Electromagnetic waves propagating thru an ionized medium with a magnetic
field present (in this case, the earth's) are split into two components - the        
ordinary (o) and extraordinary (x) ray which usually have their own distinct
(though physically close) actual paths in the ionosphere.  The phenomenon is
known as birefringence (with an earth-bound analogy, of sorts, seen in the
optical behaviour of some crystalline minerals such as Iceland spar).  It is
a consequence of the two-root solution of the Appleton quadratic formula.  In
most propagation calculations only the o-ray is considered.

Over recent years I have often been asked to "explain" the digisonde traces. The following samples are designed to illustrate a wide variety of phenomena that are commonly seen on ionograms. (Use the link near the bottom of this page for a set of the more-current Lowell Digisonde ionograms.)
Lowell Digisonde Thumbnail - Oct 12, 1998 - 2330z Oct 12, 1998 - 2330z 5Es echoes visible in this blanketing and non-blanketing Es sample Lowell Digisonde Thumbnail- Dec 19, 1999 - 1615z Dec 19, 1999 - 1615z ionogram just slightly complicated by not only the 2F2 and 2Es echoes but also the Es-F2 echo caused by the return of the outgoing pulse that had already been once returned by Es to the earth and then repenetrated the Es Lowell Digisonde Thumbnail- Jul 08, 1999 - 0200z Jul 08, 1999 - 0200z blanketing Es misleading automated digisonde into taking the Es-F echo for h'F to calculate a too-low M-factor and so a too-low MUF Lowell Digisonde Thumbnail- Feb 12, 2000 - 1900z Feb 12, 2000 - 1900z typical magnetic-storm supression of high-latitude foF2 along with increases of h'F2 resulting in greatly-reduced F2 MUF's (KBo: 5-5-6-7-5-4-4-2) Lowell Digisonde Thumbnail- Oct 22, 1999 - 0850z Oct 22, 1999 - 0850z magnetic storm almost obliterating any F echoes at night with very large h'F values creating small M-factors and thus very low MUF's (KBo: 6-6-7-5-4-4-3-3) a mix of multi-Es/F echoes with the Sep 22, 1999 magnetic storm featuring auroral Es (KBo: 3-2-3-4-4-3-5-6) Sep 22, 1999 - 2215z Sep 22, 1999 - 2310z Lowell Digisonde Thumbnail- May 17, 2000 - 0615z May 17, 2000 - 0615z spread-F echoes typical of many nighttime magnetic disturbances (The heavy Es levels are only incidental in this case.) (KBo: 4-5-5-3-2-2-2-3) Lowell Digisonde Thumbnail- Jun 18, 2000 - 1400z Jun 18, 2000 - 1400z nice example showing F1 and F2 layers, with their o and x-components well separated by half the gyrofrequency at the height of reflection (the cusp at foEp - penetration - is also easily visible near 3.5 MHz) Lowell Digisonde Thumbnail- Jul 05, 2000 - 1307z Jul 05, 2000 - 1307z case of the automated digisonde mistaking the 2Es echo for the F2 echo and so grossly miscalculating the M-factor from too low a h'F2 value and thus the resulting excessively-high F2 MUF (Many other far-worse examples have been come across!) Lowell Digisonde Thumbnail- Nov 26, 2000 - 1645z Nov 26, 2000 - 1645z D-layer absorption from X4.0-flare, 1634-1648-1656, creating high fmin value (5-min resolution NOAA GOES x-ray plots) Lowell Digisonde Thumbnail- Dec 11, 2000 - 1530z Dec 11, 2000 - 1530z As a rule-of-thumb, the higher F2 MUF's will be generated by the F2 traces that become and remain "horizontal" the longest before reaching the foF2 penetration value. (But the lower h'F2 levels will also shorten the one-hop range!) Lowell Digisonde Thumbnail- Jan 28, 2001 - 2200z Jan 28, 2001 - 2200z D/E-layer group-retardation effects on the low-frequency end of the F2-echo more accentuated near "sundown" (at that height) giving a high "artifact" h' value Lowell Digisonde Thumbnail- Jan 29, 2001 - 1200z Jan 29, 2001 - 1200z the similar effect evident in the "pre dawn" sweep Lowell Digisonde Thumbnail- Jan 31, 2001 - 2030z Jan 31, 2001 - 2030z more consequences of automation where one of the "blocked" segments of the ionosonde sweep (to avoid QRMing occupants) is mistaken for foF2 and so produces a greatly-reduced calculated MUF Assorted Chaos from the April 6-7, 2000 Magnetic Storm (most notably auroral Es) (KBo: 3-3-3-3-2-6-5-6 and 8-4-5-3-3-4-3-3) Apr 06, 2000 - 1945z Apr 06, 2000 - 2100z Apr 06, 2000 - 2130z Apr 06, 2000 - 2145z Apr 06, 2000 - 2200z Apr 06, 2000 - 2230z Apr 06, 2000 - 2315z Apr 06, 2000 - 2330z Apr 07, 2000 - 0230z Apr 07, 2000 - 0300z Lowell Digisonde Site Search

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Page Created: January 27, 2001 Last modified: February 5, 2001