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 common current scintillation models by Karasawa et al. and by ITU-R is the monthly average of wet part of refractivity Nwet at ground level, which is not directly associated with turbulence. The diurnal correlation betweenNwet and scintillation variance is very weak. Because clouds and cloud formation are closely associated with the turbulence, quantitative cloud parameters were looked for. Cloud type information based on edited synoptic cloud reports are available from common database of CDIAC and NCAR. Both diurnal and seasonal variations between scintillation variance and average amount of Cumulus type clouds are well correlated. Using this cloud information together with Nwet , a new method for tropospheric scintillation variance predicting also diurnal variations is introduced. This model is derived and tested using scintillation measurements at four sites in different climates in Finland, United Kingdom, Japan, and Texas