No it is a time slice i.e. per day of the year. So imagine the volume grid, slice it each day and then inside each slice plot the 2D vector (laplacian, dT/dt) at each node on the grid. Then vary the length of that vector proportionally by laplacian and then by dT/dt, this way you could visualize the laplacian / (dT/dt) as a quotient, which was what Daniel was concerned about.