  We present spectroscopic results of 146 water maser outbursts in W49 N,
obtained with the Metsahovi radio telescope at 22 GHz. Combining this data with
Gwinn's VLBI results, we were able to fix the free parameters in the shock
model of Hollenbach and McKee and the maser model of Elitzur, Hollenbach, and
McKee. This enabled a straightforward determination of some 20 shock and maser
parameters, among others, the kinetic temperature, postshock density, water
density, water abundance, preshock and postshock magnetic field strengths as
well as the inclination of the mean field with respect to the line of sight. A
step-by-step presentation of our diagnostic method is given and the relation
between observations and model parameters is discussed. One uniquely powerful
outburst feature, referred to as the "big flare feature", showed also the
narrowest linewidth. Observations indicate that the velocity of this feature
lies in the plane of the sky, whereas preshock and postshock magnetic fields
are directed nearly along the line of sight. Consequently, Alfvenic wave
fluctuations along the line of sight, and linewidth, are minimal, and a very
high aspect ratio is achieved. Furthermore, the big flare feature stands out
through its low space velocity, higher temperature (480 K), and larger preshock
magnetic field strength (8.2 mG).
