We present the results from a 500 ks Chandra observation of the Seyfert 1 galaxy NGC 5548 .
We detect broadened ( full width half maximum = 8000 km s ^ { -1 } ) emission lines of O vii and C vi in the spectra , similar to those observed in the optical and UV bands .
The source was continuously variable , with a 30 % increase in luminosity in the second half of the observation .
The gradual increase in luminosity occurred over a timescale of \sim 300 ks .
No variability in the warm absorber was detected between the spectra from the first 170 ks and the second part of the observation .
The longer wavelength range of the LETGS resulted in the detection of absorption lines from a broad range of ions , in particular of C , N , O , Ne , Mg , Si , S and Fe .
The velocity structure of the X-ray absorber is consistent with the velocity structure measured simultaneously in the ultraviolet spectra .
We find that the highest velocity outflow component , at - 1040 km s ^ { -1 } , becomes increasingly important for higher ionization parameters .
This velocity component spans at least three orders of magnitude in ionization parameter , producing both highly ionized X-ray absorption lines ( Mg xii , Si xiv ) as well as UV absorption lines .
A similar conclusion is very probable for the other four velocity components .

Based upon our observations , we argue that the warm absorber probably does not manifest itself in the form of photoionized clumps in pressure equilibrium with a surrounding wind .
Instead , a model with a continuous distribution of column density versus ionization parameter gives an excellent fit to our data .
From the shape of this distribution and the assumption that the mass loss through the wind should be smaller than the accretion rate onto the black hole , we derive upper limits to the solid angle as small as 10 ^ { -4 } sr. From this we argue that the outflow occurs in density-stratified streamers .
The density stratification across the stream then produces the wide range of ionization parameter observed in this source .
We determine an upper limit of 0.3 M _ { \odot } yr ^ { -1 } for the mass loss from the galaxy due to the observed outflows .