In Ted Hughes' "The Rain Horse," the use of imagery is very important in creating a mysterious and gloomy atmosphere. The descriptions used, to describe the stormy morning, are meant to instill dread and concern in the reader. With images of trench warfare breaking into the actual surroundings of the scene, the dark and ominous setting is compounded.
By setting nature both against itself and the protagonist, the setting's mystery and gloominess is heightened. Both the past and the present seem to be at odds with the protagonist's surroundings--nature fighting against nature for survival and nature fighting against the protagonist (in the horse and the storm).
Essentially, the use of imagery is the most important technique used in the story given it allows the reader to create mental images of the protagonist's surrounds.
An important literary technique he uses in addition to IMAGERY is SYMBOLISM. The horse and the man's clothes, namely are very symbolic of certain things.
Horse: represents Nature
"This land no longer recognised him, and he looked back at it coldly."
The horse being symbolic of nature attacks him as a trespasser. The horse's description is extremely vivid and ominous which helped to forward the dark and foreboding atmosphere.
Clothes: represent his worries
I won't go into detail about this since it's a little irrelevant to the 'gloomy atmosphere'.
COLOURS are also an important technique he uses. The colours grey, black and blue are mentioned repeatedly, all of which have sad and depressing connotations. Black also sets a very frightening background for the story
The WEATHER also seems to compliment the confrontation between the horse and the man. As the man decided that he can take on the horse and goes"striding carelessly",he notices that the"sky had grown much darker."This also helps with setting a gloomy atmosphere.
The story becomes mysterious at first when the reader wonders why the man is experiencing so many negative emotions, and then when along with the man, the reader too is confused as to why the horse is attacking the man. The horse behaves unlike any other animal would and displays an eerie intelligence.
The horse's very existence is debateable and this too makes the story mysterious. Does the horse exist or is the man battling with a figment of his troubled imagination?