New gridded lightning climatology datasets are compiled and released from a series of low-Earth-orbiting NASA lightning sensors: the Optical Transient Detector (OTD), Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS), and International Space Station (ISS) LIS. OTD collected data during April 1995-March 2000, TRMM LIS collected data during December 1997-April 2015, and ISS LIS collected data during March 2017-November 2023. From these, gridded lightning datasets depict the near-global distribution of annual-mean flash rate on a 0.1 degrees grid. Hourly mean and monthly mean averages allow examination of diurnal and annual cycles, although some smoothing of the released data is warranted. This paper describes the released datasets, thoroughly examines data quality and sources of bias, and makes recommendations for potential users. Examples from these datasets are shown, with well-known lightning hotspots in central Africa, northwestern South America, and along the base of the Himalayas. Comparison of how often thunderstorms are observed to those storms' conditional mean flash rates shows some striking differences, with frequent storms but relatively low per-storm flash rates over the Maritime Continent. Conversely, storms are less frequent but produce higher flash rates over central North America, subtropical South America, Pakistan, and the coasts of northern Australia.

Lightning flash rate densities measured by a series of low-Earth-orbiting NASA lightning sensors are used to explore lightning hotspots, how they vary with time of year and time of day, the diurnal cycle, annual cycle, and interannual variability. New gridded datasets are available from the Optical Transient Detector (OTD; April 1995-March 2000), Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS; January 1998-April 2015), and International Space Station (ISS) LIS (March 2017-November 2023). Taking all these lightning measurements together, the highest 0.1 degrees flash rate densities are over Lake Maracaibo in northern Venezuela, as reported previously. Other locations emerge as having the highest flash rate densities when limited to smaller subsets of the data. Maxima are located on either side of the Democratic Republic of Congo according to ISS LIS (maximum in the west) and OTD (maximum in the east). ISS LIS also records higher values over mountain slopes in Colombia than over nearby Lake Maracaibo. Summertime flash rate densities are almost as high over northern Pakistan. At the peak of the diurnal and annual cycles, July afternoons over Cuba have almost as much lightning as late nights in September over Lake Maracaibo. Flash rates peak around 1600-1700 LST and gradually decrease through the evening over most continental regions and peak in the summer with little lightning measured during winter. Time series of flash rates show Africa contributing most to the interannual variability, particularly with the sharp downturn in lightning from mid-2019 through 2022.

Identical Lightning Imaging Sensors (LIS) aboard the Tropical Rainfall Measuring Mission satellite (TRMM LIS, 1998-2015) and International Space Station (ISS LIS, 2017-23) have provided over two decades of lightning observations over the global tropics, with ISS LIS extending coverage into the midlatitudes. Quantifying the detection performance of both LIS sensors is a necessary step toward generating a combined LIS climatological record and accurately combining LIS data with lightning detections from other sensors and networks. We compare lightning observations from both LIS sensors with reference sources including the Geostationary Lightning Mapper (GLM) and ground-based Earth Networks Total Lightning Network (ENTLN), Earth Networks Global Lightning Network (ENGLN), National Lightning Detection Network (NLDN), and Global Lightning Dataset (GLD360). Instead of a relative detection efficiency (DE) approach that assumes the perfect performance of the reference sensor, we employ a Bayesian approach to estimate the upper limit of the absolute DE (ADE) of each system being analyzed. The results of this analysis illustrate the geographical pattern of ADE as well as its diurnal cycle and yearly evolution. Reference network ADE increased by ;15%-30% during the TRMM era, leading to a decline in TRMM LIS ADE. ISS LIS flash ADE has been relatively consistent at 61%-65%, about 4%-5% lower than TRMM LIS at the end of its lifetime.

Optical lightning observations from low-Earth orbit play an important role in our understanding of long-term global lightning trends. Lightning Imaging Sensors (LIS) on the Tropical Rainfall Measuring Mission (TRMM) satellite (1997-2015) and International Space Station (2017-present) capture optical emissions produced by lightning. This study uses the well-documented TRMM LIS performance to determine if the ISS LIS performs well enough to bridge the gap between TRMM LIS and the new generation of Geostationary Lightning Mappers (GLMs). The average events per group and groups per flash for ISS LIS are 3.6 and 9.9, which are 18% and 10% lower than TRMM LIS, respectively. ISS LIS has 30% lower mean group energy density and 30%-50% lower mean flash energy density than TRMM LIS in their common (+/- 38 degrees) latitude range. These differences are likely the result of larger pixel areas for ISS LIS over most of the field of view due to off-nadir pointing, combined with viewing obstructions and possible engineering differences. For both instruments, radiometric sensitivity decreases radially from the center of the array to the edges. ISS LIS sensitivity falls off faster and more variably, contributed to by the off-nadir pointing. Event energy density analysis indicate some anomalous hotspot pixels in the ISS LIS pixel array that were not present with the TRMM LIS. Despite these differences, ISS LIS provides similar parameter values to TRMM LIS with the expectation of somewhat lower lightning detection capability. In addition, recalculation of the event, group, and flash areas for both LIS datasets are strongly recommended since the archived values in the current release versions have significant errors.

Caption: Lightning discharges appear in various colours depending on the scatter of light inside the thundercloud and in the atmosphere.The intracloud lightning discharges in the centre of the thundercloud appear to be white with a bluish tint, and the cloud-to-ground discharge below appears to be orange.The right hand side of the thundercloud exhibits a green tint that is attributed to the unique composition of hydrometeors inside the thundercloud.The photo was taken in the late evening of 10 September 2013, near Tarragona in northeastern Spain.

Previous lightning climatologies derived from Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) total lightning measurements have quantified lightning frequency as a Flash Rate Density (FRD). This approach assumes that lightning flashes can be represented as points and quantifies the frequency of lightning centered in each grid cell. However, lightning has a finite extent that can reach hundreds of kilometers. A new climatology based on Flash Extent Density (FED) is constructed for LIS (including ISS‐LIS) and OTD that accounts for the horizontal dimension of lightning. The FED climatology documents the frequency that an observer can expect lightning to be visible overhead—regardless of where the flash began or ended. This new FED climatology confirms and elaborates on the previous global LIS/OTD FRD and Americas‐only Geostationary Lightning Mapper (GLM) findings. The FED climatology maintains Lake Maracaibo as the global lightning hotspot with an average of 389 flashes/day but designates Karabre in the Democratic Republic of the Congo as the global thunderstorm duty (percent of the total viewtime where lightning is observed) hotspot at 7.29%. Meanwhile, Kuala Lumpur is the national capital city with the most lightning, and its airport (KUL) is the top major airport affected by lightning (in terms of duty). The FED seasonal cycle and month‐to‐month changes in the “center of lightning” for the three continental chimney regions are also discussed.

The Lightning Imaging Sensor (LIS) was launched to the International Space Station (ISS) in February 2017, detecting optical signatures of lightning with storm ‐ scale horizontal resolution during both day and night. ISS LIS data are available beginning 1 March 2017. Millisecond timing allows detailed intercalibration and validation with other spaceborne and ground ‐ based lightning sensors. Initial comparisons with those other sensors suggest fl ash detection ef fi ciency around 60% (diurnal variability of 51 – 75%), false alarm rate under 5%, timing accuracy better than 2 ms, and horizontal location accuracy around 3 km. The spatially uniform fl ash detection capability of ISS LIS from low ‐ Earth orbit allows assessment of spatially varying fl ash detection ef fi ciency for other sensors and networks, particularly the Geostationary Lightning Mappers. ISS LIS provides research data suitable for investigations of lightning physics, climatology, thunderstorm processes, and atmospheric composition, as well as real ‐ time lightning data for operational forecasting and aviation weather interests. ISS LIS enables enrichment and extension of the long ‐ term global climatology of lightning from space and is the only recent platform that extends

The Lightning Imaging Sensor (LIS) was launched to the International Space Station (ISS) in February 2017, detecting optical signatures of lightning with storm-scale horizontal resolution during both day and night. ISS LIS data are available beginning 1 March 2017. Millisecond timing allows detailed intercalibration and validation with other spaceborne and ground-based lightning sensors. Initial comparisons with those other sensors suggest flash detection efficiency around 60% (diurnal variability of 51-75%), false alarm rate under 5%, timing accuracy better than 2 ms, and horizontal location accuracy around 3 km. The spatially uniform flash detection capability of ISS LIS from low-Earth orbit allows assessment of spatially varying flash detection efficiency for other sensors and networks, particularly the Geostationary Lightning Mappers. ISS LIS provides research data suitable for investigations of lightning physics, climatology, thunderstorm processes, and atmospheric composition, as well as realtime lightning data for operational forecasting and aviation weather interests. ISS LIS enables enrichment and extension of the long-term global climatology of lightning from space, and is the only recent platform that extends the global record to higher latitudes (± 55). The global spatial distribution of lightning from ISS LIS is broadly similar to previous datasets, with globally averaged seasonal/annual flash rates about 5-10% lower. This difference is likely due to reduced flash detection efficiency that will be mitigated in future ISS LIS data processing, as well as the shorter ISS LIS period of record. The expected land/ocean contrast in the diurnal variability of global lightning is also observed.

The Geostationary Lightning Mapper (GLM) is an instrument designed to continuously monitor lightning. It is on the GOES-16 and GOES-17 satellites, viewing much of the Western Hemisphere equatorward of 55 degrees. Besides recording lightning-flash information, it transmits background visible-band images of its field of view every 2.5 min. The background images are not calibrated or geolocated, and they only have similar to 10-km grid spacing, but their 2.5-min sampling can potentially fill temporal gaps between full-disk imagery from the GOES satellites' Advanced Baseline Imager. This paper applies an initial calibration and geolocation of the GLM background images and focuses on animations for two cases: a volcanic eruption in Guatemala and a severe thunderstorm complex in Argentina. Those locations typically have 10-min intervals between full-disk scans. Prior to April 2019, the interval was 15 min. Despite coarse horizontal resolution, the rapid updates from GLM background images appear to be useful in these cases. The 3 June 2018 eruption of Fuego Volcano appears in the GLM background imagery as an initial darkening of the pixels very near the volcano and then an outward expansion of the dark ash cloud. The GLM background imagery lacks horizontal textural detail but compensates for this lack with temporal detail. The ash cloud resembles a dark blob steadily expanding from frame to frame. Animation of the severe thunderstorm scene reveals vertical wind shear, with northerly low-level flow across a growing cumulus field and west-northwesterly upper-level flow at anvil level. Convective initiation is seen, as are propagating outflow boundaries and overshooting convective cloud tops.

Multiple records of global temperature contain periods of decadal length with flat or declining temperature trend, often termed a ‘hiatus’. Towards assessing the physical reality of two such periods (1940–1972 and 1998–2014), lightning data are examined. Lightning activity is of particular interest because on many different time scales it has been shown to be non-linearly dependent on temperature. During the earlier hiatus, declining trends in regional thunder days have been documented. During the more recent hiatus, lightning observations from the Lightning Imaging Sensor in space show no trend in flash rate. Surface-based, radiosonde-based and satellite-based estimates of global temperature have all been examined to support the veracity of the hiatus in global warming over the time interval of the satellite-based lightning record. Future measurements are needed to capture the total global lightning activity on a continuous basis.

As part of the geolocation accuracy assessment of lightning flashes detected by the Geostationary Lightning Mapper (GLM) on the GOES-16 and GOES-17 satellites (Geostationary Operational Environmental Satellite), two satellite laser ranging stations employed laser beacon systems to generate transient light pulses that simulate natural lightning around 777.4 nm to validate the pre-launch spec of 5 km. The pulse width, repetition rate, wavelength, and power of the laser pulses were configured to produce sufficient instrument response to be detected as synthetic lightning events by the GLM instrument. During the testing period from April 2017 to January 2018, the laser systems illuminated the GOES-16 satellite to observe diurnal variation of the GLM system response, with particular emphasis on geolocation accuracy. The final GOES-16 laser beacon tests, which used the latest updates of the geolocation algorithms implemented by the GOES-R Ground Segment, showed the offsets between the GLM geolocated location and the known laser locations were within 5 km.

Two overlapping efforts help to characterize the Geostationary Lightning Mapper (GLM) performance. The Post Launch Test (PLT) phase validates the predicted pre-launch instrument performance and the Post Launch Product Test (PLPT) phase validates the lightning detection product used in forecast and warning decision-making. This presentation documents the calibration and validation activities for the first 6 months of GLM on-orbit testing and validation commencing with first light on 4 January 2017. The PLT phase addresses image quality, on-orbit calibration, RTEP threshold tuning, image navigation, noise filtering, and solar intrusion assessment, resulting in a GLM calibration parameter file. The PLPT includes four main activities, the Reference Data Comparisons (RDC), Algorithm Testing (AT), Instrument Navigation and Registration Testing (INRT), and Long Term Baseline Testing (LTBT). A field campaign also provided valuable insights into the GLM performance capabilities. The PLPT tests each contribute to the beta, provisional, and fully validated GLM data.

Mission: Fly a flight-spare LIS (Lightning Imaging Sensor) on ISS to take advantage of unique capabilities provided by the ISS (e.g., high inclination, real time data); Integrate LIS as a hosted payload on the DoD Space Test Program-Houston 5 (STP-H5) mission and launch on a Space X rocket for a minimum 2 year mission. Measurement: NASA and its partners developed and demonstrated effectiveness and value of using space-based lightning observations as a remote sensing tool; LIS measures lightning (amount, rate, radiant energy) with storm scale resolution, millisecond timing, and high detection efficiency, with no land-ocean bias. Benefit: LIS on ISS will extend TRMM (Tropical Rainfall Measuring Mission) time series observations, expand latitudinal coverage, provide real time data to operational users, and enable cross-sensor calibration.

Previous total lightning climatology studies using Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS) observations were reported at coarse resolution (0.5) and employed significant spatial and temporal smoothing to account for sampling limitations of TRMM's tropical to subtropical low-Earth-orbit coverage. The analysis reported here uses a 16-yr reprocessed dataset to create a very high-resolution (0.1) climatology with no further spatial averaging. This analysis reveals that Earth's principal lightning hotspot occurs over Lake Maracaibo in Venezuela, while the highest flash rate density hotspot previously found at the lower 0.5 degrees-resolution sampling was found in the Congo basin in Africa. Lake Maracaibo's pattern of convergent windflow (mountain-valley, lake, and sea breezes) occurs over the warm lake waters nearly year-round and contributes to nocturnal thunderstorm development 297 days per year on average. These thunderstorms are very localized, and their persistent development anchored in one location accounts for the high flash rate density. Several other inland lakes with similar conditions, that is, deep nocturnal convection driven by locally forced convergent flow over a warm lake surface, are also revealed.Africa is the continent with the most lightning hotspots, followed by Asia, South America, North America, and Australia. A climatological map of the local hour of maximum flash rate density reveals that most oceanic total lightning maxima are related to nocturnal thunderstorms, while continental lightning tends to occur during the afternoon. Most of the principal continental maxima are located near major mountain ranges, revealing the importance of local topography in thunderstorm development.