Multi-plots from New England Grape cluster

[Bill Blackwell]

Hi all,

We observed huge Doppler shifts on 7-19-22 from 0700-1000 UTC coinciding with a large power drop. See attachments.

The four New England Grape nodes shown in these plots are within 17 miles of one another in Eastern MA.

We thought these would be of interest.

73, Bill AB1XB - node 33

[Phil Erickson]

Hi all,

  I corresponded separately with Bill AB1XB, so copying the list here.  There is interesting geophysical interpretation of these results.

  There was a significant change in direction of the interplanetary magnetic field at 0700 UTC on 2022-07-19, in the XY plane, not the north-south Z plane. (Z = pointing toward the north magnetic pole; X points toward dusk and Y points towards the sun, to complete a right handed coordinate system).  See attached plot from NOAA's DSCOVR solar wind monitor (upstream of Earth) - the vertical line in the middle marks the time when your measurements show a change.  

  You might say "but the changes we saw in the Grape system were at ~0800 UT, not 0700 UT".  That's because DSCOVR is about 1.6 million km upstream of Earth.  The plot shows that the solar wind speed was ~500 km/s - so the time for the disturbance to propagate from satellite to the front of the magnetosphere might be 1.6 million km / 500 km/s = 3200 seconds or 53 minutes.  (In reality, the front of the magnetosphere is about 60,000 km out in front of Earth, so I have to subtract that from the 1.6 million km, adjusting the time slightly downwards to 51 minutes or so.). 

  Add 51 minutes to 0700 UT, and you get 0751 UT - just about the time your Doppler goes strongly positive.  The reduction in amplitude at 0700 UT is more interesting to me because that appears to be a reaction to slightly earlier disturbed conditions (not the one I cite in the plot).

 

  The magnetic field plotted by DSCOVR is embedded in the solar wind, the expanding outer corona which flows in the space between planets.  Solar wind magnetic field direction changes (in 3 dimensions!) change the forcing on Earth's magnetic field and cause the magnetosphere to reconfigure - known as a "substorm".  These changes in force and electrodynamic coupling between the magnetosphere and ionosphere drive changes in the ionosphere, including enhanced motion in the form of things known as traveling ionospheric disturbances.  These would impact the line of sight Doppler measurements you're making.  The amplitude reductions could be driven by embedded irregularities in the ionosphere which were amplified by the energy input from changes (guessing), or it could be suddenly enhanced electron density which changed the HF propagation between WWV and your receivers.

  It's complex to "invert" Grape measurements in a single sense to reveal these parameters, but the Grape project and HamSCI are working on trying to fold these data in with other measurements to better understand ionospheric dynamics.

  Very nice work by the New England Grape collective, and I'm glad the data is going into the Grape system!

73

Phil W1PJE

[Phil Erickson]

PS: in case it's not clear, the thing to focus on is the second plot down in the stack, which shows "phi" = interplanetary magnetic field clock angle (X vs Y) in the plane perpendicular to a line threading the north and south terrestrial magnetic poles.  (For the geospace people on this list: yes, I'm radically simplifying SM/GSM/etc. magnetospheric coordinates here for clarity.). Notice the flip from Blue (> 180 deg angle) to red (< 180 deg angle), indicating the magnetic field direction shift.

Note as well that if you just examine the top plot - total magnetic field (Bt) and the north-south Z component (Bz), you wouldn't spot the change.  

73

Phil W1PJE