Metop Flare Repeat Cycle

From: Gerhard HOLTKAMP (grd.holtkamp@t-online.de)
Date: Sun Aug 29 2010 - 18:27:59 UTC

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    MetOp-A (2006-044A) is on a sunsychronous orbit with a sub-repeat period of 5 
    days meaning that its groundtrack will repeat itself approximately (but not 
    exactly) every five days. If conditions are right this same repeat period can 
    also be observed with Metop flares as I just realized.
    
    Five days ago on 24-AUG-2010, 20:30:12 UTC I observed a mag -0.5 flare from 
    the center left ASCAT antenna of MetOp. If it wasn't for an overcast sky I 
    would be able to see a mag -4 flare tonight (29-AUG-2010, 20:26:28 UTC) very 
    close to the position of the last flare. Another five days on there will be 
    yet another flare and on it goes all throughout September. 
    
    Each successive flare occurs about 4 minutes earlier (local time) and is about 
    1 or 2 degrees higher in elevation that the flare five days earlier. The 
    magnitude varies but stays in the negative mag range for me. Finally at the 
    beginning of October the series comes to an end (and an orbit maintenance 
    maneuver is planned for Metop at this time anyway).
    
    The groundtrack for Metop flares moves roughly South to North. Observers at 
    mid-northern latitudes which are close to my longitude of 8.7 degrees East 
    should be able to see the same phenomena. As this groundtrack is shifted by 
    about 5 degrees from one day to the next observers at longitudes with a 5 
    degree spacing from my 8.7 should be in it as well. (Observers in North 
    America should be at a five degree longitude spacing from 82.5 W or from 113 
    W).
    
    Using generic Metop orbit elements I checked different years and found that 
    you typically have to wait three years or so to see this kind of flare series 
    at a particular site. On the Northern Hemisphere this flare season lasts from 
    mid-August until mid-October with lower latitudes starting and ending earlier 
    within this interval than higher latitudes. On the Southern Hemisphere this 
    flare season is in January and February.
    
    Metop has two other antennas causing flares but I could only find pairs of 
    flares seperated by five days but not longer series for those surfaces. If 
    there is a flare series in September I would have expected another one in 
    April due to symmetry but I didn't find that. I'll have to think about this 
    asymmetry on a sleepless night (that always helps to put me asleep!)
    
    Gerhard HOLTKAMP
    Darmstadt, Germany,
    49.8822 N, 8.6558 E
     
    
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