In meteorology, a cyclone is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above. Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within the smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.
A subtropical cyclone is a weather system that has some characteristics of both tropical and extratropical cyclones.
A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interplays between the relatively larger-scale dynamics of an entire planet's atmospheric circulation.
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather, while high-pressure areas are associated with lighter winds and clear skies. Winds circle anti-clockwise around lows in the northern hemisphere, and clockwise in the southern hemisphere, due to opposing Coriolis forces. Low-pressure systems form under areas of wind divergence that occur in the upper levels of the atmosphere (aloft). The formation process of a low-pressure area is known as cyclogenesis. In meteorology, atmospheric divergence aloft occurs in two kinds of places:
In meteorology, the synoptic scale is a horizontal length scale of the order of 1,000 km (620 mi) or more. This corresponds to a horizontal scale typical of mid-latitude depressions. Most high- and low-pressure areas seen on weather maps are synoptic-scale systems, driven by the location of Rossby waves in their respective hemisphere. Low-pressure areas and their related frontal zones occur on the leading edge of a trough within the Rossby wave pattern, while high-pressure areas form on the back edge of the trough. Most precipitation areas occur near frontal zones. The word synoptic is derived from the Ancient Greek word συνοπτικός (sunoptikós), meaning "seen together".
The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend towards the poles and steer extratropical cyclones in this general manner. Tropical cyclones which cross the subtropical ridge axis into the westerlies recurve due to the increased westerly flow. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere.
The 1959 Pacific typhoon season was regarded as one of the most devastating years for Pacific typhoons on record, with China, Japan and South Korea sustaining catastrophic losses. It was an event in the annual cycle of tropical cyclone formation. The season had no official bounds, but tropical cyclones in the Western Pacific Ocean normally develop between May and October.
The 1961 Pacific typhoon season had no official bounds; it ran year-round in 1961, but most tropical cyclones tend to form in the northwestern Pacific Ocean between June and December. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean.
The 1963 Pacific typhoon season has no official bounds; it ran year-round in 1963, but most tropical cyclones tend to form in the northwestern Pacific Ocean between June and December. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean.
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of producing anything from cloudiness and mild showers to severe gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.
The 1992–93 South-West Indian Ocean cyclone season lasted longer than normal, with the first storm Aviona forming on September 27 and the final storm Konita not dissipating until May 7. It was an above-average season, with four tropical cyclones – the equivalent of a minimal hurricane – along with six tropical storms, one subtropical depression, and several depressions including one that was named. The basin is defined as the area west of 90°E and south of the Equator in the Indian Ocean, which includes the waters around Madagascar westward to the east coast of Africa. Tropical cyclones in this basin are monitored by the Regional Specialised Meteorological Centre in Réunion (MFR), as well as by the Joint Typhoon Warning Center (JTWC).
The 1974–75 South-West Indian Ocean cyclone season was an average cyclone season. The season officially ran from November 1, 1974, to April 30, 1975.
The following is a glossary of tropical cyclone terms.
The 1941 Pacific typhoon season has no official bounds; it ran year-round in 1941, but most tropical cyclones tend to form in the northwestern Pacific Ocean between June and December. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean. The scope of this article is limited to the Pacific Ocean, north of the equator and west of the international date line. Storms that form east of the date line and north of the equator are called hurricanes; see 1941 Pacific hurricane season. There were 28 tropical cyclones in the western Pacific in 1941.
The 1942 Pacific typhoon season has no official bounds; it ran year-round in 1942, but most tropical cyclones tend to form in the northwestern Pacific Ocean between June and December. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean. The scope of this article is limited to the Pacific Ocean, north of the equator and west of the international date line. Storms that form east of the date line and north of the equator are called hurricanes; see 1942 Pacific hurricane season.
The 1944 Pacific typhoon season has no official bounds; it ran year-round in 1944, but most tropical cyclones tend to form in the northwestern Pacific Ocean between June and December. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean. The scope of this article is limited to the Pacific Ocean, north of the equator and west of the international date line. Storms that form east of the date line and north of the equator are called hurricanes; see 1944 Pacific hurricane season.
There were 30 tropical cyclones in the western Pacific Ocean in 1931, including 19 typhoons, as well as one that developed in December of the previous year. The most significant typhoon was one that struck eastern China near Shanghai in the midst of the country's worst floods on record; heavy rainfall caused levees to collapse along the Grand Canal, killing an estimated 300,000 people, including about 2,000 people overnight in the city of Gaoyou.
This article encompasses the 1890s Pacific typhoon seasons.
The following is a list of weather events that occurred on Earth in the year 2002. There were several natural disasters around the world from various types of weather, including blizzards, cold waves, droughts, heat waves, tornadoes, and tropical cyclones. The deadliest disaster was a heat wave in India in May, which killed more than 1,030 people. The costliest event of the year was a flood in Europe in August, which killed 232 people and caused €27.7 billion (US$27.115 billion) in damage. In September, Typhoon Rusa struck South Korea, killing at least 213 people and causing at least ₩5.148 trillion (US$4.2 billion) in damage.
The following is a list of weather events that occurred on Earth in the year 2004. There were several natural disasters around the world from various types of weather, including blizzards, cold waves, droughts, heat waves, tornadoes, and tropical cyclones. The deadliest disaster was Hurricane Jeanne, which killed more than 3,000 people when it struck Hispaniola, mostly in Haiti. This was just four months after flooding in Hispaniola killed 2,665 people. Jeanne was also the fourth hurricane to strike the United States in the year, following Charley, Frances, and Ivan. Ivan was the costliest natural disaster of the year, causing US$26.1 billion in damage in the Caribbean and the United States.
