We will report on the first systematic comparison between global optical lightning measurements and backscatter lidar observations of cloud properties. The results suggest that lidar observations can provide significant insight into the global thunderstorm climatology and also enable new methods for quality control of spaceborne optical lightning observations. The International Space Station Lightning Imaging Sensor (ISS LIS) has been observing thunderstorms between +/-55° latitude since March 2017. During the first ~8 months of the mission the Cloud-Aerosol Transport System (CATS) lidar was co-located with LIS on the ISS. CATS provided vertical profiles of cloud and aerosol properties along a nadir curtain. For thunderstorms, CATS observations enabled retrieval of cloud-top height, the presence of liquid water vs. ice, and other important cloud properties that are relevant to the production of lightning. Through systematic comparison of ISS LIS and CATS granules, over 8000 LIS-detected flashes were matched with nearby coincident CATS profiles between 1 March and 30 October 2017. All of these flashes’ centroids were within 25 km of the CATS laser’s ground track. Two-dimensional histograms of cloud-top height and latitude show consistency with the expected global behavior of thunderstorm height – namely, that storm heights are constrained by the tropopause, which slopes downward toward the poles. The observed CATS/LIS trend was found to be consistent with long-term March-October thunderstorm 20-dBZ echo-top height climatologies derived from the Tropical Rainfall Measuring Mission (TRMM) and the Global Precipitation Measurement (GPM) mission (the latter combined with Worldwide Lightning Location Network data). However, the radar-based climatologies indicate that 20-dBZ echo tops average ~2 km lower in altitude compared to lidar-inferred cloud tops. The CATS lidar also enabled identification of potential LIS false alarms (FAs). Additional analyses, including lidar-inferred ice-cloud properties in thunderstorms (e.g., ice-water content), will be presented. Overall, this pathfinder study with a limited ~8-month dataset suggests that fruitful scientific insights may be expected from potentially larger combined lidar/lightning datasets.

Approximately eight months of co-located spaceborne lidar and lightning observations were analyzed in a pathfinder study to understand the advantages and challenges of using these combined observations to understand thunderstorms. Data from the Lightning Imaging Sensor (LIS) and the Cloud-Aerosol Transport System (CATS) lidar were used when they overlapped on the International Space Station during March-October 2017. Using simple matching criteria, 8246 LIS flashes occurred within 25 km of the CATS ground track. CATS cloud-top heights near these flashes showed similar behavior with latitude when compared to a spaceborne radar-based climatology, but the lidar cloud tops were approximately 2-km higher than 20-dBZ radar echo tops. CATS cloud phase near LIS flashes was consistent with ice or mixed-phase more than 90% of the time, showing the value of using lightning observations to validate lidar-based feature masks. In addition, correlations between a proxy for LIS flash rate and CATS ice water path, cloud optical depth, and cloud-top height were low (0.38-0.42) but positive and highly statistically significant (> 99%), suggesting lidar retrievals of cloud properties can be meaningfully compared with lightning observations despite lidar’s known inability to penetrate deeply into optically thick clouds like thunderstorms. Finally, CATS was used to help diagnose LIS false alarms due to surface-based glint. The false alarm rate was approximately 0.1%, which demonstrated the excellent performance of the surface glint filter in the LIS processing code. The results suggest that fruitful scientific insights can be expected from larger combined lidar/lightning datasets.