Clear Skies and Large Diurnal Temperature Range

A meteorological phenomenon in which, on clear days, radiative cooling at night causes temperatures to drop significantly, widening the temperature difference between day and night.

Clear Skies and Large Diurnal Temperature Range

Overview

'Clear skies and a large diurnal temperature range' refers to a meteorological condition in which clear weather and a wide difference between daytime and nighttime temperatures occur simultaneously. On clear days, there are few clouds, so the surface warms rapidly due to strong solar radiation during the day; at night, because there are no clouds, radiative cooling—the rapid release of surface heat into the atmosphere—becomes active. As a result, even within the same day, the difference between the morning minimum temperature and the daytime maximum temperature frequently exceeds 10–15°C, and it often appears especially during seasonal transitions in spring and autumn and from late autumn to early winter.

Main Content

Mechanism

The key factor increasing the diurnal temperature range is the presence or absence of clouds. Clouds reflect solar radiation during the day, reducing surface heating, and at night act as a 'blanket' that sends longwave radiation emitted from the surface back down. Therefore, on cloudy days, daytime temperatures cannot rise much and nighttime temperatures cannot fall much, so the diurnal temperature range is small. Conversely, on clear days, both daytime heating and nighttime cooling are maximized, increasing the diurnal temperature range.

In addition, the following conditions further increase the diurnal temperature range.

Dry air: When there is little water vapor, the atmosphere's heat capacity is small, so temperatures drop sharply at night.
Weak wind: When winds are strong, the atmosphere mixes (turbulent mixing), easing surface cooling, but when winds are weak, cold air stagnates near the surface.
Basin topography: In basins surrounded by mountains or inland areas, cold air cannot escape, making morning temperatures lower.
Altitude and continental climate: Inland and continental climate regions with little oceanic influence and high mountain areas inherently have large diurnal temperature ranges.

Seasonal and Regional Characteristics

Although Korea is surrounded by sea on three sides, deep inland areas (Daegwallyeong (대관령), Cheorwon (철원), Hongcheon (홍천), Chupungnyeong (추풍령), etc.) have particularly large diurnal temperature ranges. In spring, when migratory high-pressure systems pass, dry continental air flows in, and 'clear skies with a large diurnal temperature range' weather continues for several days; in autumn, under the influence of the cold, dry Siberian air mass descending from the Chinese continent, clear and chilly days persist.

Effects on Daily Life and Industry

Weather with a large diurnal temperature range has effects in several aspects.

Health: The temperature difference between morning and daytime increases the burden on the human body's thermoregulation, raising the risk of colds, vascular diseases, and allergic diseases. In particular, older adults and people with chronic diseases face greater cardiovascular burden.
Agriculture: It directly affects late frost during the flowering period in orchards (frost damage), low-temperature damage to vegetables, and changes in sugar content. On the other hand, an environment with a large diurnal temperature range can be favorable for sugar accumulation in fruits such as apples and grapes.
Energy demand: Both morning heating and daytime cooling become necessary, complicating energy use patterns between seasons.
Transportation and safety: Dawn fog, road freezing (black ice), and slipping accidents due to frost are likely to occur.

Forecasting and Use

The Korea Meteorological Administration (기상청) provides minimum and maximum temperature forecasts and separately emphasizes and informs about 'diurnal temperature range' information. In particular, when the diurnal temperature range is expected to exceed 10°C, it often recommends health management and agricultural preparation. Although the diurnal temperature range is simply defined as the difference between two temperatures, actual perceived temperature varies greatly depending on humidity, wind, and solar radiation, so it is important to interpret it together with perceived temperature information.

Recent Trends

In 2024–2025, variability in the diurnal temperature range due to climate change is drawing attention. With global warming, average temperatures are rising, but as nighttime temperatures tend to rise more than daytime temperatures (nighttime warming), some regions are observed to have a decreasing diurnal temperature range. On the other hand, some analyses suggest that due to drought and aridification, extreme 'clear skies with a large diurnal temperature range' weather occurs more frequently and more intensely in certain seasons.

In addition, in agricultural settings, frost preparation systems using diurnal temperature range forecasts, nighttime temperature control in smart farms, and fruit sugar content prediction models are spreading. In cities, because the heat island effect makes nighttime temperatures in urban cores higher than in outlying areas, the diurnal temperature range tends to be relatively smaller, and the gap in diurnal temperature range between urban and rural areas is also emerging as a research topic.