The solar transition region: a time-varying interface between the chromosphere and corona?

Using joint observations taken with the CDS and SUMER instruments onboard SOHO, we re-examine the solar transition region in an attempt to determine whether it is de-coupled from the over-lying coronal region. Line ratios calculated from temporal series observations of O iv and Fe xiii spectral lines were converted to electron density, and hence electron pressure using theoretical line ratios. Little or no evidence was found to support the constant electron density assumption, and instead a constant electron pressure is found between the transition region and corona. This lends support to the idea that the transition region is a time varying interface between the chromosphere and corona, and is not formed in unresolved finestructures that are disconnected from the corona.