DOI: 10.57932/ca9c74c0-83f4-43f1-86c8-7f3ce517b03c
title: Ground measurements of surface solar irradiance, aerosol optical properties and sky conditions estimates in Lille (North of France) over the period 2010-2022

description: Ground measurements from the ATOLL (Atmospheric Observations in LiLLE, https://www.loa.univ-lille.fr/observations/plateformes.html?p=lille) platform in Villeneuve-d'Ascq (North of France) over the period 2010-2022.

Detail of available columns:
-date: Date and time of the measurement (UTC, format: YYYY-MM-DD hh:mm:ss)
- UTC: Decimal time of day in hours associated to the measurement (UTC)
- GHI: Global Horizontal Irradiance (W/m²)
- DNI: Direct Normal Irradiance (W/m²)
- BHI: Beam Horizontal Irradiance (W/m²)
- DHI: Diffuse Horizontal irradiance (W/m²)
- SZA: Computed Solar Zenith Angle (°)
- cosineSZA: Cosine of the SZA
- clear_sky_flag: Boolean (True: Sky clear of clouds; False: Presence of clouds in the sky)
- clear_sun flag: Boolean (True: Sun direction clear of clouds; False: Cloud present between the instruments and the Sun)
- cloudy_sun_flag: Boolean (opposite of clear_sun_flag)
- clear_sun_with_clouds_flag: Boolean (True: Presence of clouds in the sky but not in the direction of the Sun; False: Cloud present between the instruments and the Sun)
- AOD_550nm: Aerosol Optical Depth at 550nm
- AOD_440nm: Aerosol Optical Depth at 440nm
- 440-870_Angstrom_Exponent: Angström Exponent between 440 and 870 nm
- aer_class_flag: Aerosol class associated to the measured aerosol optical properties (Continental, Continental polluted, Mixed, Maritime, Desert dusts or Strong events)
- Precipitable_Water(cm): Integrated precipitable water vapor content in the direction of the Sun (cm)
- Ozone(Dobson): Ozone content (Dobson units)

Irradiance measurements of DNI and DHI are performed routinely at a 1-minute resolution by a set of a pyrheliometer (Kipp & Zonen CHP1) and a pyranometer (Kipp & Zonen CMP22) placed on a sun tracking device.
BHI is computed as BHI = DNI*cos(SZA)
GHI is computed as GHI = BHI + DHI

Quality checks were applied following the recommendations from the BSRN network (https://bsrn.awi.de/fileadmin/user_upload/bsrn.awi.de/Publications/BSRN_recommended_QC_tests_V2.pdf). 
Only "Physically Possible Limits" and "Extremely Rare Limits" were checked as GHI and BHI/DHI measurements are not independent.

Measurements are reported between sunrise + 30 minutes and sunset - 30 minutes to maximize the performances of the cloud-screening methods.

The method described in Batlles et al. (2000, 10.1016/0038-092X(90)90055-H) is used to isolate clear-sun (no clouds in the direction of the Sun) moments from cloudy-sun (clouds in the direction of the Sun).
A modified version of the algorithm from Garcia et al. (2014, DOI:10.1002/2013JD020301) is used to distinguish clear-sun conditions between clear-sky (no clouds in the sky) moments and clear-sun with clouds situations (clouds present in the sky but not in the direction of the Sun).

Note: The first five measurements of each hour were also removed for long term consistency, as instrumental problems prevented the acquisition of data at such times before the year 2020. 

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Photometric measurements (aerosol optical depth, angström exponent, precipitable water vapor and ozone contents) are performed as part of the AERONET-PHOTONS network and are directly available here: https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3?site=Lille&nachal=2&level=1

Level 2.0 data is reported here from 2010 to July 2022 and level 1.5 data thereafter due to data availability. 

Aerosol Optical Depth at 550nm was computed following the methodology described by Gueymard et al. (2020, DOI:10.1016/j.atmosenv.2019.117216).

The aerosol class flag presents an estimate of the aerosol optical properties class based on AOD [440nm] and Angström Exponent data as in Chesnoiu et al. 2024 (in prep.).

Note: AERONET measurements are only performed when the Sun direction is clear of clouds with a time resolution ranging from 3 minutes (after 2016) to 15 minutes (before 2016). Blank spaces (or NaN values) are reported when AERONET data is not available.