ThemeRiver was introduced in the paper Havre, Susan, et al. "Themeriver: Visualizing thematic changes in large document collections." Visualization and Computer Graphics, IEEE Transactions on 8.1 (2002): 9-20. Link to Google Scholar
ThemeRiver is a variant of line chat, so is one way to visualize time series data.
The Processing source code is available at https://github.com/zshiba/visualization.