Context : Disk accretion onto weakly magnetized white dwarfs ( WDs ) in cataclysmic variables ( CVs ) leads to the formation of a boundary layer ( BL ) between the accretion disk and the WD , where the accreted matter loses its excess kinetic energy and angular momentum .
It is assumed that angular momentum is effectively transported in the BL , but the transport mechanism is still unknown .

Aims : Here we compute detailed model spectra of recently published optically thick one-dimensional radial BL models and qualitatively compare them with observed soft X-ray/extreme ultraviolet ( EUV ) spectra of dwarf novae in outburst .

Methods : Every considered BL model with given effective temperature and surface density radial distribution is divided into a number of rings , and for each ring , a structure model along the vertical direction is computed using the stellar-atmosphere method .
The ring spectra are then combined into a BL spectrum taking Doppler broadening and limb darkening into account .

Results : Two sets of model BL spectra are computed , the first of them consists of BL models with fixed WD mass ( 1 M _ { \odot } ) and various relative WD angular velocities ( 0.2 , 0.4 , 0.6 and 0.8 break-up velocities ) , while the other deals with a fixed relative angular velocity ( 0.8 break-up velocity ) and various WD masses ( 0.8 , 1 , and 1.2 M _ { \odot } ) .
The model spectra show broad absorption features because of blending of numerous absorption lines , and emission-like features at spectral regions with only a few strong absorption lines .
The model spectra are very similar to observed soft X-ray/EUV spectra of SS Cyg and U Gem in outburst .
The observed SS Cyg spectrum could be fitted by BL model spectra with WD masses 0.8 - 1 M _ { \odot } and relative angular velocities 0.6 - 0.8 break up velocities .
These BL models also reproduce the observed ratio of BL luminosity and disk luminosity .
The difference between the observed and the BL model spectra is similar to a hot optically thin plasma spectrum and could be associated with the spectrum of outflowing plasma with a mass loss rate compatible with the BL mass accretion rate .

Conclusions : The suggested method of computing BL spectra seems very promising and can be applied to other BL models for comparison with EUV spectra of dwarf novae in outburst .