(The following is the description of the first volume of the geography book of Senior One in People's Education Edition)
In tropical or subtropical oceans where the sea surface temperature exceeds 26℃, due to the high temperature near the ocean surface, a large amount of air expands and rises, which reduces the air pressure near the ocean surface, and the peripheral air continuously flows in and rises. Affected by the geostrophic force, the inflowing air rotates. The rising air expands and cools, and when the water vapor in it cools and condenses into water droplets, it will release heat and promote the rising of the lower air. In this way, the air pressure near the ocean surface drops lower, and the air rotates more violently, eventually forming a typhoon.
Typhoon structure Typhoon structure From the perspective of typhoon structure, the appearance of such a behemoth must have unique conditions.
First of all, there must be a vast atmosphere with high temperature and high humidity. The temperature and humidity of the bottom atmosphere on the tropical ocean surface are mainly determined by the sea surface temperature, and typhoons can only form on the warm ocean surface where the sea surface temperature is higher than 26℃-27℃ and the sea surface temperature is higher than 26℃-27℃ within 60 meters.
Second, there should be an initial disturbance that the lower atmosphere converges to the center and the upper atmosphere diffuses outward. Moreover, the divergence of the upper layer must exceed the convergence of the lower layer in order to maintain enough updraft and continuously strengthen the disturbance of the lower layer;
3. The difference of vertical wind speed should not be too big, and the relative motion of the upper and lower air is very small, so that the latent heat released by water vapor condensation in the initial disturbance can be stored in the air column in the typhoon eye area, forming and strengthening the typhoon warm center structure;
Fourth, there must be enough geostrophic deflection, and the earth's rotation is conducive to the formation of cyclonic vortices. The geostrophic deflection force is close to zero near the equator and increases at the north and south poles. Typhoons basically occur on the ocean surface about 5 latitudes from the equator. Flood: Flood refers to the disaster that the runoff flowing into the river exceeds its flood discharge capacity due to concentrated rainstorm or long-term rainfall, overflows the bank or causes dam break, resulting in flooding.
Classification: Rain and flood: In the middle and low latitudes, floods are mostly caused by rain. The river basin is large and controlled by river networks, lakes and reservoirs. When the flood peaks formed by different rainfall of different tributaries converge to the main stream, the flood processes of tributaries often overlap with each other, forming a flood peak with relatively long fluctuation. The basin area of a small river and the storage capacity of the river network are small, and a rain will form a flood peak that fluctuates rapidly. Rain and flood can be divided into two categories. Flash flood is a sudden turbulence, rushing along the river and destroying everything. Mountain torrents are deadly destructive, and the other is slow-rising floods.
Mountain torrent: In the ravine, due to the steep slope of the ground and river bed, the runoff and confluence are faster after rainfall, forming a rapidly fluctuating flood peak.
Debris flow: Rainfall causes the slope or bank wall to collapse, and a large amount of mud and stones are released with the water flow.
Snowmelt flood: In high latitude and cold areas, the snow is thick in winter, and when the temperature rises sharply in spring, a large amount of snow melts.
Ice flood: In the middle and high latitudes, rivers (reaches) flowing from low latitudes to high latitudes may form ice plugs or ice dams in winter and spring due to the difference in freezing or thawing periods between upstream and downstream.
Dam-break flood: When the reservoir burst, a large amount of water stored in it suddenly leaked out, which led to a sharp increase in water flow in the downstream reach and even a flood, which became a phenomenon that standing waves pushed downstream. When glaciers block the river, raise the water level, and then suddenly burst, huge soil landslides caused by earthquakes or other reasons block the river, causing the upstream water level to rise sharply. When the blocked dam is washed away by the current, this kind of flood also forms in the downstream area.
Lake flood: due to the exchange of water between rivers and lakes, strong winds on the lake surface or both, lake floods will occur. In a lake with steam huff and puff, when the lake water flows into the lake and is seriously supported by the river flood, the water level of the lake often rises sharply. Due to the prevailing wind, the lake moves and produces wind-driven currents, sometimes up to 5 ~ 6 m, such as Lake Superior, Lake Michigan and Lake Huron in North America.
Astronomical tide: Long-term fluctuation of sea water caused by tidal force. The highest position in a sea level fluctuation process is called high tide, the lowest position is called low tide, and the water level difference between adjacent high tides and low tides is called tidal range. The maximum tidal range in Fendi Bay is 19.6m, and that in Ganpu, Hangzhou Bay, China is 8.9mm.
Tide: Abnormal fluctuation of water surface caused by strong weather systems such as typhoon, extratropical cyclone, cold peak strong wind and sudden change of air pressure. It and the accompanying wind and waves will cause the water level to rise, which is also called surge to increase water.
Tsunami: A huge wave caused by an underwater earthquake or volcanic eruption.
Flood refers to extra-large runoff. This kind of runoff is often flooded because the river can't accommodate it. According to the water source and occurrence time of floods, floods can generally be divided into two types: spring snowmelt floods and rainstorm floods.
General flood: the return period is less than 10 year.
Great flood: return period 10 ~ 20 years.
Great flood: the return period is 20-50 years.
Extraordinary flood: the return period exceeds 50 years.