Cloud ice fraction governs lightning rate at a global scale

Lightning rate varies non-linearly with cloud ice fraction and between ocean and continent regions due to differences in convection depth, according to analyses of 20-years of lightning observations and cloud water data. We find a robust modified gamma function relationship mechanism between cloud ice fraction and lightning rate.

Like Comment
Read the paper

Thunderstorms have devastating consequences for human life and socioeconomics via damages from the gale, hail, and lightning strikes. Cloud microphysics (ice particle size, ice and supercooled liquid water content) make crucial impacts on lightning, but the relationship mechanism between lightning and cloud microphysics has not been well constrained at a global scale. Understanding of the relationships between cloud water and electrification of thunderstorms is one of the key points of theoretical and applied physics of clouds.

Uncovering the lightning mystery. On 9 August, 2021, our paper entitled “Cloud ice fraction governs lightning rate at a global scale (https://www.nature.com/articles/s43247-021-00233-4)” was published in Communications Earth and Environment. In this work, we analyzed 20 years ( during 1995-2014) of satellite-derived LIS/OTD lightning flash rate data and cloud water data from the ERA-Interim reanalysis above continental and ocean regions at a global scale (Fig.1). A robust relationship has been found between cloud and lightning. For the first time, we proposed to parameterize this relationship with a novel universal modified gamma function, which works well on both global and regional scales (for detail to see the paper).

                                                Fig.1 Spatial distribution of annual averaged lightning flash rate

Our results show that the response curve of the lightning rate to cloud ice fraction firstly increases and then decreases. By conducting the theoretical analysis with the data of LWP, IWP, convective available potential energy (CAPE), the content of total column water vapor (TCWV), and cloud type, a schematic diagram regarding the effects of cloud ice fraction on lightning activities is demonstrated in Fig. 2. Specifically, lightning rate increases initially with increasing cloud ice fraction in shallow and warm clouds (e.g. stratocumulus); maximum flash rates are reached at a critical cloud ice fraction value that is associated with deep convective clouds, whose cloud hydrometeors provide the areas where the NIC occurs efficiently through collisions between them, then produce the most lightning activities; beyond the critical value, lightning rate decreases as the ice fraction increases to values representative of ice clouds (e.g. cirrus, cirrostratus and cirrocumulus).

                      Fig. 2: Illustration of the effects of cloud ice fraction on the lightning activities.

In addition to the climatological relation mechanism between ice fraction and lightning at the global scale, this uniform law also exists in regions with various climate properties. The modified gamma function, which well described the relation between cloud and lightning, may lead to important scientific advancements in understanding lightning activities and contributing to the model lightning prediction in the climate and weather communities. We believe that the results and conclusions of this work would be beneficial to lightning disaster prevention and reduction, lightning forecast and hazard prediction. Future work should concentrate on the precise regional parameters that influence the relationship, and provide a better knowledge of the regional parameters for the empirical investigations and prognostic use.

If you are interested in this work, please to follow this link (https://www.nature.com/articles/s43247-021-00233-4 or https://doi.org/10.1038/s43247-021-00233-4) to download the paper.

And  the contributions to this work were  Yong Han,  Hao Luo,  Yonghua Wu,  Yijun Zhang and Wenjie Dong. Dr. Yong Han (Prof.), the corresponding author of this paper, is the leader of the Advanced Science & Technology of Atmospheric Physics Group (ASAG) at Sun Yat-sen University (SYSU). Dr. Wenjie Dong (Prof.) and Ph.D. student Hao Luo are from School of Atmospheric Sciences, SYSU, China. Dr. Yonghua Wu from NOAA-CESSRST, City College of the City University of New York and Dr. Yijun Zhang (Prof.) are from Department of Atmospheric and Oceanic Sciences, Fudan University, China, respectively.

Yong Han

Prof., Sun Yat-sen University