Funding for this research was provided by:
Japan Society for the Promotion of Science (17K14388, 17K01223)
Received: 2 March 2017
Accepted: 10 July 2017
First Online: 4 August 2017
: MO’s current affiliation is Weathernews Inc.
: The authors declare that they have no competing interest.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.