On the effect of cloud inhomogeneity an area averaged radiative properties of contrails

Schulz, Jörg B.

doi:10.1029/98gl51098

Cited by 9 publications

(12 citation statements)

References 14 publications

(2 reference statements)

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“…This increases the albedo of the contrail, but because it only significantly modifies the multiply scattered photons, its magnitude is quite weak for such a low optical depth. This result is consistent with the findings of Schulz (1998).…”

Section: A Sensitivity To Solar Zenith and Azimuth Anglesupporting

confidence: 96%

“…The elliptical cross section is a rough approximation to contrails both observed by lidar (Freudenthaler et al 1995;Sassen 1997) and modeled (Sassen 1997;Schulz 1998). The formula above results in peak concentrations toward the center of the contrail, in agreement with both lidar observations and model results showing extinction coefficient increasing toward the interior of the contrail.…”

Section: B Experiments Performedsupporting

confidence: 85%

“…When this option is used, the model effectively considers each column as a separate, horizontally uniform domain of infinite horizontal extent, without allowing transfer of radiation from one column to another. This is what all previous published studies of contrails except that of Schulz (1998) have assumed. references to optical depth will be for this wavelength).…”

Section: A Radiative Transfer Modelmentioning

confidence: 68%

“…The effect of 3D photon transport on the radiative forcing of clouds other than contrails has been studied in detail, and has been found to be particularly significant for shallow cumulus (e.g., Marshak and Davis 2005;Pincus et al 2005). The only such study with contrails was that of Schulz (1998) who investigated the effect of horizontal photon transport on the albedo of a contrail simulated by a large-eddy model. He studied the sensitivity to solar zenith angle, but implicitly kept the solar azimuth angle fixed and parallel to the contrail (i.e., ϭ 90°in Fig.…”

Section: Introductionmentioning

confidence: 97%

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A Sensitivity Study of the Effect of Horizontal Photon Transport on the Radiative Forcing of Contrails

Gounou

Hogan

2007

Journal of the Atmospheric Sciences

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With the rapid growth in air travel, there is concern over the radiative impact of contrails and aircraftinduced cirrus on climate. Previous radiation calculations on contrails have almost all used the independent column approximation, which neglects the transport of photons through the sides of the contrail, but in this study the 3D effects are quantified using the Spherical Harmonic Discrete Ordinate Method (SHDOM). The authors have investigated the dependence of shortwave and longwave radiative forcing on contrail aspect ratio, optical depth, solar zenith angle, solar azimuth angle relative to contrail orientation, particle size, particle habit, surface albedo, and surface temperature. It is found that inclusion of 3D transport results in an increase in the positive longwave radiative forcing of the contrail and either an increase or a decrease in the magnitude of the negative shortwave radiative forcing depending on the orientation of the contrail with respect to the sun. Although these two effects are individually quite modest (of order 10%), the fact that the total shortwave and longwave forcings largely cancel during the day means that the relative change in the net radiative forcing due to the 3D effect is substantial; in some cases this results in a doubling of the net forcing of the contrail, in other cases changing its sign. On a more general note, the relatively simple geometry of contrail cirrus provides an ideal test case for explaining the various mechanisms by which 3D photon transport can change the radiative effect of clouds, which can be rather difficult to visualize for more complex cloud scenarios.

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Section: A Sensitivity To Solar Zenith and Azimuth Anglesupporting

confidence: 96%

Section: B Experiments Performedsupporting

confidence: 85%

Section: A Radiative Transfer Modelmentioning

confidence: 68%

Section: Introductionmentioning

confidence: 97%

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A Sensitivity Study of the Effect of Horizontal Photon Transport on the Radiative Forcing of Contrails

Gounou

Hogan

2007

Journal of the Atmospheric Sciences

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“…As a consequence, the contrail forcing grows linearly with contrail cover in these models. Inhomogeneity e ects may be large in natural cirrus (Raschke et al, 1998), but were considered small for vertically thin cloud layers in the few studies addressing this issue Schulz, 1998). Fortuin et al (1995) computed the radiative forcing by contrails for ®xed atmospheric temperatures for the North Atlantic¯ight corridor.…”

Section: Radiative Properties Of Contrailsmentioning

confidence: 99%

Radiative forcing by contrails

Meerkötter¹,

Schumann²,

et al. 1999

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Abstract. A parametric study of the instantaneous radiative impact of contrails is presented using three di erent radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm A2 daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net e ect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.

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Radiative forcing by contrails

Meerkötter¹,

Schumann²,

Doelling

et al. 1999

Ann Geophysicae

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A parametric study of the instantaneous radiative impact of contrails is presented using three dierent radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm A2 daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net eect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.

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On the effect of cloud inhomogeneity an area averaged radiative properties of contrails

Cited by 9 publications

References 14 publications

A Sensitivity Study of the Effect of Horizontal Photon Transport on the Radiative Forcing of Contrails

A Sensitivity Study of the Effect of Horizontal Photon Transport on the Radiative Forcing of Contrails

Radiative forcing by contrails

Radiative forcing by contrails

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