ in very light winds. This variation is presumed to result from the geometry of buoyant plumes. The equation, which agrees very well with some data taken by Dyer, predicts a maximum value for the lapse rate at a fixed height and with given heat flux, at intermediate values of z/L. This variation suggests the concept of eddy viscosity as usually applied does not adequately describe the heat flux in unstable conditions.

Full access
William P. Elliott and Richard Egami

Abstract

Shipboard measurements of CCN show the slope of the CCN spectra to be in agreement with other estimates in marine air from aircraft. Concentrations of CCN over the open ocean are quite low with estimates of a few tens per cubic entimeter. Only a few percent of the CCN were particles containing chlorides.

The Spectra of CCN in coastal waters exhibit slopes more like marine air but number concentrations more like continental air. The reason for this are not entirely clear.

Full access
Douglas R. Caldwell and William P. Elliott

Abstract

The previous solution to the problem of determining the effect of rainfall on the sea-surface stress is found to be inadequate. A correct treatment confirms that rainfall may contribute significantly to the surface stress and may under some conditions produce stresses comparable in value to the wind stress. Also the drag of the drops in the lower air layer may induce measurable distortions from the logarithmic wind profile.

Full access
Burlie A. Brunson and William P. Elliott

Abstract

Thermal, haline and total steric departures of sea level were calculated in a zone up to 165 n mi off Newport, Ore. The thermal and haline components were about equal in magnitudes and in phase, giving low steric sea levels nearshore and high sea levels offshore in summer and the reverse pattern in winter. These results are produced by local oceanographic conditions and reflect seasonal changes in upwelling and the position of the Columbia River plume.

In the region close to shore the combined effects of steric and atmospheric-pressure-caused departures do not fully account for the observed variations of sea level. Wind stress variations are likely to be the most important cause but other factors may well contribute.

Full access
Rebecca J. Ross and William P. Elliott

Abstract

Here 21 years of radiosonde observations from stations in the Western Hemisphere north of the equator were analyzed for trends in tropospheric water vapor. Mean fields of precipitable water and relative humidity at several levels we shown. Annual trends of surface-500 mb precipitable water were generally increasing over this region except over northeastern Canada. When trends were expressed as a percentage of the climatological mean at each station, the trends south of ∼45°N represent a linear rate of increase of 3%–7% decade−1. Trends in the upper portion of this layer, 700–500 mb, were as large or larger than those of the middle (850–700 mb) or lower layer and were consistent in sign.

Annual trends in dewpoint generally agree in sign with trends in temperature. However, the dewpoint trends tended to be larger than those of temperature. This was consistent with the annual increases found in relative humidity over this period. Relative humidity increased except in Canada, Alaska, and a few stations in western mountainous areas. Largest percentage increases of relative humidity were in the Tropics.

Seasonal trends of precipitable water varied spatially more than the annual trends and fewer were statistically significant. More stations had significant trends in summer than in other seasons and these were located over the central and eastern United States and the Tropics. Spring trends were largest over the western United States, while the largest winter trends were along the Gulf Coast. The one area where significant water vapor increases were found in all four seasons was the Caribbean.

Full access
William P. Elliott and Dian J. Gaffen

Different nations use different algorithms or other techniques to convert temperatures and relative humidities from radiosonde observations to dewpoint depressions. Thus, it is possible for identical measured values to result in different reported dewpoints. On the basis of a sample of conversion methods, we calculate the possible differences among the national practices. In general, the discrepancies are not large and would often be lost in the usual round-off procedures associated with transmission over the Global Telecommunications System, but in cold, dry conditions dewpoints different by more than 1°C could be reported for identical conditions. Some of the methods have been changed over time, so there is also the possibility of inhomogeneities in climate records.

Full access
Dian J. Gaffen and William P. Elliott

Abstract

With radiosonde data from 15 Northern Hemisphere stations, surface-to-400-mb column water vapor is computed from daytime soundings for 1988–1990. On the basis of simultaneous surface visual cloud observations, the data are categorized according to sky-cover amount. Climatological column water vapor content in clear skies is shown to be significantly lower than in cloudy skies. Column water vapor content in tropical regions varies only slightly with cloud cover, but at midlatitude stations, particularly in winter, clear-sky values are much lower. The variation in column water content with cloud cover is not simply due to variations in atmospheric temperature, since the increase in water vapor with cloud cover is generally associated with a decrease in daytime temperature. Biases in radiosonde instruments associated with cloudiness do not explain the station-to-station variations in the magnitude of the increase of column water vapor with cloud cover. Statistics are presented that can be used as guidance in estimating the bias in water vapor climatologies based on clear-sky or partly cloudy-sky measurements. These may be helpful in distinguishing the clear- and cloudy-sky greenhouse effects of water vapor.

Full access