Tropospheric Effects in Ionosphere-Supported Radio Transmission

The importance of meteorological effects in tropospheric transmission has been presented by the authors in previous papers. More extended observations in the 40- to 50-Mc band, recently analyzed, substantiate high correlations with temperature, atmospheric refraction, and wind direction. Since ionospheric-supported transmissions must pass at least twice through the troposphere, investigations have been made for possible meteorological effects at frequencies from the broadcast band to 10 Mc and comparisons made with known tropospheric reception at frequencies in the 40 to 50 Mc band. Correlation coefficients as high as 0.8 ± 0.1 are shown. Reception from WBBM, Chicago, 850 miles distant, based on 3 years data, show a direct correlation with surface refraction and with atmospheric temperature changes. Night fields rise from a minimum one day before a temperature rise equal to 10°F to a maximum on the day such temperature change occurs. Similarly, a drop in field occurs one day prior to an equal temperature fall. Studies of reception at Needham of WWV, 5 Mc (Beltsville, Md.) 373 miles distant, show similar correlations as those determined for the broadcast band. Furthermore, night fields of WWV, 5 Mc tend to a maximum one day preceding a prevailing SE wind directed broadside to the transmission path. Little correlation was found with NE winds directed along the path. Variations in field intensities, range from 15 to 30 per cent of mean fields dependent upon meteorological conditions at the receiving end.