The cause of a discrepancy in the CCIR Report 322‐3 (International Radio Consultative Committee (CCIR), 1988) radio noise model is reported. The basis for this discrepancy results from the procedure used to prepare the measured noise data for the determination of a global numerical representation of the 1‐MHz data. In the development of the model, correction factors to an older CCIR model were determined for each measurement site. These corrections were interpolated for each time block and season to a grid of 100 latitude points by 84 longitude points. The correction factors at each grid point were then added to corresponding values for the older CCIR model, and finally, the resulting data for each time block and season were numerically mapped. Nineteen locations were used in the final model. Four sites used in the original CCIR model were not used. As either no correction factors were obtained for these locations or a correction factor of zero was used to maintain the status quo, the interpolation algorithm produced erroneous values near these four sites in determining the 100‐by‐84 grid of correction factors. For Bill, Wyoming, the result is not too serious; but for the other three sites at some seasons and time of day, the error is serious. For Thule, Greenland; for Ibadan, Nigeria; and for Byrd Station, Antarctica; the maximum and minimum errors were 10.1 and −10.8 dB; 12.5 and −1.5 dB; and 12.0 and 3.0 dB, respectively. Examination of the geographical extent of these errors reveals that the error is not confined to the measurement location but in fact can be very large. This geographical enhancement of the error is most serious during June, July, and August and least serious during December, January, and February. The error as a function of frequency was found to be diurnally dependent, being more serious during the daytime hours. The absence of the data locations as nodes in the interpolation affected the accuracy of the interpolation itself. The CCIR Report 322‐3 atmospheric noise model should be used with caution, especially for locations in the northern and southern high latitudes, the Arabian Peninsula, northern Africa, and the Mid‐Atlantic Ocean areas.

No abstract

In an earlier paper it was pointed out that temporal variability in the dispersive properties of the propagation medium can cause a band of wave velocities to be associated with each frequency component in the time series of a sampled quantity. This results in degrading the coherence between stations separated in the direction of propagation and can cause significant error in the apparent wave velocity as deduced from the phase of the cross spectra. This bandwidth is complementary to the concept of beamwidth, which principally degrades the coherence between stations separated perpendicular to the direction of propagation. The present paper uses numerical procedures to extend the earlier results to larger beamwidths and bandwidths.

A VLF propagation and a D‐region aeronomy model have been used to predict the effect of two solar eclipses on VLF propagation to Aztec, Arizona. Transmissions at 12.2 kHz from Hawaii were monitored during the eclipse on September 11, 1969; and transmissions at 12.0 kHz from Trinidad, at 24 kHz from transmitter NBA, at 12.5 kHz from Forestport, New York, and at 17.8 kHz from transmitter NAA were monitored during the eclipse on March 7, 1970. The VLF phase predictions were found to agree with measurements except for the two nearly coincident northerly paths from Forestport and NAA.

A practical but simplified atmospheric noise model in universal time for 1-MHz Faro usable in estimating system signal-to-noise ratios in microminicomputer-based HF propagation prediction systems is presented. Numerical mapping techniques were used to represent worldwide atmospheric noise in 24 numerical maps: one for each of six 4-hour UT time blocks and each of four 3-month periods. This representation results in a minimum reduction by one fifth in the number of coefficients necessary in computer memory over that of an earlier model in which the map represented an entire 24-hour day. The simpler expression for the median noise levels (Faro) results in significant savings in computer code and time. Several versions were produced, each with a different number of coefficients (number of harmonics) in the Fourier representation for each time block. The number of coefficients ranged from 192 coefficients per time block for the most accurate versions to 35 coefficients for the least accurate. The accuracies were determined by calculating the rms residual between values of Faro used to develop the model and the corresponding values computed from each model. The most accurate model had an average rms error for all times and seasons of 1.3 dB, whereas the least accurate had arms errol of 4.5 dB. During summer, the worst season, the most accurate model had arms error of 1.4 dB, whereas the least accurate had arms error of 5.6 dB. The International Radio Consultative Committee noise data used to generate the models had an average standard deviation of the error at 1 MHz of 5.4 dB and an error of 6.7 dB during summer; the numerical map in use in current HF prediction programs has an average rms error of 1.7 dB and an error of 2.0 dB during summer. The locations of the maximum absolute deviations of the models were confined to a small region in central Africa. several types. The most usual types are of atmospheric, galactic, and man-made origin. Below about 30 MHz, atmospheric noise usually predominates. It may change over wide limits as a function of location, frequency, bandwidth, time of day, season, and azimuthal direction. Although in the presence of local storms, atmospheric noise may be an important factor at almost any frequency, it is the ability of noise from distant thunderstorms to propagate over This paper is not subject to U.S. copyright. Published in 1983 by the American Geophysical Union. Paper number 3S0548. long distances that makes it so important at HF and below. Because ionospheric absorption is high during the daytime, the contribution from distant sources is reduced, and local sources become important. Because of the strength of propagated noise from distant storms at night, the diurnal maximum occurs at night, even for locations in the earth's major source regions. The internationally accepted method of predicting atmospheric noise is outlined by the International Radio Consultative Committee (CCIR) [1964] in CCIR Report 322. The purpose of this paper is to describe the development of a practical but...