Mesoscale Surges Through Coastal Gaps

Under suitable synoptic configurations, extremely strong winds can develop within sea-level coastal gaps. One type of strong wind occurrence is the gap surge phenomenon associated with sharp short-wave troughs. If the region of strong lower-tropospheric winds associated with the trough is aligned with the axis of the gap, extremely strong winds can develop as large momentum aloft supports downgradient acceleration associated with low-level pressure gradients. Such gradients can be enhanced by troughing to the lee of coastal orography. This presentation will describe the gap surge phenomenon and describe its relative frequency in one sea-level coastal gap: the Strait of Juan de Fuca. Compositing will be used to determine the typical synoptic conditions producing these features, and several events will be described in some detail. Finally, model simulations will be analyzed to elucidate essential structural and dynamical aspects of this important mesoscale feature of many orographic gaps.