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properties of the tropopause may influence mountain waves propagating into the stratosphere. The sharp lapse rate and wind shear change at the tropopause may cause partial reflection and discontinuous aspects of wave structure. According to linear theory, the only wave properties that are likely to be continuous across the tropopause are the momentum flux (MF) and possibly the energy flux (EF; Eliassen and Palm 1961 , hereafter EP61 ). Once the waves have entered the stratosphere, the greater static
properties of the tropopause may influence mountain waves propagating into the stratosphere. The sharp lapse rate and wind shear change at the tropopause may cause partial reflection and discontinuous aspects of wave structure. According to linear theory, the only wave properties that are likely to be continuous across the tropopause are the momentum flux (MF) and possibly the energy flux (EF; Eliassen and Palm 1961 , hereafter EP61 ). Once the waves have entered the stratosphere, the greater static
, hereinafter S16 ) provides an improved dataset for gravity wave spectral studies over mountains. All the standard physical variables (e.g., u , Ï… , w , p , and T ) were measured independently and redundantly. The Southern Alps of New Zealand are surrounded by ocean and are therefore compact. Spectral and physical analyses are easier if the disturbance is compact. The Southern Alps have rapid tectonic uplift and erosion rates ( Williams 1991 ) and one of the most rugged terrains in the world. Small
, hereinafter S16 ) provides an improved dataset for gravity wave spectral studies over mountains. All the standard physical variables (e.g., u , Ï… , w , p , and T ) were measured independently and redundantly. The Southern Alps of New Zealand are surrounded by ocean and are therefore compact. Spectral and physical analyses are easier if the disturbance is compact. The Southern Alps have rapid tectonic uplift and erosion rates ( Williams 1991 ) and one of the most rugged terrains in the world. Small
1. Introduction As stably stratified air flows over a topographic obstacle, gravity waves are generated and propagate away from the mountain. Vertically propagating mountain waves may amplify, overturn, and break, due to factors such as the decrease of atmospheric density with altitude, nonlinearity, and vertical gradients of the ambient winds and stability, all of which influence the wave amplitude. Wave breaking is thought to be a threshold phenomenon occurring when the wave grows beyond a
1. Introduction As stably stratified air flows over a topographic obstacle, gravity waves are generated and propagate away from the mountain. Vertically propagating mountain waves may amplify, overturn, and break, due to factors such as the decrease of atmospheric density with altitude, nonlinearity, and vertical gradients of the ambient winds and stability, all of which influence the wave amplitude. Wave breaking is thought to be a threshold phenomenon occurring when the wave grows beyond a
1. Introduction There are several mountain ranges worldwide that are well-known for generation of large-amplitude mountain waves. These include the Alps, the Andes, or the New Zealand Alps. In the United States, the most thoroughly documented range is the Colorado Front Range (e.g., Lilly and Zipser 1972 ; Clark et al. 2000 ). Another, the Sierra Nevada in California ( Fig. 1 ) has been until recently less well known among scientists, but it is equally well known among amateur and
1. Introduction There are several mountain ranges worldwide that are well-known for generation of large-amplitude mountain waves. These include the Alps, the Andes, or the New Zealand Alps. In the United States, the most thoroughly documented range is the Colorado Front Range (e.g., Lilly and Zipser 1972 ; Clark et al. 2000 ). Another, the Sierra Nevada in California ( Fig. 1 ) has been until recently less well known among scientists, but it is equally well known among amateur and
elevations where stronger winds normally occur. It was ultimately determined that the cause of the high winds in the foothills was due to mountain waves that accelerated the winds in the foothills. While mountain-wave events that have produced extremely high winds have been well documented near the Rocky Mountains of the western United States (i.e., Blier 1998 ; Colle and Mass 1998a , b ; Colman and Dierking 1992 ; Durran 1990 ), these events remain largely undocumented near the southern Appalachians
elevations where stronger winds normally occur. It was ultimately determined that the cause of the high winds in the foothills was due to mountain waves that accelerated the winds in the foothills. While mountain-wave events that have produced extremely high winds have been well documented near the Rocky Mountains of the western United States (i.e., Blier 1998 ; Colle and Mass 1998a , b ; Colman and Dierking 1992 ; Durran 1990 ), these events remain largely undocumented near the southern Appalachians
1. Introduction Mountain wave (MW) studies have a history spanning over 100 years ( Smith 2019 ). A survey of the earliest studies was presented in the review of the Sierra Wave Project occurring in the 1950s by Grubišić and Lewis (2004) . Increasingly quantitative airborne and ground-based studies over the Rockies in the 1970s addressed conditions contributing to strong MW breaking, momentum fluxes (hereafter MFs), and turbulence in the upper troposphere and lower stratosphere (see Lilly and
1. Introduction Mountain wave (MW) studies have a history spanning over 100 years ( Smith 2019 ). A survey of the earliest studies was presented in the review of the Sierra Wave Project occurring in the 1950s by Grubišić and Lewis (2004) . Increasingly quantitative airborne and ground-based studies over the Rockies in the 1970s addressed conditions contributing to strong MW breaking, momentum fluxes (hereafter MFs), and turbulence in the upper troposphere and lower stratosphere (see Lilly and
1. Introduction While balloon soundings and remote sensing have contributed to mountain-wave observation, the most detailed observations derive from horizontal flight legs of research aircraft. Aircraft mountain-wave projects have been carried out in many regions of the world including the Alps, the Pyrenees, the Rockies, and the Sierra Nevada. The three major innovations in measurement technology in aid of these measurements were 1) gliders with a recording variometer, 2) aircraft with
1. Introduction While balloon soundings and remote sensing have contributed to mountain-wave observation, the most detailed observations derive from horizontal flight legs of research aircraft. Aircraft mountain-wave projects have been carried out in many regions of the world including the Alps, the Pyrenees, the Rockies, and the Sierra Nevada. The three major innovations in measurement technology in aid of these measurements were 1) gliders with a recording variometer, 2) aircraft with
1. Introduction Moist processes have been largely ignored in the majority of mountain-wave studies, partially because of the complexity associated with moisture and microphysical processes. Studies of the interaction between moist airflow and mesoscale topography can be broadly classified into two categories. The first category includes quasi-analytical studies with highly simplified representations of moist processes. For example, a set of two-dimensional steady-state linear wave solutions
1. Introduction Moist processes have been largely ignored in the majority of mountain-wave studies, partially because of the complexity associated with moisture and microphysical processes. Studies of the interaction between moist airflow and mesoscale topography can be broadly classified into two categories. The first category includes quasi-analytical studies with highly simplified representations of moist processes. For example, a set of two-dimensional steady-state linear wave solutions
of magnitudes as shown in Fig. 2a are known to excite mountain waves. Usually, one assumes wind speeds V H in excess of 10 m s −1 at the crest of the ridge. The wind direction α H should be within a sector of ±30°, …, 45° to the normal of the ridge of high ground. To allow for the favorable vertical propagation, V H should increase with altitude and α H should only marginally turn over a significant height band ( Dörnbrack et al. 2001 ; Alexander et al. 2013 ). Figure 6 depicts the
of magnitudes as shown in Fig. 2a are known to excite mountain waves. Usually, one assumes wind speeds V H in excess of 10 m s −1 at the crest of the ridge. The wind direction α H should be within a sector of ±30°, …, 45° to the normal of the ridge of high ground. To allow for the favorable vertical propagation, V H should increase with altitude and α H should only marginally turn over a significant height band ( Dörnbrack et al. 2001 ; Alexander et al. 2013 ). Figure 6 depicts the
1. Introduction Mountain waves (MWs) have been the subject of numerous observational, modeling, and theoretical studies over the previous 100 years ( Smith 2018 ). Examples of important physical effects include downslope winds, turbulence at flight altitudes, and transport and deposition of energy and momentum that have major roles in weather, climate, and atmospheric composition and structure. An extensive literature has addressed their dynamics and implications extending into the middle
1. Introduction Mountain waves (MWs) have been the subject of numerous observational, modeling, and theoretical studies over the previous 100 years ( Smith 2018 ). Examples of important physical effects include downslope winds, turbulence at flight altitudes, and transport and deposition of energy and momentum that have major roles in weather, climate, and atmospheric composition and structure. An extensive literature has addressed their dynamics and implications extending into the middle
