The fog dissipates when the sun rises because the solar radiation warms the air and the earth's surface, causing an increase in temperature and faster evaporation of the water droplets that make up the fog.
In the early morning, the rays of the sun gently warm the air and the surface of the earth, gradually triggering the evaporation of the fine water droplets floating in the air. The solar heat provides energy to the water molecules, allowing them to slowly transition from a liquid state to a gaseous state. As a result, the tiny droplets making up the fog begin to disappear, visibility increases, and the previously blurred landscape gradually regains its sharp contours. The higher the sun rises in the sky, the faster this process accelerates, progressively transforming the thick mist into a fine, almost invisible vapor.
During the night, tiny droplets of water float in the air and form fog. When the sun arrives, it heats these small drops, providing them with the energy needed to transition from a liquid state to a gaseous state: this is evaporation. As they heat up, these droplets become lighter, mix with the surrounding warm air, and gradually disperse. Little by little, the humidity contained in the fog dilutes into the atmosphere until it completely disappears. The phenomenon largely depends on the temperature and somewhat on the wind: the milder and slightly agitated the air, the faster it all disappears.
When the temperature rises, the air gradually warms up and starts to absorb moisture more easily. As a result, the small water droplets that form fog begin to evaporate into invisible vapor, gradually disappearing. In short, the fog that seemed dense and persistent just a few minutes earlier eventually evaporates as soon as the sun appears, thanks to the rapid warming of the ground and the surrounding air. This phenomenon of morning warming disrupts the delicate balance between condensation and evaporation, clearly favoring evaporation. The hotter it gets, the faster it accelerates. It's exactly the same principle as a puddle of water disappearing on a hot sidewalk in full sunlight (though less obvious, of course).
The wind is a major player as it mixes humid air with dry air, which greatly helps to clear the fog. The stronger it blows, the faster the fog dissipates. Conversely, when the air is very calm, the fog can linger longer close to the ground. The humidity of the surrounding air also plays a significant role: if the air is already saturated with moisture, then the fog tends to stick around, even with the sun warming it up. Additionally, a thin layer of clouds at night limits the formation of fog, making its morning dissipation generally quicker.
Some regions, such as the California coast in the United States, regularly benefit from what is known as 'coastal fog,' which plays a positive ecological role by providing moisture and coolness to specific flora and fauna.
The thickest fog ever recorded occurred in London in 1952. This phenomenon, known as 'The Great Smog,' lasted for several days and caused hundreds of deaths due to extreme air pollution.
The whitish color of the fog is due to the scattering of light by tiny water droplets suspended in the air; it is also this scattering that significantly reduces visibility.
In aviation, fog is a critical weather phenomenon: its presence necessitates the use of specific systems such as instrument approaches to land safely.
Some regions favor the formation of fog due to geographical elements (valleys, proximity to bodies of water or seas), climatic factors (low air circulation, significant temperature variations between day and night), or human activities such as pollution.
Sure! Here’s the translation: "Yes, even without the direct intervention of the sun, other conditions such as a light breeze or a variation in ambient humidity allow the fog to disperse. However, the heat and brightness provided by the sun usually accelerate its dissipation."
Several factors may extend its duration: persistent low temperatures, very high humidity, a lack of wind, or a particular geographic context, such as a valley, which prevents the rapid movement of air masses.
The difference between fog and mist essentially lies in visibility. Fog is defined as having horizontal visibility of less than one kilometer. Conversely, if the visibility is greater than one kilometer, it is referred to as mist.
In the morning, temperatures are generally the coolest of the day. The humidity in the air can then condense into tiny visible droplets, forming fog. This fog gradually dissipates at sunrise as the temperature rises.
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