How to correctly measure the height from the world's oceans. What does "sea level" mean? Dependence of pressure on altitude above sea level

Graph showing fluctuations in sea level 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 conventional reference point. This position is determined by the law of gravity, the Earth's rotational moment, temperature, tides and other factors. There are “instant”, 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, sea level continuously changes. The long-term average sea level is independent of these sea surface fluctuations. The position of the average long-term 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 heights on land are measured. To measure the depths of seas with low tides, this level is taken as zero depth - the water level mark from which depths are measured in accordance with shipping requirements. 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 the zero gauge in Kronstadt. Depths and heights in Western European countries are calculated using the Amsterdam gauge (the level of the Mediterranean Sea is measured using the Marseille gauge). For the USA and Canada, the starting point is located at the Canadian city of Rimouski, and for the PRC - at the city of Qingdao. A tide gauge is used to measure and record fluctuations in sea level.

Since there are many factors influencing global weather changes (for example, Global Warming), predictions and estimates of sea level changes in the near future are not particularly accurate.

Sea surface height

Sea surface height (VMP) is the height (or topography or relief) of the ocean surface. During the day, it is obviously most susceptible to the influence of the tidal forces of the Moon and the Sun acting on the Earth. On large time scales, the PMF is influenced by ocean circulation. Typically, ocean circulation causes topography to deviate 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 gravity field is relatively stable over decades and centuries, ocean circulation plays a larger role in 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 (e.g. TOPEX/Poseidon, Jason 1 satellites) and are used to determine, for example, sea level rise, calculate heat content and geostrophic currents, and detect and study ocean eddies.

How to find out altitude above sea level

In the old fashioned way, the height above sea level can be viewed in special topographic maps, which display all the heights. But there are more modern methods.

You can find out what altitude above sea level using a satellite navigator running on a specific program, for example, Google or Google Earth. First, you need to download one of the applications on your smartphone or computer and, using hints, determine the distance from sea level to the object you need. Working with the programs is very simple: move the cursor over the desired location on the map, and the information is displayed automatically.
Level measurement of a specific area is available on GPS devices. The instruments determine altitudes based on information received from satellites. GPS receivers with a built-in barometer-altimeter have the highest accuracy.
In the search bar of the Yandex browser, enter “altitude above sea level” and the city, country, mountain, etc. you need. This information will be especially useful for travelers who are going to conquer mountain peaks. This way you can find out in advance what heights you will have to overcome and prepare for the ascent.
An application called Altitude, installed on smartphones, knows how to determine altitude. It determines the point above sea level in real time, as well as the speed of movement and other data. The results may not be entirely accurate with a discrepancy of one and a half to two divisions.

Also, measurements of the height of a terrain above sea level can be carried out using an altimeter - an instrument that is used to measure the height of an elevation or point above sea level. Using the altimeter is very simple:

start the device and determine the blood pressure value corresponding to the current weather conditions;
calibrate the device and hold the “Set” button. After this, the device will automatically switch to the desired mode and indicate the altitude pressure at the current time;
reduce the readings to normal using the “Set” button. Having saved the received parameters in the main menu, the altitude above sea level of the desired object will be displayed on the screen.

Altimeter - a device for measuring height above sea level

How to find out the altitude above sea level using one method or another is a purely individual matter, but the altimeter will give more accurate readings compared to mobile applications and GPS.

The highest and lowest land area above sea level

If we talk about the highest and lowest points on a global scale, then Mount Everest, whose real name is Chomolungma, belongs to the first. It is located in the Himalayan mountain system at an altitude of 8848 m above sea level. The second peak of the mountain rises at an altitude of 8760 meters.

Everest is the clear winner among all the mountains on the planet in terms of elevation. Back in the 19th century, geodetic surveyor Radhanath Sikdar from India measured its height. But since then the data has changed, and the mountain turned out to be even higher than originally stated.

The lowest point above sea level is considered not one, but two. The first is on land. This is the Dead Sea coast on the border of Israel and Jordan. The point is located at 417 meters below sea level, but as experts say, this figure increases by 1 meter every year.

The second point is called the Mariana Trench and is located deep under the waters of the Pacific Ocean. This is a bottomless crater, which at its lowest point is more than 11 thousand meters below sea level.

Dependence of pressure on altitude above sea level

At different altitudes, atmospheric pressure will also be different. Many people regularly face the problem of the close relationship between poor health and fluctuations in atmospheric parameters. For this reason, it is impossible to hike in the mountains and fly on airplanes, especially over long distances.

According to the researchers, the dependence of pressure on altitude above sea level is determined by the following indicators: an increase of 10 meters causes a decrease in pressure by one level, i.e. for every 100 m there is an average decrease of 7.5 mm. rt. Art. Until the altitude reaches 500 meters, changes are not felt, but as soon as you rise 5 kilometers, the values will be half the optimal ones, which will affect your well-being. This happens due to diluted air and a decrease in the amount of oxygen necessary for living organisms.

Altitude above sea level... This term is probably known to every schoolchild. We see it quite often in newspapers, on websites, in popular science magazines, and also when watching documentaries.

Now let's try to give it a more precise definition.

Section 1. Altitude. general information

This term should be understood as absolute height or absolute elevation, i.e. a coordinate at which shows at what height relative to sea level this or that object is located.

Two other indicators of the geographic location of an object are longitude and latitude.

Here, for example, is Moscow. The height above sea level of this city is very different: the maximum is 255 m (not far from the Teply Stan metro station), and the minimum - 114.2 m - is located near the Besedinsky bridges, exactly where the Moscow River leaves the city.

In general, if we operate with purely physical measurements, then the height above sea level is nothing more than the vertical distance from, in fact, the most individual object to the average level of the sea surface, which should not be disturbed by tides or waves.

This value can be both positive and negative. Well, everything is relatively simple here: what is located above the sea acquires a “plus” sign, and below, accordingly, a “minus” sign.

By the way, one cannot help but note the fact that with an increase in its value, a decrease in atmospheric pressure is observed.

If we talk about our country, the highest point of land in the Russian Federation is rightfully considered the 5642-meter Elbrus, but the lowest can be called with an absolute height of about 28 m.

Section 2. Altitude. The highest place on the planet

Well, of course, this is Everest - a well-known mountain located in the central part of the Himalaya mountain system, just on the border of two South Asian countries, Nepal and Tibet.

Today its height is 8848 meters. The words “today” are not accidental. According to scientists, the earth's surface is still forming, which is why this peak, although unnoticed, is growing every year.

If you delve into history, you can almost immediately find information that the first brave conquerors of Chomolungma were (New Zealand) and Tenzing Norgay (Nepal). They made their truly heroic ascent on May 28, 1953. Since then, Everest has become a kind of Mecca for hundreds and thousands of rock climbers, mountaineers and other brave adventurers.

Section 3. Altitude. Lowest place on the planet

In this case, things are a little more complicated. The fact is that there are two such points on Earth: one of them - the coast of the Dead Sea - is located on land, and the second has a name and is located deep under the water column of the Pacific Ocean.

Let's look at each of them in more detail.

So, the Dead Sea, as you know, can be found on the border of three countries: Israel, Palestine and Jordan. It is not only the saltiest body of water on the planet, but also the lowest landmass.

Now the water level in it is 427 meters, but this is not the limit, because every year, according to experts, it falls by an average of 1 meter.

Altitude above sea level... Moscow, as mentioned above, ranges from 114 to 255 m. For us, this is, in principle, the norm. Considering that the capital of the Russian Federation can hardly be called very hilly, then this difference is almost impossible to feel.

Now let’s pick up a globe or a physical map of the earth’s surface: somewhere deep, deep in the Pacific Ocean, not far away you can see a mark with the inscription So, it goes under water to a depth of just over 11 km.

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

The other day I was asked, Kirill Yasko writes, at what altitude above sea level are the Crimean cities of Yalta, Alushta and Simferopol. At first I wanted to brush this question aside, but curiosity prompted me to check what the Internet was writing on this topic.

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

To begin with, I went to Wikipedia and made inquiries about what altitude above sea level is and from which sea it should be calculated. Here's 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) is a system of absolute altitudes adopted in the USSR in 1977, which is counted from the ground zero in Kronstadt. The heights of reference geodetic points are measured from this mark, which are marked on the ground with various geodetic signs and plotted on maps. Currently, 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 can I 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 - on average 250 meters above sea level.

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

The answer literally lay on the surface, that is, on the Internet. This is 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 “cosmic” height. There certainly should be a height detection function. I downloaded the Google Earth distribution (free version), installed it and started exploring the menu. There were no altimeters there. Strange... Maybe I should read the certificate? I didn't find it either.

Almost in despair, I suddenly noticed numbers running quickly 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
St. Petersburg - 13
Arkhangelsk - 7
Novgorod - 28
Murom - 105

Altitude above sea level of some cities in Ukraine:

The height of Kyiv above sea level is from 90 (the level of the Dnieper) to 190 (the famous Dnieper steeps) meters.
Kharkov - 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
Yablunytsky pass - 930

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

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