Sea fog formation conditions

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Sea fog is a weather phenomenon in which water vapor condenses in the lower atmosphere on the sea surface. Because it can reflect light of various wavelengths, it often appears milky white. The formation of fog requires two different physical processes: the condensation of water vapor and the accumulation of condensed water droplets (or ice crystals) at low altitude. Two conditions must be met in these two processes: one is that there must be a condensation nucleus during condensation, such as salt particles or dust, otherwise it will be very difficult for water vapor to condense; the other is that water droplets (or ice crystals) must be suspended in the In the offshore surface layer, horizontal visibility is less than 1 km.

For water vapor to condense in the atmosphere, there must be sufficient water vapor. Although a large amount of water vapor evaporates day and night in the vast ocean, condensation does not occur every day. This is because once the atmosphere reaches saturation, evaporation will immediately stop. If the water vapor in the air no longer increases, it will be difficult to reach a supersaturated state, causing water vapor to condense. Only when the temperature of the water surface is much higher than the air temperature, can the water vapor on the warm water surface continue to evaporate and continuously diffuse into the cold air layer, keeping it in a supersaturated state. The condensation process can continue and a transpiration-like fog can appear. It's called advection vapor fog.

Another way of condensation relies on lowering the temperature of water vapor to achieve the appearance of supersaturated water vapor. When the warm and moist air flows through the cold sea surface, it transfers heat to the cold sea surface and lowers its own temperature. At this time, the saturated water vapor becomes supersaturated as the temperature decreases, and condensation occurs. This condensation phenomenon is common in areas where sea fog occurs, and is often called advection cooling fog. The sea fog that appears in my country's sea areas is mainly this kind of advection cooling fog. The sea fog that appears in many famous sea fog areas in the world is also mostly caused by advection cooling fog. There are many types of sea fog that are formed due to the cooling of water vapor to a supersaturated state. For example, on the sea surface covered with ice and snow at high latitudes, due to the radiative cooling on the ice and snow surface (especially at night), ice surface radiation fog can often form; in addition, the sloping effect of the island topography often causes the warm air blowing from the sea surface to face the wind on the island. If the surface rises, it is possible that the rise and fall in temperature will promote condensation into terrain fog. Sea fog can be divided into 4 types due to different causes.

The condensation of water vapor is an important condition for the formation of sea fog. How to keep the condensed water vapor in the low altitude layer without falling is another indispensable condition for the formation of sea fog. To keep condensed water vapor accumulating at low altitudes, the condensed water droplets (water droplets or ice crystals) need to be small enough. The measured diameter of fog droplets is generally about 10 microns, which is about 1,000 times smaller than ordinary raindrops. Therefore, the speed of fog droplets is very slow, only about 1 centimeter per minute. It seems to be in a state of accumulation and motionlessness, so there is fog. When the wind speed is generally very small, the mist droplets are quickly blown away or evaporated when the wind speed is high.

The analysis of sea fog droplet residues found that 50% of the condensation nuclei are combustion nuclei, 40% are salt particles, and 10% are soil particles. Why is there such a ratio? After analysis These burning nuclei are all very small, with a radius of about 1 micron, while the radius of most salt particles is between 2-4 microns. In addition, there is often a thin film of hygroscopic material on the surface of the burning nuclei, which is conducive to condensation.

Sea fog is a weather phenomenon in which water vapor condenses in the lower atmosphere on the sea surface. Because it can reflect light of various wavelengths, it often appears milky white. The formation of fog requires two different physical processes: the condensation of water vapor and the accumulation of condensed water droplets (or ice crystals) at low altitude. Two conditions must be met in these two processes: one is that there must be a condensation nucleus during condensation, such as salt particles or dust, otherwise it will be very difficult for water vapor to condense; the other is that water droplets (or ice crystals) must be suspended in the In the offshore surface layer, horizontal visibility is less than 1 km.

For water vapor to condense in the atmosphere, there must be sufficient water vapor. Although a large amount of water vapor evaporates day and night in the vast ocean, condensation does not occur every day. This is because once the atmosphere reaches saturation, evaporation will immediately stop. If the water vapor in the air no longer increases, it will be difficult to reach a supersaturated state, causing water vapor to condense. Only when the temperature of the water surface is much higher than the air temperature, can the water vapor on the warm water surface continue to evaporate and continuously diffuse into the cold air layer, keeping it in a supersaturated state. The condensation process can continue and a transpiration-like fog can appear. It's called advection vapor fog.

Another way of condensation relies on lowering the temperature of water vapor to achieve the appearance of supersaturated water vapor. When the warm and moist air flows through the cold sea surface, it transfers heat to the cold sea surface and lowers its own temperature. At this time, the saturated water vapor becomes supersaturated as the temperature decreases, and condensation occurs. This condensation phenomenon is common in areas where sea fog occurs, and is often called advection cooling fog. The sea fog that appears in my country's sea areas is mainly this kind of advection cooling fog. The sea fog that appears in many famous sea fog areas in the world is also mostly caused by advection cooling fog. There are many types of sea fog that are formed due to the cooling of water vapor to a supersaturated state. For example, on the sea surface covered with ice and snow at high latitudes, due to the radiative cooling on the ice and snow surface (especially at night), ice surface radiation fog can often form; in addition, the sloping effect of the island topography often causes the warm air blowing from the sea surface to face the wind on the island. If the surface rises, it is possible that the rise and fall in temperature will promote condensation into terrain fog. Sea fog can be divided into 4 types due to different causes.

The condensation of water vapor is an important condition for the formation of sea fog. How to keep the condensed water vapor in the low altitude layer without falling is another indispensable condition for the formation of sea fog. To keep condensed water vapor accumulating at low altitudes, the condensed water droplets (water droplets or ice crystals) need to be small enough. It has been measured that the diameter of fog droplets is generally about 10 microns, which is about 1,000 times smaller than ordinary raindrops. Therefore, the speed of fog droplets is very slow, only about 1 centimeter per minute. It seems that they are not accumulating, so there is fog. When the wind speed is generally very small, the mist droplets are quickly blown away or evaporated when the wind speed is high.

The analysis of sea fog droplet residues found that 50% of the condensation nuclei are combustion nuclei, 40% are salt particles, and 10% are soil particles. Why is there such a ratio? After analysis These burning nuclei are all very small, with a radius of about 1 micron, while the radius of most salt particles is between 2-4 microns. In addition, there is often a thin film of hygroscopic material on the surface of the burning nuclei, which is conducive to condensation.

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