“Radiance” is the first album of solo piano improvisations from Keith Jarrett in a decade. The last such was “La Scala”, recorded 1995, released 1997. (In between, in 1999, Jarrett issued the home recording “The Melody At Night With You”, a solo album of standards and folk songs). Four years ago, Jarrett told interviewers it was unlikely he would return to solo piano performance. Having been sidelined for several seasons by illness, he had attempted two solo concerts in Japan in the autumn of 1999 but, dissatisfied with the results, had concluded he still needed the safety net of his trio to play live. In 2002, however, he changed his mind and, as it turned out, changed the solo format as well.