Scientific Objectives. The thermodynamic state of the atmosphere and dynamics characteristics within and above the urban canopy are critical for the assessment and prediction of air quality, chemical hazards, human outdoor thermal comfort, and urban climate conditions. In addition to surface roughness variations, wind and turbulence respond to urban heat so that the enhanced buoyancy may encourage the vertical dispersion and mixing of pollutants and other constituents. This can improve near-surface air quality through dilution but can entrain polluted air circulating aloft (e.g. aerosol plumes from long range transport, or accumulated pollution in the residual layer) into the boundary layer, and down to the surface. Areas of reduced roughness (e.g. river) may act as ventilation pathways along which the flow  brings fresh air into the city while displacing polluted (and often warmer) air towards surrounding areas , which can again result in a heating-up of downwind suburbs. Under certain synoptic conditions (weak wind, low cloud cover), thermal contrasts can induce local circulations at neighborhood (e.g. park breeze) to regional scales (e.g. urban breeze).

Despite its importance for multiple applications, it remains challenging to describe the complex characteristics of the three-dimensional wind and temperature fields within and above the urban canopy. While numerical simulations and wind tunnel experiments increasingly provide valuable insights into flow effects under idealized conditions, real world monitoring of vertical and horizontal wind and temperature profiles within the urban boundary layer are still scarce.

The objectives of the DYNAMICS activities are (1) to better understand the response of the mean wind and turbulent flow to urban surface roughness and atmospheric stability, (2) to better characterize the temporal and spatial variations of atmospheric boundary layer characteristics (e.g. stability and height) across urban-to-rural transects, (3) to support studies of the impact of wind and atmospheric boundary layer structure on wide range of applications, including air quality interpretation, numerical weather prediction, greenhouse gas assessment and renewable energy.

Measurement plan. DYNAMICS relies on novel measurements of wind and turbulence profiles using Doppler Lidars, and atmospheric boundary layer structure using automatic backscatter Lidars and ceilometers (ALC). 

A scanning Doppler Lidar (VAISALA Windcube 400S) was purchased for the project. The scanning Doppler Lidar has been operating since January 2022 at the QUALAIR site (LATMOS, OSU ECCETERRA, Sorbonne Université) at the top of the Zamansky tower. A Leosphere V70 vertically pointing Doppler Lidar performs continuous wind profile measurements at the SIRTA atmospheric observatory (Palaiseau). The project will also benefit from additional wind profile measurements deployed by other projects (e.g. RDP Paris Olympics, Urbisphere ERC).

9 automatic backscatter Lidars and ceilometers (ALCs) operate continuously in the Paris region. 2 high power ALCs (Lufft CHM15k) provide backscatter profiles at the SIRTA observatory (Palaiseau) and the QUALAIR site (Paris), 1 high power ALC with depolarization (Vaisala CL61) operates at the Paris City Hall (Hotel de Ville de Paris), while 5 low-power ALCs (Vaisala CL31) operate as part of the Meteo-France airport network. This unprecedented regional network of ALC covers rural to suburban and urban settings and provide ABL structure information both upstream and downstream of the dense urban area.

Labs and institutes. The work is conducted as part of several projects. The Paris Region PhD project of Jonnathan Cespedes (LMD/IPSL, IPP graduate school), under the supervision of Simone Kotthaus and Martial Haeffelin (IPSL), with co-supervision by Ludovic Thobois (VAISALA). The PhD project is funded by a public-private partnership between Région Ile-de-France, VAISALA and Ecole polytechnique.

The WLS400 Scanning Doppler Lidar was purchased with the support of DIM QI2 (a program supported by Region Ile-de-France), of OBS4CLIM (an EQUIPEX+ project supported by the PIA-3 program), and of CNRS-INSU special investment funds.

The ABL stability and height monitoring project is conducted under the supervision of Simone Kotthaus (IPSL) with support from the ACTRIS and ICOS research infrastructures and E-PROFILE program.

Project website: https://ablh.aeris-data.fr/research/

The work carried out in DYNAMICS will benefit the atmospheric dynamic needs of multiple research projects associated with PANAME (ANR ACROSS, ANR H2C, H2020 ICOS-Cities PAUL, H2020 ACTRIS RI-URBANS, WMO RDP Paris Olympics projects).