At around 9pm on Wednesday, the 28th of August, the victim noticed a man opposite her on the aisle had exposed himself and was masturbating.
Detectives would like to speak to the man in the image who they believe may have information which could help with their investigation.
Anyone who recognises him is asked to contact British Transport Police by texting 61016 or by calling 0800 40 50 40, quoting reference 698 of 28 August.
Alternatively, you can contact Crimestoppers anonymously on 0800 555 111.