Polarisation
Polarisation refers to the processional orientation of the field vector.
For linear polarisation the orientation of the field is constant, so an observer towards whom the wave is travelling would see a sinusoidal growth and reduction of the field vector about the origin.
When two or more fields with different phases are present, they can interfere with each other to create elliptically polarised fields. The magnitude of magnetic field strength of an elliptically polarised field does not go to zero, so the average field strength is higher.
If two fields of equal amplitude and 90 degree phase difference interact with each other, the special case of circular polarisation is observed: To an observer towards whom the wave is travelling, the field vector is rotating. In this case the magnitude of magnetic field strength is constant at its maximum, so a higher average (RMS) magnetic field is produced.