The best search terms I've found are trabs, -is and chasma, -atis. Literally meaning a wooden beam, trabs was applied by both Pliny and Seneca to something which might be the aurora (though L&S say it was probably a meteor).
Pliny's Natural History II.26-7:
Emicant et trabes simili modo, quas δοκους vocant [...] fit et caeli ipsius hiatus, quod vocant chasma, fit et sanguinea species et, quo nihil terribilius mortalium timori est, incendium ad terras cadens inde...
The trabēs, which they call δοκοι, shine in the same way [...] Sometimes a rift is made in the sky itself, which they call chasma, and and from there a flame arises with blood-red appearance, which mortals fear more than anything else, descending toward the earth...
Seneca defines chasmata in his Natural Questions I.14.1-2:
...aliquando ardores sunt, hi nonnumquam fixi et haerentes nonnumquam uolubiles. Horum plura genera conspiciuntur: sunt bothyni, cum uelut corona cingente introrsus ingens caeli recessus est similis effossae in orbem specus; sunt pithiae, cum magnitudo uasti rotundique ignis dolio similis uel fertur uel uno loco flagrat; sunt chasmata, cum aliquod spatium caeli desedit et flammam uelut dehiscens in abdito ostentat.
Colores quoque horum omnium plurimi sunt: quidam ruboris acerrimi, quidam euanidae ac leuis flammae, quidam candidae lucis, quidam micantes, quidam aequaliter et sine eruptionibus aut radiis fului...
...from time to time there are also glowing lights; these are sometimes static and held in place, sometimes whirling around. Multiple types of these are seen. There are bothynī, when within an encircling halo (*) is a great indentation in the sky, like a ditch that's been dug in a circle; there are pithiæ, when a huge round mass of fire, like a dōlium (†), is carried past or burns in a single place; there are chasmata, when some particular area of the sky sinks back and sends out flames, as though tearing open something that had been buried.
The colors of all these things are also quite numerous: some have an incredibly dazzling redness, some a frail and weak flame, some a resplendent white glow, some are flickering, some have a uniformly deep gold color without beams or rays.
(*) According to L&S, Seneca uses corōna for Greek ἅλως earlier in the QN when talking about the sun, so "halo" seems appropriate.
(†) A type of wine jar, presumably different from urna or amphora in some very relevant way...but I have no idea how.
Seneca talks about trabēs in book VII.
Trabes vero et faces, quae nullo alio inter se quam magnitudine distant [...] praebe[n]t speciem ignis extenti...
Indeed, trabēs and facēs (torches), which are distinguished by nothing except their size [...] show the appearance of a stretched-out fire [...]
The excised passages describe Epigenes's theories about trabēs being formed from humid tornadoes, which are fascinating but not relevant to the question at hand. Seneca goes on to refute it in various ways, pointing out that trabēs unlike tornadoes do not destroy people's houses.
In VII.5.3-4 he then specifically distinguishes them from comets:
Charmander quoque, in eo libro quem de cometis a composuit, ait Anaxagorae uisum grande insolitumque caelo lumen magnitudine amplae trabis, et id per multos dies fulsisse. Talem effigiem ignis longi fuisse Callisthenes tradit, antequam Burin et Helicen mare absconderet.
Aristoteles ait non trabem illam sed cometen fuisse; ceterum ob nimium ardorem non apparuisse sparsum ignem, sed procedente tempore, cum iam minus flagraret, redditam suam cometis faciem.
Charmander also, in his book on comets, said that a large and unusual light was seen in the sky by Anaxagoras, the size of a full trabs, and that it shone for multiple full days. Callisthenes relates such an image of a line of fire right before the sea covered Buris and Helice.
Aristotle said that this had not been a trabs, but a comet; its fire had not seemed scattered because it was simply too bright, but as time went on, once it was shining less, it regained the usual look of a comet.
In other words, the "scattering" of the fire is what distinguishes a trabs from a comet. In this passage, the trabs could also be a meteor, since I find it much easier to imagine a meteor and a comet looking similar than an aurora and a comet. But that raises the question of how Aristotle could have distinguished them with the naked eye; I'll leave that to someone more knowledgeable in ancient astronomy.
Trabes enim flammam aequalem habent nec ullo loco intermissam aut languidam, in ultimis uero partibus coactam, qualem fuisse in illa de qua modo rettuli Callisthenes tradit.
For trabēs have an even flame, not faint or broken at any point, but indeed gathered together at the edges, just like the one Callisthenes reported in the [book] I spoke of.
This part sounds strange describing an aurora. I've never seen one myself, but in images they do often seem to be "broken" in various places? However, it's not clear whether Seneca has ever seen the aurora himself; he may simply be repeating others' descriptions.
In general I would prefer the words chasma or the post-classical aurōra over trabs, given the amount of uncertainty in its meaning.