Is the sound of spring thunder really worth "tens of millions of taels of gold"?

The Book of Rites, Monthly Ordinances, records: "In this month, the day and night are separated. Thunder sounds, lightning begins, stinging insects start to move, and people open their doors to come out." The Tang Dynasty poet Wei Yingwu wrote in "Observing Farmers": "A light rain makes all flowers grow new, a thunder begins the Waking of Insects, farmers have a few days of rest, and then they start farming." The ancient agricultural proverb "A spring thunder is worth a million ounces of gold" carries thousands of years of Chinese farming wisdom. Why is spring thunder worth a million ounces of gold?

01What is the difference between spring thunder and summer thunder?

To understand why spring thunder is really so valuable, let us first analyze what "different personality" spring thunder has compared to summer thunder.

Thunder and lightning mainly occur in summer. Compared with summer thunder, spring thunder is much gentler.

◎The energy source and trigger mechanism are different.

Spring thunder: mostly caused by dynamic lift. When cold and warm air converge violently in spring, the frontal system forces warm and humid air currents to climb to form thunderstorm clouds. The vertical development height of this cloud body is about 8-12 kilometers, the cloud top temperature is -40℃ to -60℃, and the charge structure shows a typical three-layer distribution.

Summer thunder: Mainly relies on thermal convection. The surface is heated by solar radiation to produce strong updrafts. The vertical thickness of the thunderstorm cloud formed can reach 16 kilometers. The cloud top temperature is as low as -70℃, and the charge density per unit volume is 50% higher than that of spring thunder.

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◎The rising air flow and discharge intensity are different.

Spring thunder: Meteorological observations show that the speed of rising air currents in spring thunder clouds is about 10-15 meters per second.

Summer thunder: In supercell thunderstorms caused by severe convection in summer, vertical wind shear can reach 25 m/s. This dynamic difference causes the discharge intensity of summer thunder to generally exceed 60 kA, with the highest record reaching 300 kA, which is three times the average current of spring thunder.

◎The discharge characteristics are different.

Spring thunder: The discharge is scattered, with a frequency of 50-80 times per hour and a single discharge lasting about 0.2 seconds. Cloud-to-ground lightning accounts for about 30%, and is often accompanied by continuous precipitation.

Summer thunder: It manifests itself as intensive discharges, with a frequency of up to 20 lightning strikes per minute. The proportion of cloud-to-ground lightning rises to 45%, and is often accompanied by hail and short-term heavy rainfall, with the maximum rainfall intensity recorded in 10 minutes reaching 50 mm.

◎Different spatial distribution.

In terms of geographical distribution, spring thunderstorms account for 35% of the annual number of days in the Yangtze River Basin, while summer thunderstorms in South China account for up to 60% of the annual number of days. Satellite monitoring shows that spring thunder systems move horizontally at a speed of about 60 kilometers per hour, and summer thunders often show quasi-stationary characteristics due to the influence of local convection.

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◎Different ecological effects.

Spring thunder: Its ecological value is particularly evident in the nitrogen cycle. Each lightning strike converts 1.5 kg of nitrogen into nitrates. When the soil temperature in spring is 10-15°C, the absorption rate of nitrogen fixation by plants can reach 65%.

Lei: The accompanying heavy rains cause more than 40% of the active nitrogen to be washed away before it penetrates. The utilization rate of nitrogen deposition from summer thunderstorms in South China is less than 40% of that in spring.

◎The climate indications are different.

Spring thunder : The first day of spring thunder advances by 1.2 days every decade, which is related to changes in the Arctic Oscillation Index.

Xia Lei : The increase in intensity is related to the increase in convective effective potential energy under the background of global warming. Meteorological models show that when the convective effective potential energy value exceeds 2000 joules/kilogram, the probability of severe thunderstorms exceeds 80%.

02Is spring thunder worth "a ton of gold"? Even more precious!

Spring thunder not only heralds the change of seasons, but is also an important regulator of the earth's ecosystem. It is truly more valuable than ten thousand ounces of gold.

◎ Nitrogen fixation. Lightning nitrogen fixation is the most efficient nitrogen conversion system in nature. The high temperature (about 30,000°C) generated by each spring thunder discharge can directly decompose nitrogen molecules, combining them with oxygen to form nitrates. Statistics show that a single lightning strike can convert 1.5 kg of nitrogen into active nitrogen. The global nitrogen input through lightning exceeds 100 million tons per year, which is equivalent to the nitrogen content of 80 million tons of urea fertilizer. Summer thunder can also fix nitrogen, but most of it is washed away by rain. Spring thunder has a better nitrogen fixation effect.

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◎Synergistic effect. The synergistic effect of spring thunderstorms and nitrogen deposition is significant. During thunderstorms, the pH value of rainwater drops from 5.6 to 4.2, which enhances the ability to dissolve soil minerals. Studies have shown that within 48 hours after a thunderstorm, the effective nitrogen content in the soil increases by 12-18%, and the biological effectiveness of phosphorus and potassium increases by 8-10%. In the rice-growing areas of the middle and lower reaches of the Yangtze River, rice production increased by an average of 7.3% in years with frequent spring thunderstorms.

◎Seed germination. The electromagnetic pulse of lightning stimulates seed germination. Experiments show that the germination rate of rice seeds treated with simulated lightning increased by 23% and the root vitality of seedlings increased by 31%.

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◎ Climate regulation. Spring thunderclouds have a significant reflective and regulating effect on solar radiation. Mature thunderclouds have an albedo of 0.8 and can reflect 70% of incident solar radiation back into space. Meteorological satellite observations show that during the period of active spring thunderstorms in the Yangtze River Basin, the average daily surface temperature dropped by 1.2-1.8℃, effectively alleviating the extreme temperature fluctuations of "late spring cold" and "warm spring".

◎ Carbon removal. Spring thunder promotes the regeneration of trace gases in the atmosphere. The high-energy electrons produced by lightning dissociate carbon dioxide into reactive oxygen species, accelerating the oxidation of greenhouse gases such as methane. Model calculations by the National Center for Atmospheric Research in the United States show that the efficiency of atmospheric methane removal during the spring thunder season increases by 25%, equivalent to reducing the greenhouse effect of 12 million tons of carbon dioxide equivalent per year.

summary:

In fact, the ecological value that spring thunder brings to mankind is more than that. Modern meteorology has discovered that the infrasound waves generated by lightning can propagate thousands of kilometers and may affect the migration of marine life. The Schumann resonance frequency (7.83 Hz) stimulated by lightning coincides with the alpha rhythm of brain waves, suggesting a deeper ecological connection.

Author: Wang Yuanhong, Senior Weather and Climate Engineer, Member of the Chinese Writers Association

Produced by: Science Popularization China