Extended optical spectroscopic monitoring of wind structure in HD 152408

New perspectives are provided on significant spatial structure and temporal variability in the nearstar wind regions (i.e. < 3 R-*) of the massive lum inous star HD 152408 (classified as O8:Iafpe or WN9ha). This study is prima rily based on the analysis of high-quality echelle spectra secured during 2 1 nights between 1999 July to August, using tile Landessternwarte-developed (fibre-fed) FEROS instrument on the ESO 1.52-m telescope. These extended t ime-series data, with a total simultaneous wavelength coverage of <lambda>l ambda 3600-9200 Angstrom, were exploited to monitor absorption and emission fluctuations (of similar to5-10% of the line flux) in several He I and Bal mer lines, together with more deep-seated (near-photosphere) disturbances i n weaker metallic emission and absorption lines. Organised large-scale Rind structure in HD 152408 is principally betrayed by sequential episodes of d iscrete absorption and emission features, which migrate from near zero velo city to almost the wind terminal velocity. This evolution is extremely slow , however, typically spanning similar to \4 days for an individual episode. We demonstrate that tile blue-shifted absorption episodes in He-I are very closely mirrored tin velocity and time) by absorption features (i.e. reduc ed not enhanced flux) in tile blue wings of tile mainly recombination forme d broad HN emission line. Tile implication is that there is: detailed balan cing between ground state photoionization and recombination in the substant ially optically thick Balmer lines. Surprisingly, the velocity behaviour of the red-ward and blue-ward migrating features is highly assymmetric, such that the mean acceleration of tile former is less than 50% of the latter. F ourier analysis reveals a modulation time-scale for tile wind activity of s imilar to7.7 days, plus its harmonic at 3.9 days. The longer period is simi lar to 28 times greater than the characteristic radial wind flow time of HD 152408. We also detect a similar to1.5 day periodic variation in the radia l velocity of the weak C IV lambda lambda 5801, 5812 absorption lines, whic h are the closest approximation to "pure" photospheric lines in the optical spectrum of HD 152408. Tile wind-formed optical lines of HD 152408 are als o affected by fluctuations in the central peak emission, particularly evide nt in H alpha where the equivalent width may vary by up to 20%. Data secure d between 1995 and 1999 reveal, however, that the epoch-to-epoch mean profi les: are remarkably similar. Non-LTE steady-state stellar atmosphere models are used to synthesis profiles to match representative H alpha and He-I la mbda 5876 line profiles. Only a slow (tailored) velocity law (compared to b eta = 1) provides a good match to the H alpha emission peak and wings, but the models predict excess H alpha absorption. The observed extreme Ho emiss ion variations can be reproduced by the synthetic profiles with an implied +/- 10% variation in mass-loss rate. The results on optical line profile va riability in HD 152408 are discussed in tile context of models for co-rotat ing; interaction regions (CIRs) in tile wind. Several constraints are provi ded that argue against simple velocity fields in such streams, including (i ) tile slow acceleration of features to high velocities, within similar to3 R-*, (ii) the strong asymmetry in projected acceleration of the approachin g and receding stream material, (iii) Balmer line absorption effects in the approaching material, (iv) the rise of localised features from very low ve locities, and (v) the stability of the large-scale CIRs against turbulent s mall-scale wind structure. We suggest that it may be worth exploring hydrodynamic simulations of CIRs that incorporate different velocity fields on the leading (faster accelerat ing; blue-ward absorption) and trailing (slower accelerating; red-ward emis sion) edges of tile spiral structures.