R e s e a r c h 

T h e   B O A C   L a b r a d o r   s i g h t i n g   of   J u n e   2 9,   1 9 5 4   

visitor responses
 Possible explanations

4.2. Stratospheric balloons

A second theory proposed by Wim VAN UTRECHT is that what was seen could have been a train of high-altitude research balloons or the like. Such balloons can be huge, hundreds of feet in diameter when at float altitude, and when still only partially inflated at lower altitude (due to higher atmospheric pressure) might present a similar appearance to the morphing blob reported. Indeed, Capt. HOWARD remarks that his initial impression was of a possible balloon. Jet-stream winds might blow such balloons along at considerable speed.

research balloon Fig. 5 : A research balloon with two smaller balloons (one visible on the left, the other on the right) about to lift a payload with measuring instruments into the stratosphere. [Image borrowed from]

The mean summer mid-latitude or polar jet roughly follows the Canadian border and curls ENE towards the Newfoundland area (PETTERSSEN, 1958). In zonal flow it generally remains well south of the sighting location. During so-called meridional flow it can kink and curl sharply north so could in principle have been in the right area and blowing in a similar direction to the Stratocruiser's 49° flightpath. However meteorological evidence does not indicate that jet winds were a likely factor.

First, as noted in Chapter 4.1, the wind in the sighting area at the 19,000 ft level (500 mbar) measured by radiosonde ascents between 10:00 p.m. and 11 p.m. EST June 29, 1954 (just after the sighting) was only 25 kt. [Appendix A (ix)], an order of magnitude too slow. There is no sign of violent wind at 19,000 ft in the sighting area. This fits the fact that due to a continental blocking high over Labrador the mid-latitude jet was not only abnormally weak in the East through June 1954, its average position [traced at the 700 mbar level in Appendix A (x)] was confined in a zonal flow far to the South.

Secondly, the altitude of the jet core would typically be 30-40,000 ft or more [41]. Even when apparently co-altitudinal with the plane at 19,000 ft, the objects would have been well below the jet core. (In Capt. HOWARD's 1982 account they were initially visible at a depression angle and climbed into view from below a broken stratocumulus layer which was well below the plane. If true this would further rule out jet-stream winds; but this detail does not appear in the 1954 account[42].)

If the jet stream was unusually low, low enough to carry a balloon at the same altitude as the plane, and if the balloon was near enough to the plane to be observed as a substantial object subtending about 1, then both plane and balloon must have been inside the jet (as mentioned planes may well seek the jet, and anyway the jet core would be typically 5-10 of lat/long in width). This being so, the wind speed cancels out in both vectors and a balloon would still be outdistanced by the plane at its True Airspeed of 230 kts just as though the balloon were standing still.

The geometrical arguments against a flock of birds are even more troublesome for a balloon, which can only be a few hundred feet across. Its distance from the plane (given angular width ~1 for the main morphing blob) would be in the region of 1 mile for every 100 ft of diameter, so it could only be a few miles away. To reduce its angular rate of displacement to the required ~0.5 of bearing per minute (or so) it would need to be hundreds of miles away, impossibly inconsistent with the required angular size.

Perhaps the plane and balloon happened to be near the edge of an exceptionally sharply-defined jet core, with a steep wind gradient between them, so that the plane just outside the core had a relatively small following wind whilst the balloon, perhaps a few miles away, was well inside the jet core [43]? It seems even more highly unlikely that this delicate situation could persist for 18 min [44], but in any case mean wind speeds in the core of the summer jet (PETTERSSEN, 1958) are given as about 50 knots. Relative speeds in this case are still going to be about the same as between a bird flock and the plane, or > 200 mph. The balloon would be very rapidly left behind [45].

And what sort of balloon train is this, one wonders, with little balloons or reflectors disposed to left and right (fore and aft) rather than suspended below, and for 18 min [46]? Do we have a model, drawing or description of any contraption that might resemble this? I am not aware of one. Moreover, an intact balloon with positive buoyancy ought to climb thousands of feet during the 18 min sighting, and at (say) 5 miles range 10,000 ft. of ascent corresponds to about a 20 change of elevation, a very large angle with respect to the horizon and the plane's level wing. Yet these objects seemed to stay co-altitudinal with the plane, remaining no more than a degree or two above the horizon (see p. 15 et seq). A slow-leaking balloon might have neutral buoyancy for many minutes, but it's another layer of unlikelihood.

So is the theory strong enough on other grounds to be worth defending a very contrived relationship between the plane and some very extreme and unusual winds, with the jet stream altitude anomalously low? At present I don't believe that it is.

 Notes & references

[41] Wim VAN UTRECHT points out that situates the polar jetstream "at an altitude from 7,600 metres to 10,600 m (25,000-35,000 ft)" and that according to it is "typically 20,000 feet or more".

It's true that the height of the polar frontal jet varies widely and can be much lower than 30 kft. Generally the jet occurs just below the tropopause, so the height is governed by the mechanisms that govern the height of the tropopause.

There are 3 factors here: the latitude; the season; and the local synoptic pressure regime. Height is greatest at the equator, least at the poles; greatest in summer, least in winter; greatest in stable high pressure weather, least just behind a deep low pressure weather front. Lowest global average height occurs at the N pole, where it's about 8 km (26,000 ft) Average height at 50 N is 10 km (call it 30,000 ft). The sighting date is midsummer, favouring >30 kft, and the sighting occurred over high pressure extending from the surface through at least the 500 mbar level (~19,000ft), also favouring >30 kft. With information about the variance of these distributions we could be on stronger ground, but taken together probability favours a tropopausal jet core at least 10,000 ft above the aircraft. See e.g.:

The wind at the Stratocruiser's flight altitude that evening according the the US Weather Bureau 500 mbar constant pressure chart [Appendix A (ix)] was approximately SW, but only 25 kt, and the dominating presence of an unusual "blocking high" (high pressure) over Labrador (see p.29 et seq.) seems to have been responsible for keeping the Atlantic end of the 700 mbar low-level jet abnormally weak and confined on average below about 40 latitude through June 1954. This may reflect a similar constraint on the higher level jet.

[42] And is almost certainly not reliable (see p. 21 et seq.). But in any case it should be pointed out that the images "paced" the 230 kt aircraft from the start, so a balloon needs the benefit of all of the relative velocity of winds in the core of a fast jet stream. Yet the balloon scenario assumes that the undistorted (pear-shaped) balloon is initially being seen at a lower altitude before climbing into the unusually sharply-defined fast jet and getting splatted.

Winds outside this hypothetical jet must be relatively very weak because we need all the advantage of wind speed to be on the side of the balloon within the jet, to enable it to keep up with the 230 kt plane. So the relative velocity of plane and balloon during phase #1 of the sighting when the balloon is not yet in the distorting jet must be in the region of -200 kt, meaning that the balloon falls aft the plane at about 3 miles/minute, or fully 20 of arc per minute even if the range is as much as 10 miles (the maximum balloon range consistent with the angular size argument, see later).

This would be very obvious and the balloon would have to have started out well ahead of the wing, off the nose of the plane, yet Capt. HOWARD reported that it kept station in the same position off the wing where it was first noticed, not that they spotted it ahead and drew level with it, and this is shown in his contemporary drawing which has the initial "pear" phase in the same relative position off the wing.

Anyway a buoyant stratosphere balloon should have continued to climb through the jet layer, probably gaining more than 10,000 ft and tens of degrees of elevation during the sighting. There is no "lid" on the jet. Is it likely to stop dead a balloon filled with hundreds of thousands of cubic feet of hydrogen and trap it for 80 miles? I see nothing in the literature that says jet steams behave like this. Commercial planes fly in and out of jet cores negligently according to need (except for being careful of turbulence).

Perhaps a balloon was suddenly ruptured by extreme wind shear. But if it was drastically damaged (as the shape-distortion might suggest) it would catastrophically lose buoyancy and its payload would soon drag it down out of the (ex hypothesi) very narrow jet. The payloads of the 'Moby Dick' balloons of Project Genetrix (see later) were cubic-metre gondolas containing sensors, cameras and radio telemetry equipment weighing 400 lbs (180 kilos) and the weight of polyetheylene would not be negligible either.

That both the direction and speed components of the jet wind vector remained essentially identical to the direction and speed components of the totally independent aircraft vector for 18 minutes is already quite a coincidence. For a leaking balloon to also achieve neutral buoyancy just as it enters the jet and maintain it for 18 minutes is an added order of unlikelihood .

[43] Wim VAN UTRECHT concedes that this is a condition for the balloon theory to work. It is worth emphasising why it is a difficult condition to fulfil.

The plane has to be essentially outside the jet, with the "pacing" balloon in the jet core, thus for the observers to get near enough to see the balloon visually the wind shear gradient across the effective "side wall" of the jet has to be steep. But:

"The jet stream is significantly wider than it is deep (...) This produces stronger vertical wind shears than horizontal shears (...) We can best describe the basic structure of a jet stream as a river flowing horizontally through the atmosphere. They are normally thousands of miles in length, hundreds of miles wide, and a few miles deep. Wind speeds in a jet stream vary along each of its dimensions"

Thus, a plane flying vertically above or below the jet core would be looking up or down along the minor axis of the jet's elliptical section and could have the closest view of a balloon (possibly a couple of miles) through the steepest wind gradients, but a plane flying alongside the core is looking along the major axis of the jet and through a shear gradient typically in the order of ten times less steep. So for the plane to be "outside" the jet with the balloons having the full speed advantage of the jet core winds the plane has to be typically in the order of ten times as far away - a distance typically degrees of lat/long or many tens to hundreds of miles.

Note also that: "Looking into the spiralling column in the direction of flow, you can see the change in speed across the jet stream width and through its height (...) Notice the displacement of the core to the left and top within the jet stream. Therefore, change in wind speed over distance (speed shear) is greatest above and to the left of the jet stream core as you look in the direction of flow", i.e. the wind velocity lines are bunched on the N (cool) side and widely spaced on the S side. The Centaurus was flying so as to look from the warm S side of the core and thus along the axis of gentlest speed shear.

To underscore how far from the median the theory assumes conditions to be, note that the average gradient on the south (warm) side of the summer polar jet core - corresponding to the position of the Centaurus in this case - is about 1.5 kt/degree lat according to PETTERSSEN (1958, p. 183) so that on average the plane would need to be 20? or ~1,400 miles away from an average 30 kt jet core for the balloon to have a 30 kt windspeed advantage! Or more favourably says: "The average rate of change in wind speed is 100 kts for every 100 miles to the north of the core and 25 kts for every 100 miles to the south of the core. (b) A decrease of 30 to 40 kts in 1,000 ft above or below the core of maximum winds is not uncommon". This figure would mean that the Centaurus need have been only 230 miles from the balloon in an average jet!

But the "balloon" was clearly resolved in shape with an angular width comparable to "an ocean liner at 5 miles" which indicates an angular size in the order of a degree of arc. Note that this is consistent with HOWARD's sketch #1 (Fig. 1), showing the setting sun, to within an error factor of about 2, so I take the magnitude order as reliable. Take it to be 0.5 according to HOWARD's drawing (although as pointed out elsewhere the sun diameter may be exaggerated as is often the case). Then, even at a close distance of ten miles range a balloon would have to be approaching 500 ft across (even though still only partially inflated at this level, tens of k/ft below its float altitude) to subtend this angle, and at the minimum physically realistic distance to permit 230 kt of horizontal speed shear between balloon and plane the real size would be a factor ten larger than that.

[44] Wim VAN UTRECHT questions if this is really such a "delicate situation". In Everybody's Weekly Capt. HOWARD stated: "I was tempted to change course and take a closer look at the things, but I didn't". So one might argue that it was the Captain himself who contributed to this delicate situation by consciously maintaining a steady distance between the plane and the objects.

However, reading his report further we discover that what he maintained was not his relative position but his preset course. He was on autopilot and did not disengage or over-ride it - "I was tempted to change... but didn't" - so the autopilot was maintaining a straight magnetic heading. Jet streams are curving wind channels, and they do not respect gryocompasses - they flex and they have spiralling currents and waves propagating along them. These instability fluctuations are what make "delicate" an 18-minute persistence of the situation.

Such a situation also entails risk of clear air turbulence which is usually found alongside the jet, which can be highly dangerous and is proportional to the shear gradient, so the sharper the gradient required (and we require exceptional sharpness) the more the likelihood of turbulence. With a weaker jet most of the turbulence is on the low pressure side, where the wind isotachs bunch more closely, which would be on the opposite side from the Centaurus in the usual case. But because we need such an intense jet with very steep windshear amounting to 230 kts in ~10 miles or less on the near side of the jet (to get the balloon fast enough and the plane close enough) there should have been significant turblence on the near side also. I don't see any hint of such. Passengers had just eaten dinner, some were asleep or relaxing or shaving at the sink, weather was said to be perfect, crystal clear, no mention of a bumpy flight. According to an FAA source:

"Common dimensions of a turbulent area associated with a jetstream are on the order of 100 to 300 miles long, elongated in the direction of the wind, 50 to 100 miles wide, and 5,000 feet deep. These areas may persist for from 30 minutes to a day (...) The threshold windspeed in the jetstream for CAT is generally considered to be 110 knots. Windspeed in jet streams can be much stronger than 110 knots [we need twice this] and the probability of encountering CAT increases proportionally with the windspeed and the windshear it generates....Moderate CAT is considered likely when the vertical windshear is 5 knots per 1,000 feet, or greater, and/or the horizontal windshear is 40 knots per 150 miles or greater".

[45] Of course these are mean windspeeds. The mean wind in the much faster winter jet is ~95 kts (again as of 1958, PETTERSSEN, op. cit.) but can exceed 300 kts. Wim VAN UTRECHT points out that a peak of 364 kts (656 km/h) was measured on December 11, 1967 above South Uist in the Outer Hebrides ( Pro rata, the summer maximum could be assumed to peak at 190 kt. But these maxima occur in small domains that themselves shift down the jet at a few tens of knots, i.e. with the phase velocity of the short waves that run through the jet, periodically breaking up and reforming. In other words there is a spectrum of speeds within the jet at any one time, and the hypothetical balloon was not forced to rise into the jet just where a peak velocity zone happened to be, so the theory again tends to require a form of the jetstream model uncomfortably far from the median, where a balloon happens to enter and remain within a peak velocity zone (which happens to keep the same speed, direction and altitude as the Centaurus). It would be possible, but it's an added tension in the theory.

[46] Wim VAN UTRECHT proposes that "strong turbulence, created by the horizontal and vertical winds inside the jet stream, may have caused a balloon to swirl around its axis with the smaller balloons and radar targets moving in a horizontal plane around the balloon, creating the impression of smaller blobs dancing around a much bigger object" (personal communication, op. cit.). I don't see evidence of strong turbulence affecting the plane, which the angular size argument tells us cannot have been more than a few miles from a balloon at least hundreds of feet across in an extremely sharply-defined jet core, and that is already a highly strained scenario because typically the wind shear gradient required will occur over horizontal distances an order of magnitude larger, making the balloon probably thousands of feet in diameter. This in turn would make the fore-aft spread of "smaller balloons and radar targets" most likely in the region of a couple of miles. No known balloon project, including the then-SECRET 'Moby Dick' project (Project Genetrix; see Chapter 5) was ever on this sort of scale.