Topband: Meanook rises again

[Robert Brown]

Friends in Radio Land,
 
     September is upon us again and another 160 meter DX season
is about to begin.  Let me give you the bad news first - magnetic
storminess peaks at the equinoxes, as shown in the historical data
appended to this note. So I tell you with considerable fear and
trepidation just what the records from the Meanook magnetometer
suggest for the month of September.  But, history indicates that
solar streams in September may not be as stable as the data from
August would predict.
 
     Be that as it may, as far as K-sums are concerned, the five
quietest days in August were 24, 16, 11, 20, and 8, with K-sums
ranging from 5 to 12.  Beyond that, the five most disturbed days
were 5, 13, 31, 17, and 22, also in descending order.  Add 27 days
for another solar rotation and you should have an idea of what is
in store for September, both good and bad.
 
     As a bonus, this DX season starts with a DXpedition, JT1FZW,
in the field from September 18 to 27.  This effort will surely
draw a crowd and distances to North America are the greatest along
the East Coast, up to about 11,000 km.  Oddly enough, a modest
amount of magnetic activity, say Kp=1 or so, may be an aid, not a
hindrance, for propagation from the East Coast.  Let me explain.
 
     The longitude difference between the East Coast and Mongolia
is close to 180 degrees, putting the two on opposite sides of the
polar cap and with a dawn-dusk path connecting them at the best
times for a contact.  Thus, the path is well-removed from strong
auroral activity around local midnight; as a result, ionospheric
electric fields which drive the aurora and the magnetic current
systems may also have a novel effect on the path region.
 
     In particular, electric fields in the polar cap increase the
energy or ion temperature of O+ ions above the E-region and then
two ionospheric reactions which are very temperature-sensitive
 
                    O+ + N2 -----> NO+ + N
                    O+ + O2 -----> O2+ + O
 
speed up, with the result of copious production of those two
molecular ions and enhanced electron recombination
 
                    NO+ + e- ----> N + O
                    O2+ + e- ----> O + O
 
in the region.  Those reactions aid propagation across the polar
cap as they can lower electron densities up to 20% at altitudes
below 175 km, where 160 meter RF is propagated, making sort of a
"polar hole" and reducing absorption and skewing in the region.
 
     Looking at the quiet days in August, a favorable situation
like that given above might develop close to the equinox.  So stay
tuned; things may not be as bleak as history would indicate.
 
------------------------------------------------------------------

 
                 Magnetic storms per month
 
               1,475 storms from 1868 to 1992
 
        Number
 
         180
                                       *
         160         *                 *  *
                     *  *              *  *
         140         *  *              *  *
                  *  *  *              *  *
         120      *  *  *  *        *  *  *  *
                  *  *  *  *        *  *  *  *
         100   *  *  *  *  *        *  *  *  *
               *  *  *  *  *        *  *  *  *
          80   *  *  *  *  *  *  *  *  *  *  *  *
               *  *  *  *  *  *  *  *  *  *  *  *
          60   *  *  *  *  *  *  *  *  *  *  *  *
               *  *  *  *  *  *  *  *  *  *  *  *
          40   *  *  *  *  *  *  *  *  *  *  *  *
               *  *  *  *  *  *  *  *  *  *  *  *
          20   *  *  *  *  *  *  *  *  *  *  *  *
               *  *  *  *  *  *  *  *  *  *  *  *
               J  F  M  A  M  J  J  A  S  O  N  D
 
Data from the National Geophysical Data Center, Boulder, CO.