What's the difference between sea water temperature and air temperature in summer?
I. Temperature distribution of surface seawater
Surface water temperature refers to the seawater temperature between the surface of seawater and the depth of 0.5m
1, the distribution of ocean surface water temperature
According to calculation, among the oceans, the annual average surface water temperature is the highest in the Pacific Ocean (19. 1℃), the Indian Ocean (17.0℃) and the Atlantic Ocean (16.9℃). The average surface water temperature of the three oceans is 17.4℃, which is about 3℃ higher than the annual average temperature near the surface (14.3℃).
1) isotherm is generally parallel to latitude, and the water temperature gradually decreases from low latitude to high latitude. Generally speaking, with the latitude increasing by 1, the water temperature drops by about 0.3℃. This shows that the main factor affecting the surface water temperature of the ocean is solar radiation.
2) The surface water temperature in the northern hemisphere is relatively high (average 19.3℃), while that in the southern hemisphere is relatively low (average 16.0℃). This is due to the different distribution of land and sea.
3) The influence of ocean current on water temperature is also remarkable. Wherever the warm current goes, the temperature of seawater rises; Wherever the cold current goes, the temperature of the sea drops. At the junction of cold current and warm current in the western part of the northern hemisphere, the horizontal temperature gradient is large, forming an isothermal line dense area, which is called "ocean front". This phenomenon is particularly evident in the North Atlantic. The existence of "ocean front" not only directly affects the movement of seawater itself, but also plays an important role in the formation of cyclones and fronts. The sky above the ocean front is usually an active area of atmospheric storms.
To sum up, the distribution of ocean surface water temperature mainly depends on three factors: solar radiation, ocean current and land-sea distribution. And in the long run, the annual average temperature of the whole ocean is basically unchanged. This shows that the heat budget of the whole ocean is basically balanced within one year.
2. Distribution of surface water temperature in China offshore.
China offshore is close to the Asian continent, which is greatly influenced by continental climate on the one hand and coastal river runoff on the other, with shallow water depth and complicated surface water temperature distribution. Generally speaking, it has the following two characteristics:
1) The surface water temperature is the lowest in February; In winter, the distribution of surface water temperature is large (the temperature difference is up to 26℃), and the isotherm is almost parallel to the coastline. Compared with latitude, the surface water temperature along the coast is lower than that in the open sea.
2) The surface water temperature is the highest in August; In summer, the surface water temperature distribution is small (the temperature difference is only 3 ~ 4℃); Compared with the same latitude, the surface water temperature along the coast is higher than that in the offshore map.
Second, the vertical distribution of seawater temperature.
The vertical distribution of water temperature is influenced by two factors: one is solar radiation, and the other is the vertical movement of seawater. The general characteristics are: the upper water temperature changes rapidly, while the lower water temperature changes slowly. Between about 45 degrees north and south latitude, the vertical structure of seawater is generally divided into three layers from top to bottom: mixed layer, thermocline and constant temperature layer. The depth of mixed layer is generally 0 ~ 100 m, and the temperature of this layer is very uniform, and the vertical temperature gradient is almost zero. Thermocline is located between the mixed layer and the constant temperature layer, so it is named because of its large temperature gradient. The constant temperature layer is the lowest layer, and its water temperature changes very little, between 2℃ and 6℃, with a difference of only 4℃, so it is also called gradient layer.
Iii. Daily and annual variations of sea surface temperature
The diurnal variation of ocean surface water temperature is relatively small, and the diurnal range is usually less than 0. 4℃, while the surface water temperature in the offshore area varies greatly, reaching or even exceeding 3 ~ 4℃. Generally, the lower the mid-latitude of the ocean, the greater the daily range; The daily amplitude in winter is smaller than that in summer. The highest water temperature generally appears at 2 ~ 3 pm, and the lowest water temperature generally appears at around 6 am, and the specific time varies slightly with latitude and season.
The annual variation of surface water temperature is greater than the daily variation. Annual range in equatorial, tropical and frigid seas is relatively small, generally only 2 ~ 3℃; It is larger in temperate waters, about 5 ~ 10℃. In addition, the annual variation of SST in the northern hemisphere is larger than that in the southern hemisphere, which is mainly related to prevailing winds and differences in land and sea distribution. The monthly average maximum value of surface water temperature in the northern hemisphere appears in August-September, and the minimum value appears in February-March, which is generally 1-2 months behind the annual change of temperature.
Compared with the temperature change, the daily and annual changes of surface water temperature have two characteristics: first, the change range of seawater temperature is small; Second, the change phase of water temperature lags behind that of air temperature, with water temperature higher in winter and lower in summer.
Fourthly, the difference of thermal properties between land and sea and its influence on temperature change.
Sea surface and land surface are two underlying surfaces with very different thermal properties, which are mainly manifested in three aspects: First, the difference of solar radiation penetration ability. The penetration of solar radiation into land is limited to a very thin layer on the surface, but it can reach tens of meters deep in the ocean. The same amount of solar radiation can act on sea surface and land surface, and the change of land surface temperature is greater than that of sea surface. Second, the heat capacity is different. The heat capacity of seawater is much larger than that of soil, so the temperature change of water surface is much smaller than that of soil when the same amount of heat is absorbed. Third, seawater is mobile. Sea water flows in both vertical and horizontal directions, which makes heat evenly distributed in a larger and deeper level, while land does not have this performance.
It can be seen that the land surface temperature is much more sensitive to solar radiation than the sea surface temperature. When absorbing the same heat, the sea surface temperature changes slowly and the land surface temperature changes sharply, so the ocean has great thermal inertia. Under the adjustment of the ocean, the change of seawater temperature is also moderate. For example, the daily and annual temperature differences in the ocean are much smaller than those on land at the same latitude.
V El Niñ o and La Niñ a phenomena
"El Nino refers to the abnormal warming of large areas of seawater in the eastern and central equatorial Pacific. Studies have shown that El Nino phenomenon may be caused by the unstable interaction between the ocean and the atmosphere. When El Nino phenomenon appears, it not only affects the weather in the eastern and central tropical Pacific, but also affects the whole world, causing worldwide weather anomalies, such as heavy rains in some places and severe drought in others. The strongest El Nino phenomenon in the 20th century occurred in 1997 ~ 1998. Under its influence, in the summer of 1998, catastrophic floods occurred in the middle and lower reaches of the Yangtze River, Nenjiang River and Songhua River basins in China.
La Nina phenomenon is an abnormal drop of water temperature in the eastern Pacific near the equator, which is just the opposite of El Niñ o phenomenon, also known as anti-El Niñ o phenomenon. La Nina and El Niñ o have become the strongest signals to predict global climate anomalies.
The sea water temperature and temperature difference you mentioned in summer can't give a fixed value, and the factors that cause the sea water temperature change are more complicated. The above is a more detailed answer.