Analysis of small-scale patterns of atmospheric motion in a sheared, convective boundary layer

Multiresolution feature analysis has been applied to data from NOAA's Phoenix II dual Doppler radar observations of a convective boundary layer near Boulder, Colorado, during June 1984 and to large eddy simulation (LES) results (using the regional atmospheric modeling system (RAMS) developed at Colorado State University) corresponding to a subset of that data. The data and LES results provide winds on a three-dimensional grid with spacing of similar to 200 m to a depth of about 2 km over a 9 x 9 km square for the observations. LES results were for an elongated (in the east-west direction) volume. The prevailing circulation maintained a strong shear (synoptic westerlies aloft above upslope easterlies at the surface) despite strong afternoon heating. The analysis defined preferred motion patterns (for both the observed and the simulated data) over 3 x 3 x 3 grid points using empirical orthogonal functions. In the case of the observations the patterns strengthened or weakened the shear locally for the most stable cases, but other patterns became relatively more important with increasing convection. Among these were a vortical pattern tilted in the shear direction. Differences in the peak intensity statistics for two different smoothings were used to estimate their support dimension from the observed data during moderately unstable conditions; most fell between 2.2 and 2.6. When the LES results corresponding to a moderately unstable observed atmosphere were analyzed, they showed that the preferred motion patterns were more like the observed stable case than the unstable cases, and the support dimension estimates were all greater than 2.6, indicating less intermittency than was observed.