Project Stormfury

Last updated
1966 photo of the crew and personnel of Project Stormfury Project Stormfury crew.jpg
1966 photo of the crew and personnel of Project Stormfury

Project Stormfury was an attempt to weaken tropical cyclones by flying aircraft into them and seeding with silver iodide. The project was run by the United States Government from 1962 to 1983.

Tropical cyclone Is a rotating storm system

A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".

Cloud seeding form of weather modification

Cloud seeding is a type of weather modification that aims to change the amount or type of precipitation that falls from clouds by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud. The usual intent is to increase precipitation, but hail and fog suppression are also widely practised in airports where harsh weather conditions are experienced.

Silver iodide inorganic compound

Silver iodide is an inorganic compound with the formula AgI. The compound is a bright yellow solid, but samples almost always contain impurities of metallic silver that give a gray coloration. The silver contamination arises because AgI is highly photosensitive. This property is exploited in silver-based photography. Silver iodide is also used as an antiseptic and in cloud seeding.

Contents

The hypothesis was that the silver iodide would cause supercooled water in the storm to freeze, disrupting the inner structure of the hurricane. This led to the seeding of several Atlantic hurricanes. However, it was later shown that this hypothesis was incorrect. It was determined that most hurricanes do not contain enough supercooled water for cloud seeding to be effective. Additionally, researchers found that unseeded hurricanes often undergo the same structural changes that were expected from seeded hurricanes. This finding called Stormfury's successes into question, as the changes reported now had a natural explanation.

Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid.

Water chemical compound

Water is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient temperature and pressure. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.

The last experimental flight was flown in 1971, due to a lack of candidate storms and a changeover in NOAA's fleet. More than a decade after the last modification experiment, Project Stormfury was officially canceled. Although a failure in its goal of reducing the destructiveness of hurricanes, Project Stormfury was not without merit. The observational data and storm lifecycle research generated by Stormfury helped improve meteorologists' ability to forecast the movement and intensity of future hurricanes.

Weather forecasting application of science and technology to predict the conditions of the atmosphere for a given location and time

Weather forecasting is the application of science and technology to predict the conditions of the atmosphere for a given location and time. People have attempted to predict the weather informally for millennia and formally since the 19th century. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere at a given place and using meteorology to project how the atmosphere will change.

Hypothesis

The working hypothesis of Project Stormfury Project stormfury hypothesis.png
The working hypothesis of Project Stormfury

Cloud seeding was first attempted by Vincent Schaefer and Irving Langmuir. After witnessing the artificial creation of ice crystals, Langmuir became an enthusiastic proponent of weather modification. [1] Schaefer found that when he dumped crushed dry ice into a cloud, precipitation in the form of snow resulted. [2]

Vincent Joseph Schaefer was an American chemist and meteorologist who developed cloud seeding. On November 13, 1946, while a researcher at the General Electric Research Laboratory, Schaefer modified clouds in the Berkshire Mountains by seeding them with dry ice. While he was self-taught and never completed high school, he was issued 14 patents.

Irving Langmuir American chemist and physicist

Irving Langmuir was an American chemist and physicist. He was awarded the Nobel Prize in Chemistry in 1932 for his work in surface chemistry.

Weather modification act of intentionally manipulating or altering the weather

Weather modification is the act of intentionally manipulating or altering the weather. The most common form of weather modification is cloud seeding, which increases rain or snow, usually for the purpose of increasing the local water supply. Weather modification can also have the goal of preventing damaging weather, such as hail or hurricanes, from occurring; or of provoking damaging weather against the enemy, as a tactic of military or economic warfare like Operation Popeye, where clouds were seeded to prolong the monsoon in Vietnam. Weather modification in warfare has been banned by the United Nations under Environmental Modification Convention.

With regard to hurricanes, it was hypothesized that by seeding the area around the eyewall with silver iodide, latent heat would be released. This would promote the formation of a new eyewall. As this new eyewall was larger than the old eyewall, the winds of the tropical cyclone would be weaker due to a reduced pressure gradient. [3] Even a small reduction in the speed of a hurricane's winds would be beneficial: since the damage potential of a hurricane increased as the square of the wind speed, [4] a slight lowering of wind speed would have a large reduction in destructiveness. [4]

Eye (cyclone) region of mostly calm weather at the center of strong tropical cyclones

The eye is a region of mostly calm weather at the center of strong tropical cyclones. The eye of a storm is a roughly circular area, typically 30–65 km (20–40 miles) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds occur. The cyclone's lowest barometric pressure occurs in the eye and can be as much as 15 percent lower than the pressure outside the storm.

Latent heat Thermodynamic phase transition energy

Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.

In atmospheric science, the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure increases the most rapidly around a particular location. The pressure gradient is a dimensional quantity expressed in units of Pa/m

Due to Langmuir's efforts, and the research of Schaefer at General Electric, the concept of using cloud seeding to weaken hurricanes gathered momentum. Indeed, Schaefer had caused a major snowstorm on December 20, 1946 by seeding a cloud. [2] This caused GE to drop out for legal reasons. Schaefer and Langmuir assisted the U.S. military as advisors for Project Cirrus, the first large study of cloud physics and weather modification. Its most important goal was to try to weaken hurricanes. [5]

General Electric American industrial company

General Electric Company (GE) is an American multinational conglomerate incorporated in New York City and headquartered in Boston. As of 2018, the company operates through the following segments: aviation, healthcare, power, renewable energy, digital industry, additive manufacturing, venture capital and finance, lighting, and oil and gas.

Cloud physics Study of the physical processes in atmospheric clouds

Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of atmospheric clouds. These aerosols are found in the troposphere, stratosphere, and mesosphere, which collectively make up the greatest part of the homosphere. Clouds consist of microscopic droplets of liquid water, tiny crystals of ice, or both. Cloud droplets initially form by the condensation of water vapor onto condensation nuclei when the supersaturation of air exceeds a critical value according to Köhler theory. Cloud condensation nuclei are necessary for cloud droplets formation because of the Kelvin effect, which describes the change in saturation vapor pressure due to a curved surface. At small radii, the amount of supersaturation needed for condensation to occur is so large, that it does not happen naturally. Raoult's law describes how the vapor pressure is dependent on the amount of solute in a solution. At high concentrations, when the cloud droplets are small, the supersaturation required is smaller than without the presence of a nucleus.

Project Cirrus

Project Cirrus was the first attempt to modify a hurricane. It was a collaboration of the General Electric Corporation, the US Army Signal Corps, the Office of Naval Research, and the US Air Force. [1] After several preparations, and initial skepticism by government scientists, [6] the first attempt to modify a hurricane began on October 13, 1947 on a hurricane that was heading west to east and out to sea. [5]

An airplane flew along the rainbands of the hurricane, and dropped nearly 180 pounds (82 kilograms) of crushed dry ice into the clouds. [1] The crew reported "Pronounced modification of the cloud deck seeded". [5] It is not known if that was due to the seeding. Next, the hurricane changed direction and made landfall near Savannah, Georgia. The public blamed the seeding, and Irving Langmuir claimed that the reversal had been caused by human intervention. [6] Cirrus was canceled, [5] and lawsuits were threatened. Only the fact that a system in 1906 had taken a similar path, as well as evidence showing that the storm had already begun to turn when seeding began, ended the litigation. [5] This disaster set back the cause of seeding hurricanes for eleven years.

At first the seeding was officially denied and it took years before the government admitted it. According to the Sept. 12, 1965 edition of the Fort Lauderdale News and Sun-Sentinel, in 1947 a hurricane "went whacky" and "Twelve years later it was admitted the storm had in fact been seeded." [7]

Between the projects

Eye of Hurricane Esther Fly00716.jpg
Eye of Hurricane Esther

The United States Weather Bureau's National Hurricane Research Project, founded in 1955, had as one of its objectives to investigate the scientific validity of hurricane modification methods. To this end, silver iodide dispensers were tested in Hurricane Daisy in August 1958. The flares were deployed outside of the hurricane eyewall, so this was an equipment test rather than a modification experiment. The equipment malfunctioned in all but one of the flights, and no conclusive data was acquired. [5]

The first seeding experiment since the Cirrus disaster was attempted on September 16, 1961, into Hurricane Esther by NHRP and the United States Navy aircraft. Eight cylinders of silver iodide were dropped into Esther's eyewall, and winds were recorded as weakening by 10 percent. [8] The next day, more seeding flights were made. This time, the silver iodide did not fall into the eyewall, and no reduction in windspeed was observed. These two results were interpreted as making the experiment a "success". [9]

The seedings into Hurricane Esther led to the establishment of Project Stormfury in 1962. Project Stormfury was a joint venture of the United States Department of Commerce and the United States Navy. [9]

Project BATON

The objective of Project BATON was the analysis of the life history of thunderstorms. A Department of Defense research activity supported by the Advanced Research Project Agency, Project BATON sought to expand understanding of storm physics as an aid to weather forecasting, fire prevention, and, possibly, for artificially controlling the weather. Dr. Helmut Weickmann, as an employee of the U.S, Army Signal Research and Development Laboratory, and Dr. Paul MacCready of Meteorology Research, Inc., were joint leaders of the Project BATON team. [10]

During the 1962 July–August storm season in Flagstaff, Arizona, the scientists, selected "guinea pig" storms, and seeded them with chemicals. Effects were thoroughly analyzed from the ground and from the air with time-lapse motion picture cameras, stereo still cameras, storm radar, lightning detectors, and airborne heat sensors. Among the agents inserted in selected clouds were "condensation nuclei" which temporarily increased the number of water droplets in the cloud, and pulverized dry ice, which turns a portion of the cloud to fine snow crystals that remain aloft. The utilization of these agents facilitated study of a storm's characteristics. [10]

Project STORMFURY begins

Robert Simpson became its first director, serving in this capacity until 1965. [11] There were several guidelines used in selecting which storms to seed. The hurricane had to have a less than 10 percent chance of approaching inhabited land within a day; [12] it had to be within range of the seeding aircraft; and it had to be a fairly intense storm with a well-formed eye. [8] The primary effect of these criteria was to make possible seeding targets extremely rare. [13]

No suitable storms formed in the 1962 season. Next year, Stormfury began by conducting experiments on cumulus clouds. From August 17 to 20 of that year, experiments were conducted in 11 clouds, of which six were seeded and five were controls. In five of the six seeded clouds, changes consistent with the working hypothesis were observed. [14]

On August 23, 1963, Hurricane Beulah was the site of the next seeding attempt. It had an indistinct eyewall. In addition, mistakes were made, as the seedings of silver iodide were dropped in the wrong places. As a consequence, nothing happened. [9] The next day, another attempt was made, and the seeders hit their targets. The eyewall was observed to fall apart and be replaced by another eyewall with a larger radius. [14] The sustained winds also fell by twenty percent. [14] All in all, the results of the experiments on Beulah were "encouraging but inconclusive." [15]

In the six years after Beulah, no seedings were conducted for several different reasons. In 1964, measurement and observation equipment was not ready to be used. [14] The year after that, all flights were used for additional experimentation in non-hurricane clouds. [14]

Joanne Simpson became its director beginning in 1965. [11] [16] While out to sea in August of the 1965 Atlantic hurricane season, Stormfury meteorologists decided that Hurricane Betsy was a good candidate for seeding. [12] However, the storm immediately swung towards land, and on September 1, the planned flights were canceled. For some reason, the press was not notified that there were no seedings, and several newspapers reported that it had begun. [12] As Betsy passed close to the Bahamas and smashed into southern Florida, the public and Congress thought that seeding was underway and blamed Stormfury. [12] It took two months for Stormfury officials to convince Congress that Betsy was not seeded, and the project was allowed to continue. [12] A second candidate, Hurricane Elena, stayed too far out to sea. [14]

After Betsy, two other hurricanes came close to being seeded. Hurricane Faith was considered a likely candidate, but it stayed out of range of the seeding planes. [14] That same year, recon flights were conducted into Hurricane Inez, but there were no seedings. [14] Both the 1967 and 1968 seasons were inactive. Because of that, there were no suitable seeding targets in either of those two seasons. [14]

The eye of Hurricane Debbie on August 20 Eye of hurricane debbie (1969).jpg
The eye of Hurricane Debbie on August 20

Dr. R. Cecil Gentry became the director of Stormfury in 1968. [17] There were no more near-seedings until 1969. In the interim, equipment was improved. What once was the primitive method of hand-dumping dry ice was replaced with rocket canisters loaded with silver iodide, and then gun-like devices mounted on the wings of the airplanes that fired silver iodide into the clouds. Observation equipment was improved. [12] Additional reconnaissance data was utilized to modify the working hypothesis. The new theory took cumulus towers outside the eyewall into account. According to the revised theory, by seeding the towers, latent heat would be released. This would trigger the start of new convection, which would then cause a new eyewall. Since the new eyewall was outside the original one, the first eyewall would be choked of energy and fall apart. In addition, since the new eyewall was broader than the old one, the winds would be lower due to a less sharp pressure difference. [12]

Hurricane Debbie in 1969 provided the best opportunity to test the underpinnings of Project Stormfury. In many ways it was the perfect storm for seeding: it did not threaten any land; it passed within range of seeding aircraft; and was intense with a distinct eye. [18] On August 18 and again on August 20, thirteen planes flew out to the storm to monitor and seed it. On the first day, windspeeds fell by 31%. [14] On the second day, windspeeds fell by 18%. [14] Both changes were consistent with Stormfury's working hypothesis. Indeed, the results were so encouraging that "a greatly expanded research program was planned." [19] Among other conclusions was the need for frequent seeding at close to hourly intervals. [20]

The 1970 and 1971 seasons provided no suitable seeding candidates. [14] Despite this, flights were conducted into Hurricane Ginger. Ginger was not a suitable storm for seeding, due to its diffuse, indistinct nature. The seeding had no effect. Ginger was the last seeding done by Project Stormfury. [14]

After the seedings

Stormfury inside Tropical Storm Dorothy Tropical storm dorothy recon (1970).jpg
Stormfury inside Tropical Storm Dorothy

Atlantic hurricanes meeting all of the criteria were extremely rare, which made duplication of the "success" reached with Hurricane Debbie extremely difficult. Meanwhile, developments outside of meteorology hindered the cause of hurricane modification.

In the early 1970s, the Navy withdrew from the project. [21] Stormfury began to refocus its efforts on understanding, rather than modifying, tropical cyclones. [22] At the same time, the Project's aircraft were nearing the end of their operational lifetimes. At the cost of $30 million (year unknown) [21] two Lockheed P-3's were acquired. Due to the rarity of Atlantic hurricanes meeting the safety requirements, plans were made to move Stormfury to the Pacific and experiment on the large number of typhoons there. [13] This action required many of the same safety requirements as in the Atlantic, but had the advantage of a much higher number of potential subjects. [21]

The plan was to begin again in 1976, and seed typhoons by flying out of Guam. However, political issues blocked the plan. The People's Republic of China announced that it would not be happy if a seeded typhoon changed course and made landfall on its shores, [13] while Japan declared itself willing to put up with difficulties caused by typhoons because that country got more than half of its rainfall from tropical cyclones. [13]

Similar plans to operate Stormfury in the eastern north Pacific or in the Australian region also collapsed. [23]

Failure of the working hypothesis

Multiple eyewalls had been detected in very strong hurricanes before, including Typhoon Sarah [24] and Hurricane Donna, [25] although the double eyes were usually seen in very intense systems. Double eyewalls were also seen post-seeding in some of the seeded storms. At the time however, the only known times that rapid changes in eyewall diameter, other than during presumably successful seedings, was during rapid changes in intensity. [26] It remained controversial whether the seedings caused the secondary eyewalls or whether it was just a natural cycle [27] (as without further information, correlation does not imply causation). Basically, if eyewall changes similar to those observed in seeded hurricanes were rare in unseeded tropical cyclones, it would provide powerful evidence that Project Stormfury was successful. Conversely, if such changes were common in unseeded systems, it would throw doubt on the very hypothesis and assumptions driving Project Stormfury. [28]

Data and observations began to accumulate that debunked Stormfury's working hypothesis. Beginning with Hurricanes Anita and David, flights by Hurricane Hunter aircraft encountered events similar to what happened in "successfully" seeded storms. [28] Anita itself had a weak example of a concentric eyewall cycle, and David a more dramatic one. [27] In August 1980, Hurricane Allen passed through the Atlantic, Caribbean, and Gulf of Mexico. It also underwent changes in the diameter of its eye and developed multiple eyewalls. All this was consistent with the behavior that would have been expected of Allen had it been seeded. Thus, what Stormfury thought to have accomplished by seeding was also happening on its own. [29]

Other observations in Hurricanes Anita, David, Frederic, and Allen [30] also discovered that tropical cyclones have very little supercooled water and a great deal of ice crystals. [31] The reason that tropical cyclones have little supercooled water is that the updrafts within such a system are too weak to prevent water from either falling as rain or freezing. [32] As cloud seeding needed supercooled water to function, the lack of supercooled water meant that seeding would have no effect.

Those observations called the basis for Project Stormfury into question. In the middle of 1983, Stormfury was finally canceled after the hypothesis guiding its efforts was invalidated. [33]

Legacy

In the sense of weakening hurricanes to reduce their destructiveness, Project Stormfury was a complete failure because it did not distinguish between natural phenomena in tropical cyclones and the impact of human intervention. [31] Millions of dollars had been spent trying to do the impossible. In the end, "[Project] STORMFURY had two fatal flaws: it was neither microphysically nor statistically feasible." [33]

In addition, Stormfury had been a primary generator of funding for the Hurricane Research Division. While the project was operational, the HRD's budget had been around $4 million (1975 USD; $16 million 2008 USD), with a staff of approximately 100 people. [34] Today, the HRD employs 30 people and has a budget of roughly $2.6 million each year. [35]

However, Project Stormfury had positive results as well. Knowledge gained during flights proved invaluable in debunking its hypotheses. [35] Other science resulted in a greater understanding of tropical cyclones. In addition, the Lockheed P-3's were perfectly suitable for gathering data on tropical cyclones, allowing improved forecasting of these monstrous storms. [35] Those planes are still used by the NOAA today. [36]

Former Cuban president Fidel Castro alleged that Project Stormfury was an attempt to weaponize hurricanes. [37]

See also

Notes

  1. 1 2 3 Davies p 85
  2. 1 2 Whipple p. 150
  3. Landsea D9
  4. 1 2 Landsea D5
  5. 1 2 3 4 5 6 Whipple p 151
  6. 1 2 Willoughby, Jorgensen, Black, and Rosenthal p 505
  7. Vinciguerra, T. (12 Sept. 1965). Betsy's Turnaround Stirs Big Question. Fort Lauderdale News and Sun-Sentinel. Section C, page 1.
  8. 1 2 Davies p 89
  9. 1 2 3 Davies p 90
  10. 1 2 staff writers (August 1962). "Project BATON Probes Thunderstorm Origins To Improve Forecasts" (PDF). Army Research and Development. p. 12. Retrieved September 22, 2013.
  11. 1 2 Rob Gutro (1 June 2005). "Meet Dr. Joanne Simpson: Chief Scientist Emeritus for Meteorology, Earth Sun Exploration Division". Goddard Space Flight Center. Archived from the original on 17 June 2008.
  12. 1 2 3 4 5 6 7 Whipple p 153
  13. 1 2 3 4 Whipple p 154
  14. 1 2 3 4 5 6 7 8 9 10 11 12 13 Willoughby, Jorgensen, Black, and Rosenthal p 507
  15. R. Cecil Gentry, quoted in Davies p 90
  16. Herbert Leib (October 1966). "Project Stormfury" (PDF). ESSA World. Environmental Satellite Services Administration: 4.
  17. Staff (October 1968). "ESSA, Navy, Air Force Alert for 1968 Stormfury Season" (PDF). ESSA World. Environmental Satellite Services Administration: 34.
  18. Whipple p 153-54
  19. Gentry, quoted in Davies p 91
  20. Black, Senn, and Courtright p 216
  21. 1 2 3 Davies p 91
  22. Williams
  23. Willoughby, Jorgensen, Black, and Rosenthal p 508
  24. Black, Senn, and Courtright p 210
  25. Jordan and Schatzle pp 354-56
  26. Black, Senn, and Courtright p 213
  27. 1 2 Willoughby, Clos, and Shorebah p 396
  28. 1 2 Willoughby, Jorgensen, Black, and Rosenthal p 511
  29. Goldenberg
  30. Willoughby, Jorgensen, Black, and Rosenthal p 509
  31. 1 2 Hurricane Research Division
  32. Landsea C4
  33. 1 2 Willoughby, Jorgensen, Black, and Rosenthal p 513
  34. Davies p 92
  35. 1 2 3 Davies p 93
  36. Swanson and Williams
  37. Jack Shafer (March 22, 2010). "Schooling Ross Douthat in Conspiracy Theory". Slate .

Related Research Articles

Cyclone large scale air mass that rotates around a strong center of low pressure

In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. 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 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 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.

This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.

Atlantic hurricane tropical cyclone that forms in the North Atlantic Ocean

An Atlantic hurricane or tropical storm is a tropical cyclone that forms in the Atlantic Ocean, usually between the months of June and November. A hurricane differs from a cyclone or typhoon only on the basis of location. A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a cyclone occurs in the south Pacific or Indian Ocean.

Hot tower

A hot tower is a tropical cumulonimbus cloud that reaches out of the lowest layer of the atmosphere, the troposphere, and into the stratosphere. In the tropics, the border between the troposphere and stratosphere, the tropopause, typically lies at least 15 kilometres (9.3 mi) above sea level. These formations are called "hot" because of the large amount of latent heat released as water vapor condenses into liquid and freezes into ice. The presence of hot towers within the eyewall of a tropical cyclone can indicate possible future strengthening.

Landfall event of a storm moving over land after being over water

Landfall is the event of a storm or waterspout moving over land after being over water.

Central dense overcast

The central dense overcast, or CDO, of a tropical cyclone or strong subtropical cyclone is the large central area of thunderstorms surrounding its circulation center, caused by the formation of its eyewall. It can be round, angular, oval, or irregular in shape. This feature shows up in tropical cyclones of tropical storm or hurricane strength. How far the center is embedded within the CDO, and the temperature difference between the cloud tops within the CDO and the cyclone's eye, can help determine a tropical cyclone's intensity. Locating the center within the CDO can be a problem for strong tropical storms and with systems of minimal hurricane strength as its location can be obscured by the CDO's high cloud canopy. This center location problem can be resolved through the use of microwave satellite imagery.

Atlantic hurricane reanalysis project

The Atlantic hurricane reanalysis project of the National Oceanic and Atmospheric Administration seeks to correct and add new information about past North Atlantic hurricanes. It was started around 2000 to update HURDAT, the official hurricane database for the Atlantic Basin, which has become outdated since its creation due to various systematic errors introduced into the database over time. This effort has involved reanalyses of ship observations from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) as well as reanalyses done by other researchers over the years. It has been ongoing as of 2016, and should last another four years.

The National Hurricane Research Laboratory (NHRL) was formed in December 1964 out of the National Hurricane Research Project, the U. S. Weather Bureau's effort to scientifically examine tropical cyclones in order to make better predictions. Laboratory status signified that this effort was now a permanent part of the Weather Bureau's activities.

South-West Indian Ocean tropical cyclone type of tropical cyclone located in South West Indian Ocean and measured by Météo-France La Reunion scale

In the south-west Indian Ocean, tropical cyclones form south of the equator and west of 90° E to the coast of Africa.

The maximum sustained wind associated with a tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are determined via their sampling and averaging the sampled results over a period of time. Wind measuring has been standardized globally to reflect the winds at 10 metres (33 ft) above the Earth's surface, and the maximum sustained wind represents the highest average wind over either a one-minute (US) or ten-minute time span, anywhere within the tropical cyclone. Surface winds are highly variable due to friction between the atmosphere and the Earth's surface, as well as near hills and mountains over land.

Hurricane Debbie (1969) Category 3 Atlantic hurricane in 1969

Hurricane Debbie was an intense and long-lived hurricane that formed during August 1969. The fifth tropical cyclone, fourth named storm, third hurricane and second major hurricane of the 1969 Atlantic hurricane season, Debbie formed on August 14 in the southern Atlantic Ocean and took a general northwesterly path until turning northward into the central Atlantic. The storm was characterized by numerous fluctuations in intensity, and it reached winds corresponding to Category 3 status on the Saffir–Simpson Hurricane Scale on four separate occasions. The hurricane bypassed the island of Bermuda to the southeast on August 22, before ultimately brushing southeastern Newfoundland with strong winds. It dissipated over the cold waters east of Greenland. Although Debbie had little effect on land, it was extensively researched and was subject to a weather modification experiment by Project Stormfury, in which it was seeded with silver iodide.

Eyewall replacement cycle

Eyewall replacement cycles, also called concentric eyewall cycles, naturally occur in intense tropical cyclones, generally with winds greater than 185 km/h (115 mph), or major hurricanes. When tropical cyclones reach this intensity, and the eyewall contracts or is already sufficiently small, some of the outer rainbands may strengthen and organize into a ring of thunderstorms—an outer eyewall—that slowly moves inward and robs the inner eyewall of its needed moisture and angular momentum. Since the strongest winds are in a cyclone's eyewall, the tropical cyclone usually weakens during this phase, as the inner wall is "choked" by the outer wall. Eventually the outer eyewall replaces the inner one completely, and the storm may re-intensify.

Tropical convective clouds play an important part in the Earth's climate system. Convection and release of latent heat transports energy from the surface into the upper atmosphere. Clouds have a higher albedo than the underlying ocean, which causes more incoming solar radiation to be reflected back to space. Since the tops of tropical systems are much cooler than the surface of the Earth, the presence of high convective clouds cools the climate system.

Weather modification in North America has been taking place since at least the 1950s. Programs related to this field have been authorized by the governments of both the United States and Canada.

References