Moriarty, 24, is one of the most promising young spinners in English cricket but has found himself playing second-team cricket this summer. Surrey have relied heavily on their seamers in the Championship and have picked allrounder Will Jacks and Cameron Steel ahead of their specialists.
Yorkshire have brought Moriarty in for their next four Championship fixtures, including Sunday’s home game against Gloucestershire, and their managing director Darren Gough said he was “a brilliant addition”.
Gough added: “With Yorkshire’s focus shortly turning to Championship cricket again, alongside the busy Blast schedule, it was important to add another addition to our bowling resources.”
It remains to be seen if he will play straightaway, though Yorkshire’s main spinner, Dom Bess, has struggled this season, taking 12 wickets at 51.33 in five appearances.
Moriarty has only played two Championship games in the last 18 months, but Alec Stewart, Surrey’s director of cricket, said he could still play a role in the title run-in later this season.
“This is a really good opportunity for Dan to play a number of first-class games over the next month or so,” Stewart said. “Hopefully he’ll put in some really good performances which will prepare him well should he get selected in the Championship run-in during September.”