Fine-scale structure and mixing within an inversion

Abstract

This paper describes some of the results that were obtained in an experimental study of an inversion capping a convective boundary layer, during which a balloon-borne probe was flown through the actual interface at the same time as it was scanned by a high power 10-cm Doppler radar. The initial analysis has revealed several interesting features including the possible presence of small-scale Kelvin-Helmholtz billows at the crest of the 'hummocks' of the inversion and the absence of an inertial subrange. A model is proposed for the transfer of sensible heat downwards across the inversion. This is hypothesised as a two-stage process -sporadic thickening by the entrainment of air from above and below due to the action of the breaking billows, and a continual erosion of the lower surface by convective activity.

The structure of an inversion above a convective boundary layer as observed using high-power pulsed doppler radar

“…In bursts D and E the temperature decreased to about 8 °C, consistent with the inference from the radar data that a large part of the inversion had risen above the level of the probes. Far more detail was available from the tethered-balloon instrumentation than is shown here; these data are analysed in detail by Readings et al (1973), where they are interpreted in terms of small-scale KelvinHelmholtz billows forming within the inversion. Figure 8 shows the variations with time of the mean velocity component towards 242 ° in the vicinity of the inversion.…”

“…In the absence of precise knowledge of Lo, M and F, and indeed in the absence of a fully developed inertial subrange (see Readings et al, 1973), the magnitude of t/ has had to be used in this paper in only a qualitative sense, as an indicator of the height of the inversion. On the other hand, the information regarding the velocity structure in the vicinity of the inversion, which is available from the Doppler shift of the radar echo, is valid quantitatively, and the analysis of this is an important part of the study.…”

“…The broad features of the balloon-borne measurements will be used in this paper insofar as they clarify the interpretation of the Doppler radar data. A more detailed analysis of the combined results from the radar and other probes is reported in this issue (Readings et al, 1973). Further supporting data were obtained using sequential radiosonde and pilot balloon ascents and the entire observational set-up is summarized in Figure 1.…”

Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C, Antarctica

“…The internal structure of an inversion layer capping a convective ABL was observed by Browning (1971), Browning et al (1973a) and Readings et al (1973) using pulsed Doppler radar, tethered balloon and radiosonde ascents. They showed how convective circulations in the ABL perturb the height of an inversion, thereby producing undulations of the entire inversion layer.…”

“…They showed how convective circulations in the ABL perturb the height of an inversion, thereby producing undulations of the entire inversion layer. Readings et al (1973) also hypothesised the possibility of the presence of trapped gravity waves within an inversion. Air motions within KH billows at a height of ≈7 km were investigated by Browning et al (1973b) using radar, aircraft and radiosonde measurements.…”