A preliminary survey of tropospheric refractive index measurements for U. S. interior and coastal regions

This paper summarizes the results of approximately 700 tropospheric refractive index soundings carried out between July, 1952 and December, 1952, using aircraft-mounted direct-reading refractometers. Extensive observations up to heights as great as 25,000 feet have been made in the southern Ohio region and off the U. S. East and West Coasts. Preliminary statistical analyses on the occurrence of standard and non-standard average gradients are presented together with qualitative meteorological correlations. The existence of large scale index variations near certain cloud boundaries is confirmed and these are tentatively explained in terms of the contrast between the free air refractive index and that of a vertically moving air current having a refractive index representative of some lower atmospheric level.