Change Forcefield power by keyframe?

First let me apologize: I am pretty new to Blender and 3d animation …
I am using a forcefield to act as a wind tunnel for my animation, but I need to control wind speed based on time. I have selected the forcefield, but none of the selectable properties for a keyframe seems to do the trick.
What am I missing?

Have you tried keyframing the Strength property of the Wind? You can also type #frame into any number field and that field will increase as the timeline advances. The field will turn purple indicating that it is now controlled by a driver.