Ubuntu LTS releases are already available from the Microsoft Store (link) as apps, but there are other ways of installing Ubuntu for the Windows Subsystem for Linux. You can import the Ubuntu tarball with the wsl command or use graphical interfaces listed at https://wiki.ubuntu.com/WSL#Third-party_tools for custom managing tarballs.

Such Ubuntu tarballs were not publicly available in the past, but now I proudly present the downloadable WSL tarballs for Ubuntu 16.04 LTS (Xenial), 18.04 LTS (Bionic), 19.04 (Disco), and the for the still in development 19.10 (Eoan) release. Thanks to everyone in the Ubuntu Foundations, Certified Public Cloud and Desktop Teams who helped to make this happen!

While we still recommend installing the Ubuntu WSL app from the Microsoft Store, using the tarballs lets you maintain more parallel Ubuntu instances which can be handy for experiments and you can also take a look at the next Ubuntu versions!

If you find a program or HOW-TO that installs other Ubuntu tarballs for WSL, please help by asking their author to use the official tarballs, because only the WSL tarballs include the WSL integration packages as described in the previous post!