Abstract: The Peetre K-modulus and the generalized. Riesz summability operators on the sphere are introduced. The convergence and boundedness of the Riesz operators are discussed. The strong and weak equivalence relationships of the K-moduli and the Riesz operators are presented. The Riesz operators can serve as a realization of the corresponding K-modulus.

Key words: K-modulus, Riesz operator, spherical harmonic expansion