Дата публикации: 01 ноября 2021
Автор(ы): Albert BONDARENKO →
Публикатор: Научная библиотека Порталус
Рубрика: ЭКОЛОГИЯ →
Источник: (c) Science in Russia, №2, 2013, C.28-31 →
Номер публикации: №1635766382
Albert BONDARENKO, (c)
by Albert BONDARENKO, Dr. Sc. (Geogr.), Senior Research Assistant of the RAS Institute of Water Problems
It would seem that waves in the ocean and in the atmosphere of our planet outwardly have little in common. But under closer examination it turns out that they can have similar manifestations and properties. Mechanisms with alike regularities triggered development of such different atmospheric anomalies of the summer of 2010 as extreme heat in Russia and catastrophic floods in Pakistan. Studies of wave processes and streams in the World Ocean help scientists understand these acts of nature better.
People all remember the extraordinary summer of 2010 in the European part of Russia: July and early August were extremely hot, there were no rains, we evidenced mass fires in forests and peatbogs that resulted in smogs even in the cities. Nothing similar has ever been registered for the whole history of meteorological observations. According to meteorological reports, a vast anticyclone-an atmospheric phenomenon characterized by high atmospheric pressure and low humidity-hang over the European part of our country. Normally, anticyclones pass this territory by and do not stay in one place for more than one or two weeks. But this time the anomaly lasted for 1.5 months. Almost all people residing in this territory suffered from an unusual heat. According to some specialists the probability of recurrence of such phenomena is only once in 5,000 years!
Concurrently, mass media reported on abundant rainfalls in Pakistan resulting in catastrophic floods: similar floods had been observed in this country 80 years ago. Scientists also noticed: this rainy period coincided with a summer monsoon or a rainy season; a cyclone, i.e. an atmospheric phenomenon characterized by a decreased atmospheric pressure, hung over Pakistan.
Extraordinary natural phenomena required an explanation by scientists, but the proposed explanations were not sufficiently convincing. Some experts, including the author of this article, explained them by impact of atmospheric Rossby waves (mechanisms of these processes are described below), but interpretations varied. From the very beginning I'd like to say that I'm not going to argue with those who advocate different standpoints (you can get acquainted with them in the Internet, if you wish), but I'll try to set forth my viewpoint.
Let's start from afar. In 1939, the famous Swedish scientist Carl Gustav Rossby, who later moved to the USA, published a study, where he proved a possibility of existence of long-period waves propagating in the atmosphere (with a lifespan from a couple to tens of days); then he proposed a mathematical description of these waves. Such formations were called atmospheric Rossby waves. Later on he assumed that similar phenomena could exist in the oceans too. Moreover, according to the
scientist, such currents as the Gulf Stream, Kuroshio, etc. are nothing else but orbital movements of water particles participating in the formation of waves. In the early 1960s, scientists proved existence of long-period waves in the oceans, which confirmed Rossby's theory.
Now I'll tell you more details about them and waves in general. Research works, carried out by the author, make it possible to assume: real long-period ocean waves are better described by means of the mathematical apparatus of nonlinear waves-solitons*, than that of Rossby
*Soliton-a structurally stable solitary wave propagating in the nonlinear environment. Solitons behave like particles: when interacting with each other or with some other disturbances, instead of decomposing they move and preserve their structure invariable.-Ed.
waves. These structures were first discovered in 1834 by the English shipbuilder-engineer and scientist John Scott Russel on the surface of water of one of the channels near Edinburgh: he noticed a phenomenon that he called a "solitary wave"-a secluded wave (later it was renamed to a "soliton"). But, since real ocean waves are called Rossby waves, according to the generally accepted terminology, we shall also keep to traditional definitions, but remember that they are more like solitons.
Such waves are observed as a continuous series of waves; in the open ocean they propagate westwards, and near coastline, so that it is to the right relative to the direction of their movement.
Scheme of the lines of force of the oceanic Rossby waves: The effects of forces on the water particles as well as the direction of currents are shown by the arrows. Upper figure: the lines of force on the vertical plane through the center of the wave, which corresponds to the case of the Gulf Stream center. Lower figure: the force lines at the water surface. The red letter C designates the center of the cyclone; the blue letters AC designate the center of the anticyclone.
Now, let's pass to the processes that "launch" Rossby waves. As any other processes, they have a field of force covering their "habitat", in our case ocean water or atmospheric air. The field produces effect on their particles and makes them move, i.e. creates currents in water and wind in air, which means that they are not attributes of the wave itself, but are a result of its activity. Analysis of current or wind parameters enables scientists to determine existence of waves in oceans and in the atmosphere. The field itself is characterized by its lines of force that determine direction of force effect produced on the particles of the medium, air or water. Its size is assessed on the basis of the density of its lines of force. If only the wave were motionless, the trajectory of the particles would strictly coincide with the lines of force. In propagating waves, water particles move along trajectories close to circular, i.e. without forward movements. This characteristic-not to transfer the existence medium (water or air) in one direction-is typical of all types of waves, including ocean and atmospheric waves.
While studying Rossby waves in the natural medium of oceans, it was established: in the middle latitudes the value of their field of force, and, consequently, of the current in the upper part of the wave is against the direction of its propagation, and in the equatorial latitudes-coincide with it. The conclusion is that direction of the field of force depends on the latitude.
Movements of water particles form oceanic currents and reverse currents, as well as its movements in a vertical direction. In the center of the wave, lines of force are most dense; such density is typical of high-speed currents, such as the Gulf Stream (in oceanology it and similar streams are called jet streams, due to their stable character and high speeds). To the left of the current, water particles move like in cyclones, i.e. counterclockwise, and to the right-like in anticyclones, i.e. clockwise. These formations were called cyclone (C) and anticyclone (AC). Besides, they produce pressure on water, which moves it towards the center of the cyclone and vice versa, from the center of the anticyclone. In the first case warm surface water is accumulated; it then goes down to the bottom. This is how warm anomalies form. In the second case water moves from the center to the periphery and a cold stream goes from the bottom upwards; this is how cold anomalies form. These temperature deviations caused by Rossby waves are confirmed by measurements.
As we have already pointed out, waves exist in oceanic water, and they cannot transport atmospheric air. However bodies, let's call them foreign bodies, not related to this very medium, sometimes move in space and even make ellipsoidal movements practically in one and the same place together with water particles. Bodies of natural origin (plankton, algae, living and dead organisms) and anthropogenic bodies (wastes, oil residues) can be considered foreign for the oceanic medium; as for foreign bodies for the atmosphere-they are moisture, burning, dust, etc.
The author of this article studied behavior of foreign bodies in oceanic Rossby waves. For this purpose I used a drifter, or a float, equipped with a device enabling to get information on its location and thus on parameters of water movements, i.e. data on the currents.
The drifter put in the center of the wave (in our case, in the center of the Gulf Stream) moves rectilinearly, in one direction, but its motion speed is pulsating. At the same time, wave water particles move in the vertical plane around a certain center of equilibrium along a closed trajectory. If you place the drifter in a point far away from the wave center (in this case from the Gulf Stream), it will move along a rotational and transla-tional trajectory. And, finally, it can move along an elliptical trajectory together with water particles around a relatively fixed center. Such conditions occur when vertical speeds of movement of wave water particles are equal to zero. Mathematical description of the last model was called Rossby soliton wave.
Formed cyclones and anticyclones move together with the wave when it is in the Rossby wave state, i.e. when vertical component of the movement of water particles is
Scheme of the force lines of the Rossby waves in the atmosphere. Arrows designate the effects of force on water particles (in fact, it is wind). Direct arrows designate directions of wind in the cyclone (C) and anticyclone (AC).
essential. Foreign bodies in this case spread over a big area and are hardly visible.
Very often motionless cyclones and anticyclones are observed in the ocean. As we have already pointed out, this takes place when Rossby waves turn into Rossby soliton waves. Such cyclones and anticyclones accumulate energy of the Rossby waves that pass by and become enormous, water and foreign bodies rotate in them on the spot. Such structures can be "seen" by drifter measurements or waste heaps at the ocean surface. In the area of the Gulf Stream we managed to observe cyclones that are motionless for about a year.
Let's get down to the atmosphere. As in the case of the ocean surface, we can locate atmospheric surface at a height of about 10 km. The stable and standing anticyclone over Russia and a cyclone over Pakistan reached that height; scientists registered strong winds between them, "blowing" with high speeds. This windy area was called a jet stream. Here, as in the ocean, anticyclone is to the right and a cyclone to the left relative to the direction of the jet stream. The wind speed in the cyclone is by an order of magnitude higher than near the Earth surface. Such current was registered in the summer of 2010. Speeds of jet streams in the ocean, as in the atmosphere, are by an order of magnitude higher as compared with average speeds of ordinary oceanic currents. For example, in the Gulf Stream it is 1 m/s, while the average ocean current speed is 10 cm/s.
Thus, we can establish similarity of processes in the ocean and in the atmosphere. We mean jet streams, cyclones and anticyclones. Waves in the atmosphere, as in the ocean, move westwards, while a jet steam in the middle latitudes in the ocean moves eastwards and in the south latitudes-westwards, and this is what was observed in the summer of 2010. All these factors show that in both cases, in the ocean and in the atmosphere, we deal with similar Rossby waves.
To tell the truth, there are some differences in the course of processes occurring in two media, preconditioned by their nature-gas and water. In the atmospheric anticyclones air moves outwards and goes down in the center. This downstream movement results in a reduced humidity of air, which in turn leads to cloudlessness: air becomes dry, under the exposure of solar radiation it warms up, and heat energy accumulates at the expense of duration of the process itself. This produces high air temperature, fires and smogs.
In the atmospheric cyclone, air moves inwards and due to a differential pressure is forced upwards. As this takes place, atmospheric moisture condenses and precipitates in the form of rains. This process is accompanied by drop of pressure. Consequently, pressure differential both inside and outside the cyclone increases, which leads to the increased inflow of humid air, and then everything is repeated. Thus, there is observed a closed circuit of the processes mutually strengthening each other. They are typical of such atmospheric vortexes as tropical storms, tornadoes, tsunami, etc. The main source the cyclone takes power from is atmospheric moisture. The more it flows in, the more it precipitates. Atmospheric processes in Pakistan were observed in the time of a summer monsoon bringing humid air in the form of a wind from the ocean. This period is typically associated with heavy rains, while then they were accompanied by rains caused by the cyclone standing at one place for a long time. There are the reasons of catastrophic floods.
Let me make some conclusions. Hot summer in Russia and rainy summer in Pakistan were caused by the Rossby atmospheric waves, which in the given conditions turned into Rossby soliton waves. They formed powerful and long atmospheric formations: the anticyclone over Russia and the cyclone over Pakistan. The first one made air dry and hot, which caused fires, and the second one produced heavy rains accompanying summer monsoons, which resulted in catastrophic floods in Pakistan. It becomes clear that analysis of the forecast of atmospheric phenomena considered in the article is associated with the studies of the Rossby waves in the atmosphere, their characteristics and regularities of development. We have to understand under what conditions and how often Rossby waves turn into Rossby solitons.
Опубликовано на Порталусе 01 ноября 2021 года
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