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Robert A. McClatchey

Abstract

Empirical data on transmission functions are used to set up a general program to calculate the infrared radiation flux in the atmosphere in the two major regions of water vapor absorption. These empirical data are used as input together with atmospheric soundings and the problem is solved through the use of an electronic computer.

The northern hemisphere average soundings for March determined by London are used as input to the computer program and the results obtained are compared with his cooling rate calculations. The results for an additional sounding are displayed to demonstrate the effect of lapse-rate stability on cooling rate.

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Robert A. McClatchey
and
J. H. Shaw

Abstract

No abstract available.

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Miao-Ling Lu
,
Robert A. McClatchey
, and
John H. Seinfeld

Abstract

Significant enhancements in humidity around cumulus clouds, that is, the “cloud halos” observed in many aircraft penetrations, are simulated using a three-dimensional dynamic model. Five case studies show that humidity halos occur mainly near lateral cloud boundaries and also occur at cloud top and base when the cloud dissipates. The humidity halo broadens as the cloud ages and is also broader in the presence of wind shear than in its absence, especially on the downshear side of the cloud. The broadband calculation over the solar spectrum (0.2–4.0 μm) shows that the shortwave (SW) heating rate in the halo is about 11%–18% larger than the ambient environmental heating rate. The strongest halo-induced surface SW radiative forcing for all cases studied is about −0.2 W m−2, which is approximately a 0.02% change from the forcing without a halo.

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Miao-Ling Lu
,
Jian Wang
,
Richard C. Flagan
,
John H. Seinfeld
,
Andrew Freedman
,
Robert A. McClatchey
, and
Haflidi H. Jonsson

Abstract

Regions of enhanced humidity in the vicinity of cumulus clouds, so-called cloud halos, reflect features of cloud evolution, exert radiative effects, and may serve as a locus for new particle formation. Reported here are the results of an aircraft sampling campaign carried out near Oahu, Hawaii, from 31 July through 10 August 2001, aimed at characterizing the properties of trade wind cumulus cloud halos. An Aerodyne Research, Inc., fast spectroscopic water vapor sensor, flown for the first time in this campaign, allowed characterization of humidity properties at 10-m spatial resolution. Statistical properties of 60 traverses through cloud halos over the campaign were in general agreement with measurements reported by Perry and Hobbs. One particularly long-lived cloud is analyzed in detail, through both airborne measurement and numerical simulation, to track evolution of the cloud halos over the cloud's lifetime. Results of both observation and the simulation show that cloud halos tend to be broad at lower levels and narrow at upper levels, and broader on the downshear side than on the upshear side, broadening with time particularly in the downshear direction. The high correlation of clear-air turbulence distribution with the halo distribution temporally and spatially suggests that the halo forms, in part, due to turbulent mixing at the cloud boundary. Radiative calculations carried out on the simulated cloud and halo field indicate that the halo radiative effect is largest near cloud top during mature and dissipation stages. The halo-enhanced atmospheric shortwave absorption, averaged over this period, is about 1.3% of total solar absorption in the column.

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