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Abstract. The new space-based Lightning Imager (LI) onboard the Meteosat Third Generation (MTG) geostationary satellite will improve the observationof lightning over Europe, the Mediterranean Sea, Africa and the Atlantic Ocean from 2021 onwards. In preparation for the use of the upcoming MTG-LI data,we compare observations by the Lightning Imaging Sensor (LIS) on the International Space Station (ISS), which applies an optical technique similar to MTG-LI, toconcurrent records of the low-frequency (LF) ground-based network Meteorage. Data were analyzed over the northwestern Mediterranean Sea from1 March 2017 to 20 March 2018.Flashes are detected by ISS-LIS using illuminated pixels, also called events, within a given (2.0  ms ) frame and during successive frames.Meteorage describes flashes as a suite of intra-cloud and cloud-to-cloud (IC) pulses and/or cloud-to-ground (CG) strokes. Both events as well as pulses and strokes are grouped to flashesusing a novel in-house algorithm. In our study, ISS-LIS detects about 57  % of the flashes detected by Meteorage. The flash detection efficiency (DE) of Meteorage relative to ISS-LISexceeds 80  % . Coincident matched flashes detected by the two instruments show a good spatial and temporal agreement. Both peak and mean distances between matchesare smaller than the ISS-LIS pixel resolution (about 5.0  km ). The timing offset for matched ISS-LIS and Meteorage flashes is usuallyshorter than the ISS-LIS integration time frame (2.0  ms ). The closest events and the pulses and strokes of matched flashes achieve sub-millisecond offsets.Further analysis of flash characteristics reveals that longer-lasting and more spatiallyextended flashes are more likely detected by both ISS-LIS and Meteorage than shorter-duration and smaller-extent flashes. The ISS-LIS relative DE is lower for daytime versus nighttime as well as for CG versus IC flashes. A second ground-based network, the very high-frequency (VHF) SAETTA Lightning Mapping Array (LMA), further enhances and validates the lightning pairing between ISS-LIS and Meteorage. It also provides altitude informationon the lightning discharges and adds a detailed lightning mapping to the comparison for verification and better understanding of the processes. Both ISS-LISand Meteorage flash detections feature a high degree of correlation with the SAETTA observations (without altitude information). In addition, Meteorage flasheswith ISS-LIS match tend to be associated with discharges that occur at significantly higher altitudes than unmatched flashes. Hence, ISS-LIS flash detection suffers from degradation, with low-level flashes resulting in lower DE.

atmospheric measurement techniques

Concurrent satellite and ground-based lightning observations from the Optical Lightning Imaging Sensor (ISS-LIS), the low-frequency network Meteorage and the SAETTA Lightning Mapping Array (LMA) in the northwestern Mediterranean region