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G. W. Paltridge

Abstract

An elementary model is devised which suggests that atmospheric radiation can be a dominant factor determining the thickness, water content, and general character of some forms of stratified cloud-stratocumulus in particular. For stratocumulus at the top of the mixing layer the theory predicts an equilibrium situation where the upward flux of water vapor E into the cloud is balanced by turbulent entrainment of drier air from above the inversion. The amount of entrainment is determined by radiative cooling which, in turn, is governed by, and generally increases with, the water content and thickness of the cloud. The equilibrium is generally stable and is such that the deck maintains a constant water content but rises overall at a rate determined by E and the relative dryness of the air above cloud top. Any phenomenon which increases the radiative cooling of the cloud should tend to make it thinner, and an actual observation of decreased shortwave absorption confirms this. Conversely, one might expect Sc over the sea to be thicker during the daytime when shortwave heating is significant or when extensive high cloud reduced the longwave cooling. The model suggests that cloud turrets will penetrate the inversion surmounting stratocumulus when the local mixing ratio difference across the inversion exceeds a value of the order of 8 gm kg−1.

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G. W. Paltridge

Abstract

No abstract available.

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G. W. Paltridge

Abstract

Aircraft measurements of the vertical profile of net shortwave flux and atmospheric water vapor over the ocean agree with Yamamoto's calculated relation between shortwave absorptivity and water path over the range of water paths 0.01 to 3 cm. The measurements indicate also that some fairly severe form of pressure correction needs to be applied to water path information used in this connection. Data obtained on two very hazy days indicate extra absorption on those days of about 5%.

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G. W. Paltridge

Abstract

Global mean cloud cover θ and surface temperature T are not independent and must satisfy the requirement of global energy balance, i.e., that the absorbed solar radiation must equal the loss to space of longwave radiant energy. Values of their “full” differentials with respect to the solar constant (dθ/dR 0 and dT/dR 0) are obtained using simple energy balance considerations and a qualitative concept from a model of the growth and dissipation of cloud systems. The values are +0.009 and +0.35K for a 1% increase in solar constant. Previous solutions for the partial differential |∂T/∂R 0|θ are of the order 1–1.5K per 1%. The present results are highly speculative since they involve feedback only to cloud amount and not, for instance, to such things as cloud height or cloud character. However they are supported by the observed change of about 5% in global cloud cover between the times of maxima and minima in the annual cycle of sun-earth distance.

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G. W. Paltridge and S. Woodruff

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G. W. Paltridge and S. L. Sargent

Abstract

The instrumentation and flight results of a balloonborne package of radiometers which measure the upward and downward fluxes of both shortwave and longwave atmospheric radiation are described. Ten flights wore conducted at Mildura and at Longreach, Australia. In most cases the balloon was launched just prior to dawn so that ascent data were obtained covering the period of sunrise, and float data (at altitudes between 21.5 and 31.5 km) were obtained covering the range of solar elevations from 4° to 45°. Composite experimental curves of the clear-sky planetary albedo, net radiation balance, and upward long-wave flux at the top of the atmosphere are presented as functions of solar elevation; the results from which these curves are constructed are remarkably consistent from one time and place to another, and can be regarded as representative for most of continental Australia. Angular intensity distributions of the short-wave radiation emerging from the top of the clear atmosphere are derived from all-Sky color photographs taken simultaneously with the flux measurements. The effect of atmospheric dust is very apparent at low sun elevations, and the derived Mie scatter polar diagram has a beam width of 48° An approximate calculation is used to show, however, that the effect of the dust on the upward shortwave flux is negligible except when the sun is close to the horizon when the increase may he of the order of 1.5%. Longwave and shortwave transmissivities of 0,23 and 0.7, respectively, are obtained for a cirrostratus cloud (visually 5/8 cover) from a flight through and above a typical deck. The reduction in out-going longwave radiation caused by this cirrus was 6 mW cm−2, twice the reduction observed on a flight over 8/8 cover of uniform altocumulus.

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G. W. Paltridge and M. R. Platt

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No abstract available.

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G. L. Stephens, G. W. Paltridge, and C. M. R. Platt

Abstract

Six case studies of “uniform” planetary boundary layer clouds are reported where the solar and infrared radiation fields, liquid water content, drop-size distributions and temperature and humidity profiles were measured simultaneously. The measurements are compared with theoretical prediction from a detailed radiative transfer model in an attempt to verify the performance of the model and its associated parameterization schemes (Parts 1 and 2). The measurements support the parameterization of both shortwave and longwave radiative characteristics in terms of vertical liquid water path (LWP) i.e., without the need to define cloud drop-size distributions. Within experimental error, there are no significant discrepancies between theory and measurement. However, there is some evidence in the present study, supported by measurements of others in (generally) thicker and denser clouds that solar absorption is in excess of theoretical prediction.

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