Briefly, The K index is more immediate - it is measured and reported a 4-hour intervals. The A index is a logarithmic derivative of the values of K over a longer preceding period. Therefore you will see the K spike in response to geomagnetic activity several hours before you will see the corresponding increase in the A index.
Typically auroral conditions will manifest themselves as the K increases. Usually it take a change in the K of 2 units or more to be notable. Except for the fact that the K is still leading the A timewise, the reverse is true as the activity wanes. Here though, the residual auroral activity takes longer to decay than it took to rise so the decline in the A index may be more reflective of what's actually happening with reception. A K index of 4+ indicates watching the bands, although one isolated 4-hour period at that level isn't significant. A single isolated period may be indicative of an auroral substorm, which may create moderate auroral DX conditions which will fade more quickly. An A index over 20 may or may not lead to auroral DX conditions, however an A index of 30+ usually does. A really serious auroral storm resulting in strongly auroral conditions may have an A index value of anywhere from 50 to 150, which may persist for a few days. The longer the duration of the high activity, the more the conditions can be impacted, and therefore the longer it will take to decay. Many times the best auroral conditions are found after the peak and early in the decay phase. Any questions ? :-} Russ Edmunds 15 mi NW Phila Grid FN20id <[email protected]> AM: Modified Sony ICF2010's (4) barefoot w/whip FM: Yamaha T-80 & T-85, each w/ Conrad RDS Decoder; Onkyo T-450RDS; Tecsun PL-310 ( 4); modified Sony ICF2010's (3) w/APS9B @ 15'; modified Sony ICF2010 w/whip On Wed, Oct 5, 2016 at 10:06 PM, <[email protected]> wrote: > Colin, I for one (of many?) would appreciate a refresher on what to expect > with varying indices of A and K. > > For example...the comment below is useful...and borne out by CX this > morning. > > Thanks in advance! > > > Mark Durenberger > > -----Original Message----- From: R. Colin Newell > Sent: Wednesday, October 05, 2016 3:30 PM > To: Mailing list for the International Radio Club of America ; Paul Walker > Subject: Re: [IRCA] WWV Solar Report > > Although the A index has trended upwards, the K is trending downward - > > For those that do not pay a lot of attention to these charts, that is an > indicator of potentially improved listening conditions. > > > -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Trends -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- >> Date 04 04 04 04 04 04 04 05 05 05 05 05 05 05 >> UTC 0000 0300 0900 1200 1500 1800 2100 0000 0300 0600 0900 1200 1500 1800 >> SFlx 88 88 88 88 88 88 93 93 93 93 93 93 93 93 >> A-in 14 14 14 14 14 14 25 26 26 26 26 26 26 26 >> K-in 3 4 4 4 4 2 3 4 4 4 3 3 2 2 >> Current Solar information available at http://www.am-dx.com/wwv.htm >> >> >> >> >> -- > Colin Newell - Editor and creator *of *Coffeecrew.com > <http://www.Coffeecrew.com> and DXer.ca <http://www.DXer.ca> - > VA7WWV | Twitter @CoffeeCrew | Victoria - Canada > _______________________________________________ > IRCA mailing list > [email protected] > http://montreal.kotalampi.com/mailman/listinfo/irca > > Opinions expressed in messages on this mailing list are those of the > original contributors and do not necessarily reflect the opinion of the > IRCA, its editors, publishing staff, or officers > > For more information: http://www.ircaonline.org > > To Post a message: [email protected] > _______________________________________________ > IRCA mailing list > [email protected] > http://montreal.kotalampi.com/mailman/listinfo/irca > > Opinions expressed in messages on this mailing list are those of the > original contributors and do not necessarily reflect the opinion of the > IRCA, its editors, publishing staff, or officers > > For more information: http://www.ircaonline.org > > To Post a message: [email protected] > > _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
