Pinker and Laszlo of the University of Maryland processed the satellite data analyses held in the ISCCP archive, see Schiffer and Rossow (1985), to create five global radiation products. The 2.5 deg. x 2.5 deg. ISCCP data were used to generate estimates of the surface and top of the atmosphere (TOA) incident and upwelling shortwave fluxes. In addition, the surface downwelling PAR flux was also calculated. These estimates were generated every 3 hours based on GMT observing times, i.e., 0000Z, 0300Z, 0600Z, etc. To reduce the noise in their products, Pinker and Laszlo averaged the observations for each 3-hour period by month to produce a mean diurnal cycle of eight (monthly-averaged) values for each month in 1987-1988. NASA LaRC used a similar methodology to generate monthly means (not diurnally resolved) of surface incident and net shortwave and longwave radiation, and net radiation, see Darnell et al. (1992).
Documentation available on CD-rom (volume1)
This data is available on Volume 1.