He rides on the back of a swan to the land of the Hyperboreans during the winter months, and the absence of warmth in winter is due to his departure.
hiː ɹˈaɪdz ɔnðə bˈæk əvə swˈɑːn tə ðə lˈænd ʌvðə hˌaɪpɚbˈoːɹiənz dˈʊɹɹɪŋ ðə wˈɪntɚ mˈʌnθs, ænd ðɪ ˈæbsəns ʌv wˈɔːɹmθ ɪn wˈɪntɚɹ ɪz dˈuː tə hɪz dᵻpˈɑːɹtʃɚ.