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  • Author or Editor: B. P. Briegleb x
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B. P. Briegleb
,
P. Minnis
,
V. Ramanathan
, and
E. Harrison

Abstract

We have taken an important first step in validating climate models by comparing model and satellite inferred clear sky TOA (top-of-atmosphere) albedos. Model albodos were computed on a 1° × 1° latitude-longitude grid, allowing for variations in surface vegetation type, solar zenith angle, orography, spectral absorption/scattering at surface and within the atmosphere. Observed albedos were inferred from GOES-2 minimum narrowband (0.55–0.75 μm) brightness for November 1978 over South America and most of North America and adjacent ocean regions. Comparisons of TOA albedos over ocean agree within ±1% (the unit for albedo is in percent and the differences in percent denote absolute differences), and thus lie within both theoretical uncertainties (due to water vapor and aerosol concentrations, and ocean surface spectral reflectivity), as well as observational uncertainties. The ocean comparisons also show significant latitudinal variations in both model and observations. Albedos over land mostly agree within ±2% for the entire range of significant geographical variation of albedo from 13% over the Amazon Basin to 24% over mountains of western North America. These agreements lie within both theoretical uncertainties (due to surface type and spectral/zenith angle dependencies), as well as observational uncertainties (due to spectral and angular conversions of observed brightness to broadband albedos).

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R. D. Cess
,
B. P. Briegleb
, and
M. S. Lian

Abstract

At low latitudes the seasonal variation in the radiation budget of the earth-atmosphere system is due largely to seasonal variability in cloudiness. Making use of this, we have estimated, from three different sets of satellite data, the relative albedo versus infrared modifications associated with cloudiness variability at low latitudes. Employing satellite data sets due to Ellis and Vonder Haar (1976) and Campbell and Vonder Haar (1980), we find that the albedo modification is somewhat less than that of the infrared. But when use is made of radiation budget data derived from NOAA–NESS scanning radiometer measurements, the albedo modification dominates over that of the infrared by nearly a factor of 2. This obviously suggests that estimates of climate feedback associated with changes in cloudiness are highly dependent on the satellite data set which is employed. It is further suggested that these differences might be in part attributable to the NOAA–NESS data being derived from narrow spectral measurements.

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Ruth S. Lieberman
,
Conway B. Leovy
,
Byron A. Boville
, and
Bruce P. Briegleb

Abstract

In this paper, the authors assess the suitability of the heating fields in the latest version of the NCAR Community Climate Model (CCM2) for modeling the thermal forcing of atmospheric tides. Accordingly, diurnal variations of the surface pressure, outgoing longwave radiation, cloudiness, and precipitation are examined in the CCM2. The fields of radiative, sensible, and latent beating are similarly analyzed. These results are subjectively compared with available data.

Equatorial diurnal surface pressure tides are fairly well simulated by CCM2. The model successfully reproduces the semidiurnal surface pressure tides; however, this may result in part from reflection of wave energy at the upper boundary. The CCM2 large-scale diurnal OLR is generally consistent with observations. The moist-convective scheme in the model is able to reproduce the diurnally varying cloudiness and precipitation patterns associated with land-sea contrasts; however, the amplitudes of CCM2 diurnal continental convective cloudiness are weaker than observations. The CCM2 boundary-layer sensible heating is consistent with a very limited set of observations, and with estimates obtained from simple models of diffusive heating. Although the CCM2 tropospheric solar radiative heating is similar in magnitude to previous estimates, there are substantial differences in the vertical structures. A definitive assessment of the validity of the CCM2 diurnal cycle is precluded by the lack of detailed observations and the limitations of our CCM2 sample. Nevertheless, the authors conclude that the global-scale components of the CCM2 diurnal heating are useful proxies for the true diurnal forcing of the tides.

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Jennifer A. MacKinnon
,
Zhongxiang Zhao
,
Caitlin B. Whalen
,
Amy F. Waterhouse
,
David S. Trossman
,
Oliver M. Sun
,
Louis C. St. Laurent
,
Harper L. Simmons
,
Kurt Polzin
,
Robert Pinkel
,
Andrew Pickering
,
Nancy J. Norton
,
Jonathan D. Nash
,
Ruth Musgrave
,
Lynne M. Merchant
,
Angelique V. Melet
,
Benjamin Mater
,
Sonya Legg
,
William G. Large
,
Eric Kunze
,
Jody M. Klymak
,
Markus Jochum
,
Steven R. Jayne
,
Robert W. Hallberg
,
Stephen M. Griffies
,
Steve Diggs
,
Gokhan Danabasoglu
,
Eric P. Chassignet
,
Maarten C. Buijsman
,
Frank O. Bryan
,
Bruce P. Briegleb
,
Andrew Barna
,
Brian K. Arbic
,
Joseph K. Ansong
, and
Matthew H. Alford

Abstract

Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean and, consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Away from ocean boundaries, the spatiotemporal patterns of mixing are largely driven by the geography of generation, propagation, and dissipation of internal waves, which supply much of the power for turbulent mixing. Over the last 5 years and under the auspices of U.S. Climate Variability and Predictability Program (CLIVAR), a National Science Foundation (NSF)- and National Oceanic and Atmospheric Administration (NOAA)-supported Climate Process Team has been engaged in developing, implementing, and testing dynamics-based parameterizations for internal wave–driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here, we review recent progress, describe the tools developed, and discuss future directions.

Open access