Marine Boundary Layer Effects on Gravity Wave Launching during DEEPWAVE

The first stage in the lifecycle of mountain waves propagating into the middle atmosphere is their launching by the surface topography. During the DEEPWAVE field campaign, stereo time-lapse images were collected of cloud formations upwind of the New Zealand Alps. One photography session, from 1223-1529 LST 14 June, occured just hours prior to the aircraft flight for the first major wave event of the project, identified as IOP 3.

A major feature in the time-lapse is the passage of a surface boundary that brings about a change in the cloud and by inference a change in the character of the boundary layer. Initially, the clouds are confined to the crests of the Alps and occasional isolated cumulus that moves parallel to the shore from north to south. The boundary crosses the site at 1426 LST and is marked by an extensive layer of altocumulus with undulatus at the leading edge. Beneath this layer, lines of cumulus apparently organized into rolls eventually appear and continue to move over throughout the period. This suggests the arrival of cooler air and the transition from a barrier jet situation to a more convective boundary layer.

These photos and a preliminary photogrammetric analysis were used to design a series of idealized simulations using the Naval Research Laboratory's COAMPS. The resolution was chosen based on a calculated horizontal scale for the convective rolls of 500-650 meters, while sensitivity tests followed the likely changes in the boundary layer. A baseline with all land was followed by an upwind sea surface of matching temperature, and then the SSTs were raised and lowered to match the photographed conditions. When possible the results are also compared with data from the evening's research flight.