=  NOW 35 WPM  =  TEXT IS FROM DECEMBER 2020  QST  PAGE 80 =

JON JONES, N0JK, N0JK ARRL.  ORG THE WORLD ABOVE 50 MHZ AUTUMN WEATHER
BRINGS TROPO DX CRISP SEPTEMBER MORNINGS AND SUNNY DAYS BROUGHT SEVERAL
OUTSTANDING TROPOSPHERIC OPENINGS IN SEPTEMBER.  ON SEPTEMBER 15 AND 16, A
HIGH PRESSURE SYSTEM SETTLED OVER THE EASTERN HALF OF NORTH AMERICA.
STATIONS INCLUDING KR1ST FN21, WZ1V FN31, AND K1HTV FM18 WORKED AS FAR WEST
AS WA0I EM39 IN CENTRAL MISSOURI ON 2 METERS.  RON, WZ1V, CALLED IT THE
BEST TROPO OPENING IN 10 YEARS.  TROPO APPEARED AGAIN ON SEPTEMBER 25 AND
26.  THAT EVENING, STATIONS IN THE DALLAS FORT WORTH METROPLEX WORKED TO
NEW ENGLAND.  USING TROPOSPHERIC PROPAGATION FOR DX TROPOSPHERIC
PROPAGATION OCCURS WHEN THE DIFFERENCES IN AIR TEMPERATURE AND HUMIDITY
CAUSE A GRADIENT THAT CAN REFRACT RADIO SIGNALS BACK TO THE EARTH BEYOND
THE LINE OF SIGHT HORIZON.  IT IS QUITE DIFFERENT THAN SKIP ON HF RADIO,
WHERE THE IONOSPHERE BENDS AND REFLECTS RADIO SIGNALS.  THIS TAKES PLACE 50
250 MILES HIGH.  TROPOSPHERIC PROPAGATION, OR TROPO, TAKES PLACE ONLY A
MILE OR SO ABOVE THE EARTHS SURFACE.  IT IS CAUSED BY A TEMPERATURE
INVERSION.  THIS IS A BOUNDARY LAYER WHERE A SHARP CHANGE TAKES PLACE IN
TEMPERATURE AND HUMIDITY, USUALLY CAUSED BY A LAYER OF WARM, DRY AIR OVER
COOL, MOIST AIR.  NORMALLY THE MOISTURE CONTENT AND TEMPERATURE OF THE
LOWER ATMOSPHERE DECREASE WITH ALTITUDE.  IN AN INVERSION, THE TEMPERATURE
=  END OF 35 WPM TEXT  =  QST DE W1AW  <