WRF simulations of north flow across the Alaska Peninsula: General characteristics of wakes, jets and mountain waves
Using a series of WRF simulations the nature of air movement over the terrain is investigated within the nondimensional mountain height parameter space of 0.7-3.0. In general, the results of this study are in agreement with the numerous studies of a similar nature but which have used idealized terrain as well as homogenous upstream wind and temperature profiles. The main results indicate the importance of the distance between the base of the inversion and the top of the terrain to the nature of the flow downstream. Significant differences in flow properties are generated downstream of the various terrain features due to subtle changes in the height and strength of the inversion as well as in wind shear.
Specifically, the model indicates that wakes form in association with either strong or weak vertical vorticity (curl). Wave breaking typically generates wakes which contain stagnation and reverse flow; however, wakes of significant size also form in cases where mountain waves do not break. In addition, wake intensity and spatial extent can vary significantly in the vertical. If the base of an inversion descends below the crest of a mountain the flow impinging the upper mountain is diverted laterally (flow-splitting) with the result that the wake maybe weaker than when the base of the inversion was higher. As a rule-of-thumb the length of a wake extends 5-8 mountain half-widths downstream while the minima speed within a wake typically occurs 500-1000 m AGL but may vary at times. Jets emanating from sea-level gaps typically range from 150-200% of the upstream wind speed but values in excess of 250% can occur at times. In general, lee-side wind speeds evolve during the lifetime of a particular event and are difficult to categorize by one or two flow parameters.