Correlations between the local kinetic energy producing terms in the Bora flow

A case of strong Bora flow was modeled with the WRF/ARW model in a 333 m horizontal resolution. All relevant model variables were archived for all model grid-points in 1 second time intervals. From these the terms of energy equation in transport (or balance) form that describe contributions to local changes of energy were computed. Besides many other characteristics, correlation fields in space and in time (different time lags) were computed between these 3D fields. This enables the determination of spatial and temporal structure of local and non-local causes for gusts and lulls which are among the most important features in such flow. Two examples of a cross-correlation filed for a certain time lag are shown here. Auto- and cross-correlation 3D fields offer information on spatial structures, on interconnection between different terms of local kinetic energy and its local tendencies inside the main Bora flow, as well as between distant locations. The correlations in time give information on growth and decrease of influences of different causes of local kinetic energy changes, as well as on the displacement and displacements velocity of these influences.

Figure: Cross-correlations in a vertical cross-section (bottom) between 100 min time course of local change of kinetic energy (∂(W_k))⁄∂t in point marked with the cross with time courses of advective term - ∇∙(W_k v ⃗ ) all gridpoints of the same duration, but with the time lag delta t = 10 minutes earlier.