What month does the fog at sea usually appear? Why? Thank you, everyone.

Sea fog is a dangerous weather phenomenon, which occurs all year round. It is like a gray veil hanging over the sea or low altitude along the coast, which brings great trouble to maritime traffic and operation, and can be called a "silent killer". 60% ~ 70% of ship collisions at sea are caused by sea fog. Sea fog is formed under specific marine hydrometeorological conditions. The lower atmosphere is in a stable state. Due to the increase of water vapor and the decrease of temperature, the air near the sea surface is gradually saturated or supersaturated. At this time, water vapor condenses into tiny water droplets, ice crystals or their mixture with hygroscopic particles such as tiny salt particles as the core, and is suspended at a low altitude of several meters, dozens of meters or even hundreds of meters above the sea surface. When the number of condensed water drops increases, fog is formed, which makes the sky gloomy and further reduces visibility. Fog composed of ice crystals is called ice crystal fog. According to the formation characteristics of sea fog and the characteristics of marine environment, sea fog can be divided into four types: advection fog, mixed fog, radiation fog and topographic fog. 1. advection fog, advection fog is a fog generated when air flows horizontally on the sea surface. When warm and humid air moves over the cold sea surface, the bottom layer cools and water vapor condenses to form advection cooling fog. This kind of fog has a large thickness, a wide range and a long duration, and is mostly produced in cold areas. Spring is more common in the waters near the Thousand Islands in the Pacific Ocean and Newfoundland in the Atlantic Ocean. In spring and summer in China, the sea fog in the East China Sea and the Yellow Sea mostly belongs to this category. The fog produced by cold air flowing through the warm sea surface is called advection evaporation fog, which mostly appears in the high latitude sea surface in cold season. Double mixed fog mixed fog is the fog produced by mixing two kinds of humid air with large temperature difference in the ocean. Due to storm activity, air with humidity close to or reaching saturation is generated, which is mixed with cold air from high latitudes in cold season to form mixed fog in cold season and mixed with warm air from low latitudes in warm season to form mixed fog in warm season. Third, radiation fog When the sea surface is covered by a layer of suspended matter or sea ice, the fog generated by radiation cooling at night is called radiation fog. Appears around dawn and gradually dissipates after sunrise. In coastal areas, harbors and high-latitude inland seas, the fog generated by oil pollution or impurities covering the sea surface is called floating film radiation fog; The fog formed on the salt particle layer accumulated at low altitude due to seawater evaporation is called salt layer radiation fog; Fog formed on the ice-covered sea surface or the surface of huge icebergs in high latitudes is called ice radiation fog. 4. Terrain fog In the process of climbing to islands and coasts, the fog formed by the cooling and condensation of warm and humid air on the sea surface is called terrain fog. For example, the southeast slope of Laoshan Mountain in Qingdao and Putuo Mountain in Zhoushan Islands are often foggy in spring and summer. In fact, the formation process of any kind of sea fog is not single, but the result of the comprehensive action of many factors. Advection cooling fog is the most common in the offshore of China. In spring, the fog season in Zhixia is extended from south to north: the fog in the South China Sea mostly appears from February to April, mainly in the coastal areas of Guangdong, Guangxi and Hainan, with the most in the eastern part of Leizhou Peninsula; The sea fog in the East China Sea is mostly from March to July, especially from the Yangtze River estuary to Zhoushan Islands and the northern mouth of the Taiwan Province Strait. The foggy season in the Yellow Sea is from April to August, and the whole sea area is foggy. The sea area near Chengshantou is commonly known as "fog cave", with an average of nearly 83 days of fog every year. Sea fog is common in Bohai Sea from May to July, more in the east than in the west, and concentrated in Liaodong Peninsula and the northern coast of Shandong. Every spring in bloom, when the coastal areas in China turn from cold to warm, there will often be foggy and drizzly weather, and the visibility will be obviously reduced, even several meters apart, which is also commonly known as sea fog. Sea fog is a weather phenomenon of water vapor condensation in the lower atmosphere of the sea surface. Because it can reflect light of various wavelengths, it is often milky white. The formation of fog has gone through two different physical processes: water vapor condensation and the accumulation of condensed water droplets (or ice crystals) at low altitude. In these two processes, there are two conditions: first, there must be condensation nuclei, such as salt particles or dust, otherwise water vapor condensation is very difficult; The other is that water droplets (or ice crystals) must be suspended on the offshore surface, so that the horizontal visibility is less than 1 km. In order to condense water vapor in the atmosphere, it is necessary to have enough water vapor. Although a large amount of water vapor evaporates day and night in the vast ocean, condensation does not occur there every day. This is because once the atmosphere is saturated, evaporation will stop immediately, and it is difficult to achieve supersaturation without increasing the water vapor in the air, which will cause water vapor condensation. Only when the water surface temperature is much higher than the air temperature, it is possible for the warm water surface to continuously evaporate water vapor and diffuse it into the cold air layer to keep it supersaturated, and the condensation process can continue to produce transpiration fog, which is called advection steam fog. Another condensation method is to reduce the temperature of water vapor, so as to achieve the appearance of supersaturated water vapor. When the warm and humid airflow passes through the cold sea surface, it transfers heat to the surface of Leng Hai and lowers its temperature. At this time, saturated water vapor will be saturated with the decrease of temperature, and condensation will occur. This condensation phenomenon is common in the area where sea fog occurs, and is usually called advection cooling fog. The sea fog in China's sea areas is mainly caused by this advection cooling fog, and most of the sea fog in many famous sea fog areas in the world is also caused by advection cooling fog. There are many kinds of sea fog, all of which are formed by supersaturation of water vapor due to cooling. For example, on the sea surface covered with snow and ice at high latitudes, due to the radiation cooling of the snow and ice surface (especially at night), ice radiation fog can often be formed; In addition, the oblique uplift of the island topography often lifts warm air blown from the sea surface to the windward side of the island, which may condense into topographic fog due to the uplift and cooling. Sea fog can be divided into four types for different reasons. Water vapor condensation is an important condition to produce sea fog. How to keep the condensed water vapor in the lower layer from falling is another indispensable condition for the formation of sea fog. In order to keep the condensed water vapor accumulated at low altitude, it is necessary that the water droplets (water droplets or ice crystals) condensed by water vapor are small enough. The measured droplet diameter is generally around 10 micron, which is about 1000 times smaller than the usual raindrops. Therefore, the picking speed of fog is very slow, only about 1 cm per minute, which seems to be in a state of stationary accumulation. Therefore, when there is fog, the wind speed is generally very small, and when the wind speed is high, the droplets are quickly blown away or evaporated. According to the analysis of sea fog droplet residue, it is found that burning nuclei account for 50%, salt particles account for 40% and soil particles account for 10%. Why is there such a ratio? After analysis, these combustion nuclei are very small, with a radius of about 1 micron, while the radius of most salt particles is between 2 and 4 microns. In addition, the surface of the combustion core is often covered with a layer of hygroscopic substances, which is conducive to condensation.