La campagne Passy-2015 : dynamique atmosphérique et qualité de l’air dans la vallée de l’Arve

Paci, Alexandre; Staquet, Chantal; Allard, Julie; Barral, H.; Canut, Guylaine; Cohard, Jean‐Martial; Jaffrezo, Jean-Luc; Martinet, Pauline; Sabatier, Tiphaine; Troude, Florence; Arduini, Gabriele; Burnet, Frédéric; Brun, Christophe; Chemel, Charles; Dabas, Alain; Donier, Jean-Marie; Garrouste, Olivier; Largeron, Yann; Legain, D.; Maurel, William; Tzanos, Diane; Barrau, Sébastien; Barret, Manuel; Barrié, Joël; Belleudy, Anne; Bouhours, G.; Bourrianne, Thierry; Chevrier, Florie; Douffet, Thierry; Etcheberry, Jean-Michel; Gustave, Laurent; Mazoyer, Marie; Mercier, Sébastien; Moulin, E.; Pellan, Yann; Piguet, Bruno; Rodier, Quentin; Zin, Isabella

doi:10.4267/pollution-atmospherique.5903

Cited by 10 publications

(9 citation statements)

References 12 publications

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“…In this paper, we investigate the role of local and non-local controls, the latter including the synoptic wind above the valley boundary layer and flows from the surrounding tributary valleys affected by the large-scale flow, in the evolution of a PCAP using numerical model simulations. The PCAP event occurred in the section of the Arve River Valley around Passy in the French Alps, in February 2015, during the first intensive observation period (IOP1) of the PASSY-2015 field campaign (Staquet et al, 2015;Paci et al, 2016). To reach this aim, the mass and heat budgets in the Passy valley are analysed and compared to the ones for a semi-idealised simulation in which the synoptic flow in the initial condition is at rest.…”

Section: Introductionmentioning

confidence: 99%

Local and non‐local controls on a persistent cold‐air pool in the Arve River Valley

Arduini

Chemel

Staquet

2020

Quart J Royal Meteoro Soc

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A numerical model is used to simulate a persistent cold‐air pool (PCAP) event that occurred in the section of the Arve River Valley around Passy in the French Alps. During this period, an upper‐level ridge from the Atlantic moved over Europe, allowing a PCAP to form and persist over time. The impact of the upper‐level ridge on the PCAP and on the dynamics within the valley section is quantified by examining the mass and heat budgets of the valley atmosphere. During the persistent stage, the magnitude of the flow through the tributary valleys is enhanced by the large‐scale flow. Also, the direction of the flow through one of the tributaries is found to be determined by the height of the PCAP with respect to that of the tributary above the valley floor. The tributary flows, together with subsiding motions at the valley top, control by and large the night‐time valley‐scale circulation and the thermal structure of the upper part of the PCAP, whereas thermally driven valley flows control its lower part. When the upper‐level ridge passes over the Arve River Valley, warm air advection through the tributaries continuously erodes the upper part of the PCAP during night‐time, thereby reducing its depth, while down‐valley flows export the air mass out of the valley. As the ridge moves away from the valley, the near‐surface air is found to be trapped within the valley. This trapping results from the advection of warm air in the upper part of the PCAP by the large‐scale flow channelled through one of the tributaries. This reduces the thermally induced pressure difference in the down‐valley direction, thereby suppressing the near‐surface down‐valley flow. The study therefore highlights the interplay between the large‐scale flow, the tributary flows and the thermal structure of the PCAP.

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Section: Introductionmentioning

confidence: 99%

Local and non‐local controls on a persistent cold‐air pool in the Arve River Valley

Arduini

Chemel

Staquet

2020

Quart J Royal Meteoro Soc

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“…Among them are microwave radiometers, wind profilers, ceilometer, sodar, lidars, tethered balloons and instrumented towers. A detailed presentation of the field campaign can be found in Paci et al (2016). Two intensive observation periods (IOPs) have been carried out during the campaign.…”

Section: The Passy-2015 Field Campaignmentioning

confidence: 99%

Combining ground-based microwave radiometer and the AROME convective scale model through 1DVAR retrievals in complex terrain: an Alpine valley case study

Martinet

Cimini²,

Angelis

et al. 2017

Atmos. Meas. Tech.

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Abstract. A RPG-HATPRO ground-based microwave radiometer (MWR) was operated in a deep Alpine valley during the Passy-2015 field campaign. This experiment aims to investigate how stable boundary layers during wintertime conditions drive the accumulation of pollutants. In order to understand the atmospheric processes in the valley, MWRs continuously provide vertical profiles of temperature and humidity at a high time frequency, providing valuable information to follow the evolution of the boundary layer. A one-dimensional variational (1DVAR) retrieval technique has been implemented during the field campaign to optimally combine an MWR and 1 h forecasts from the French convective scale model AROME. Retrievals were compared to radiosonde data launched at least every 3 h during two intensive observation periods (IOPs). An analysis of the AROME forecast errors during the IOPs has shown a large underestimation of the surface cooling during the strongest stable episode. MWR brightness temperatures were monitored against simulations from the radiative transfer model ARTS2 (Atmospheric Radiative Transfer Simulator) and radiosonde launched during the field campaign. Large errors were observed for most transparent channels (i.e., 51-52 GHz) affected by absorption model and calibration uncertainties while a good agreement was found for opaque channels (i.e., 54-58 GHz). Based on this monitoring, a bias correction of raw brightness temperature measurements was applied before the 1DVAR retrievals. 1DVAR retrievals were found to significantly improve the AROME forecasts up to 3 km but mainly below 1 km and to outperform usual statistical regressions above 1 km. With the present implementation, a root-mean-square error (RMSE) of 1 K through all the atmospheric profile was obtained with values within 0.5 K below 500 m in clear-sky conditions. The use of lower elevation angles (up to 5 • ) in the MWR scanning and the bias correction were found to improve the retrievals below 1000 m. MWR retrievals were found to catch deep near-surface temperature inversions very well. Larger errors were observed in cloudy conditions due to the difficulty of ground-based MWRs to resolve high level inversions that are still challenging. Finally, 1DVAR retrievals were optimized for the analysis of the IOPs by using radiosondes as backgrounds in the 1DVAR algorithm instead of the AROME forecasts. A significant improvement of the retrievals in cloudy conditions and below 1000 m in clear-sky conditions was observed. From this study, we can conclude that MWRs are expected to bring valuable information into numerical weather prediction models up to 3 km in altitude both in clear-sky and cloudy-sky conditions with the maximum improvement found around 500 m. With an accuracy between 0.5 and 1 K in RMSE, our study has also proven that MWRs are capable of resolving deep near-surface temperature inversions observed in complex terrain during highly stable boundary layer conditions.

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“…Data from the Passy-2015 field experiment are used to analyse the flow structure within the basin during both episodes, to highlight the main differences and to initialize numerical simulations. A summary of the sensors used in this paper is given in Table 1 while the complete list can be found in Paci et al (2016). The flow structure in the basin centre (SITE1) is characterized by a combination of four sonic anemometers deployed on a 10 m mast and a profiler Doppler wind lidar (WLS8-5) which provides measurements from 40 m up to 500 m above ground level (a.g.l.).…”

Section: Observationsmentioning

confidence: 99%

Semi‐idealized simulations of wintertime flows and pollutant transport in an Alpine valley: Origins of local circulations (Part I)

Sabatier

Paci

Lac

et al. 2020

Quart J Royal Meteoro Soc

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Mountainous terrains are known for driving their own dynamics which respond to the local morphological arrangement of the area. Thermally driven flows in particular develop at slope and valley scales and ensure a certain degree of pollutant dispersion under quiescent wintertime synoptic conditions. The present study focuses on a section of the Arve River valley situated close to Mont Blanc which frequently suffers from severe pollution episodes under stable wintertime conditions whilst surrounding valleys appear to be less affected. The particular shape of this basin‐like section and its location at the confluence of several tributary valleys raises the question of the extent to which local circulations participate in pollutant trapping over restricted sectors. A set of high‐resolution numerical simulations are designed in order to improve our understanding of the local flow structure and their sensitivity to thermal stratification, radiative forcing and snow cover. The tributary valleys play a major role in both daytime and night‐time dynamics by deflecting the entering daytime flux and constraining the night‐time flow trajectories. In addition, the basin morphology greatly influences the circulations. During daytime a two‐layer wind structure is developed and driven by spatial variations in sun exposure which is particularly heterogeneous under wintertime forcing. Early spring radiative forcing or the presence of snow allow both of them to develop more homogeneous circulations through the reduction of sun exposure variations, except when snow cover is restricted to shaded basin sidewalls. At night, a three‐layer wind structure is developed. It favours air mass ventilation in the western linear branch of the basin whilst stagnation and recirculation prevail in the curved part of the valley which is also the most polluted. This study therefore highlights spatial variations in circulation patterns consistent with the accumulation of observed pollutants and their heterogeneous distribution.

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La campagne Passy-2015 : dynamique atmosphérique et qualité de l’air dans la vallée de l’Arve

Cited by 10 publications

References 12 publications

Local and non‐local controls on a persistent cold‐air pool in the Arve River Valley

Local and non‐local controls on a persistent cold‐air pool in the Arve River Valley

Combining ground-based microwave radiometer and the AROME convective scale model through 1DVAR retrievals in complex terrain: an Alpine valley case study

Semi‐idealized simulations of wintertime flows and pollutant transport in an Alpine valley: Origins of local circulations (Part I)

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