[25] On 29 January 1946 the biggest ever sunspot group (about 1% of the total hemisphere) was recorded on the East limb [Pettit, 1946]. On 8 February, there was a strong and short geomagnetic storm. It was not against possible expectations in such cases. No forecasts were issued in the report of March by Pettit, but as we know, the biggest eruptive prominence ever observed from the Earth on the solar limb, happened on 4 June. Quite natural, no big geomagnetic storm followed after this eruption because of its unfavorable position. The previous similar in size enormous sunspot groups documented in October 1858 and ever biggest solar flare of 1 September 1859 probably confirm the common belief in the relation between subphotospheric origins of these extreme eruptive events.
[26] V. Grigoriev et al. (Astronomy Letters, 2007, in press) reported about an interesting observation based on SOHO/MDI data. Photospheric motions with vertical and horizontal velocities of the order ~1 km s -1 started to rise, rotate, and fall plasma before the appearance of the new powerful active region seen as magnetic enhancement with rapidly evolving sunspots even before first magnetic pores. According to our interpretation, a thermal pulse of convection under the photosphere penetrated up to upper layers and provoked the cyclone formation at the site of future sunspots and active region birth. The regular observation of the white light fluctuations, Doppler velocities, and thermal fields in the photosphere could be promising tool of possible forecasts using the nonmagnetic signatures of the future birth of the active region as an indicator.
Powered by TeXWeb (Win32, v.2.0).