Abstract. This paper discusses SPA's measured at long VLF propagation paths in the lower ionosphere and their association with soIar X-ray bursts observed by USNRL satellites in the 0-3 A, 0-8 A_ and 8-20 ~ bands. Excellent correlations were found between the SPA importances (in degrees per Mm) and the logarithm of the X-ray burst peak intensities. A hardening of the X-ray burst spectra is evident for increasing importance of SPA's; the threshold energy required for the occurrence of such anomalies was estimated, it is 4.3 × 10 -5 ergs cm -2 sec -1 in the main ionizing band of 0-3 A.. It was also possible to derive the effective recombination coefficient at the normal D-region height of 70 kin, this being c~r ~ 6 x 10 -6 cm 3 sec-1; furthermore ion production rates were estimated during SPA's at heights below the reference level.

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The circular polarization from coronal condensations at ). =4.3 cm correspond to the extraordinary mode of propagation, due to the contribution of preceding spots' polarities, being usually left-handed. The fewer cases of right-handed polarization are normally associated to an excess of sunspot plages in the southern hemisphere, thus making it difficult to give evidence for magnetoionic coupling phenomena as a general rule.

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