On the Very Highs
July 1944 QST
first complete column devoted to the subject [of v.h.f. and u.h.f. signal
variation], presenting material similar to that which follows, was withheld
from publication at that time in compliance with censorship."
July 1944 QST
of Contents]These articles are scanned and OCRed from old editions of the
ARRL's QST magazine. Here is a list of the
QST articles I have already posted. All copyrights (if any) are hereby acknowledged.
That is an amazing statement from a time when almost any form of
technical information that was not already public knowledge was withheld
for the sake of the war effort. Nothing that might even remotely give
the enemy an edge, and consequently possibly harm our troops, got past
the government censors at the War Department. Most citizens and even
media editors willingly complied. Compare that with today's 5th column
traitors at most of the media outlets that not only can't wait to publish
information that will aid and abet our country's enemies, but have been
manufacture stories in order to make the U.S. look bad.
all available vintage
QST articles.< img alt="RF Cafe - On the Very Highs" src="images/on-the-very-highs-july-1944-qst.jpg"
style="width: 500px; height: 53px">
On the Very Highs
Conducted by E. P. Tilton, W1HDQ
Shortly after the
outbreak of war we proposed, in these pages, a study of aerology as
a substitute for amateur operating activity. The response we received
indicated a considerable interest in the subject, but this was at the
time when the submarine menace along our coasts was at its height and,
as a result, we were scarcely permitted even to print the word "weather,"
much less to go into a discussion of the means by which weather may
be foretold by observation of v.h.f. and u.h.f. signal variation. Our
first complete column devoted to the subject, presenting material similar
to that which follows, was withheld from publication at that time in
compliance with censorship.
Now, with wartime radio developments
accentuating the role that the v.h.f. and u.h.f. portions of the spectrum
are destined to play in the future of all forms of radio activity, it
behooves us to learn as much as we can about the effects of weather
on propagation at these frequencies. So, if the experienced weathermen
in the audience will find something else to do for a few minutes, we
shall attempt a sketchy review of some of the points where observing
amateurs in both aerology and radio meet on common ground.
Like all sciences, aerology can become very involved in mathematics
if one goes into it deeply enough; but, unlike most scientific pursuits,
it also affords many opportunities for interesting work for anyone who
is equipped with nothing more pretentious than a barometer, a thermometer
and a pair of good eyes. If the person so equipped happens to be a ham
who is casting about for something to do to while away a spare hour
now and then, he will do well to get hold of a receiver which is capable
of tuning the frequencies above 30 Mc. With nothing to be heard on Five,
and with the probable reception on 112 Mc. limited to the WERS test
periods, the f.m. broadcast band now offers undoubtedly the best opportunity
for observation of variations in v.h.f, conditions.
the end of 1941 most of us had already become used to regarding strong
v.h.f. signals from beyond visual distances as an advance warning of
a storm on the way, but many were content to let the matter rest there.
Perhaps there would have been more interest in daily operation on 56
and 112 Mc. in the dear, dead days prior to December 7th if more of
us had taken the correlation between radio and weather a little further.
Early morning radiation fog, as it appears here filling the valleys
in Vermont's Green Mountains, indicates a mild temperature inversion
of the local type, with fair weather and. moderate v.h.f. bending
The familiar fair weather cumulus, appearing at midday or in the
early afternoon as the result of warm air rising at a moderate rate,
will dissipate in late afternoon, Prediction: fair weather and moderate
The rapidly billowing wind-blown cumulus pictured here indicates
turbulent conditions aloft. Thunderstorms may follow in warm weather,
accompanied by high noise levels and generally poor radio conditions.
V.h.f. hams should watch for DX openings in early summer, however.
Cirrus "mare's tails," tell-tale vanguard of an advancing cold front,
presage a change from fair to stormy weather and may possibly portend
strong v.h.f. bending.
Nature's best but least-known visual warning of the presence of
a temperature inversion resulting from an overrunning tropical air
mass is the clearly defined smoke or dust layer marking the base
of the warm moist mass. Look for it before sunrise or at dusk in
clear calm weather; at any season. When you see it, rain is 36 to
48 hours away in summer; rain or snow 12 to 24 hour away in winter.
Excellent radio conditions with strong v.h.f. signals may he expected
at any time of the year.
A thickening altostratus haze veiling the sun, as shown above, is
the result of warm, moist air aloft. This is the stage following
that pictured at the bottom of this page, occurring immediately
As most extensions
of the normal operating range of v.h.f. stations result from a temperature
inversion of one sort or another, we should first understand what this
term means in order to recognize the visible and audible effects associated
with it. We all know that air temperature normally drops with an increase
in altitude. The year-round average rate of decrease for the world's
atmosphere is about 3° F. for each 1000 feet of altitude. Whenever the
rate of decrease (commonly called lapse rate) is less than this figure
an inversion may be said to exist, even though the air aloft may not
actually be warmer than that at ground level. Under certain conditions,
to be outlined later, the temperature up to several thousand feet may
be several degrees higher than the ground reading.
of v.h.f. waves arises from the fact that the top of the radiated wave
hits the warmer and rarer medium first, and thus is accelerated. As
the warm air seldom is at any great height the bending usually serves
merely to keep the wave traveling more or less parallel to the earth's
surface, although in rare instances something approximating a skip zone
is noticed. A pronounced inversion at low altitude, a common occurrence
in warm weather, may increase the strength of a signal coming from the
other side of town; while the maximum distance at which atmospheric
bending, uncomplicated by other factors, has resulted in two-way work
on 56 Mc. is somewhere between 350 and 400 miles. It is at distances
between 75 and 200 miles that the effect of temperature inversions seems
to be most pronounced, and the degree of variation in signal strength
from night to night is greater with increasing frequency.
Temperature inversions may be said to fall into two general classifications:
those resulting from air-mass movement which may be continental in character,
and the more limited type resulting from localized atmospheric convection.
This is not the place to go into an involved discussion of air-mass
analysis1 other than to say that a temperature inversion
results when a mass of warm moist air (such as those originating in
the Gulf of Mexico or out over the Pacific) overruns a mass of cool
dry air of polar origin. This type of inversion can develop almost anywhere
in the United States, at almost any time of the year. As warm moist
air is of low density, it overruns the heavier cold air whenever the
two types come in contact. The sloping "discontinuity" thus produced
means interesting times for the v.h.f. enthusiast.
A typical weather cycle may
consist of a period of cool clear weather, with high barometer and good
visibility for two or three days: followed by gradually increasing cloudiness
and warmer weather until the advent of a storm. Toward the end of the
fair stage the strength of v.h.f, signal from points beyond the visual
horizon will show a gradual improvement, increasing until about the
time that the storm breaks, wiping out the inversion condition. Almost
everyone knows from what direction storms come in his own locality.
By watching the clouds2 and listening for variations in strength
of stations in that general direction, the approach of a change in the
weather may often be foretold as much as several days in advance.
If one is fortunately situated as to altitude of the receiving
location this correlation is particularly striking. An example is the
prewar location of W1HDQ, which was several hundred feet above the surrounding
country with a clear path of 50 miles or more toward the southwest.
Here the signal-weather relationship showed up beautifully on 56 and
112 Mc. and, to a certain extent, on 28 Mc. also.
evening following a clear day in spring, for instance, 56-Mc.- signals
might be heard from points as far southwest as Washington, D. C. - more
than 300 miles away. Stations all along the line up to Philadelphia,
about 200 miles in the same direction, would also be very strong, but
signals from the New York area,125 miles away, would be only slightly
above normal. This would place the maximum inversion area below New
By the following evening we would have lost the stations
below Philadelphia as rain moved up from the southwest, wiping out the
inversion as it came toward us. By this time the amateurs in Springfield
and Hartford would be working into the New York metropolitan area, with
ordinary low-elevation locations at both ends of the 100-150-mile path.
Around this time we would be noticing an increase in the strength
of signals from the Boston area and up into New Hampshire, some 90 miles
to the northeast. If our period of observation was continuous we would
note a sudden drop in the strength of the New York signals, coinciding
almost exactly with the arrival of rain in that area. Just preceding
this some of the New York stations would have been working up into the
Boston area. Cloudiness would have become general over Western New England
by this time, and Bostonarea signals would be very strong, even though
1200-foot elevations intervene along the path. Until the storm broke
signals from the east and northeast would remain strong, though it would
have become impossible to hear any but the very strongest stations to
Thus far we have been dealing only with the continental
air-mass type of inversion, the idealized case described above occurring
most frequently during the late spring or early fall. In winter we find
the air-mass inversion in a practically pure state, although the extremes
of bending are not so great as in warmer weather. In mid-summer the
picture can be complicated) by so many factors that it took us several
months of operation from our Wilbraham Mountain location before we could
resolve any very reliable system for predicting weather by radio conditions,
or vice versa.
With certain variations, which each observer
will have to learn for his own locality, the appearance of the clouds
and the movements of the barometer furnish quite reliable warnings of
the approach of good v.h.f. weather. With the exception of midsummer
a rising barometer means increasing signal strength, while a falling
or low barometer indicates lower signal levels. The appearance of cirrus
clouds, those beautiful wispy "mare's tails" high in an otherwise clear
blue sky, often gives advance warning of the approach of a storm by
as much as 36 hours. The old saying about "mackerel scales and mare's
tails" is useful for v.h.f. enthusiasts as well as for mariners. A hazy
ring around the moon, evidence of warm, moist air aloft, has been recognized
as a good sign by five-meter men since the earliest days of work on
that band; and the periods around both full moon and new moon invariably
are times of improved signal strength. "New moon, full moon, and over
thirty on the barometer" is a good ruleof-thumb basis for predicting
good times on the very-highs.
We come now to the more localized
convection type of inversion, a product of hot weather, which gives
the boys fortunate enough to be located along our sea coasts, or near
the Great Lakes or other large bodies of water or even adjacent to heavily
forested areas, some of their most exciting moments.
all know that heated air rises; when it does, other air must come from
somewhere to take its place. Cool air is heavier (at higher pressure)
and therefore will tend to flow in to replace air which has risen as
the result of heating by direct radiation from the sun or re-radiation
from the earth. Thus, when we have a clear hot day along the seacoast,
by noon there is a fresh cooling breeze coming in from over the ocean,
the air inland having been heated sufficiently to cause it to rise.
The heated air, in turn, flows out over the ocean at high levels, creating
an inversion condition which holds until well into the evening of practically
every fair summer day.
V.h.f. men who operate from points
remote from the ocean know that mid-afternoon is the time during which
the lowest signal strength of the whole day occurs, but the enthusiast
located on Cape Cod, Long Island or the California Coast will find things
interesting practically all day long in summer time.
the man located farther inland, the two hours around sunset will show
strong signal peaks any sunny day in warm weather. As the earth cools
more rapidly than the air above it, an inversion develops close to the
ground shortly after sunset in almost any locality. The chilly spots
frequently encountered when riding through open country at dusk after
a hot day constitute a familiar example. The effects of the seacoast
inversion described above may show up at points as much as 100 miles
or more inland as the evening wears on; and when this sort of thing
is combined with an inversion resulting from the approach of a tropical
air mass, v.h.f. enthusiasts experience an evening which goes down in
the history of "big nights."
The coastal inversion is
a phenomenon well known to occupants of the 112-Mc. band along the California
coast. The tremendous updraft of warm air from the superheated desert
country far inland moving out over the relatively cold Pacific produces
a degree of bending of 112-Mc. signals seldom equaled elsewhere in the
United States. So pronounced is the bending that fleapowered pack sets
operating in the hills near Los Angeles frequently worked into San Diego,
more than 100 miles away, and two-way work between home stations in
San Diego and Los Angeles, using nothing more than simple receiving-tube
rigs and half-wave antennas, was a common occurrence during the peak
of the inversion season.
The coast of Northern New England
is blessed with very cold water, as Maine vacationists will testify.
Although the country inland is not heated to the extent that prevails
in California, the "inversion by subsidence" is a daily affair in midsummer.
A rare combination of subsidence and air-mass inversions prevailed on
that now-famous date of August 21, 1941, when W2MPY made the long climb
to the summit of Mt. Katahdin in the heart of Maine, arriving on the
scene at the peak of the bending. The result is now history: a dozen
or more contacts beyond the former 255-mile record for 112-Mc. work,
and a 335-mile QSO with WIJFF at Newport, R. L - a record which will
take some breaking when we get back to such things again.
In describing his Katahdin experiences, W2MPY reported that on this
trip, and on many others when he has worked long distances from high
elevations, he was actually able to "see the inversion," a phenomenon
also observed by your conductor in his mountain-climbing days. It took
an aerology textbook3 to give us the answer to this one.
In practice, its appearance has turned out to be one of the most reliable
visual warnings of the existence of both subsidence and air-mass inversions.
Smoke and Dust Layers
hot weather, particularly after a dry spell, the rising heated air carries
aloft a considerable amount of dust. When this dust strikes an overrunning
layer of moist tropical air it can rise no further, with the result
that it spreads out at the bottom of the warm layer, clearly marking
the height at which v.h.f. signals are bent. In industrial areas smoke
in the air serves the same purpose, with the added advantage that the
smoke generally rises whether there is any appreciable warming of the
earth's surface or not. We have observed the occurrence of this brownishgray
smoke/dust layer on many occasions, both in winter and in summer, and
it has never yet failed as a warning of a storm on the way. Its appearance
may give 36 hours or more warning of a change in the weather (from fair
to stormy) in the summer, when air-mass movement is slower, and 12 to
24 hours in winter. It should be an equally good harbinger of periods
of strong v.h.f. signals.
The foregoing is just a meager
glimpse of the vistas which will be open to the v.h.f.-minded amateur
after the war, but it will serve to show that operation on the very-highs
can be a whole lot more than a nightly round of friendly chats with
the gang in our own locality, important though these contacts loom in
our picture of amateur radio as a source of relaxation and enjoyment.
The events of December 7, 1941, interrupted ten years
of continuous operation on the v.h.f. bands on our part, but we've found
this weather business a splendid antidote for that empty feeling we
used to get when we looked across the Connecticut River Valley to that
tower of ours high up on Wilbraham Mountain.
Most of the time during our six-month sojourn
in Key West, now concluded, we kept an eye peeled for interesting cloud
formations, trying all the while to imagine what operation on 56 and
112 Mc. would have been like down there. There, as elsewhere in open
flat country, the general trends were much easier to discern than in
rugged country like our native New England; and therein lies the beauty
of cloud chasing as a hobby. If one takes the trouble to learn a little
about aerology (and he need not get to the calculus-andslide-rule stage)
he will still have to figure out conditions for his own locality' himself
when it comes to tying weather and radio "signs" together.
Since Pearl Harbor we've been finding an ever-increasing interest in
books dealing with the weather, and we've been stalking clouds with
a camera whenever we could get the necessary film. We find this a most
enlightening pursuit, especially when carried on in conjunction with
a daily log of radio and weather observations, even though the latter
may include nothing more than an occasional glance at the barometer
and a check on the gyrations of the weather cock on the steeple of the
town hall. Operation on the very-highs is going to be a source of even
greater pleasure and satisfaction, as a result of this enforced interlude,
when the current unpleasantness is over.
Before this material appears in print we shall have returned to Boston,
where we will remain for a short period, following which we expect to
be off on another assignment afield, this time outside the continental
limits of the United States.
We shall continue to submit copy
whenever time and conditions permit, and we will especially appreciate
hearing from any of the amateur fraternity who care to write. For the
time being, the mailing address had better be: % ARRL, 38 LaSalle Road,
West Hartford 7, Conn.
And the Ocean of Air," by Major W. H. Wenstrom (Houghton-Mifflin Co.),
provides the most readable discussion of air-mass theory we have yet
found. More strictly technical, but still understandable, is the paper,
"An Introduction to the Study of Air Mass Analysis," by Jerome Namias
and others, contained in the Bulletin of the American Meteorological
Society, Vol. 17, Nos. 6 and 7.
2 The accompanying photographs
show the appearance of typical formations. Scenes (1) and (2) were taken
from the summit of Glastenbury Mountain, near Bennington, Vermont; the
others at various points around Springfield, Massachusetts.