Dynamics of precipitating convection  Applications of Dynamic Retrieval  Applications of Dynamic Retrieval

Boundary layer investigations

In early study using retrieval technique similar to the one discussed here, Gal-Chen and Kropfli (1984) deduced boundary layer statistics from multiple Doppler measurements. This study provided an important validation of this approach as E_r values close to 0.2 were obtained. They also reported scan-to-scan temporal correlation as high as 0.80, which is quite encouraging. They noted however, that to obtain such good correlation requires careful data processing (e.g., correction for advection as suggested by Gal-Chen, 1982).

Comparison in a non-dimensional form of their derived statistics against other methods showed that reliable boundary layer statistics can be computed from retrieved quantities. The non-dimensional form was used as is customary in boundary layer research so that, if the similarity theory is applicable, profiles taken under vastly different environmental parameters would collapse into one universal curve (Sorbjan 19xx). For example, using mixed layer similarity theory one may define

$$w_*=[z_ig({\overline{\mathstrut {w^\prime\theta^\prime}}})_0/......heta_*=({\overline{\mathstrut {w^\prime\theta^\prime}}})_0/w_*$$ (13.18)

 

where z_i is the height of the mixed layer $g/\theta_0$ the buoyancy parameter and ${\overline{\mathstrut ({w^\prime\theta^\prime}}})_0$ the heat flux at the surface. In Fig. 13.3 we show a plot of the non-dimensional temperature perturbations, ($\theta_*$) from measurements taken in three different parts of the world:

 

Figure 13.3: Non-dimensional profiles of temperature perturbations within the boundary layer from the aircraft data of Caughey and Palmer (1979) as indicated with crosses, the simulations of Deardroff (1974) indicated with filled circles and the retrieval results of Gal-Chen and Kropfli (1984).

The open circles are data derived using the retrieval technique. The particular field experiment is the Phoenix I experiment (Kropfli and Hildebrand, 1980). The closed circles are from the Deardorff (1974) numerical simulation of Day 133 in the Wangara experiment while the the crosses are based on Caughey and Palmer (1979) airplane data. For the Phoenix I experiment the height of the mixed layer was close to 2 km, while for the other cases it was approximately 1 km. From it is seen that despite the different environmental parameters the data points at the mixed layer "collapse" into a single curve. Deviations from similarity theory are found in the stable layer above the mixed layer.

A unique contribution from the dynamic retrieval technique to boundary layer meteorology is the ability to compute pressure perturbation in the entire boundary layer. Such measurements are difficult with tower or airplane data because typical pressure perturbations are of the order of $10^{-2}{\rm\ mb}$. Fig. 13.4 is a vertical profile of the non-dimensional pressure perturbations retrieved using the Phoenix I data (Gal-Chen and Kropfli, 1984). The results are consistent within the lower half of the mixed layer with temporal changes taking place above. For more details, the reader is referred to Gal-Chen and Kropfli (1984).

 

Figure 13.4: Non-dimensionalized pressure perturbations within the boundary layer retrieved from three different radar volumes (from Gal-Chen and Kropfli 1984).

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