Dear Firedrakers, Latest results, I have just done my first solution of a mixed Helmholtz equation on the extruded spherical annulus (the volume between two nested spheres, i.e. the geometry we need to solve for the atmosphere). This works thanks to: * extruded mesh iterators from Doru * extruded FEM spaces from Andrew * The "Hedgehog" mesh and help on how to use the preconditioner from Lawrence * everything else in Firedrake... See attached for a picture showing the solution a couple of slices through the solution (obviously the resolution is quite coarse!). For those in the know, this is actually using the "shallow atmosphere approximation" which neglects the increase in spherical surface area with radial direction (obviously a bad approximation for this O(1) mesh!). Next step is to use the hedgehog trick to add the curvature terms so that we remove this approximation, and of course some validation tests. Then we'll move on to building an atmosphere model using this setup. Keep up the good work! --cjc