Flip ups and wings
The device is a "flip up" much like the ones used by BAR and Sauber. It is designed to improve flow over the rear of the car and the rear wheels, it also directly provides some downforce.
The Jordan version at first appears to be a winglet made of two parts the front element (black) and a rear element (Yellow).
(The difference being a winglet has an aerofoil cross-sectional shape and is designed solely to produce downforce, a "flip up" acts to deflect airflow and generally have a consistent thin cross-section.)
But looking at the image below, you can see that in fact the yellow panel of bodywork runs from the sidepod to the endplate (with "Imation" on) and runs totally under the winglet (Black) and hence is a "Flip Up" the Black winglet server to direct the airflow over the large "Flip up".