It starts with the gathering of clouds into a storm. In the center of the growing storm, tiny flecks of ice and supercooled water droplets collide and exchange charge, with positive charge billowing into the storm’s spreading anvil. The flow of particles creates an imbalance; the system needs to neutralize. Finally, with a zap having more power than 100,000 radio stations, all concentrated at a single point, lightning strikes.
Today, private and public services monitor lightning to track the locations of individual strokes and to generate warnings of severe storms and heavy precipitation [Nag et al., 2015]. Knowing where lightning strikes is important: Lightning causes many fatalities and injuries worldwide every year [Holle, 2015]. It also ignites forest fires, damages electrical infrastructure, and causes numerous other forms of loss and damage (see, e.g., National Lightning Safety Institute  for data pertaining to the United States), and the storms that come with the lightning cause even more damage.
But scientists are starting to recognize that lightning has a broader story to tell. Lightning frequency is changing, as climate is changing. For example, lightning’s close relationship to thunderstorms and precipitation makes it a valuable indicator for storminess, which makes lightning a particularly useful means of observing a variable and changing climate [Price, 2013; Williams, 2005].
What’s more, lightning is not only an indicator of climate change; it also affects the global climate directly. Lightning produces nitrogen oxides, which are strong greenhouse gases [Price et al., 1997].
In recent years, measurements of lightning have become more extensive, and new satellite instruments have further enhanced measurement coverage [Albrecht et al., 2016; Goodman et al., 2013; Yang et al., 2017]. However, the monitoring of lightning for climate science and services is still limited on a global scale.
To overcome this gap and explore the opportunities and challenges of lightning observations for climate, the scientists involved with the Global Climate Observing System (GCOS)—a group that seeks to ensure that data necessary for climate studies is made available to the public— together with the Commission for Climatology (CCl) of the World Meteorological Organization (WMO), established a Task Team for Lightning Observations for Climate Applications (TTLOCA) in October 2017.
Lightning: An Essential Climate Variable
About 45 flashes of lightning occur every second at any given time on planet Earth [Christian et al., 2003]. However, this rate can vary by as much as 10%–20% across a spectrum of timescales, from seasonal to interannual [Albrecht et al., 2016; Cecil et al., 2014; Markson, 2007; Price, 1993; Williams, 1994].
In efforts to better understand how these variabilities, as well as changing lightning frequencies, affect climate change, lightning has been added to the Global Climate Observing System’s (GCOS) list of Essential Climate Variables (ECVs) [Global Climate Observing System, 2016]. These ECVs provide the empirical evidence needed to understand and predict the evolution of climate as well as to guide mitigation and adaptation measures in support of scientists, governments, agencies, and the international climate policy in general under the United Nations Framework Convention on Climate Change (UNFCCC) and its Intergovernmental Panel on Climate Change [Bojinski et al., 2014].
Goals of the Task Team
GCOS is the dedicated body of UNFCCC for coordinating global climate observations [World Meteorological Organization (WMO), 1998]. It is cosponsored by WMO, the United Nations Educational, Scientific and Cultural Organization, the United Nations Environment Programme, and the International Council for Science.
The role of WMO’s CCl is to “stimulate, lead, implement, assess and coordinate international technical activities to obtain and apply climate information in support of sustainable socio-economic development and environmental protection” [Commission for Climatology, 2011].
To support this mission, the new lightning task team has taken on several specific issues. The team plans to do the following:
- explore potential climate applications for lightning observations and identify related challenges
- review current requirements for lightning observations in the GCOS implementation plan in the light of potential climate applications
- define data management and metadata standards that ensure that lightning data can be reprocessed in the future and ensure that changes in observation or processing techniques are fully documented
- develop a strategy for open data access for lightning data in climate applications, including providing access to data from the private sector
- encourage space agencies and operators of ground-based systems to provide global coverage and reprocessing of existing data sets
- review current data storage facilities and explore the options of a global data center for lightning data for climate applications
The team’s goal of reviewing requirements for lightning observation efforts, to ensure the quality and consistency of the data, is of particular importance. Satellite agencies have adopted WMO’s observation requirements for individual ECVs and have included these requirements in their planning for current and future missions. The GCOS implementation plan includes a first attempt to set these requirements for lightning, but the task team will review these requirements.
The task team, which was established for an initial period of 1 year, consists of international experts from science and operational weather and climate services. Over the past year, we have almost completed our initial tasks, and we have prepared recommendations on the team’s goals, including an initial set of specific requirements for lightning observations from a climate perspective. We are currently finalizing these draft guidelines, which will be presented to WMO for inclusion in their international standards. The guidelines will be published by WMO and will be available soon in WMO’s online library.
We are seeking all relevant data sets to address climate questions using information about lightning. We also seek proxy lightning data sets. For instance, we started an initiative to extend lightning data into the distant past using “thunder day” data [WMO, 1953]. Identifying these and related data sets with regional or global coverage is important for the task team.
The task team has also started to address the detailed questions of who will archive these data and who should be offered access. Some of the data are naturally in the public domain, but most of the ground-based lightning network data are privately owned and copyrighted.
We encourage the community to provide comments on any of the goals listed above. These comments can be submitted to Valentin Aich ([email protected]).