It is a common belief that the hottest part of the day occurs at noon when the sun is at its highest point in the sky. While the sun’s rays are most direct and intense around midday, this assumption about peak temperature is often incorrect. The actual warmest period of the day typically arrives later, influenced by Earth absorbs and releases solar energy.
The Hottest Time of Day
The hottest part of the day generally falls in the mid-to-late afternoon. This usually occurs between 2 PM and 5 PM, though the precise timing can vary based on geographical location and season. Tropical regions might experience peak temperatures earlier, often between 1 PM and 3 PM, due to high solar absorption. In temperate zones, the peak can shift to later in the afternoon, between 3 PM and 5 PM.
The Science Behind the Delay
The delay between the sun’s peak intensity at solar noon and the day’s highest temperature is explained by a concept known as thermal inertia. Earth’s surface absorbs solar radiation, and it takes time for this absorbed energy to translate into a rise in air temperature.
Similar to heating a pot of water, it takes time for the water to warm up after the burner is turned on. The Earth’s surface and the air above it require several hours to reach their maximum temperature as they slowly release the accumulated solar energy.
Temperatures climb as long as incoming solar radiation exceeds heat loss to the atmosphere. Peak temperature is reached when these rates become equal, often hours after solar noon.
Other Influencing Factors
Several environmental and geographical elements can modify the timing and intensity of the hottest part of the day. Cloud cover, for instance, can significantly reduce incoming solar radiation, leading to lower peak temperatures. Clouds can also trap heat during the night, reducing the daily temperature range.
High humidity levels can absorb and re-emit infrared radiation, reducing the diurnal temperature range by trapping heat. Wind can prevent heat from accumulating by mixing warmer air near the surface with cooler air from higher altitudes.
Proximity to large bodies of water can moderate temperatures due to water’s high thermal inertia, leading to less extreme daily temperature fluctuations. The urban heat island effect, caused by heat absorption by concrete and asphalt, can lead to higher temperatures in cities compared to rural areas.