PREDICTION MODEL FOR THE DIURNAL BEHAVIOR OF THE TROPOSPHERIC SCINTILLATION VARIANCE

Tropospheric scintillation is caused by variations of refractive index due to turbulence. The only meteorological input parameter for two co mmon current scintillation models by Karasawa et al. and by ITU-R is t he monthly average of wet part of refractivity N-wet at ground level, which is not directly associated with turbulence. The diurnal correlat ion between N-wet and scintillation variance is very weak. Because clo uds and cloud formation are closely associated with the turbulence, qu antitative cloud parameters were looked for. Cloud type information ba sed on edited synoptic cloud reports are available from common databas e of CDIAC and NCAR. Both diurnal and seasonal variations between scin tillation variance and average amount of Cumulus type clouds are well correlated. Using this cloud information together with N-wet, a new me thod for tropospheric scintillation variance predicting also diurnal v ariations is introduced, This model is derived and tested using scinti llation measurements at four sites in different climates in Finland, U nited Kingdom, Japan, and Texas.