The structure of gradually transforming marine stratocumulus during the ASTEX first Lagrangian experiment

摘要: SUMMARY An analysis of the mean and turbulent structure planetary boundary layer is presented, using aircraft data obtained during Atlantic Stratocumulus Transition Experiment e rst Lagrangian experiment. The vertical relies mostly on slant proe le data, however, part also uses socalled ‘porpoise’ runs in vicinity cloud top. turbulence utilizes all horizontal eight legs as well les, presents both scaled statistics a spectral analysis. purpose to investigate details temporal development experiment, study order nd scale relations that can be utilized improved modelling stratocumulus-capped layer. hypothesis so-called ‘cloud decoupling’ has signie cant impact scaling. measured water corrected become consistent between two participating aircraft. maximum more constant time than previous studies erst Lagrangian; it suggested previously analysed variability may an artefact different instruments measure water. cloud-top jump equivalent potential temperature positive three eights, sufe ciently large for stable top, but decreases becomes negative last eights line with breaking up eeld. upper warms dries rapidly lower, suggesting entrainment dominant factor cloud. porpoise ight illustrates how sharp features at inversion are smoothed out while analysing several or even entire rather normalizing each height local Scaling uxes velocity variances shows decoupled throughout almost Lagrangian. It shown surface-layer scaling appropriate marine atmospheric (MABL) cloud-layer scales convective lowfrequency spectrum no gap, exception velocity, continues increase decreasing frequency only change slope; this indicates presence mesoscale motions. cospectra euxes very noisy throughout. When averaging spectra into intervals, indicated by peak averaged appear vary above surface MABL height-independent attempt calculate dissipation length-scale scatter, increasing linearly MABL, being roughly possibly parabolic