Hainan issued a Class IV storm surge warning. What is a storm surge?

Storm surge, also known as storm surge, is caused by strong climatic systems such as tropical cyclone, temperate cyclone, cold front and strong wind, and sudden pressure change, and is also known as storm surge, storm tsunami, meteorological tsunami or tidal wave. This kind of storm surge disaster is called "current", "transgression", "tsunami" and "tidal wave" in China historical documents.

The spatial range of storms is generally from tens of kilometers to thousands of kilometers, and the time scale or period is 1- 100 hour, which is between the earthquake tsunami and the low-frequency astronomical tide wave. However, sometimes the affected area of storm surge will move with the movement of atmospheric disturbance factors, so a storm surge process sometimes affects one or two kilometers of coastline and lasts for several days.

Basic cause of formation

Wave is a serious natural disaster, which combines strong wind and high tide level to cause floods in some areas, thus causing major disasters. The storm will cause the tide level in the affected sea area to greatly exceed the normal tide level. When the storm surge coincides with the astronomical climax affecting the sea area, it will lead to the surge of water level and the influx of seawater into the inland. The height of the storm is directly proportional to the pressure difference between the typhoon or low pressure center and the periphery. When the central air pressure decreases by 1 hectopascal, the sea surface rises by about 1 cm.

Whether the storm surge can cause disasters mainly depends on whether its maximum storm position overlaps with the astronomical tide high tide level, especially with the astronomical tide high tide level. The socio-economic conditions of the affected areas, especially the coastal areas (disaster-bearing bodies) certainly depend on the geographical location, coastal morphology, coastal and seabed topography of the affected areas. If the highest tide level is superimposed with the high tide level in astronomical tides, it will cause catastrophic tidal disasters. It is true that if the tide level of the storm is high, even if there are no big waves, it will cause serious tides.

Formation condition

Dominant terrain, that is, the coastal or bay terrain is trumpet-shaped, and the beach is gentle, so that the waves go straight to the top of the bay and are not easy to spread around. The strong wind blowing ashore, due to the influence of strong wind and sudden change of sea surface pressure, caused the waves to rise sharply.

In the astronomical tide on the first and fifteenth day of the lunar calendar, it is the main body of storm surge. Destructive storm surges are formed under the constant impact of astronomical tides and outward winds.

General characteristics

Storm refers to the abnormal rise of sea level caused by tropical cyclones (typhoons, hurricanes) and temperate cyclones (cold waves). Wave fluctuation is usually a comprehensive feature of sea surface changes caused by long-wave vibrations such as astronomical tide, storm surge and tsunami, such as wave fluctuation. The universal tide gauge filters out the sea surface fluctuations caused by waves with short wave periods of several seconds. If the storm surge coincides with the astronomical high tide period (especially the astronomical high tide period), then the storm surge will be mixed with strong winds and waves, which will often make the tides in the coastal areas affected by it soar, and even the tides will destroy dikes and seawalls, erode docks, factories and urban and rural areas, and prevent people and animals from escaping, resulting in great disasters.