Thermal inversion and the Titanic: a study by Tim Maltin and Professor Andrew T Young
Part 1 – Collision
When the Titanic sank on the moonless night of 14/15th April 1912 she was surrounded by icebergs and on the edge of a large ice field. As Captain Rostron of the rescue ship Carpathia explained:
“…about two or three miles from the position of the “Titanic’s” wreckage we saw a huge ice-field extending as far as we could see, N.W. to S.E….I sent a Junior Officer to the top of the wheelhouse, and told him to count the icebergs 150 to 200 feet high; I sampled out one or two and told him to count the icebergs of about that size. He counted 25 large ones, 150 to 200 feet high, and stopped counting the smaller ones; there were dozens and dozens all over the place”
And this was confirmed by Titanic’s Quartermaster Hitchens: “In the morning, when it turned daybreak, we could see icebergs everywhere; also a field of ice about 20 to 30 miles long, which it took the Carpathia 2 miles to get clear from when it picked the boats up. The icebergs was up on every point of the compass, almost.”
These giant bergs and field ice were flowing southwards in the meltwater of the swollen Labrador Current, bringing freezing air up to a height of the tallest of these bergs into an area of sea normally occupied by the 12 degrees Celsius Gulf Stream, like a cold river in flood, bursting its banks and flowing over much warmer land.
The sharpness of the boundary between the warm waters of the Gulf Stream and the freezing waters of the Labrador Current, and its proximity to Titanic’s wreck site, was recorded after the disaster by the SS Minia, who whilst drifting and collecting bodies near Titanic’s wreck site noted in her log: “Northern edge of Gulf Stream well defined. Water changed from 36 to 56 [degrees Fahrenheit] in half mile”.
The rescue ship Mackay Bennett, also recovering bodies in 1912, drew the following map of water temperatures at Titanic’s wreck site, which also records this sharp boundary between the warm waters of the Gulf Stream and the cold waters of the Labrador current, and its proximity to Titanic’s wreck site (the red crosses mark where the bodies of victims were found floating, and recovered):
The sudden temperature change as Titanic crossed from the warm waters of the Gulf Stream into the much colder waters of the Labrador Current was recorded by her Second Officer, Charles Lightoller, who testified that there was a drop in temperature of four degrees Celsius in the half hour between 7pm and 7.30pm on the night of the fatal collision, and a drop in temperature of ten degrees Celsius in the two hours between 7pm and 9pm that night, when the air approached freezing.
The cold icebergs and icy meltwater in the Labrador Current had chilled the formerly warm air, which had previously been heated to approximately 10 degrees Celsius by the warm waters of the Gulf Stream; so the air column at Titanic’s crash site was freezing from sea level, up to a height of about 60 meters – almost the height of the tallest icebergs, and then about 10 degrees Celsius above that height.
This arrangement of warm air over freezing air at Titanic’s crash site is known as a thermal inversion. This was observed from the lifeboats as Titanic sank, when the warm smoke from the sinking ship was seen to rise up through the cold air near the sea surface quickly, in a column; but when it hit the capping inversion, the smoke was cooler than the much warmer air above and so immediately stopped rising, flattening out at the top of the column. This was observed by Titanic First Class passenger Philipp Edmund Mock from Lifeboat Number 11:
“We were probably a mile away when the Titanic’s lights went out. I last saw the ship with her stern high in the air going down. After the noise I saw a huge column of black smoke slightly lighter than the sky rising high into the sky and then flattening out at the top like a mushroom.”
Strong thermal inversions like this one are highly significant for navigation as they cause light to bend strongly downwards, around the curvature of the earth, allowing you to see much further than normal and making distant objects appear nearer than they really are. This phenomenon, known as super-refraction, frequently occurs over cold water, especially near the boundary with warmer water or land. The light rays bending more strongly downwards than the curvature of the earth have the effect of raising the level of the apparent sea horizon, producing a superior mirage of the distant sea. In the daylight a superior mirage over sea ice looks like this:
But at night the miraging on the horizon appears like a narrow bank of haze, due to light scattering in the very long air path over the unusual distance you can see for, and the trapping of light in a duct beneath the inversion. Titanic’s lookouts noticed this apparent haze around the horizon, despite the remarkable clarity of the night, and they testified that the fatal iceberg appeared to come out of this haze at the last moment:
Reginald Lee, Titanic Lookout:
2401. What sort of a night was it?
– A clear, starry night overhead, but at the time of the accident there was a haze right ahead.
2402. At the time of the accident a haze right ahead?
– A haze right ahead – in fact it was extending more or less round the horizon. There was no moon.
2403. And no wind?
– And no wind whatever, barring what the ship made herself.
2404. Quite a calm sea? – Quite a calm sea.
2405. Was it cold? – Very, freezing.
2408. Did you notice this haze which you said extended on the horizon when you first came on the look-out, or did it come later?
– It was not so distinct then – not to be noticed. You did not really notice it then – not on going on watch, but we had all our work cut out to pierce through it just after we started. My mate happened to pass the remark to me. He said, “Well; if we can see through that we will be lucky.” That was when we began to notice there was a haze on the water. There was nothing in sight.
2409. You had been told, of course, to keep a careful look-out for ice, and you were trying to pierce the haze as much as you could?
– Yes, to see as much as we could.
2441. Can you give us any idea of the breadth [of the iceberg]? What did it look like? It was something which was above the forecastle?
– It was a dark mass that came through that haze and there was no white appearing until it was just close alongside the ship, and that was just a fringe at the top.
2442. It was a dark mass that appeared, you say?
– Through this haze, and as she moved away from it, there was just a white fringe along the top.
2447. Quite right; that is where she hit, but can you tell us how far the iceberg was from you, this mass that you saw?
– It might have been half a mile or more; it might have been less; I could not give you the distance in that peculiar light.
Several ships in the area where Titanic sank recorded seeing mirages at the horizon or noted the refraction on the horizon, including the Wilson Line steamer Marengo, bound from New York to Hull under the command of Captain G. W. Owen. On the night of the collision and sinking of the Titanic on the 14/15th April 1912 she was in the same longitude as the Titanic and only one degree south, and her log records both the clear, starlit night and the great refraction on the horizon:
Second Class passenger Lawrence Beesley also noticed the very bright stars that night, and the very abnormal weather conditions:
“First of all, the climatic conditions were extraordinary. The night was one of the most beautiful I have ever seen: the sky without a single cloud to mar the perfect brilliance of the stars, clustered so thickly together that in places there seemed almost more dazzling points of light set in the black sky than background of sky itself; and each star seemed, in the keen atmosphere, free from any haze, to have increased its brilliance tenfold and to twinkle and glitter with a staccato flash that made the sky seem nothing but a setting made for them in which to display their wonder. They seemed so near, and their light so much more intense than ever before, that fancy suggested they saw this beautiful ship in dire distress below and all their energies had awakened to flash messages across the black dome of the sky to each other, telling and warning of the calamity happening in the world beneath…the stars seemed really to be alive and to talk.
The complete absence of haze produced a phenomenon I had never seen before: Where the sky met the sea the line was as clear and definite as the edge of a knife, so that the water and the air never merged gradually into each other and blended to a softened rounded horizon, but each element was so exclusively separate that where a star came low down in the sky near the clear-cut edge of the water-line, it still lost none if its brilliance. As the earth revolved and the water edge came up and covered partially the star, as it were, it simply cut the star in two, the upper half continuing to sparkle as long as it was not entirely hidden, and throwing a long beam of light along the sea to us.
In the evidence before the United States Senate Committee the captain of one of the ships near us that night [Captain Lord of the Californian] said the stars were so extraordinarily bright near the horizon that he was deceived into thinking that they were ships’ lights: he did not remember seeing such a night before. Those who were afloat will all agree with that statement: we were often deceived into thinking they were lights of a ship.
And next the cold air! Here again was something quite new to us: there was not a breath of wind to blow keenly round us as we stood in the boat, and because of its continued persistence to make us feel cold; it was just a keen, bitter, icy, motionless cold that came from nowhere and yet was there all the time; the stillness of it – if one can imagine “cold” being motionless and still – was what seemed new and strange.”
Beesley is describing the strange, motionless cold air beneath the thermal inversion, but stars can never really be seen setting on the horizon, as they always become extinct as they approach the real horizon, due to the depth of air one is having to see them through at such a low altitude. What Beesley was actually seeing was the reflections of the stars on the distant sea surface, reflecting in the miraging duct at the horizon. Here is a photograph kindly supplied to me by the brilliant mirage photographer Pekka Parviainen. It shows the glitter of sunlight on the distant sea being miraged at the horizon, in much the same way as the reflected starlight on the distant sea surface was being miraged at the horizon the night the Titanic sank, creating the impression that the stars themselves were actually setting on the horizon, sending long beams of light along the sea towards the observers in Titanic’s lifeboats:
Titanic’s second officer Charles Lightoller also noticed this phenomenon, and he discussed it with First Officer Murdoch as he handed over Titanic’s watch prior to the collision:
CHL457. What was said between you [Lightoller and Murdoch]?
– We remarked on the weather, about its being calm, clear. We remarked the distance we could see. We seemed to be able to see a long distance. Everything was very clear. We could see the stars setting down to the horizon.
Like Beesley in the lifeboat, what Murdoch and Lightoller were observing from Titanic’s bridge that night was not stars actually setting on the real horizon, but abnormal refraction reflecting starlight on the distant sea below a false horizon, which raised the apparent sea horizon higher up, behind the icebergs they were looking for, making them even harder to spot than they would normally have been on that starlit night.
It was the combination of this refraction reducing the contrast of icebergs below the false horizon, together with the moonless night that raised the contrast threshold for their detection, plus the unusually high eye heights of the observers on the giant Titanic’s bridge and crows nest that increased the dip of the horizon, thus putting the icebergs even farther below the false horizon, that made the icebergs at Titanic’s crash site impossible to detect until it was too late to avoid a collision.
Part 2 – Tragedy
Not only did the raised horizon at Titanic’s crash site make the icebergs more difficult to spot, but it also caused Captain Lord on the nearby Californian to conclude that the Titanic was a 400ft ship about five miles away, instead of a more than 800ft ship about 10 miles away.
You can see how a raised horizon behind Titanic would have this effect in the below image, where the ship within the horizon appears nearer, and therefore seems smaller than the ship on the horizon; but if you measure the two hulls in the image below you will see that in fact they are both the same size:
The tragic result of this natural deception was that it caused Captain Lord on the Californian to come to the incorrect conclusion that the ship they were watching did not have any wireless:
7093. What reason have you for thinking that this steamer, a steamer which you say was, at all events, as big as your own, had not got wireless?
– At 11 o’clock when I saw her the operator told me he had not got anything only the “Titanic.” I remarked then, “That is not the ‘Titanic,” judging from its size and the number of lights about it.
7083. This steamer had been in sight, the one that fired the rocket, when we sent the last message to the “Titanic,” and I was certain that the steamer was not the “Titanic”, and the operator said he had not any other steamers, so I drew my conclusion that she had not got any wireless.
He therefore decided to signal what he thought to be the nearby, small ship, about four miles away, with his powerful electric morse lamp. But his signals were not replied to, as the scintillation caused by the turbulence in the air path along the approximately 10 miles distance between the two ships (which effect Beesley has noticed was causing the stars to appear to be flashing messages across the sky to one another) in fact scrambled the meaning out of the real Morse lamp communications between these two vessels. Captain Lord described this incident as follows:
“She came and lay at half-past 11, alongside of us until, I suppose, a quarter past, within 4 miles of us. We could see everything on her quite distinctly, see her lights. We signalled her, at half-past 11, with the Morse lamp. She did not take the slightest notice of it. That was between half-past 11 and 20 minutes to 12. We signalled her again at 10 minutes past 12, half-past 12, a quarter to 1 o’clock. We have a very powerful Morse lamp. I suppose you can see that about 10 miles, and she was about 4 miles off, and she did not take the slightest notice of it.”
We know that in reality these two vessels were about 10 miles apart because in the morning, when the breeze which sprang up with the dawn had dispersed the thermal inversion, restoring normal refraction, it was clear from the rescue ship Carpathia that the Californian was about 10 miles away, as the Carpathia’s Second Officer, James Bisset, recorded on page 291 of his memoirs, “Tramps and Ladies”:
“While we had been picking up survivors, in the slowly increasing daylight after 4.30am, we had sighted the smoke of a steamer on the fringe of the pack ice, ten miles away from us to the northwards. She was making no signals, and we paid little attention to her, for we were preoccupied with more urgent matters; but at 6am we had noticed that she was under way and slowly coming towards us”. “When I took over the watch on the bridge of the Carpathia at 8am, the stranger was little more than a mile from us, and flying her signals of identification. She was the Leyland Line cargo-steamer Californian, which had been stopped overnight, blocked by ice.”
And Bisset’s observation of the Californian being 10 miles north of Titanic’s wreck site until 6am on 15th April 1912 is corroborated by the following evidence of Captain Moore of the Mount Temple, who raced to Titanic’s distress position but found himself on the west side of the ice barrier, while Titanic sank to its east:
JHM276. “…when I got the position in the morning I got a prime vertical sight; that is a sight taken when the sun is bearing due east. That position gave me 500 9 1/2′ west. [10 miles west of Titanic’s wreck site at 49.46W]
JHM289. On which side of the ice pack was the Californian?
– The Californian was to the north, sir. She was to the north of the Carpathia…
JHM290. And you were also cut off from the Carpathia by this ice pack?
– Yes, sir; by this ice pack. He [Californian] was then north of the Carpathia, and he must have been, I suppose, about the same distance to the north of the Carpathia as I was to the westward of her.”
Due to the abnormal refraction at Titanic’s crash site causing light to bend very strongly downwards, around the curvature of the earth, Captain Lord had first spotted Titanic approaching at about 10.30pm, when she was more than 50km away from the stopped Californian. He noticed that the light he could see right on the horizon [actually Titanic’s miraging masthead light at more than 50km distance] “was a most peculiar light”:
STL227. – “When I came off the bridge, at half-past 10, I pointed out to the officer [Third Officer Groves] that I thought I saw a light coming along, and it was a most peculiar light, and we had been making mistakes all along with the stars, thinking they were signals. We could not distinguish where the sky ended and where the water commenced. You understand, it was a flat calm. He said he thought it was a star, and I did not say anything more. I went down below.”
Groves later studied this strange light himself, just before Titanic’s collision, when she was still about 12 miles away and he realised that the peculiar-looking masthead light now in fact appeared to be two lights:
8143. What lights did you see?
– At first I just saw what I took to be one light, one white light, but, of course, when I saw her first I did not pay particular attention to her, because I thought it might have been a star rising.
8144. When do you think you began to pay particular attention to her? – About 11.15.
8145. About five minutes after you first saw her? – About five minutes after I first saw her.
8146. Did you then see more lights than one?
– About 11.25 I made out two lights – two white lights.
8147. Two masthead lights? – Two white masthead lights.
This could have been Titanic’s one masthead light, appearing as two in the miraging conditions. An example of this is seen in the following photograph where the single lights on the top of two aerial masts are each multiplied in the miraging conditions. One light above the other could also have been interpreted as the fore masthead and main masthead lights of an approaching ship:
Two aerial masts, with just one light on the top of each, multiply in the miraging conditions in this photograph taken by Pekka Parviainen.
These strange conditions caused Titanic’s distress rockets to appear to Californian’s Second Officer Herbert Stone to be much lower than they really were:
7921. …these rockets did not appear to go very high; they were very low lying; they were only about half the height of the steamer’s masthead light and I thought rockets would go higher than that.
In fact Titanic’s distress rockets were exploding at a height of approximately 600 feet above Titanic, in the warm, normally refracting air above the abnormally refracting duct near the sea, but they were not noticed from Californian until they were seen in the very cold, magnifying air within the optical duct near the sea, when they appeared much brighter.
The effect involved here is very similar to the atmospheric focusing and defocusing that caused the twinkling of the stars which Beesley recorded, and which effectively scrambled Titanic and Californian’s Morse lamp signals to each other. There, the cause was random fluctuations in refraction due to slight turbulence in the air; but here the changes in magnification by the atmosphere produced an increase in the brightness of Titanic’s rockets in the cold air near the sea surface, as the glowing rockets sank slowly down into the sea.
This effect was also observed by Earnest Gill, a Greaser on the Californian, as he was having a smoke on deck:
ERG016. What kind of rockets were they? What did they look like? – They looked to me to be pale blue, or white.
ERG017. Which, pale blue or white?
– It would be apt to be a very clear blue; I would catch it when it was dying [i.e. low down]. I did not catch the exact tint, but I reckon it was white.
ERG018. Did it look as if the rocket had been sent up and the explosion had taken place in the air and the stars spangled out?
– Yes, sir; the stars spangled out. I could not say about the stars. I say, I caught the tail end of the rocket.[i.e. when the rocket was low down]
ERG028. You think it may have been the Titanic?
– Yes; sir. I am of the general opinion that the crew is, that she was the Titanic.
At the British Inquiry into the Titanic disaster Gill explained the same phenomenon again, of the rockets only being noticeable as they sank low down near the sea, like falling stars, and his testimony also includes a reference to the false horizon “what appeared to be the water’s edge – a great distance away”, which was causing so much confusion that night:
18157. – I had pretty nearly finished my smoke and was looking around, and I saw what I took to be a falling star. It descended and then disappeared. That is how a star does fall. I did not pay any attention to that. A few minutes after, probably five minutes, I threw my cigarette away and looked over, and I could see from the water’s edge – what appeared to be the water’s edge – a great distance away, well, it was unmistakably a rocket; you could make no mistake about it. Whether it was a distress signal or a signal rocket I could not say, but it was a rocket.
When Captain Lord was eventually informed that this strange vessel within sight was firing rockets, he decided not to risk his ship and crew in going to investigate what he thought was a small, nearby stranger who would not even reply to his Morse lamp signals, until daylight, when it was safe to do so.
There is no doubt that Captain Lord should have gone to the aid of that vessel, despite the very dangerous conditions that night. But had it not been for the abnormal refraction, which caused him not to recognise that it was the biggest ship in the world sinking on her maiden voyage, he would have gone to her aid.