What Is The Limit Of Heat?-Chushu

The solar term “Chushu” is the 14th of the 24 solar terms and the second solar term of the autumn season. It falls around August 22-24 in the Gregorian calendar and signifies the end of the hottest days of summer, known as the “final heat” of the three periods of extreme heat.

After Chushu, the sun’s direct rays continue to move southward, leading to a decrease in solar radiation. The subtropical high pressure system also retreats southward, gradually reducing the heat. Thunderstorm activity becomes less intense compared to the peak of summer, and heavy rainfall tends to decrease across the country. Chushu marks the transition to a cooler period.

Historical Origin

The term “Chushu” literally means “departing from heat,” indicating the waning of the scorching summer temperatures. In ancient times, people associated this time with the end of extreme heat. The “three heats” and “three fu” represent the hottest periods of the year, including Xiaoshu, Dashu, Lixia, and Chushu. Chushu is part of the “three heats,” which refers to a sequence of the hottest solar terms. The concept of “three fu” involves the idea that after the third fu, the heat begins to wane.

Solar Phenomena

During Chushu, the handle of the Big Dipper points toward the southwest (Wu direction), and the sun’s ecliptic longitude reaches 150 degrees. The sun’s declination has moved from 23 degrees and 26 minutes north latitude at the Summer Solstice to around 11 degrees and 28 minutes north latitude during Chushu. This signifies the sun’s continued southward movement and the approach of the latter half of the Shen month in the Chinese calendar.

Meteorological Changes

Chushu, meaning “out of heat,” marks the gradual retreat of high temperatures. After Chushu, the sun’s direct rays continue to move southward, resulting in a weakening of solar radiation. The subtropical high-pressure system also shifts southwards, causing a decline in heat. While the weather remains hot during this period, it is showing a decreasing trend. The dissipation of summer heat is a gradual process, and a decrease in temperature doesn’t immediately lead to coolness. True cooling usually occurs after the “white dew” period.

Following Chushu, temperatures gradually decrease, and the difference between daytime and nighttime temperatures increases. However, daytime temperatures remain relatively high. This phenomenon is due to the continued southward movement of the sun’s direct rays, leading to reduced solar radiation, as well as the retreat of the subtropical high-pressure system. The Mongolian cold high-pressure system starts to exert its influence, hinting at the approaching “xiaoluzheng,” or slight dew.

After the Chushu solar term, while the subtropical high-pressure system retreats significantly, it doesn’t easily relinquish its control and completely withdraw to the western Pacific Ocean. In the regions under its influence, people often experience another period of hot weather known as the “autumn tiger.” The duration of the autumn tiger can vary, usually lasting from two weeks to two months. Its formation is attributed to the subtropical high-pressure system of the western Pacific, which gradually moves southward in autumn while also shifting northward. Under the control of the subtropical high-pressure system, clear skies and intense sunlight lead to a rise in temperature.

Thunderstorm activity following Chushu becomes less intense than during the peak of summer, leading to a weakening trend in heavy rainfall across the country. In the transitional period around Chushu, the rainfall distribution in South China shifts from being more prominent in the west to being more significant in the east. In regions like the southwest and west of China, where they are on the edge of the subtropical high-pressure system, thunderstorm activity remains relatively high. By September, most of China enters a period of reduced rainfall, although the western regions, particularly the western part of China, experiences more rainfall. This is a unique weather phenomenon during the autumn season. Under the influence of the cold high-pressure system, descending and dry cold air ends the rainy season (“qi xia ba shang”) in the northern regions of China, including the northeast, north China, and northwest.

Agricultural Activities

During Chushu, the majority of southern China is busy with the harvest of mid-season rice. In most years, the sun is still quite abundant in South China during Chushu, except for the western parts, and the rainy days are not frequent. This is favorable for cutting and drying mid-season rice and for the cotton plants to bloom. During Chushu, most regions in China witness the maturation of orchards and crops. Farmers intensify their harvesting efforts and seize the optimal agricultural window to manage tasks such as fertilizing and weeding in the rice fields. Traditional sayings such as “Grains turn yellow after Chushu, be cautious of strong winds” and “After Chushu, the field changes overnight” illustrate how crops ripen quickly after this solar term. Other proverbs highlight the imminent harvest.

Phenological Phenomena

In ancient Chinese literature, Chushu was divided into three phenological periods: “The first period sees eagles offering birds as sacrifices; the second period witnesses the beginning of solemnity in heaven and earth; the third period notes that crops are ready for harvest.” During this solar term, eagles start hunting a large number of birds. All living things in heaven and earth begin to wither. The term “crops are ready for harvest” refers to the maturation of various grains such as millet, barley, rice, and sorghum, symbolizing a bountiful harvest.

Traditional Customs

Ancestral Worship and Welcoming Autumn

The customs before and after the Chushu solar term are closely related to ancestral worship and welcoming autumn. Folk activities celebrating “Mid-July” or “Zhongyuan Festival” are common around this time. The Book of Changes (Yijing) states, “Repetition of the Dao takes seven days to return; this is the motion of heaven.” Seven is a yang number representing heaven. After the extinction of yang energy between heaven and earth, it can be regenerated in seven days. This concept aligns with the cyclical nature of yin and yang, making the 14th day of the seventh lunar month an occasion for ancestral worship associated with the number seven. The Mid-July Festival is a time for people to celebrate the harvest, express gratitude to the land, and offer new rice as sacrifices to their ancestors, reporting on the autumn’s yield.

Eating Duck

“Mid-July for ducks, mid-August for taro.” Ancient people believed that ducks around the middle of the seventh lunar month were the most delicious and nutritious. On the day of Chushu, people in old Beijing would buy Baihe ducks. In Jiangsu, when preparing a duck dish, it’s customary to send a bowl of it to neighbors as a sign of goodwill and friendship.

Floating River Lanterns

River lanterns are lamps or candles placed on floating platforms. Before and after Chushu, there are activities celebrating Zhongyuan (Mid-July), where river lanterns are floated on water to commemorate the departed and pray for safety.

Fishing Festival

Post-Chushu marks the period of harvest in the fishing industry. Coastal regions in China often hold various activities to bid farewell to fishermen departing for their harvest expeditions, hoping for a fruitful catch. During this time, ocean temperatures remain relatively high, and fish tend to stay near the coast. Fish and shellfish mature and become ready for harvest. Thus, people can enjoy a variety of seafood from this time onward.

Fishing festivals are significant for coastal fishermen. Annually after Chushu, Zhejiang Province holds a grand Fishing Festival to mark the end of the fishing ban in the East China Sea. This event includes solemn sea-related ceremonies, cultural, tourism, and economic activities, attracting participants from home and abroad. This festival allows attendees to experience the vibrant maritime culture and savor fresh seafood.

Worshipping the Land Deity

During the Chushu solar term, as crops are harvested, rural communities perform various rituals to express gratitude to the Land Deity. Some offer sacrificial animals at the land deity temple, while others plant flags in the center of fields as a gesture of thanks. There’s a belief that if one works in the fields on this day and returns home without washing their feet, they might wash away the harvest they’ve gained. On the 15th day of the seventh lunar month, there’s also a tradition of worshiping the land and crops, by spreading offerings in the fields and attaching strips of multicolored paper to crop ears. This practice is believed to prevent hail and ensure a bountiful autumn harvest.

Water Splashing Carnival

In Yunnan’s Xishuangbanna, there’s a tradition of water splashing carnival.

Lifestyle and Health

Chushu reflects changes in temperature. In southern China, high temperatures can recur during the late Chushu period, earning it the nickname “autumn tiger.” While daytime temperatures can still be high, the difference between day and night temperatures increases, which calls for guarding against catching a cold. Traditional Chinese medicine divides the year into five seasons: spring, summer, long summer, autumn, and winter. Long summer covers four solar terms: Xiaoshu, Dashu, Liqiu, and Chushu, characterized by humid and hot weather.

After Chushu, sweating decreases noticeably, and the body’s water-salt metabolism gradually rebalances, entering a period of physiological rest. This can lead to a feeling of fatigue called “autumn fatigue.” To mitigate this fatigue, ensure sufficient sleep, maintain a regular sleep schedule, and avoid staying up late. Consume a light diet, including foods like tomatoes, eggplants, potatoes, grapes, and pears.

With autumn’s arrival after Chushu, the season becomes more pronounced, providing an excellent time for outdoor activities, appreciating autumn scenery, and enjoying leisurely walks and hikes. Exercise options can include brisk walking, hiking, and playing sports. For older individuals, the benchmark for exercise should be to avoid excessive fatigue. It’s best to exercise in the early morning or evening, as midday temperatures remain high, necessitating caution against outdoor activities.

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