The 11.08.1999 solar eclipse and the ionosphere: a search for the distant bow-wave

The advantage of studying eclipse disturbances is the perfect predictability of their 4D source geometry, which allows for preparation of adapted systems and schedules. The total solar eclipse period of August 11, 1999 across Europe was notable for exceptionally uniform solar disk, steady solar wind and quiet magnetospheric conditions. Large-scale gravity wave activity prior to the eclipse however disturbed the initial 0900 LT thermosphere weather. This rapid letter is an advance summary about one particular aspect of the West European ionosonde and radar results of the eclipse experiment. It focusses on the possible emergence of a distant eclipse frontal bow-wave. This was expected as a consequence of the supersonic shock of stratospheric Ozone cooling. First-look data of Vertical Incidence Digisonde records are greatly improved by their Real-Time acquisition of inverted true-height profiles. The EBRE (Tortosa, Spain) foF1 and foF2 simultaneous oscillations observed from the second to the fourth hour following maximum solar occultation appear as convincing indicators of the bow-wave signature. Large fluctuations in foF1 and foF2 during some of our control days, of usual gravity wave character, emphasize the importance of meteorologic disturbances on mid-latitude ionosphere variability. (C) 2001 Elsevier Science Ltd. All rights reserved.