Alpine gravity waves: Lessons from MAP regarding mountain wave generation and breaking

Abstract

ABSTRACT:The two-month special observing period of the Mesoscale Alpine Programme (MAP) in autumn 1999 included a variety of complex mountain wave events. Seven wave events were carefully analyzed, compared with numerical models and described in published papers. These detailed investigations revealed some common dynamical elements, i.e. the importance of low-level processes involving the slow-moving boundary layer, low-level wind shear causing either wave absorption or decoupling/spilling, upstream blocking, and latent heat release. Based on these studies, it is clear that any quantitative prediction of mountain wave generation must take full account of these lower troposphere processes. The newest numerical models show significant skill in simulating these effects. Using these models, the climatology of waves over the Alps can be studied.

The effect of indiscriminate nudging time on large and small scales in regional climate modelling: Application to the Mediterranean basin

“…Indeed, when low-level flow splitting or wave breaking occurs, dissipative processes in the turbulent regions generate PV that streams downwind in 'PV banners' (e.g. Smith, 1989;Smith et al, 2007). For instance, the mistral is qualified as a primary PV banner Guénard et al, 2006), contrary to smaller streams of vorticity which wrap up into pairs of eddies of opposite signs due to the irregular peak and pass structure of the mountain ridges forming eventually multiple PV banners (Aebischer and Schär, 1998;Schär et al, 2003;Flamant et al, 2004).…”

Downslope Windstorms of San Diego County. Part I: A Case Study

“…Despite steady improvement in operational numerical weather prediction models over the last several decades as well as advancements in the understanding of mountain meteorology dynamics, forecast skill for downslope windstorms is still limited by several factors, including dependence and/or sensitivity to model resolution (e.g., Reinecke and Durran 2009b;Jackson et al 2013), numerical schemes (e.g., Reinecke and Durran 2009b), vertical coordinates and diffusion (e.g., Smith et al 2007), physical formulations [especially the boundary layer; see Smith (2007)] and initial condition uncertainties (e.g., Reinecke and Durran 2009a). Our work was motivated by the need to forecast winds that could affect electrical transmission lines in San Diego County operated by the San Diego Gas and Electric (SDG&E) company.…”

The role of advection and of work done by forces in the gustiness of the Bora flow

“…The choice of parameterisation thus in particular affects the overall wave-turbulence interaction (e.g. smith et al, 2007;Gohm et al, 2008). in our diagnostic approach, this term will not be computed explicitly, but diagnosed from the values of all the other terms:…”

“…The traditional explanation (AMs Glossary) was that the Bora is "a fall wind with a source so cold that, when the air reaches the lowlands or coast, the dynamic warming is insufficient to raise the air temperature to the normal level for the region". This dynamic explanation of the Bora was revised after an intensive measurement campaign in ALPEX (Smith, 1987), numerical modelling (e.g. Klemp and Durran, 1987), and additional conceptual models (e.g.…”

“…Klemp and Durran, 1987), and additional conceptual models (e.g. Smith and Sun, 1987). Some recent studies reveal that certain instances of Bora exhibit a downslope windstorm or hydraulic jump structure (AMs Glossary).…”