Below Zero
Overview
Below zero (零下, yeongha) refers to a state in which the temperature is lower than 0 degrees Celsius (0℃), and is written numerically as a negative temperature (e.g., -5℃). It is a practical distinction that takes 0℃, the freezing point of water, as its reference, and in absolute temperature it corresponds to anything below 273.15 K. Below zero is not merely a number but a physical boundary that governs the phase changes of water, the survival of living organisms, and the operating limits of transportation and industrial facilities; it is a core indicator consulted in common by meteorology, materials engineering, medicine, and energy engineering.
Main Content
Definition and Notation
- A temperature below 0℃. In Korean it is written with a negative sign, as in 'yeongha 5 do' (5 degrees below zero) or '-5℃'.
- The triple point of water is 0.01℃, and its freezing point at 1 atmosphere is 0℃, so below zero marks the beginning of the region in which water undergoes a phase change into ice.
- The Korea Meteorological Administration compiles statistics on days when the daily minimum temperature falls below zero as 'below-zero days', and a cold wave advisory is issued when the morning minimum temperature is expected to drop by more than 10℃ compared with the previous day or to fall to -12℃ or lower.
Changes in Water and Nature
Below zero, water turns to ice and expands in volume by about 9%. This expansion force is a major cause of burst water pipes, frost shattering of rock (weathering), and cracks in roads. Sublimation, in which water vapor in the atmosphere turns directly into ice crystals, produces frost and snow crystals, while frost heaving (凍上), in which moisture in the soil freezes and swells, pushes up the foundations of structures. Water can exist as a liquid below zero in a supercooled state, but it freezes rapidly when foreign matter or an impact is applied.
Effects on Living Organisms and the Human Body
In below-zero environments the human body constricts surface blood vessels to preserve core temperature. When skin temperature falls to around 0℃, freezing begins within the tissue and frostbite occurs, and when core body temperature drops below 35℃ it leads to hypothermia. The perceived temperature (wind chill index) falls sharply as wind speed increases; at an air temperature of -5℃ with a wind speed of 30 km/h, the perceived temperature drops to around -13℃. Plants use cold-hardiness mechanisms that raise the concentration of sugars and proteins to prevent freezing within their cells, and for field crops that overwinter outdoors, the below-zero threshold temperature is determined for each variety.
Below Zero in Industry and Daily Life
- Automobiles: In lithium-ion batteries, the viscosity of the electrolyte rises below zero, reducing output and charging speed, and driving range may decrease by 20–40%.
- Roads: Black ice, formed when snow melts and then refreezes, greatly increases the risk of accidents.
- Construction: Insulation and condensation-prevention design, freeze-protection heaters, and avoidance of thermal bridges become mandatory requirements.
- Refrigeration and logistics: The cold chain uses the below-zero range of -18℃ or lower as its standard for storing food and vaccines.
- Data centers and industry: Free cooling that utilizes below-zero outside air is drawing attention as a means of reducing cooling electricity consumption.
Records and Extremes
Korea's official lowest temperature record is -32.6℃ in Yangpyeong on January 5, 1981, and Seoul's lowest record is -23.1℃ in 1927. The world's official record is -89.2℃ at Vostok Station in Antarctica (1983), and satellite observations have confirmed levels of around -93.2℃ on the Antarctic Plateau. Winter cold waves on the Korean Peninsula tend to become extreme when the expansion of the Siberian High combines with a negative phase of the Arctic Oscillation.
Latest Trends
The discourse of the 2024–2025 winter season can be summarized as 'below-zero performance' and 'the reappearance of extreme cold waves'. First, as the electric vehicle market increased the share of LFP batteries, degradation of charging time and driving range at low temperatures below -10℃ emerged as a key consumer issue, and battery preconditioning and heat-pump-based thermal management systems have become de facto standard specifications. Second, as Arctic warming proceeds due to climate change and the jet stream meanders, the debate over 'Arctic Oscillation variability'—in which cold waves stall for long periods over specific regions—has intensified, and in Korea as well, heavy snow in December–January and cold waves below -15℃ have been repeatedly observed. Third, the view of below-zero environments as a resource has spread, and in Northern Europe and Canada, models combining waste-heat recovery from data centers with natural cooling have entered the commercialization stage, while the winter sports and tourism industries are responding with artificial snowmaking technology and the development of low-temperature-durable materials. Fourth, the medical community is reorganizing emergency treatment protocols for hypothermia and frostbite and strengthening response manuals for cold-wave-vulnerable groups (the homeless and elderly people living alone).
Related Topics
- [[Cold Wave]]
- [[Perceived Temperature]]
- [[Black Ice]]
- [[Frostbite]]
- [[Lithium-ion Battery]]
- [[Arctic Oscillation]]