  Using abelian differentials and periods of the universal Mumford curve, we
study the universal expression and asymptotic behavior of tau functions defined
for stably degenerating families of algebraic curves with additional data.
Furthermore, we apply this study to constructing solutions to the KP hierarchy
which are expressed by nonarchimedean theta functions and by mixtures of
quasi-periodic solutions with solitons containing real solutions defined on
families of M-curves.
