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It is shown that amplitude modulated HF heating in the ionospheric E-region, can produce substantial power in the ELF/ULF range even in the absence of ambient ionospheric currents. The signals are associated with spontaneous generation of magnetic fields caused by the coupling of the hot spot temperature gradient to the ambient ionospheric density gradient (Vn × VT). The mechanism produces values for PC5 micropulsations consistent with those observed by Stubbe and Kopka (1981).