Explosive cyclogenesis (also referred to as a weather bomb, [1] [2] [3] meteorological bomb, [4] explosive development, [1] bomb cyclone, [5] [6] or bombogenesis [7] [8] [9] ) is the rapid deepening of an extratropical cyclonic low-pressure area. The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 millibars (0.71 inHg) or more in 24 hours. [10] [11] This is a predominantly maritime, winter event, [10] [12] but also occurs in continental settings. [13] [14] This process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is entirely different from that of tropical cyclones, bomb cyclones can produce winds of 74 to 95 mph (120 to 155 km/h), the same order as the first categories of the Saffir–Simpson scale, and yield heavy precipitation. Even though only a minority of bomb cyclones become this strong, some weaker ones can also cause significant damage.
In the 1940s and 1950s, meteorologists at the Bergen School of Meteorology began informally calling some storms that grew over the sea "bombs" because they developed with a great ferocity rarely seen over land.
By the 1970s, the terms "explosive cyclogenesis" and even "meteorological bombs" were being used by MIT professor Fred Sanders (building on work from the 1950s by Tor Bergeron), who brought the term into common usage in a 1980 article in the Monthly Weather Review . [5] [10] In 1980, Sanders and his colleague John Gyakum defined a "bomb" as an extratropical cyclone that deepens by at least (24 sin φ / sin 60°) mb in 24 hours, where φ represents latitude. This is based on the definition, standardised by Bergeron, for explosive development of a cyclone at 60°N as deepening by 24 mb in 24 hours. [15] Sanders and Gyakum noted that an equivalent intensification is dependent on latitude: at the poles this would be a drop in pressure of 28 mb/24 hours, while at 25 degrees latitude it would be only 12 mb/24 hours. All these rates qualify for what Sanders and Gyakum called "1 bergeron". [10] [13] Sanders' and Gyakum's 1980 definition, which is used in the American Meteorological Society's Glossary of Meteorology, said that the "bomb" was "predominantly" a "maritime, cold season event". [10] [12]
In October 2010, an unusual weather system that reached the strength of a Category 3 hurricane and spanned 31 states in the United States and six Canadian provinces, underwent bombogenesis, according to Environment Canada. [16] Severe weather warnings included "tornadoes, blustery blizzards, powerful gales, wind-driven rains, heavy snows and thunderstorms". [16] The storm had the greatest impact in the Canadian province of Manitoba with the city of Winnipeg setting an "all-time record for its lowest-ever barometric pressure". [16]
In early 2014 in the North Atlantic, fourteen wind events out of twenty that had reached hurricane-force, underwent bombogenesis, the process that creates a bomb cyclone, according to National Oceanic and Atmospheric Administration (NOAA). [17] NOAA said that bombogenesis "occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours." [17]
A bomb cyclone developed near the Great Lakes during the late December 2022 rapidly intensifying North American winter storm, when large, frigid, polar air masses from the polar vortex, propelled by high-pressure systems in Canada, met with the low-pressure mass of very warm air, resulting in a sharp and rapid drop in atmospheric pressure. [18] [19] [20] It reached the criteria to be classified as bombogenesis when the atmospheric pressure dropped 24 millibars within 24 hours. [21] [19] The US National Weather Service's meteorologist, John Moore, reported a sharp pressure difference or gradient from 1,047 millibars (30.9 inHg) to about 962 millibars (28.4 inHg). [19] As warm air was drawn into the storm, the winds got stronger, and air pressure and temperatures fell rapidly. [18] [22] The US National Weather Service reported a drop in temperature of 26 degrees in Montana in three minutes on December 24. [19] The storm hit "large swaths" of North America leaving 55 fatalities in the United States and four in Canada. [19] [23] Strong winds and blizzard-like conditions intensified in the Northern Plains. [24] With no Canadian province and territory spared [ tone ], there was a total of 425 emergency weather warnings on December 24—an "almost unprecedented number". [25] Extreme conditions included wind chill readings of −50 °C (−58 °F), heavy snow, "storm surges, ice fog, strong winds", and "ice bombs"—in reference to chunks of accumulated ice that threatens to fall on cars when crossing certain bridges. [25] The storm in the United States was described as "historic" by the NPR. It affected about 60% of the population, and resulted in the issuance of "one of the greatest extents of winter weather warnings and advisories ever". [20] At its peak on December 24, 1.5 million households in the United States and 500,000 in Canada were without electricity. [25]
In the last week of December 2022 through the first week of January 2023, a bomb cyclone hit the American West Coast, leading to the death of at least two people in California. [26] [27]
Baroclinic instability has been cited as one of the principal mechanisms for the development of most explosively deepening cyclones. [28] However, the relative roles of baroclinic and diabatic processes in explosive deepening of extratropical cyclones have been subject to debate (citing case studies) for a long time. [29] Other factors include the relative position of a 500-hPa trough and thickness patterns, deep tropospheric frontogenetic processes which happen both upstream and downstream of the surface low, the influence of air–sea interaction, and latent heat release. [30]
The four most active regions where extratropical explosive cyclogenesis occurs in the world are the Northwest Pacific, the North Atlantic, the Southwest Pacific, and the South Atlantic. [31]
In the Northern Hemisphere the maximum frequency of explosively deepening cyclones is found within or to the north of the Atlantic Gulf Stream and Kuroshio Current in the western Pacific, [10] and in the Southern Hemisphere it is found with Australian east coast lows above the East Australian Current, which shows the importance of air-sea interaction in initiating and rapidly developing extratropical cyclones. [32]
Explosively deepening cyclones south of 50°S often show equator-ward movement, in contrast with the poleward motion of most Northern Hemisphere bombs. [30] Over the year, 45 cyclones on average in the Northern Hemisphere and 26 in the Southern Hemisphere develop explosively, mostly in the respective hemisphere's winter time. Less seasonality has been noticed in bomb cyclogenesis occurrences in the Southern Hemisphere. [30]
The term "weather bomb" is popularly used in New Zealand to describe dramatic or destructive weather events. Rarely are the events actual instances of explosive cyclogenesis, as the rapid deepening of low pressure areas is rare around New Zealand. [33] [34] This use of "bomb" may lead to confusion with the more strictly defined meteorological term. In Japan, the term bomb cyclone (爆弾低気圧, bakudan teikiatsu) is used both academically and commonly to refer to an extratropical cyclone which meets the meteorological "bomb" conditions. [35] [36]
The term "bomb" may be somewhat controversial. When European researchers protested that it was a rather warlike term, Fred Sanders, the coauthor of the paper which introduced the meteorological usage quipped: "So why are you using the term 'front'?" [37]
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.
A subtropical cyclone is a weather system that has some characteristics of both tropical and extratropical cyclones.
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:
South Atlantic tropical cyclones are unusual weather events that occur in the Southern Hemisphere. Strong wind shear, which disrupts the formation of cyclones, as well as a lack of weather disturbances favorable for development in the South Atlantic Ocean, make any strong tropical system extremely rare, and Hurricane Catarina in 2004 is the only recorded South Atlantic hurricane in history. Storms can develop year-round in the South Atlantic, with activity peaking during the months from November through May. Since 2011, the Brazilian Navy Hydrographic Center has assigned names to tropical and subtropical systems in the western side of the basin, near the eastern coast of Brazil, when they have sustained wind speeds of at least 65 km/h (40 mph), the generally accepted minimum sustained wind speed for a disturbance to be designated as a tropical storm in the North Atlantic basin. Below is a list of notable South Atlantic tropical and subtropical cyclones.
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.
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. Cyclogenesis is an umbrella term for at least three different processes, all of which result in the development of some sort of cyclone, and at any size from the microscale to the synoptic scale.
The Great Blizzard of 1978 was a historic winter storm that struck the Ohio Valley and Great Lakes regions of the United States as well as Southern Ontario in Canada from Wednesday, January 25 through Friday, January 27, 1978. It is often cited as one of the most severe blizzards in US history. The third lowest non-tropical atmospheric pressure ever recorded in the mainland United States occurred as the storm passed over Mount Clemens, Michigan, where barometer readings fell to 956.0 mb (28.23 inHg) on January 26.
The 1976 Pacific typhoon season has no official bounds; it ran year-round in 1976, 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.
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.
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.
A tropical cyclone is a rapidly rotating storm system with a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn or more.
The 2006 Central Pacific cyclone, also known as Invest 91C or Storm 91C, was an unusual weather system that formed in 2006. Forming on October 30 from a mid-latitude cyclone in the north Pacific mid-latitudes, it moved over waters warmer than normal. The system acquired some features more typical of subtropical and even tropical cyclones. However, as it neared the western coastline of North America, the system fell apart, dissipating soon after landfall, on November 4. Moisture from the storm's remnants caused substantial rainfall in British Columbia and the Pacific Northwest. The exact status and nature of this weather event is unknown, with meteorologists and weather agencies having differing opinions.
The New Year's Day Storm, known in Scotland as the 'Hogmanay Hurricane', was an extremely powerful and record-breaking European windstorm, comparable to a category 4 major hurricane, that affected much of northern Scotland and western Norway on 1 January 1992. DNMI estimated the strongest sustained winds and the strongest gusts to have reached 103 mph and 138 mph, respectively. Unofficial records of gusts in excess of 170 knots (87 m/s) were recorded in Shetland, while Statfjord-B in the North Sea recorded wind gusts in excess of 145 knots (75 m/s). There were very few fatalities, mainly due to the rather low population of the islands, the fact that the islanders are used to powerful winds, and because it struck in the morning on a public holiday when people were indoors. In Norway there was one fatality, in Frei, Møre og Romsdal county. There were also two fatalities on Unst in the Shetland Isles. Despite being referred to by some as a 'Hurricane', the storm was Extratropical in origin and is classified as an Extratropical Cyclone.
The Braer Storm was the most intense extratropical cyclone ever recorded over the northern Atlantic Ocean. Developing as a weak frontal wave on 8 January 1993, the system moved rapidly northeast. The combination of the absorption of a second low-pressure area to its southeast, a stronger than normal sea surface temperature differential along its path, and the presence of a strong jet stream aloft led to a rapid strengthening of the storm, with its central pressure falling to an estimated 914 hPa on 10 January. Its strength was well predicted by forecasters in the United Kingdom, and warnings were issued before the low initially developed.
The November 2011 Bering Sea cyclone was one of the most powerful extratropical cyclones to affect Alaska on record. On November 8, the National Weather Service (NWS) began issuing severe weather warnings, saying that this was a near-record storm in the Bering Sea. It rapidly deepened from 973 mb (28.7 inHg) to 948 mb (28.0 inHg) in just 24 hours before bottoming out at 943 mbar, roughly comparable to a Category 3 or 4 hurricane. The storm had been deemed life-threatening by many people. The storm had a forward speed of at least 60 mph (97 km/h) before it had reached Alaska. The storm began affecting Alaska in the late hours of November 8, 2011. The highest gust recorded was 93 mph (150 km/h) on Little Diomede Island. One person was reported missing after being swept into the Bering Sea, and he was later pronounced dead.
Australian east coast lows are extratropical cyclones or low-pressure systems on the coast of southeastern Australia that may be caused by both mid-latitude and tropical influences over a variety of levels in the atmosphere. These storms should not be confused with Australian region tropical cyclones which typically affect the northern half of the continent.
The November 2014 Bering Sea cyclone was the most intense extratropical cyclone ever recorded in the Bering Sea, which formed from a new storm developing out of the low-level circulation that separated from Typhoon Nuri, which soon absorbed the latter. The cyclone brought gale-force winds to the western Aleutian Islands and produced even higher gusts in other locations, including a 97 miles per hour (156 km/h) gust in Shemya, Alaska. The storm coincidentally occurred three years after another historic extratropical cyclone impacted an area slightly further to the east.
The October 2017 nor'easter was a major explosive cyclogenesis storm, also called a bomb cyclone, in the Northeastern United States and Atlantic Canada from October 29–31, 2017. Forming from an extratropical cyclone on October 29 the system moved rapidly up the East Coast of the United States, bombing out with a minimum pressure of 975 millibars (28.8 inHg) on October 30. It brought heavy rain and extremely strong winds, and power outages, over 1.3 million customers being without power in the Northeast. Hurricane-force wind gusts resulted in downed trees, power lines, and widespread damage to buildings. The number of power outages in the state of Maine surpassed the Ice Storm of 1998.
An extremely powerful extratropical bomb cyclone began in late October 2021 in the Northeast Pacific and struck the Western United States and Western Canada. The storm was the third and the most powerful cyclone in a series of powerful storms that struck the region within a week. The cyclone tapped into a large atmospheric river and underwent explosive intensification, becoming a bomb cyclone on October 24. The bomb cyclone had a minimum central pressure of 942 millibars (27.8 inHg) at its peak, making it the most powerful cyclone recorded in the Northeast Pacific. The system had severe impacts across Western North America, before dissipating on October 26. The storm shattered multiple pressure records across parts of the Pacific Northwest. Additionally, the bomb cyclone was the most powerful storm on record to strike the region, in terms of minimum central pressure. The bomb cyclone brought powerful gale-force winds and flooding to portions of Western North America. At its height, the storm cut the power to over 370,500 customers across the Western U.S. and British Columbia. The storm killed at least two people; damage from the storm was estimated at several hundred million dollars. The bomb cyclone was compared to the Columbus Day Storm of 1962, in terms of ferocity.
The October 2022 Southern Ocean cyclone, also referred to as the Peter I storm or EC2022 was the most intense extratropical cyclone on record. Forming as a weak depression near Tonga late on 9 October, the extratropical cyclone tracked slowly southeastward across the South Pacific, remaining weak. Starting on 14 October, the cyclone began rapid deepening as it moved towards Antarctica. Deepening rates peaked on 16 October, where the pressure fell as rapidly as 19 mbar (0.56 inHg) over a six-hour period. The storm peaked early on 17 October in the Bellingshausen Sea, with a minimum pressure of around 900 mbar (26.58 inHg). The cyclone moved slowly in a loop, rising in pressure over the next few days before dissipating on 20 October.
{{cite web}}
: CS1 maint: multiple names: authors list (link)