Earth’s atmosphere is a distinct feature that makes it unique among all other planets in the solar system. The atmosphere, which consists of different layers and variations of gases, has a constant interplay with each other, which makes it dynamic. To be more specific, the troposphere layer has a constant gas circulation that is quite distinct in various regions of the world. Atmospheric circulation is dynamically active due to varied factors like thermal radiation, air pressure, and forces like gravity, coriolis, and frictional forces. Due to the changing patterns and uncertainty, they cause disturbances which sometimes become massive and affect a larger area. These atmospheric disturbances are termed cyclones and anticyclones. The characteristics of both cyclones and anticyclones vary according to the earth’s thermal belt. As a result, the focus of this article is on the climatic significance of atmospheric disturbances, as well as their genesis, characteristics, variability, and the nomenclature of cyclones, specifically tropical cyclones.
Climatic Significance of Atmospheric Disturbances
The zones and wind belts, which are often represented as the thermal and dynamic effects of general circulation, give rise to secondary circulations which create the most obvious weather variations. Although the word “secondary circulation” refers to atmospheric phenomena such as monsoon circulations, air masses, fronts, and upper-level vortices, it is most often used to describe moving disturbances that start in the middle and high latitudes, as well as inside the tropics. Extratropical cyclones, anticyclones, and tropical cyclones are some of the few examples of these types of disturbances. Indeed, the general circulation pattern can be thought of as a backdrop against which atmospheric disturbances of varied magnitudes are superimposed.
Aside from the basic characteristics of secondary circulation, the weather in a given location is also influenced by local occurrences classified as third-order circulations. Gravity winds, fall winds, valley and mountain breezes, sea breezes, thunderstorms, and tornadoes are just a few examples. The meteorological consequences of these local disruptions can be quite dramatic at times. The most fascinating feature of second and third-order circulations is that they can often mask the overall or general circulation. The general circulation resembles the flow of a stream and distinct types of atmospheric disturbances, which resemble eddies and cross-currents that characterise it.
Atmospheric disturbances play a crucial role in the intricate processes of heat transfer between latitude zones. True, the middle latitude zone has the most control over these disturbances and its effects on day-to-day weather. Because of the uncertainty in their arrival timing and frequency, travelling cyclones and anticyclones cause weather to be highly unpredictable. The mid-latitude zone’s general circulation and pressure systems are superimposed with several wave cyclones and vortices.
Precipitation, an essential climate factor, is influenced by a variety of atmospheric disturbances that pass through temperate regions. The cyclones’ convergent wind systems aid in the lifting and cooling of large air masses, resulting in precipitation. Humidity is created by extratropical cyclones that travel from adjacent oceans to continents. These cyclones are responsible for a large portion of the rainfall in various parts of the world. On the other hand, anticyclones provide dry weather due to their diverging wind systems. Atmospheric disturbances have an important role in maintaining the latitudinal heat balance and transferring heat across different latitudinal zones. Furthermore, these disturbances influence the transport of humidity from one region of the earth to another.
Understanding the various magnitudes of atmospheric disturbances allows weather scientists to make predictions about when and where they will occur. Furthermore, storm warnings can be sent ahead of time so that precautionary measures can be taken to save lives and property. Additionally, environmental protection and weather manipulation are both closely tied to our ability to comprehend, as completely as possible, the natural environmental processes involved in these weather occurrences and to put this knowledge to constructive use.
The tropical atmosphere can be found between the Tropic of Cancer and the Tropic of Capricorn. However, the high-pressure cells of the subtropics in both hemispheres dictate the boundary of the tropical atmosphere from a meteorological standpoint. The tropics cover roughly half of the earth’s surface and house 40% of the world’s population. As a result, climatological research into the tropical atmosphere has become even more significant. It’s worth noting that, prior to World War II, tropical weather was thought to be repetitive and uneventful. When military planes had to fly through this atmosphere during the war, the idea of the low-latitude weather being generally pleasant and uneventful was debunked.
The main obstacles to developing a proper picture of tropical weather were a lack of weather observations and observational data. That is why, particularly in the West, weather scientists have a relatively simple understanding of the tropical atmosphere. Since 1990, a slew of weather satellites, including Tiros, Nimbus, Essu, Itos, Nova, and others, have been tasked with probing the upper atmosphere. As a result, shocking findings regarding tropical weather and climate have emerged. These weather satellites have aided in the understanding of the tropical atmosphere’s diverse weather processes and weather systems. With more data concerning the current weather conditions in the tropics, a lot of variety in weather elements, including temperature, precipitation, pressure, etc., has been noticed.
Climatologists have only investigated the most violent tropical storms, such as hurricanes and typhoons. These severe storms are not only limited in number but they are also restricted to limited areas. The weaker and milder kinds of tropical disturbances, on the other hand, have a significant impact on the weather and help to disrupt the so-called tropical weather monotony. The weak and shallow low-pressure systems that dominate the humid tropics’ weather cause the majority of the vast tropical disturbances. When the meteorological phenomena of the tropical and temperate zones are compared, substantial disparities arise. The tropical region does not experience the same rapid and severe variations in weather as the middle latitudes. The tropical weather is undeniably unpredictable. Even back then, the tropical region’s greatest distinguishing attributes were depressing and continuous hot weather. The pressure gradients are often extremely minor on the surface pressure charts made for lower latitudes. As a result, the isobars are fewer and more widely spread. It should be noted that many of the weather phenomena seen at lower latitudes occur within a single air mass with no fronts. This feature alone makes analysing tropical weather with conventional approaches even more challenging.
The tropical atmosphere should be conceived of as a heat sink for radiant energy emitted by short-wave solar and terrestrial radiation. The vastness of tropical oceans contributes significantly to the supply of atmospheric heat. According to data from weather satellites, the amount of insolation received in the tropics is larger than what was previously thought. Our predictions of solar energy depletion due to albedo and cloud cover were significantly in excess of the actual amount. Ocean currents that originate in tropical oceans also play an important role in the transport of heat to higher latitudes. The tropics have a higher rate of energy exchange between the oceans and atmosphere than any other location. Two such meteorological occurrences that more than compensate for the loss of radiant energy in the atmosphere are the transfer of sensible heat to the lower layers of the atmosphere near the sea and the latent heat derived therefrom. In this region’s warm and humid climate, the latent heat of condensation is a primary source of energy for different atmospheric disturbances and tropical cyclones of various magnitudes. Another distinctive feature of the tropical environment is that precipitation is not distributed randomly but rather is concentrated in a variety of small-scale atmospheric disturbances.
Understanding the Phenomena
Atmospheric disturbances around a low-pressure area are responsible for cyclones, which are characterised by rapid and often destructive air circulation. The cyclones are characterised by spiralling winds and low-pressure centres. The spiral has a unique direction because the winds blow counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. Simple thunderstorms can produce cyclones. However, both the ocean and the atmosphere must work together for these thunderstorms to reach cyclonic power. To begin, the ocean water must be warmer than a certain temperature, such as 28oC. Cyclones derive their energy from the heat and moisture in this heated water. Hence, the heat and moisture from the warm waters act as a source of energy for cyclones. When cyclones pass over land or over colder ocean waters, they will quickly weaken due to a lack of heat and/or moisture supplies. For cyclone development, high relative humidity in the lower and middle troposphere is also necessary. Because there is greater precipitation, the amount of evaporation in clouds is reduced, and the latent heat released gets maximised. In a tropical cyclones environment, vertical wind shear is equally crucial. The amount of variation in the wind’s direction or speed with increasing altitude is known as wind shear. When the wind shear is weak, the cyclonic storms build vertically, and latent heat from condensation is released into the air directly above the storm, aiding in its development. However, the storms become more tilted when there is greater wind shear and the latent heat released dissipates across a much larger region.
Tornadoes, hurricanes, and typhoons are several types of cyclones. Tornadoes are cyclones that are smaller than hurricanes. A hurricane is a tropical cyclone that arises over tropical waters in the North Atlantic or eastern North Pacific oceans and has winds of 119 km/hr or higher. Typhoons arise in the western Pacific when cyclones form with 119 km/hr winds or greater. High winds, torrential rainfall, tremendous thunder, and lightning are common features of all of these storms. Subsequently, tropical cyclones are the common name for them in the northern Indian Ocean.
Winds, as we all know, steer cyclones. The wind belt in which the cyclone is located has a significant impact on its track. For example, a cyclone that forms in the eastern tropical Pacific is pushed westward by the tropical easterly trade winds. These storms eventually travel north-westward across the subtropical high and into higher latitudes. Local steering winds may occasionally deviate from this pattern.
In comparison to cyclones, anticyclones play a significantly smaller role in the meteorological drama at the earth’s surface. Because anticyclones provide clear conditions and are nearly weatherless, no major research into their genesis, structure, or movement has been conducted. Anticyclones are commonly thought to be related to pleasant weather. This isn’t always the case, though. When cumuliform clouds form within an anticyclone, they deliver heavy rainfall or snowfall under specific conditions. Sir Francis Galton was the first to use the term “anticyclone” in 1861. It refers to an atmospheric system that is the complete antithesis of a cyclonic system.
Anticyclone location and energy are two of the most essential aspects of weather forecasting at all latitudes. All of the major anticyclones, however, are found in the form of semi-permanent high-pressure cells over the oceans at 30oC north and south latitudes. The cold-core and warm-core migratory anticyclones, on the other hand, have origins in locations that are farther apart. As a high-pressure system, it blows clockwise in the northern hemisphere and counterclockwise in the southern hemisphere.
The actual mechanism of anticyclone generation is as yet unknown. However, the most likely reason for their creation appears to be the radiational cooling of atmospheric layers close to the snow-covered surface, which are often called thermal anticyclones. Because of the subsidence within these anticyclones, the atmosphere experiences subsidence inversion, resulting in atmospheric stability. An anticyclone can grow in a unique way and become rather intense under specific circumstances. Even then, anticyclones never reach the same levels of intensity as fully established cyclones. However, it is to be remembered that individual anticyclones are made up of different types of air masses at different periods.
The temperature of the air masses involved, the humidity of the air, and the season of the year all influence the surface temperature conditions in an anticyclone. Cold anticyclones originating in the snow-covered sub polar areas always produce very cold temperatures and blizzards in the winter, making the winter chill excruciating. Anticyclones in the middle latitudes always bring the season’s coldest temperatures. In the summer, heat waves are caused by a stagnant form of heated anticyclones in combination with air from subtropical or tropical regions. During the day, clear weather permits the most solar radiation to be received. As the high-pressure system travels into sub-polar regions, tropical air masses transport heat to the north. The diurnal temperature range is going to be large since anticyclonic conditions favour clear weather. During the winter, anticyclonic conditions favour the development of radiation fogs at night. Warm and moist air currents from over the ocean form advection fogs at the rear of these anticyclones. The dissipation of fog at the surface is caused by daytime surface heating in some instances; however, fog persists at higher levels. These upper-level fogs appear as low stratus clouds when viewed from the earth’s surface. These foggy layers prevent light rays from reaching the earth’s surface. In the middle latitude region, this phenomenon of subdued daylight is termed the anticyclonic gloom. On the contrary, the anticyclones that form over the ocean surface have warm air in their upper parts. Such anticyclones are called dynamic anticyclones. These anticyclones maintain their vigour up to considerable heights.
Nomenclature of Cyclones
The practise of naming the cyclones, to be precise tropical cyclones, began years ago to aid in the quick identification of storms in warning bulletins because names are thought to be far simpler to recall than numbers and technical words. Many people believe that giving storm names makes it easier for the media to report on tropical cyclones, enhances public awareness of warnings, and improves community preparedness. According to experience, the use of short, distinct given names in written and spoken communications are faster and less prone to error than the older, more complicated latitude-longitude identification systems. These benefits are especially valuable when exchanging comprehensive storm information among hundreds of stations, coastal bases, and ships at sea. Storms were given names at random in the beginning. Antje’s hurricane was named after an Atlantic storm that ripped the mast off a boat named Antje. Then, in the mid-nineteenth century, storms began to be given feminine names. Meteorologists later opted to identify storms using names from an alphabetical list in search of a more structured and efficient naming system. As a result, a storm with an A-letter name, such as Anne, would be the first storm of the year. Forecasters began using masculine names for those developing in the Southern Hemisphere before the turn of the century.
Meteorologists later opted to identify storms using names from an alphabetical list in the search for a more structured and efficient naming system. As a result, a storm with an A-letter name, such as Anne, would be the first storm of the year. Forecasters began using masculine names for those developing in the Southern Hemisphere before the turn of the century. Since 1953, tropical storms in the Atlantic have been named using lists created by the National Hurricane Centre. They are now maintained and updated by a World Meteorological Organization international committee. The only time the list is updated is when a storm is so devastating or costly that using its name on another storm would be improper due to sensitivity concerns. If this happens, the offending name is removed from the list, and a new name is chosen to replace it during an annual meeting of the WMO Tropical Cyclone Committees (convened largely to discuss numerous other issues). Mangkhut (Philippines, 2018), Irma and Maria (Caribbean, 2017), Haiyan (Philippines, 2013), Sandy (USA, 2012), Katrina (USA, 2005), Mitch (Honduras, 1998), and Tracy (Darwin, 1974) are examples of well-known cyclone names.
There is a strict procedure to determine a list of tropical cyclone names in an ocean basin by the Tropical Cyclone Regional Body responsible for that basin at its annual/biennial meeting. The ESCAP/WMO Typhoon Committee, the WMO/ESCAP Panel on Tropical Cyclones, the RA I Tropical Cyclone Committee, the RA IV Hurricane Committee, and the RA V Tropical Cyclone Committee are the five tropical cyclone regional bodies. At its yearly meeting, the Hurricane Committee, for example, determines a pre-determined list of hurricane names for the next six years. Members, which include the National Meteorological and Hydrological Services in North and Central America and the Caribbean, proposed the pre-designated list of hurricane names. While tropical cyclones are named in general according to regional rules,
It’s worth noting that tropical cyclones, hurricanes, and typhoons aren’t named after anyone in particular. The names chosen are those that people in each region are familiar with. Hence, storms are given names so that people can quickly recognise and remember the tropical cyclone/hurricane/typhoon that is now affecting their area, making disaster risk awareness, preparation, management, and reduction easier. Countries must adhere to certain guidelines when naming cyclones. The name is accepted by the panel on tropical cyclones (PTC), which finalises the selection if certain requirements are met. These are the rules: The proposed name should be politically neutral, as well as respect religious beliefs, cultures, and gender. The name should be chosen in such a way that it does not offend any group of people anywhere on the planet. Its nature should not be unpleasant and cruel. It should be short, easy to say, and not objectionable to any of the members. The name’s maximum length will be eight letters. The pronunciation and voiceover for the proposed name should be provided. Tropical cyclone names in the north Indian Ocean will not be repeated. It can no longer be used after it has been used.
Naming of Tropical Cyclones over the North Indian Ocean
The area of responsibility of Regional Specialized Meteorological Centre RSMC- New Delhi covers Sea areas of the north Indian Ocean north of the equator between 400E and 1000E and includes the member countries of WMO/ESCAP Panel on Tropical Cyclones viz, Bangladesh, India, Iran, Maldives, Myanmar, Oman, Pakistan, Saudi Arabia, Sri Lanka, Qatar, Thailand, United Arab Emirates and Yemen.
At its twenty-seventh session in Muscat, Sultanate of Oman, in 2000, the WMO/ESCAP Panel on Tropical Cyclones agreed in principle to name tropical cyclones in the Bay of Bengal and the Arabian Sea. The naming of tropical cyclones over the north Indian Ocean began in September 2004 by RSMC New Delhi, following lengthy discussions among member countries. The initial name given was “ONIL,” which evolved over the Arabian Sea (30 September to 3rd October 2004). A list of 64 names in eight columns has been generated in accordance with established guidelines. Panel members came up with the name. The RSMC tropical cyclones of New Delhi assign a name to a tropical storm from this list. Each column lists the names of panel members alphabetically by nation. The names are used in column sequence. The first name begins on the first row of column one and continues to the eighth row. In contrast to the Atlantic and Eastern Pacific lists, the names are not rotated every few years. All of the names in the first list, which became effective in September 2004, were used. The second list in the series, with 169 names, was announced in April 2020, with representation from all 13 WMO member countries.
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