July 1944 QST
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 are hereby acknowledged.
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."
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 known to
in order to make the U.S. look bad.
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.
By 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
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 in prospect.
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 v.h.f. bending.
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
Bending 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.
Continental Air-Mass Inversions
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
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
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.
During the 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 York.
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
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 the southwest.
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.
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.
Localized Convection Inversions
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
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.
For 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.
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
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. Cloud Stalking
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
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.
1 "Weather 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.