lmd_Cheruy1991_abstracts.html

1991 .

F. Cheruy, R. S. Kandel, and J. P. Duvel. Outgoing longwave radiation and its diurnal variations from combined Earth Radiation Budget Experiment and Meteosat observations :2. Using Meteosat data to determine the longwave diurnal cycle. Journal of Geophysical Research, 96:22623, December 1991. [ bib | DOI | ADS link ]

For April and July 1985, applying the narrow to broadband conversion of part 1 to Meteosat observations obtained at 3-hour intervals (ISCCP B2 data), we determine the monthly mean radiant exitance as well as the mean diurnal variation, over 2.5deg×2.5deg latitude-longitude regions of tropical Africa and the neighboring Atlantic Ocean. We compare these determinations with those obtained directly from the ERBS and NOAA 9 Earth Radiation Budget Experiment (ERBE) data for this month, for which the time sampling is sparser and not so uniform. Excellent agreement is obtained in most cases, in particular for the overall monthly means. However, for the monthly mean diurnal variation there are situations in which the ERBE time sampling, the nature of the ERBE diurnal modeling scheme and the convolution of weather system changes with the diurnal cycle, combine to produce significant differences between the ERBE determination and the Meteosat result. These differences would mostly have been much smaller had the third ERBE instrument package been in operation (at 0730/1930 LT) as originally planned. We consider possible improvements in diurnal interpolation procedures, but note that there is no general way to remove bias resulting from inadequate time sampling.

F. Cheruy, R. S. Kandel, and J. P. Duvel. Outgoing longwave radiation and its diurnal variation from combined ERBE and Meteosat observations: 1. Estimating OLR from Meteosat data. Journal of Geophysical Research, 96:22611, December 1991. [ bib | DOI | ADS link ]

Radiative transfer calculations show that measurements in two relatively narrow spectral domains, corresponding to the atmospheric infrared window and to a band of water vapor absorption, can account for nearly all of the variance of outgoing longwave radiation integrated over the entire thermal spectrum. Statistical analyses of simultaneous colocated Meteosat radiance and Earth Radiation Budget Experiment (ERBE) radiant exitance data, for the months of November 1984 and April and July 1985, yield regression coefficients for estimating longwave radiant exitance M_LW from radiances observed in the Meteosat infrared (IR) window and water vapor (WV) channels, with root-mean-square errors of the order of or less than 10 W m^-2. The coefficients thus obtained are in good agreement with coefficients relating M_LW, IR and WV from analysis of results of radiative transfer calculations. Meteosat data can then be used to estimate M_LW at times not sampled by ERBE. Although some biases appear to exist over areas of heterogeneous cloud cover, they should not significantly affect studies of strong diurnal variations.

F. Cheruy and R. S. Kandel. Use of meteosat data for validation of the diurnal variation of the outgoing longwave radiation produced by ERBE. Dynamics of Atmospheres and Oceans, 16:73-84, October 1991. [ bib | DOI | ADS link ]

Radiative transfer calculations have been performed to demonstrate the usefulness of the Meteosat observations in the relative narrow-band of the water vapour absorption (WV, 5.7-7.1 μm) in addition to the observations in the atmospheric infrared window (IR, 10.5-12.5 μm) to deduce the integrated thermal outgoing longwave radiation (OLR). A statistical analysis of colocated and nearly simultaneous Meteosat and the Earth Radiation Budget Experiment (ERBE) data has yielded regression coefficients for estimating the OLR with Meteosat data during the months of April and July 1985. These results have been used to study the mean diurnal variation of the outgoing longwave radiation. The results show that in some cases, because of inadequate time sampling, the form (and especially the phase) of the longwave (LW) diurnal cycle is incorrectly determined by ERBE, but that Meteosat data can improve the determination. In nearly all cases, such errors have little or no influence on the determination of monthly mean LW flux fields.