EWoT:Sierin Vayu (pronounced: see-EH-rihn VEYE-oo) was the Amyrlin Seat from 979 to 984 NE. She was raised from the Gray Ajah after Tamra Ospenya was murdered.
She was plump but hard eyed, with a round face and a stern bearing.
In TWoTC Sierin strength is described at level 18(6).
Sierin was elected Amyrlin Seat in the year 979 NE but despite the Tradition after her election she did not grant petiotions and relief from penances.
In fact she was extremely hard and strict as Amyrlin, and imposing strict disciplinary measures on the Tower, even public castigation to many Aes Sedai: she exiled three sisters from the Tower and two more were birched.
Sierin has been described as having "more than a touch of Red in her." Many sisters were surprised that she had chosen Gray instead of Red Ajah when she was raised to the shawl. Contravening the tradition of appointing high officials from the Amyrlin's own former Ajah, she chose Duhara Basaheen as her Keeper of the Chronicles and Amira Moselle as her Mistress of Novices, both from the Red. And she had a great reputation for misandry; she fired all the male clerks in the White Tower, for such offenses as "flirting with Novices and Accepted" or "inappropriate glances and looks," accusing even harmless elderly men and men known to be homosexual.
She was secretly warned by Siuan Sanche about the Black Ajah and its relation with the deaths of five Aes Sedai, Tamra Ospenya's Searchers. It is possible that she hinted her suspicions for she died mysteriously in 984 NE; later Chesmal Emry revealed that she induced a small group of Red Ajah sisters to murder her. The Black Ajah was not directly involved.
In TWoTC is revealed also that Sierin was about to put a stop to "The Vileness" but her assassination prevented it. Also it is reported that Angharad Juerissen was Keeper of the Chronicles for Sierin Vayu insted of Duhara; a possible explanation is that Duhara may have stepped down from the office in 984 NE and was briefly replaced by Angharad. Maybe the involvement of Duhara in the Vileness was discovered early and she was forced to resign as Keeper and severely punished before Sierin's death. In any case it is unlikely that Duhara was directly involved in Sierin's murder as the Companion attests that the Black was not responsible of it.