Cold wave of February 2018 above Europe observed by rotational Raman lidar Alexandre Baron, Patrick Chazette, Julien Totems LSCE – IPSL, Gif-sur-Yvette, France

Presentation plan The Weather and Aerosol LIdar (WALI) Observations in February 2018 Its calibration against radiosonde Origins of the air masses Associated weather situations Comparison with: Model reanalyses Spaceborne observations

WALI, its characteristics and assets Fig. 1: WALI 60 cm 130 cm Fig. 2: The Mobile Atmospheric Station (MAS) Eye safe lidar operating at 355 nm Compact (Fig. 1) and transportable (Fig. 2) Aerosols, WVMR, Temperature Short overlap function (~ 200 m) Temporal resolution 30 min Vertical resolution 100 m T uncertainty < 1 K T profile up to 6 km / 2 km Nigh / Day Using lens, it is compact, as shown in this picture It is also easily transportable in an instrumented truck named MAS for « mobile atmospheric station » represented here WALI measures aerosols optical properties, water vapor mixing ratio and atmospheric temperature with a short overlap function, full overlap at about 2 hundred meters For temperature measurements, error is below 1 k up to 5 km of altittude for profiles averaged 30min with a spatial resolution of 100m This system has proven its worth in different campaigns where you can find more specifications on this lidar system especially for the Aerosol and the WVMR Involvement in former field studies: HyMeX and ChArMEx (P.Chazette et al, 2014; AMT), PARCS (J.Totems et al, 2019; QJRMS) …

WALI, its temperature measurements in February 2018 Cold air Free troposphere Warm air PBL Top Cold air advection PBL Temperature in color in the interval -20 to 5 Celsius degree, in function of altitude from the 21 Feb to the 27 Feb 2018 In the PBL = diurnal cycle with thermal inertia of atmosphere Two air masses stand out: a warm one on the 24 Feb and a very cold one on the 26 and 27 of Feb

Calibration of the Rotational Raman channel 𝑄 𝑇,𝑧 = 𝑆 𝑅𝑅2 𝑇,𝑧 𝑆 𝑅𝑅1 𝑇,𝑧 =𝑓(𝑇) Night time radiosondings: Meteo-France site of Trappes ~15 km from the lidar [1] 20deg smoothed RMSN Z < 6 km = 0.96 K RMSD Z < 3 km = 1.14 K [1] A. Behrendt, “Temperature measurement with Lidar,” in Lidar Range-Resolved Optical Remote Sensing of the Atmosphere (C. Weitkamp, 2005), Ch. 10.

Origins of the air masses and synoptic weather situation Backward Ensemble mode: Every 6h from 26/02 0000 UTC to 28/02 1200 UTC Every 250m from 1250m to 2750m 77 runs ; 5 days calculation H Lagrangian model HYSPLIT from NOAA H L L L Backward Ensemble mode: 24/02 at 0000, 0600 and 1200 UTC Starting altitude: 2000 m (AGL) 3 days calculation Blocked weather situation with an high above Scandinavia = polar air from Siberia guided through Europe to a low off the coast of Portugal

Consistency with modeling Noter quelques differences et faire seulement 2 à trois profiles max ECMWF ERA5 reanalysis (hourly, 33 pressure levels)

Lidar – Model differences (unbiased) PBL Top issue Correlation > 0.92 Max(Cor) > 0.99 around Z = 2 km Mean bias = -1.35 K Root Mean Square Deviation (unbiased) ~ 1 K

Consistency with modeling P1 P2 Noter quelques differences et faire seulement 2 à trois profiles max

Comparison of lidar, ERA5 and AIRS profiles AIRS/AQUA transit  AIRS Level 3 daily Temperature product Daily average of Lidar and ERA5 data Weighting function of AIRS is peaked above 1 km agl AIRS does not observed the slope discontinuity of T(z) (P1) Good agreement of the 3 datasets, for a ~constant T gradient (P2) Profile journalier plutot que horaire

Conclusions & Perspectives Successful calibration with RS (RMS ~1 K). Differences induced by Lidar and RS not co-located  can be improved using ultra-light aircraft and/or UAV to calibrate the RR channel right on site Complementarity with spaceborne measurements (e.g. AIRS, IASI B&C) especially where spaceborne spectrometers failed, in the low troposphere (PBL) Suitable tool for validation of next generation of spaceborne spectrometers (e.g. IASI NG) Reliable performances for model assimilation of lidar network into meteorological model Unmanned aerial vehicul