The large VṛddhaSūryĀrunaKarmavipāka, that is quite well known in the literature, casts Sūrya as one of the main interlocutors.  I don't know if that somehow explains the -arka.  Probably not, but I thought I'd mention it.

The VSAK was published by Khemarāja Śrīkṛṣṇadāsa in Mumbai in 1909; the edition and also a fine manuscript of the work are both available in the Wellcome Library in London.

Dominik Wujastyk