Which sea is considered height. What is altitude above sea level? Highest and lowest piece of land above sea level

Graph showing fluctuations in the level of the World Ocean over the past 550 million years

Sea level- the position of the free surface of the World Ocean, measured along a plumb line relative to some conditional reference point. This position is determined by the law of gravity, the moment of rotation of the Earth, temperature, tides and other factors. There are "instantaneous", tidal, average daily, average monthly, average annual and average long-term sea levels.

Under the influence of wind waves, tides, heating and cooling of the sea surface, fluctuations in atmospheric pressure, precipitation and evaporation, river and glacial runoff, the sea level is constantly changing. The mean long-term sea level does not depend on these fluctuations of the sea surface. The position of the mean long-term sea level is determined by the distribution of gravity and the spatial unevenness of hydrometeorological characteristics (water density, atmospheric pressure, etc.).

The mean long-term sea level constant at each point is taken as the reference level from which land heights are measured. To measure the depths of seas with low tides, this level is taken as the zero depth - the water level mark, from which the depths are measured in accordance with the requirements of navigation. In Russia and most other countries of the former USSR, as well as in Poland, the absolute heights of points on the earth's surface are measured from the average long-term level of the Baltic Sea, determined from zero footstock in Kronstadt. Depths and heights in Western European countries are calculated using the Amsterdam footstock (the level of the Mediterranean Sea is measured using the Marseille footstock). For the USA and Canada, the starting point is at the Canadian city of Rimouski, and for the PRC, at the city of Qingdao. A tide gauge is used to measure and record sea level fluctuations.

Since there are many factors that affect global weather changes (for example, Global warming), predictions and estimates of ocean level changes in the near future are not particularly accurate.

sea ​​surface height

sea ​​surface height (VMP) is the height (or topography or topography) of the ocean surface. During the day, it is obviously most susceptible to the influence of the tidal forces of the Moon and the Sunacting on the Earth. On large time scales, the PMF is affected by ocean circulation. Typically, the circulation of the ocean causes deviations of the topography from the mean level by a maximum of ±1 m. The slowest changes in the PMF occur due to changes in the Earth's gravitational field (geoid) as a result of the redistribution of continents, the formation of seamounts, and the like.

Because the Earth's gravitational field is relatively stable over decades and centuries, ocean circulation plays a larger role in the observed PMF variability. Seasonal changes in heat distribution and wind forcing affect ocean circulation, which in turn affects the PMF. PMF variations can be measured using satellite altimetry (eg TOPEX/Poseidon, Jason 1) and are used to determine, for example, sea level rise, heat content and geostrophic currents, and detection and study of ocean eddies.

see also

• Regression and Transgression of the sea - local or global depressions and rises in sea level in the geological past.
• Modern sea level rise

Sea level, the position of the free surface of the water of the seas and oceans, measured along a plumb line relative to the conventional reference point. There are “instantaneous”, tidal, average daily, average monthly, average annual, and average long-term sea levels. Under the influence of wind waves, tides, heating and cooling of the sea surface, fluctuations in atmospheric pressure, precipitation and evaporation, and river and glacial runoff, sea levels change continuously. The long-term mean sea level does not depend on these oscillations of the sea surface. The position of the long-term mean sea level is determined by the distribution of gravity and the spatial unevenness of hydrometeorological characteristics (water density, atmospheric pressure, etc.). The average long-term sea level, constant at each point, is taken as the initial level, from which the heights on land are measured. To measure the depths of seas with low tides, this level is taken as the zero depth - the water level mark, from which the depths are measured in accordance with the requirements of navigation. In the USSR, the absolute heights of points on the earth's surface are counted from the long-term average level of the Baltic Sea, determined from the zero of the footstock in Kronstadt.

Lit.: Duvanin A.I., Sea level, L., 1956; Duvanin A. I., Kalinin G. P., Klige R. K., On long-term fluctuations in the level of the oceans, some seas and lakes, “Bulletin of Moscow State University. Series 5. Geography, 1975, No. 6.

Great Soviet Encyclopedia M.: "Soviet Encyclopedia", 1969-1978

How to determine the height of a city above sea level?

The other day I was asked, Kirill Yasko writes, about the altitude at which the Crimean cities of Yalta, Alushta and Simferopol are located. At first I wanted to dismiss this question, but curiosity prompted me to check what the Internet writes on this topic.

It turned out that it is almost impossible to find references to the height of most cities of the former Soviet Union on the net. Struck by this fact, I decided to correct the situation.

To begin with, I climbed into Wikipedia and made inquiries about what the height above sea level is and from which sea it should be considered. Here is what they write there:

Height above sea level- a coordinate in three-dimensional space (the other two are latitude and longitude), showing at what level, relative to the sea level taken as zero, this or that object is located.

Baltic height system(BSV) - the system of absolute heights adopted in the USSR in 1977, which is counted from zero footstock in Kronstadt. From this mark, the heights of reference geodetic points are counted, which are marked on the ground with various geodetic signs and plotted on maps. At present, the BSV is used in Russia and a number of other CIS countries.

In theory, everything is clear - you need to take a detailed topographic map and see what heights are indicated there. But where did she get this card?

The first thing that came to mind was to look into OziExplorer. This is a special program for working with GPS (satellite navigator). One of its functions allows you to determine the height simply by pointing the cursor at a place on the map. With her help, I easily found out that Alushta is located at altitudes from 0 to 130 meters above sea level. Yalta - from 0 to 200 meters, Sevastopol - from 0 to 100, Simferopol - an average of 250 meters above sea level.

However, this method is not very versatile. After all, the question still remains “where to get a map?”, This time digitized. I had maps of Crimea, but it didn’t work out with the rest of the world ...

The answer literally lay on the surface, that is, on the Internet. It's not the first year that the service has been operating there. Google Earth- a kind of digital globe, glued together from photographs of the earth's surface from a "space" height. There must be a function for determining the height. I downloaded the Google Earth distribution (free version), installed it and started exploring the menu. There were no altimeters. Strange ... Maybe you need to read the help? Didn't find it either.

Already almost desperate, I suddenly noticed numbers running fast at the bottom of the screen. Eureka! This was the altimeter.

To celebrate, I began to run around the map and measure the height of all the cities in a row.

• The height of Yekaterinburg above sea level is 250 meters.
• The height of Moscow above sea level is 130 meters.
• Saratov - 40
• Makhachkala - 15
• Krasnoyarsk - 140
• Perm - 150
• Chelyabinsk - 250
• Ufa - 125
• Kazan - 90
• Nizhny Novgorod - 70
• Ivanovo - 130
• Yaroslavl - 98
• Voronezh - 104
• Petersburg - 13
• Arkhangelsk - 7
• Novgorod - 28
• Murom - 105

Altitude above sea level of some cities of Ukraine:

• The height of Kiev above sea level is from 90 (the level of the Dnieper) to 190 (the famous Dnieper steeps) meters.
• Kharkiv - 122
• Chernivtsi - 240
• Khmelnitsky - 299
• Ternopil - 336
• Vinnitsa - 294
• Cherkasy - 80
• Krivoy Rog - 85
• Zaporozhye - 75
• Kherson - 50
• Donetsk - 241
• Dnepropetrovsk - 68
• Sumy - 125
• Poltava - 150
• Chernihiv - 117

In the western part of Ukraine, I was interested in the heights of such settlements:

• Lviv - 270
• Ivano-Frankivsk - 343
• Uzhgorod - 187
• Mukachevo - 181
• Rakhiv - 430
• Yasinya - 650
• Yablonitsky pass - 930

I hope you understand that all the data received is not too accurate. Google Earth is not a professional tool with guaranteed accuracy and reliably known errors. She has very different goals.

In addition, the very term "height of the city above sea level" is very conditional. After all, a city is not a point, but a huge object, different areas of which have different heights.

ocean surface level is the free water surface of the oceans and seas, close to the geoid shape (Fig. 1).

Rice. 1. Ocean surface level

The reference level of the ocean is the standard from which the absolute height of the land surface and the depth of the seas are measured. In our country, this is the average long-term level of the Baltic Sea near the city of Kronstadt (Baltic height system).

Level fluctuations can be periodic - These are daily fluctuations due to tides and non-periodic- arising from tropical cyclones, tsunamis, etc.

Periods of fluctuations in the level of the World Ocean are short(high-low tide after 6 hours 12.5 minutes) and lengthy or century old(hundreds of years) (Fig. 2).

Rice. 2. Ocean level fluctuations over the past 200 thousand years

Secular changes occur for a number of reasons, such as changes in the volume of water in the ocean or changes in ocean capacity. The first of them occurred during glaciations, when a huge mass of water in the form of ice was conserved on land, and the ocean level dropped by 100-200 m. During the interglacial period, when water entered the ocean as a result of ice melting, the ocean level rose by 20-30 m. According to calculations, as a result of climate warming on Earth, a further increase in the level of the World Ocean by about 30 cm by the middle of the 21st century is possible. The second type of secular fluctuations in the level of the World Ocean is caused by tectonic disturbances of the ocean floor, which entails a change in the volume of the ocean's capacity.