width of the isolated and prominent plume 4 from viewpoints of EUVI A and B by fitting the radiance profiles around this plume with Gaussian distributions. For the plume width $w$ at a given height $h$ we use the definition of @Aschwanden:etal:2008b $$w(h)=\frac{\int_{x_{b1}}^{x_{b2}}[I(h,x)-b(h,x)]\mathrm{d}x}{\mathrm{max}[I(h,x)-b(h,x)]},$$ where $x_{b1}$ and $x_{b2}$ are the $x$ coordinates of the two plume boundary points determined by the two local minima on either side of the plume (Figure \[fig:width\_method\]). Here, $b(h,x)$ is the linearly varying background radiance between $x_{b1}$ and $x_{b2}$. $I(h,x)-b(h,x)$ then denotes the background subtracted plume radiance distribution as a function of height $h$. The intensities associated with this plume along two epipolar lines are shown in Figure \[fig:width\_method\] as an example. By using the epipolar geometry, we identify the corresponding plume point in two images and calculate the plume width from EUVI A and EUVI B, respectively. Subsequently the plume widths along the corresponding epipolar lines are transformed to the widths perpendicular to the plume direction within the frame of the epipolar geometry.

For this plume, we found from both viewpoints that the width very slightly decreases by around $10~\%$ in the height range from 20 Mm to 90 Mm in 3D. The mean width 