Lightning activity is a key feature of convective storms and often a precursor for other severe weather phenomenon. Near real-time lightning data provides an important basis for severe weather monitoring and warnings. Lightning is also listed as a Global Climate Observing System Essential Climate Variable . The most comprehensive long-term global lightning datasets can be built by combining data from ground-based and space-borne lightning location systems (LLSs). Ground-based LLSs date back to 1980s e.g., and have gained an increasingly central role in meteorology and research in the last thirty years. Large-scale lightning observations are provided by continental and global LLSs. Continental ground-based LLSs worth mentioning are the National Lightning Detection Network NLDN; over continental United States, the European Cooperation for Lightning Detection EUCLID; and the United Kingdom Met Office Lightning Electromagnetic Emission Location by Arrival time difference Leela; over continental Europe. Global ground-based LLSs are the Global Lightning Detection network GLD360;, the World Wide Lightning Location Network WWLLN; and the Earth Networks Total Lightning Network ENTLN;. Global systems miss most of the intra-cloud lightning (IC) and also some weaker cloud-to-ground (CG) lightning e.g.,. Continental systems are more sensitive, e.g., NLDN is capable of detecting more than 50 % of IC lightning in some storms in its core region . However, their sensitivity drops rapidly outside the coverage of the network. In addition, both continental and global ground-based LLSs suffer from spatial variations in sensitivity due to lack of sensors in remote areas and over the oceans.

Space-based geostationary lightning sensors are a valid alternative to ground-based LLSs for monitoring total lightning activity, i.e., the combination of IC and CG lightning, globally. They offer consistent, uniform, and continuous coverage over hemispheric scales (encompassing land, oceans and remote regions) with high detection efficiency during both day and night e.g.,. Such instruments detect lightning by imaging photons which reach cloud-tops after being emitted by lightning discharges and scattered through clouds. Early attempts of optical lightning detection from space were reported by and . The first missions devoted to lightning monitoring from space were The Optical Transient Detector OTD; and the Tropical Rainfall Measurement Mission Lightning Imaging Sensor TRMM-LIS;. These two instruments enabled the monitoring of lightning from space, but with considerable limitations due to the limited viewing time stemming from their low-Earth orbits. Geostationary LLSs were developed for continuous monitoring of lightning over large (hemispheric) areas. The first Geostationary Lightning Mapper (GLM) was launched in November 2016, aboard the first of the GOES-R series of Geostationary Operational Environmental Satellites now GOES-16; e.g.,. Currently, four different GOES-GLM instruments are flying aboard GOES-16, 17, 18 and 19 satellites, respectively. These enable the monitoring of total lightning activity from New Zealand to the western coast of Africa. In December 2016, the Chinese Lightning Mapping Imager was launched aboard the Fengyun-4A satellite FY-4A-LMI; e.g.,. FY-4A-LMI's field-of-view (hereafter FOV) encompasses China, southern Indian Ocean and the Western part of Australia, i.e., it ofers fairly limited geographical coverage. In December 2025, a second LMI instrument has been launched aboard the Fengyun-4C (FY-4C-LMI). FY-4C-LMI delivers hemispheric coverage.

The Meteosat Third Generation Lightning Imager (MTG-LI) is the first space-borne geostationary LLSs ever developed and operated in Europe. The instrument is part of the Meteosat Third Generation Programme and is aboard the Imaging satellite MTG-I . The first MTG-LI was launched on 13 December 2022, and continuously monitors total lightning activity over hemispheric scales: Europe, Africa, and part of the Atlantic Ocean, South America, middle East and Indian Ocean (see Fig. ). Since 31 October 2024 (pre-operationally since July 2024), MTG-LI has been delivering near real-time lightning data products which enable monitoring and characterization of total lightning activity within its FOV from global scale down to individual storms and flashes e.g.,. The MTG-LI Programme will be operated for about 20 years, with one MTG-LI operational instrument and at least one back-up in orbit. Table  provides the reader with key design and performance figures of both MTG-LI and GOES-GLM (for direct comparison). Both systems shall be regarded to be evolutions of OTD and LIS.

The MTG-LI System has been introduced in detail in , together with key information regarding data processing approach and performances. In the context of this paper, the following performance figures are worth highlighting: (i) average absolute flash detection efficiency of 87.4 % with values larger than 90 % over the entire continent of Africa and large part of Europe (derived using the Global Lightning Detection network GLD360 and applying a two-system Bayesian detection efficiency approach described by ) and (ii) flash false alarm rate below 0.5 flashes s⁻¹ and average fraction of false flashes of 0.16 % of the total observed.

The present paper presents some of the key properties/features of MTG-LI observations from July 2024 to June 2025, i.e., the first year of operations. Results illustrate how MTG-LI enables monitoring spatial, seasonal and diurnal patters of lightning over hemispheric, regional/national and local scale.

During its first year of observations, MTG-LI captured all the major spatial lightning patterns in its field of view (Fig. ) as described in previous studies using OTD/LIS and ground-based lightning data e.g.,. In the largest scale, the land-sea contrast and the high concentration of lightning in the tropics was observed. The absence of lightning at high latitudes and over the tropical South Atlantic Ocean is also in line with previous studies. The impact of MTG-LI false alarms can be noticed as a “halo” and a couple of north-west to south-east oriented line features over the tropical South Atlantic Ocean. Such false flashes can originate from different sources, including Read-Out-Noise (RON) of the cameras, high energy particles and space debris transiting in the MTG-LI field-of-view. For more details about MTG-LI false flashes and their origin one should refer to .

The highest MTG-LI flash density of 189 flashes km⁻² yr⁻¹ was observed in the eastern part of The Democratic Republic of the Congo (Figs.  and ). The location and the spatial extension of this prominent global lightning hot-spot are well in line with earlier studies using ground-based lightning location systems like WWLLN and GLD360 . The MTG-LI flash density values in the region exceeded significantly ground-based observations but were well in line with view-time corrected OTD and LIS results, reporting 160–232 flashes km⁻² yr⁻¹ in the same area . Over the coming years, sustained MTG-LI observations will fundamentally advance our characterization of the world's primary lightning hot-spot.

The maximum MTG-LI flash density in Europe was found to be 44 flashes km⁻² yr⁻¹ in the northeast of Italy approximately 50 km to the north of Venice (Fig. ). This is significantly higher than ≈ 6 cloud-to-ground flashes km⁻² yr⁻¹ reported by EUCLID and 8 total lightning flashes km⁻² yr⁻¹ observed by ATDnet in the same area. Meanwhile, it is close to 50 flashes km⁻² yr⁻¹ in view-time corrected lightning climatology datasets from TRMM-LIS, ISS-LIS and OTD by . In other European lightning hot-spots in the north of Italy and east of Spain, MTG-LI typically observed 15–25 flashes km⁻² yr⁻¹, i.e, 3–6 times more than ATDnet and EUCLID.

The higher flash counts of the MTG-LI relative to ground-based networks stem from two inherent advantages of space-borne LLSs. First, they provide comprehensive coverage over remote and mountainous terrain where short-range networks, such as EUCLID over Europe, often suffer from limited detection efficiency. Second, they feature a heightened sensitivity to IC flashes, which are often difficult to detect with ground systems. Given the 3–6 times higher MTG-LI flash density compared to EUCLID cloud-to-ground flash density and the fact that EUCLID has been shown to detect > 95 % of cloud-to-ground flashes , it can be inferred that the majority of LI observations are associated with IC flashes. However, it should be noted that MTG-LI (like other space-borne optical lightning detectors) does not provide flash type classification. Therefore, in regions with well-established ground-based lightning location systems, a combined lightning dataset integrating ground-based and space-borne observations should be considered. Such an approach would combine the reliable flash type classification provided by ground-based lightning location systems with the heightened sensitivity to IC flashes of the MTG-LI.

When interpreting the first MTG-LI flash density maps presented here, the length of the study period has to be considered especially at high latitudes and over the oceans where lightning activity is low. A longer study period would be needed to smoothen out the local-scale impact of individual intense storms and reveal the properties of the lightning climatology. For example, the small-scale stretched features of higher flash density in many places across Europe (Fig. ) reflect paths of individual strong storms during the study period. Such storm tracks can intersect, creating small local hot-spots with notably high flash density as seen, for example, in the south of Sweden or in some locations in Germany, France and elsewhere. This effect is not seen in central Africa where the amount of lightning is high enough to produce meaningful climatological patterns even over the 1-year study period.

The spatial distribution of the month of maximum lightning activity (Fig. ) and the complementary monthly MTG-LI flash distribution histograms (Fig. ) demonstrate the MTG-LI ability to characterize the seasonal patterns of convection within its FOV. The summer maximum over the continental Europe and autumn maximum over the Mediterranean are well in line with the ATDnet 10-year lightning climatology . Over Africa, the month of maximum lightning activity reflects the seasonal migration of the Intertropical Convergence Zone (ITCZ) with June to August maximum in the north and December to February maximum in the south of the continent e.g.,. In South America, MTG-LI observed Northern Hemisphere autumn/winter maximum which is in line with the fact that its field of view in South America is mainly in the southern hemisphere, visited by the ITCZ during this time of the year.

Mid-latitude oceans on both hemispheres were characterized by local autumn and winter lightning maximum that stems from the seasonal peak in atmospheric instability . Frequent autumn and winter cyclones transport cooler polar air masses over relatively warmer waters, resulting in convection and sometimes lightning. The overall low flash density (Fig. ) suggests that mid-latitude oceanic thunderstorms are normally weak and short-lived. Over the tropical oceans, the most interesting seasonal features was the late summer/autumn lightning peak observed around 10° N across the Atlantic Ocean. This probably represents mesoscale convective systems developing on African easterly waves, crossing the ocean from east to west and sometimes developing into hurricanes during this season .

A sharp land/sea contrast was observed in the diurnal cycle of lightning activity (Figs.  and ). A strong afternoon peak and a deep morning minimum was characteristic to virtually all land areas. This is well in line with previous regional e.g., and global studies and stems directly from the diurnal air temperature and convection cycle over land. Much weaker diurnal lightning cycle with a tendency towards nocturnal or (early) morning maximum was seen over the tropical Atlantic and Indian Ocean (Figs.  and ). This reflects the typical early morning convection and precipitation maximum over the tropical oceans e.g.,.

The detection of small local features was demonstrated in the Congo Basin where the very high lightning frequency allows one to derive fine-scale climatological patterns despite of limited length of the study period (Fig. ). MTG-LI flash density on a 0.02° × 0.02° (i.e., 2.2 km × 2.2 km) spatial grid revealed small-scale details such as the lower flash density over the Congo River in the north and the very sharp drop in lightning frequency along the mountain ranges in the eastern border of The Democratic Republic of the Congo. No significant artifacts or issues were observed despite of the fact that the used spatial resolution was well below the MTG-LI pixel size (≈ 5 km in the area). This shows that the method of computing MTG-LI flash locations as radiance weighted centroids of all contributing lightning events might reveal some interesting sub-pixel scale local details.

High-resolution spatial lightning patterns can be combined with high-resolution diurnal lightning statistics to further explore some specific local-scale weather patterns such as nocturnal lightning maxima over larger African lakes (Fig.  right plot and Fig. ). Those maxima have been reported in previous studies e.g., and attributed to the convergence of nocturnal land breezes over the warm lakes that triggers convection . Such local factors can lead to a very pronounced nocturnal lightning maximum (Fig.  middle plot) as opposed to the relatively weak night time lightning maximum over the tropical oceans (Fig. ). It is also interesting to note that similar nocturnal lightning maximum is found over Lake Catatumbo in South America e.g., where also the highest lightning incidence on the planet (up to 250 flashes km⁻² yr⁻¹) has been reported .

The potential of merging different geostationary lightning datasets was demonstrated by comparing the MTG-LI and GOES-GLM flash density maps (Fig. ). Despite the differences in technology, pixel resolution and frame rate (Table ), the two instruments produced virtually identical spatial patterns of annual flash density over most of the intersection of their FOVs. Notable differences were only observed close to the edge of the MTG-LI FOV in South America where MTG-LI flash density was up to three times lower than GOES-GLM flash density. On the contrary, there was no notable drop in GOES-GLM flash density over the Atlantic Ocean near the edges of GOES-GLM FOV. This difference can be attributed to the smaller FOV of the GOES-GLM, which is limited to approximately 55° from the sub-satellite point. Consequently, the viewing angle along the edges of the GOES-GLM FOV is comparable to that of the MTG-LI over eastern South America, where the flash densities recorded by both instruments remain closely aligned. Furthermore, because the eastern boundary of the GOES-GLM FOV lies predominantly over the Atlantic Ocean, detection at these wide viewing angles is further facilitated by the naturally higher optical intensity of oceanic lightning e.g.,.

Finally, given the very good agreement between MTG-LI and GOES-GLM flash density, a simple annual merged flash density map was produced by taking the highest flash density value per grid cell (Fig. ). This is the most primitive, but at the same time very intuitive, way of producing a simple merged lightning distribution map. Selecting the highest value in each grid cell provides a simple filtering criterion, ensuring that the flash density measurement from the instrument with the highest detection efficiency in that cell is retained in the final merged map. This results in a smooth transition from MTG-LI data to GOES-GLM data when moving from east to west through the overlap between the FOVs of the two instruments. The resulting flash density map shows very natural lightning patterns that are well in line with earlier OTD and LIS results . Further development is needed to upgrade this simple approach into a sophisticated merging algorithm that operates at the flash level to eliminate false alarms. However, Fig.  is already very encouraging and clearly shows the potential of achieving near-global total lightning monitoring by merging datasets of multiple geostationary lightning mappers in the near-future.

The MTG-LI system is the first European geostationary mission dedicated to the continuous monitoring and characterization of total lightning activity on a hemispheric scale. This paper demonstrates its capability to capture precise spatial and temporal lightning patterns across its entire FOV, which encompasses Europe, Africa, the Middle East, South America, and parts of the Atlantic and Indian Oceans.

MTG-LI detected a total of 595 × 10⁶ flashes during its first year of continuous observations from July 2024 to June 2025. In the largest scale, lightning was mostly concentrated to the tropical land regions while high latitudes and oceans were characterized by much lower lightning incidence. The highest observed annual lightning flash density of 189 flashes km⁻² yr⁻¹ was found in the well-known lightning hot-spot in the east of The Democratic Republic of the Congo. The location of the European lightning hot-spot in the north-east of Italy is also in line with previous studies, while the observed MTG-LI lightning frequency of 44 flashes km⁻² yr⁻¹ at this location notably exceeded ground-based observations, reflecting the heightened IC lightning sensitivity of the MTG-LI. Given that MTG-LI does not provide flash type classification, a combined lightning dataset integrating the benefits of ground-based lightning location systems (e.g. flash type classification) and space-borne observations (e.g. considerably higher sensitivity to cloud lightning) should be considered in the future.

The seasonal lightning maximum over land typically occurred during local summer months while the mid-latitude oceans were characterized by autumn/winter lightning maximum. Strong diurnal cycle with maximum lightning activity during the local afternoon was observed everywhere over land while much weaker nocturnal maximum prevailed over the seas and oceans. MTG-LI was also very good at detecting local-scale features such as the strong nocturnal lightning maximum over Lake Victoria in Africa.

All observed lightning patterns align closely with previous studies utilizing ground-based networks and low-Earth-orbiting space-borne detectors, such as the OTD and LIS. Crucially, however, the flash densities recorded by the MTG-LI are systematically higher than those from ground-based systems, underscoring the added value of MTG-LI's sensitivity to IC lightning. Alongside the findings of , this paper demonstrates that the MTG-LI is an exceptional tool for both real-time operational tracking and long-term climatological monitoring of total lightning activity across its entire field of view.