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T. Dale Bess

Abstract

Outgoing longwave radiation (OLR) measurements from the Nimbus-6 ERR wide field-of-view (WFOV) instrument are used to study daytime and nighttime radiation variability on a 15° regional, zonal and global scale. An analysis of components of variance is used to determine how much of the total variability is due to between-region and within-region variance. Most of the analysis is on July and January data from one yr of Nimbus-6 ERB. Different geographical scales are considered: regions within latitude zones and latitude zones within hemispheres. Results show that much of the variability is spatial, peaks in the tropics and subtropics, and is concentrated in the Northern Hemisphere. Daytime variability is generally larger than nighttime variability for July but not for January. Variance in OLR in the tropics and subtropics is largely a function of cloud variability.

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G. Louis Smith and T. Dale Bess

Abstract

Monthly averaged, resolution enhanced global distributions of the Earth's emitted radiation, as measured by the Nimbus-6 Earth Radiation Budget (ERB) wide field of view radiometers, have been analyzed for 1 year of data from July 1975 to June 1976. These distributions am expressed in terms of spherical harmonic coefficients, and time and space variability of the emitted radiation field is studied in terms of these coefficients. The average annual distribution amounts for 78% of the space-time power, and the annual cycle accounts for 17% of the power. Spatial variations over the globe are described in terms of degree variance, and longitudinal variations are described in terms of spectral power as a function of latitude. The longitudinal spectra were found to vary strongly with lime.

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T. Dale Bess and G. Louis Smith

Abstract

Eighteen months of wide field-of-view (WFOV) outgoing longwave radiation (OLR) measurements from the Earth Radiation Budget Experiment (ERBE) NOAA-9 and NOAA-10 spacecraft have been deconvolved to produce resolution-enhanced flux maps at the top of the atmosphere. NOAA-9 had a 0230 LST equator-crossing time, and NOAA-10 a 0730 LST equator-crossing time. Intercomparison of these results with ERBE scanner and numerical filtered WFOV results is made. Results have also been compared with corresponding months of deconvolved results from the Nimbus-7 spacecraft (1200 LST equator crossing). Comparisons have been made of zonal profile plots of OLR for the different sensors and of contour maps of differences in OLR between sensors. In general Nimbus-7 OLR results show reasonable agreement with NOAA-9 and NOAA-10 over most regions of the globe. The largest differences occur over the extratropies, noticeably over land and especially over deserts. This study suggests that long-term monitoring of OLR with WFOV sensors is feasible for globally averaged trends to an accuracy of less than 1 W m−2, for the global absolute mean to within 3 W m−2, and for regional monthly means to within 8 W m−2 for most of the globe. Global averages for numerical filtered and deconvolved NOAA-9 WFOV results are consistently higher than Nimbus-7 deconvolved results because NOAA-9 results over land and deserts are higher. However, the ERBE NOAA-9 scanner gives smaller values of OLR over most regions ofthe globe than either the NOAA-9 WFOV numerical filtered or WFOV deconvolved results.

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T. Dale Bess, Richard N. Green, and G. Louis Smith

Abstract

One year of longwave radiation data from July 1975 through June 1976 from the Nimbus 6 satellite Earth Radiation Budget (ERB) experiment is analyzed by representing the longwave radiation field by a spherical harmonic expansion. The data are from the wide field-of-view (WFOY) instrument. Results show that the limit of the spherical harmonic representation is 12th degree, based on degree valiance plots from 12 months. Degree variance plots also show that most of the power is in the lower degree terms. The axisymmetric (zonal) terms dominate with their coefficients representing approximately 80% of the degree variance. Contour maps of the radiation field show the geographical distribution of earth-emitted radiant exitance (W m−2) and reveal areas of high and low emitted radiation. The analysis also shows differences between the Northern and Southern Hemispheres which is presumably due to land/ocean distribution.

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T. Dale Bess, G. Louis Smith, and Thomas P. Charlock

Monthly mean outgoing longwave radiation (OLR) measurements in the form of global contour maps and coefficients of spherical-harmonic functions for each month of the 10-year period July 1975 through October 1985 have recently been completed. One data set contains three years (July 1975 to June 1978) of “continuous” data from the wide field-of-view sensor of the Earth Radiation Budget experiment (ERB) aboard the Nimbus-6 satellite. The other data set contains seven years (November 1978 to October 1985) of “continuous” data from the ERB experiment aboard the Nimbus-7 satellite.

The OLR broadband time series could be used, for example, to study the interannual variability of OLR. An example is given of two E1 Niños that occurred in the 10-year timeframe.

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Thomas P. Charlock, Fred G. Rose, T. Dale Bess, and G. Louis Smith

Abstract

The relationship between low frequency variations in extratropical fields of outgoing longwave radiation (OLR) and geopotential teleconnection patterns as determined by rotated principal components (RPC) analysis of the NMC 500-mb heights is investigated in the Northern Hemisphere. The monthly broadband OLR is obtained from the Nimbus-6 and Nimbus-7 Wide-Field-Of-View (WFOV) radiometer record.

Each of the main 500-mb teleconnection patterns has a characteristic signal in the OLR field for the month in which the 500-mb pattern occurs. The OLR signals mark cloud and diabatic heating events that are associated with the Reconnection patterns. Our demonstration of correlation between extratropical monthly OLR and geopotential height, coupled with the expected tropospheric response to radiation on monthly time scales, stresses the importance of the radiation simulation in model studies of the low frequency variability of atmospheric circulation.

The extratropical OLR does not appear to be a useful predictor for the 500-mb teleconnection patterns on a monthly time scale.

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David A. Short, Gerald R. North, T. Dale Bess, and G. Louis Smith

Abstract

Empirical studies of total outgoing infrared radiation IR and surface temperature T have shown them to be well correlated for large time and space scales. An analysis of one year of Nimbus-6 data shows that the simple form IR = A + BT (with A = 204 W m−2, B = 1.93 W m−2K−1) explains 90% of the area-weighted variance in the annual mean and annual cycle of the zonally averaged IR field. The geographical distribution of the annual cycle in IR shows a large amplitude over the continental interiors, as is found in the observed temperature field, and the ratio of the large amplitudes (Blocal) is approximately 2 W m−2K−1. This helps to explain our recent success in modeling the geographical distribution of the annual cycle in T with a two-dimensional, time-dependent energy balance climate model (EBCM) which makes use of the A + BT rule. The parameterization works well in regions where the thermal inertia is small and the annual cycles of T and IR are large and in phase. Those regions where Blocal differs markedly from 2 W m−2K−1 are where the IR is strongly affected by the cloudiness of seasonal precipitation regimes. This effect is especially evident over the tropical oceans where the parameterization fails; but that is where the thermal inertia is large, the seasonal cycle in T is small, and even large errors in the radiative cooling approximation will have little impact on seasonal cycle simulations by simple climate models.

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T. Dale Bess, Ann B. Carlson, Calvin Mackey, Fredrick M. Denn, Anne Wilber, and Nancy Ritchey

Five years of scanner data from the Earth Radiation Budget Experiment (ERBE), eight years of surface radiation budget (SRB) data, and one year of scanner radiation budget data from the French–Russian–German experiment, ScaRaB, will be available for use by colleges and universities [and primary and secondary (K–12) schools] over a World Wide Web browser. The database for ERBE is a 5-yr monthly average time series from February 1985 through December 1989, and ScaRaB is a 1-yr dataset from February 1994 to March 1995. ERBE and ScaRaB include shortwave radiative fluxes, emitted longwave radiative fluxes, and the earth's albedo measured at the top of the atmosphere. The SRB dataset spans the period from July 1983 through June 1991 and includes surface downward shortwave fluxes, surface downward longwave fluxes, surface albedos, and cloud percent. Students will have access to the data in three ways. They can display general image format images of any month and visually observe month-to-month or interannual variations. The data files for each month also have a spreadsheet format and can be downloaded in their entirety into any spreadsheet application program for further analysis. Third, using a live access server (LAS), students can interact directly with the data to select and subset datasets in terms of month, year, latitude, and longitude. The LAS allows students to view images of subsetted regions, and to subset data values to a file for further analysis. The server for this dataset is located at the National Aeronautics and Space Administration Langley Research Center, Hampton, Virginia.

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