Is the Local Fluff Typical?

The very local interstellar medium (LISM) has physical characteristics that are typical of the warm neutral medium throughout the disk of the Milky Way. Recent high resolution surveys of the Galactic plane in the λ21 cm line of hydrogen show that structures like the local bubble and the local clouds within it are very common. On smaller scales, observations predict that inside the local clouds there should be structure in the density and velocity field that might be detectable by direct measurements. With a time baseline of a few years or more, even an upper limit on the variation in these parameters would be useful to clarify the interpretation of controversial 21 cm VLBI observations. © 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.