  Let $\Omega\subset \mathbb{C}^2$ be a bounded convex domain with $C^1$-smooth
boundary and $\varphi\in C^1(\overline{\Omega})$ such that $\varphi$ is
harmonic on the nontrivial disks in the boundary. We estimate the essential
norm of the Hankel operator $H_{\varphi}$ in terms of the $\overline{\partial}$
derivatives of $\varphi$ "along" the nontrivial disks in the boundary.
