Comparing mountain breezes and their impacts on CO2 mixing ratios at three contrasting areas

Román‐Cascón, Carlos; Yagüe, Carlos; Arrillaga, Jon A.; Lothon, Marie; Pardyjak, Eric R.; Lohou, Fabienne; Inclán, R.; Sastre, Mariano; Maqueda, Gregorio; Derrien, Solène; Meyerfeld, Yves; Hang, Chaoxun; Turki, I.

doi:10.1016/j.atmosres.2019.01.019

Cited by 23 publications

(12 citation statements)

References 51 publications

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“…The objective of the paper is to study how the HOST theory behaves in the complex terrain environment for the BLLAST field experiment in the nocturnal boundary layer. In the area, during night-time when thermally-driven flows can be developed, a katabatic flow going down from the mountain to the plain is established, through valley and downslope winds (Román-Cascón et al, 2018). Since the HOST theory proposed by Sun et al (2012Sun et al ( , 2016 during the CASES-99 campaign corresponds to nights with clear skies and intense radiative cooling allowing the development of local and mesoscale winds, we first select the nights that meet these conditions during the BLLAST campaign.…”

Section: Flow Characterisation During the Bllast Field Campaignmentioning

confidence: 99%

“…During the BLLAST field campaign the occurrence of katabatic winds coming from the south valleys was quite common (Román-Cascón et al, 2018). They are usually generated after the near calm situation of the evening transition, first as shallow drainage flows, which later are broken by the arrival of a larger and deeper mountain-plain flow with greater values of V.…”

Section: Turbulence Intermittency: Categories a And Bmentioning

confidence: 99%

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Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

Yus-Díez¹,

Udina²,

Soler³

et al. 2019

Preprint

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Abstract. A night-time turbulence regime classification, the so-called HOckey-Stick Transition (HOST) theory, proposed by Sun et al. (2012) from the Cooperative Atmosphere-Surface Exchange Study 1999 (CASES-99) is explored using data from the Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign which took place during the summer 2011 in the north of the central French Pyrenean foothills. Results show that the HOST turbulence relationships for the BLLAST field campaign data is strongly dependent on both the meteorological and orographic features. The HOST pattern only appears for nights when a stably stratified boundary layer can be developed, corresponding to fair weather and clear sky nights, when the flow is generated by the nearby orography, from the south and southeast directions. Those flows strongly influenced by the orography may generate intermittent or enhanced turbulence. When considering the whole dataset for these flow directions, several enhanced turbulence points are found to be associated with sudden wind speed and directional shear transitions. In contrast, flows from other directions do not reproduce the HOST relationship and the turbulence relationship is almost linear, independent of the vertical temperature gradients, corresponding to flows driven by mesoscale or synoptic scales. In addition we identify examples of gravity waves and top-down turbulent events that lead to transitions between the turbulence regimes.

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Section: Flow Characterisation During the Bllast Field Campaignmentioning

confidence: 99%

Section: Turbulence Intermittency: Categories a And Bmentioning

confidence: 99%

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

Yus-Díez¹,

Udina²,

Soler³

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…According to previous studies from BLLAST campaign (e.g., [61,62]), northern and western components are mostly associated with large scale circulation, such as frontal passages and strong synoptic flows. The observed light winds from the N and NE directions corresponding to daytime mountain breezes [63] are misrepresented in the MESO and LES simulations. Instead, the S and SE nocturnal flows are well captured by the LES simulation, although simulations tend to exaggerate the frequency of SE flows, specially LES, and to shift slightly the wind towards the east.…”

Section: Model Performance: Mean Quantitiesmentioning

confidence: 96%

WRF-LES Simulation of the Boundary Layer Turbulent Processes during the BLLAST Campaign

Udina

Montornès²,

Casso³

et al. 2020

Atmosphere

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A real case long-term nested large eddy simulation (LES) of 25-day duration is performed using the WRF-LES modelling system, with a maximum horizontal grid resolution of 111 m, in order to explore the ability of the model to reproduce the turbulence magnitudes within the first tens of metres of the boundary layer. Sonic anemometer measurements from a 60-m tower installed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign are used for verification, which is focused on the turbulent magnitudes in order to assess the success and limitations in resolving turbulent flow characteristics. The mesoscale and LES simulations reproduce the wind speed and direction fairly well, but only LES is able to reproduce the energy of eddies with lifetimes shorter than a few hours. The turbulent kinetic energy in LES simulation is generally underestimated during the daytime, mainly due to a vertical velocity standard deviation that is too low. The turbulent heat flux is misrepresented in the model, probably due to the inaccuracy of the sub-grid scheme.

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“…Connected also to the dynamics of the SBL, another relevant issue on this topic is the impact of downslope winds of different nature on the concentration of scalars of high relevance such as the CO 2 . Previous studies have documented its influence in coastal areas (Cristofanelli et al, 2011;Legrand et al, 2016) and mountainous regions (Sun et al, 2007;Román-Cascón et al, 2019). Sun et al (2007) found that downslope flows transported CO 2 -rich air from the Rocky Mountains, and Román-Cascón et al (2019) observed that horizontal CO 2 advection can be relatively important over heterogeneous surfaces affected by different emission areas.…”

Section: Introductionmentioning

confidence: 99%

“…Not only advection but also local turbulence fluxes can be influenced: Sun et al (2006) observed an anomalous positive CO 2 flux just after sunset, suggesting that it was due to the sudden transition from upslope to downslope flow. Being able to better quantify the influence of mesoscale flows on the CO 2 budget can help to reduce the large discrepancy from modelling studies in reproducing the land-atmosphere exchange for this gas (Rotach et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

From weak to intense downslope winds: origin, interaction with boundary-layer turbulence and impact on CO2 variability

et al. 2019

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Abstract. The interconnection of local downslope flows of different intensities with the turbulent characteristics and thermal structure of the atmospheric boundary layer (ABL) is investigated through observations. Measurements are carried out in a relatively flat area 2 km away from the steep slopes of the Sierra de Guadarrama (central Iberian Peninsula). A total of 40 thermally driven downslope events are selected from an observational database spanning the summer 2017 period by using an objective and systematic algorithm that accounts for a weak synoptic forcing and local downslope wind direction. We subsequently classify the downslope events into weak, moderate and intense categories, according to their maximum 6 m wind speed. This classification enables us to contrast their main differences regarding the driving mechanisms, associated ABL turbulence and thermal structure, and the major dynamical characteristics. We find that the strongest downslope flows (U > 3.5 m s−1) develop when soil moisture is low ( < 0.07 m3 m−3) and the synoptic wind not so weak (3.5 m s−1 < V850 < 6 m s−1) and roughly parallel to the direction of the downslope flow. The latter adds an important dynamical input, which induces an early flow advection from the nearby steep slope, when the local thermal profile is not stable yet. Consequently, turbulence driven by the bulk shear increases up to friction velocity (u*) ≃ 1 m s−1, preventing the development of the surface-based thermal inversion and giving rise to the so-called weakly stable boundary layer. On the contrary, when the dynamical input is absent, buoyancy acceleration drives the formation of a katabatic flow, which is weak (U < 1.5 m s−1) and generally manifested in the form of a shallow jet below 3 m. The relative flatness of the area favours the formation of very stable boundary layers marked by very weak turbulence (u* < 0.1 m s−1). In between, moderate downslope flows show intermediate characteristics, depending on the strength of the dynamical input and the occasional interaction with down-basin winds. On the other hand, by inspecting individual weak and intense events, we further explore the impact of downslope flows on CO2 variability. By relating the dynamics of the distinct turbulent regimes to the CO2 budget, we are able to estimate the contribution of the different terms. For the intense event, indeed, we infer a horizontal transport of 67 ppm in 3 h driven by the strong downslope advection.

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Comparing mountain breezes and their impacts on CO2 mixing ratios at three contrasting areas

Cited by 23 publications

References 51 publications

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

WRF-LES Simulation of the Boundary Layer Turbulent Processes during the BLLAST Campaign

From weak to intense downslope winds: origin, interaction with boundary-layer turbulence and impact on CO<sub>2</sub> variability

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Comparing mountain breezes and their impacts on CO2 mixing ratios at three contrasting areas

Cited by 23 publications

References 51 publications

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

WRF-LES Simulation of the Boundary Layer Turbulent Processes during the BLLAST Campaign

From weak to intense downslope winds: origin, interaction with boundary-layer turbulence and impact on CO&lt;sub&gt;2&lt;/sub&gt; variability

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From weak to intense downslope winds: origin, interaction with boundary-layer turbulence and impact on CO<sub>2</sub> variability