The reigning champions have promoted their assistant coach to the top job after the ex-Socceroos boss departed the A-League to challenge himself in Japan's top flight
Moss is elevated from his role as assistant after three years and will lead the defending A-League champions until the end of the 2015-16 season.
The 42-year-old was widely tipped to fill the vacancy and is just the third coach in the Mariners history, following on from Arnold and foundation boss Lawrie McKinna.
Moss was quick to praise his predecessor, who inked a two-year contract with Sendai after Makoto Teguramori left to become head coach of Japan's U-23 National Team.
"What Graham has done for this Club, the Coast, the playing and coaching staff has been quite remarkable," Moss said.
"For me he is a mentor, a father figure, and a man who has left a legacy for football on the Central Coast."
"With Arnie (Arnold) leaving the Hyundai A-League it will now become evident as to what a great coaching brain the competition has lost. But Arnie would be the first to tell me that the show must go on, and it will."
Arnold is no stranger to Japan and returns to the country after spending one season of his playing days at Sanfrecce Hiroshima in 1997-98.
The 50-year-old, who narrowly missed out on the Guangzhou R&F job to Sven Goran Eriksson, is the second championship-winning coach to leave Australia in the space of a month after Ange Postecoglou was picked to lead the Socceroos.
"Together at the Mariners we have achieved a lot over the past three seasons," Arnold said.
"But just like players I have the determination and drive to coach at the highest level I possibly can."
"Naturally, this opportunity with Vegalta Sendai excites me. The J-League is an amazing competition with quality players, highly professional clubs, and passionate fans.
"I hope to help Sendai achieve success, and help pave the way for more Australian coaches to work in top leagues around the world."
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