Also, the FCOM has no information about what data the GPWC uses to issue the windshear alerts. I assume it's something to to with rate of change of groundspeed versus airspeed... does anyone know for sure?
I am pretty sure it is a combination of airspeed and accelerometer imputs. Can not speak for sure about the 737 but in most type aircraft the FCC plays a large part and on a coupled approach will level wings 10 deg nose up and toga.