Simulated Kelvin–Helmholtz Waves over Terrain and Their Microphysical Implications

Conrick, Robert; Mass, Clifford F.; Zhong, Qi

doi:10.1175/jas-d-18-0073.1

Cited by 17 publications

(18 citation statements)

References 42 publications

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“…It is also well noted that, above the boundary layer (approximately from 2.1 km to 3 km AGL), a fluctuation forms downwind from the mountain top. This agrees with the findings of Conrick et al [36] that the Kelvin-Helmholtz instability is likely to develop over complex terrain when there is a veering in wind direction. In Figure 11f, the water vapor mixing ratio distributes more evenly within the boundary layer, whereas the maximum value reduces compared to the morning time.…”

Section: Vertical Structuresupporting

confidence: 93%

A Numerical Study of Mountain-Plain Breeze Circulation in Eastern Chengdu, China

Tian

Miao

2019

Sustainability

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The spatiotemporal structure and evolution of the thermally-induced mountain-plain breeze circulation in the Longquan Mountain, eastern Chengdu, are studied by the WRF-ARW model based on a two-day case. Turbulence characteristics are also examined to better understand the local circulation of the area. Simulation results show that the 2 m temperature distribution of the plain and mountain areas is peculiar due to the occurrence of the temperature inversion. The plain and mountain breezes can be predicted explicitly by the model, and the consequent circulations are coupled with other factors such as turbulent movement and vertically propagating mountain waves. Owing to this unique terrain feature, the north portion of the mountain demonstrates more evident mountain and plain breezes compared to the south and middle portions. Stronger turbulences are formed over the mountain area compared to the plain area. Vertical cross-sections of turbulent heat, moisture and momentum fluxes show that turbulent transport plays an important role in the development and elimination of mountain-plain breeze circulation.

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Section: Vertical Structuresupporting

confidence: 93%

A Numerical Study of Mountain-Plain Breeze Circulation in Eastern Chengdu, China

Tian

Miao

2019

Sustainability

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“…The model's difficulty in producing critical layers may be attributed to resolving complex terrain-induced flows. Conrick et al (2018) also used the WRF Model to analyze critical layers based on the Richardson number albeit with more success. A likely explanation may exist in the different scales of essential features being simulated.…”

Section: Discussionmentioning

confidence: 99%

“…A likely explanation may exist in the different scales of essential features being simulated. The wind shear in the simulations by Conrick et al (2018) was produced by synoptic features (terrain-modified shallow frontal passage and a low-level jet) while the terraindriven features we simulate are smaller scale. Only the blocked flow case produces dynamic instability (i.e., 0 , Ri , 0.25) in the actual KH wave region and the blocked flow (and postfrontal air mass) is deep enough to be resolved by the model.…”

Section: Discussionmentioning

confidence: 99%

“…Other studies have used numerical models to describe KH waves using either large-eddy simulations (e.g., Sauer et al 2016) or high-resolution numerical weather prediction models such as WRF (e.g., Mahalov et al 2011;Conrick et al 2018). However, in this study, we do not attempt to resolve the KH waves themselves (900-m grid spacing is insufficient for the small wavelengths we observe), only the environment in which they form.…”

Section: Case-specific Wrf Simulationsmentioning

confidence: 92%

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Detailed Dual-Doppler Structure of Kelvin–Helmholtz Waves from an Airborne Profiling Radar over Complex Terrain. Part I: Dynamic Structure

Grasmick

Geerts

2020

Journal of the Atmospheric Sciences

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Kelvin–Helmholtz (KH) waves are remarkably common in deep stratiform precipitation systems associated with frontal disturbances, at least in the vicinity of complex terrain, as is evident from transects of vertical velocity and 2D circulation, obtained from a 3-mm airborne Doppler radar, the Wyoming Cloud Radar. The high range resolution of this radar (~40 m) allows detection and depiction of KH waves in fine detail. These waves are observed in a variety of wavelengths, depths, amplitudes, and turbulence intensities. Proximity rawinsonde data confirm that they are triggered in layers where the Richardson number is very small. Complex terrain may locally enhance wind shear, leading to KH instability. In some KH waves, the flow remains mostly laminar, while in other cases it breaks down into turbulence. KH waves are frequently locked to the terrain, and occur at various heights, including within the free troposphere, at the boundary layer top, and close to the surface. They are observed not only upwind of terrain barriers, as has been documented before, but also in the wake of steep terrain, where the waves can be highly turbulent. Vertical-plane dual-Doppler analyses of KH waves reveal the mixing of layers of differential momentum across the high-shear zone. Doppler radar data are used to explore the dynamics of KH waves, including the response of thermodynamic and kinematic variables above, below, and within the instability layer.

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“…However, Terradellas et al (2001) [48] showed that the periods induced by gravity waves were between 12 and 14 min, which was much shorter than the observed periods (15~40 min) in this study, and stated that the periods longer than 16 min might be caused by other processes such as KHI. Moreover, using the Weather Research and Forecasting (WRF) Model, Conrick et al (2018) [49] showed that KHI developed within the melting layer of stratiform precipitation when easterly flow near the surface increased, wind shear increased, and low-level stability decreased. As shown in Table 3, Type 1 cases where wave motions occurred are also characterized by increase in wind speed and u hs , but a decrease in N 2 .…”

Section: Discussionmentioning

confidence: 99%

Influence of Quasi-Periodic Oscillation of Atmospheric Variables on Radiation Fog over A Mountainous Region of Korea

Yum

Gültepe

et al. 2020

Atmosphere

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To enhance our understanding of fog processes over complex terrain, various fog events that occurred during the International Collaborative Experiments for Pyeongchang 2018 Winter Olympics and Paralympics (ICE-POP) campaign were selected. Investigation of thermodynamic, dynamic, and microphysical conditions within fog layers affected by quasi-periodic oscillation of atmospheric variables was conducted using observations from a Fog Monitor-120 (FM-120) and other in-situ meteorological instruments. A total of nine radiation fog cases that occurred in the autumn and winter seasons during the campaign over the mountainous region of Pyeongchang, Korea were selected. The wavelet analysis was used to study quasi-period oscillations of dynamic, microphysical, and thermodynamic variables. By decomposing the time series into the time-frequency space, we can determine both dominant periods and how these dominant periods change in time. Quasi-period oscillations of liquid water content (LWC), pressure, temperature, and horizontal/vertical velocity, which have periods of 15–40 min, were observed during the fog formation stages. We hypothesize that these quasi-periodic oscillations were induced by Kelvin–Helmholtz instability. The results suggest that Kelvin–Helmholtz instability events near the surface can be explained by an increase in the vertical shear of horizontal wind and by a simultaneous increase in wind speed when fog forms. In the mature stages, fluctuations of the variables did not appear near the surface anymore.

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Simulated Kelvin–Helmholtz Waves over Terrain and Their Microphysical Implications

Cited by 17 publications

References 42 publications

A Numerical Study of Mountain-Plain Breeze Circulation in Eastern Chengdu, China

A Numerical Study of Mountain-Plain Breeze Circulation in Eastern Chengdu, China

Detailed Dual-Doppler Structure of Kelvin–Helmholtz Waves from an Airborne Profiling Radar over Complex Terrain. Part I: Dynamic Structure

Influence of Quasi-Periodic Oscillation of Atmospheric Variables on Radiation Fog over A Mountainous Region of Korea

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