  We investigate the diversity in the wind density, supernova ejecta energy,
and ejecta mass in Type IIn supernovae based on their rise times and peak
luminosities. We show that the wind density and supernova ejecta properties can
be estimated independently if both the rise time and peak luminosity are
observed. The peak luminosity is mostly determined by the supernova properties
and the rise time can be used to estimate the wind density. We find that the
ejecta energy of Type IIn supernovae needs to vary by factors of 0.2-5 from the
average if their ejecta mass is similar. The diversity in the observed rise
times indicates that their wind density varies by factors of 0.2-2 from the
average. We show that Type IIn superluminous supernovae should have not only
large wind density but also large ejecta energy and/or small ejecta mass to
explain their large luminosities and the rise times at the same time. We also
note that the shock breakout does not necessarily occur in the wind even if it
is optically thick, except for the case of superluminous supernovae, and we
analyze the observational data both with and without assuming that the shock
breakout occurs in the dense wind of Type IIn supernovae.
