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    Re: Susceptibility of GPS to CME, Rationale for CN?
    From: Brad Morris
    Date: 2018 Sep 29, 18:37 -0400
    Dr. Langley, perhaps you misunderstood my question.  In review, perhaps it was poorly phrased.  I will try again:

    Given your (meaning Dr. Langley's) knowledge of the GNSS system and its susceptibility to solar events, is celestial navigation a prudent backup to GPS navigation if a solar event occurs?  

    I've kept this quite short, so the question could remain in focus.  I found the articles informative and I do appreciate the time you have taken to point them out.  


    On Sat, Sep 29, 2018, 9:25 AM Richard B. Langley <NoReply_Langley@fer3.com> wrote:

    " The paucity of precise data from prior solar cycles may limit your ability to predict future levels of activity."

    It's impossible to predict when a strong solar flare or CME large enough to disrupt GNSS might occur. They can even strike near the minimum of the roughly 11-year solar cycle. Most outbursts are not severe enough to prevent GNSS being used but simply reduce positioning accuracy with the vertical coordinate (as is always the case) being a few times worse than the horizontal coordinates. Potentially more impactful are strong solar radio storms, which drown out the GPS signals. NOAA reported on such a storm in December 2006 here: https://web.archive.org/web/20071213212715/http://www.noaanews.noaa.gov/stories2007/s2831.htm (from the "Wayback Machine" as the original item is missing or got moved on the NOAA site).

    Much more impactful would be a repeat of the 1859 Carrington Event: https://science.nasa.gov/science-news/science-at-nasa/2008/06may_carringtonflare

    -- Richard Langley

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