I. Introduction to Meteorology

Hurricane Isabel (2003) as seen from orbit during Expedition 7 of the International Space Station. The eye, eyewall and surrounding rainbands that are characteristics of tropical cyclones are clearly visible in this view from space. (Image:

1. Intriguing weather and climate
2. Monsoon and local circulation
3. Weather nouns and jargon
4. Common phraseology in weather forecast
5. What is the probability of precipitation forecast?
II. The Atmosphere
1. Vertical temperature profile of the atmosphere
2. Greenhouse effect and cooling effect of the atmosphere
3. Air mass
4. Front
5. Low pressure and high pressure
6. Cloud and weather
7. Winds and wind systems on the Earth
8. Beaufort scale8a. SaffirSimpson Hurricane Wind Scale
III. Weather Phenomena
1. Haze
2. Hail
3. Tornado
4. Rainbow and secondary rainbow
5. Halo
6. Foehn
7. Fog
8. Land-sea breezes
9. Mountain-valley breezes
10. Thunderstorm
11. Typhoon
12. Special weather phenomena in Taiwan
13. Mist
IV. Climate Phenomena
1. El Niño
2. La Niña
3. The formation of monsoons
4. Mei-Yu in Taiwan
V. Artificial Rain
1. The principle of artificial rain
2. The practice of artificial rain
3. The effectiveness of artificial rain

US National Weather Service JetStream Online School for Weather

Jetstream Topics:

  1. Why JetStream?
  2. The Atmosphere
  3. The Ocean
  4. Global Weather
  5. Synoptic Meteorology
  6. Thunderstorms
  7. Lightning
  8. Tropical Weather
  9. Doppler Radar
  10. Remote Sensing
  11. Weather on the Web
  12. The National Weather Service
  13. Appendix


Zooniverse Cyclone Center is a web-based interface that enables the public to help analyze the intensities of past tropical cyclones around the globe. The global intensity record contains uncertainties caused by differences in analysis procedures around the world and through time. Patterns in storm imagery are best recognized by the human eye, so scientists are enlisting the public. Interested volunteers will be shown one of nearly 300,000 satellite images. They will answer questions about that image as part of a simplified technique for estimating the maximum surface wind speed of tropical cyclones. This public collaboration will perform more than a million classifications in just a few months—something it would take a team of scientists more than a decade to accomplish. The end product will be a new global tropical cyclone dataset that provides 3-hourly tropical cyclone intensity estimates, confidence intervals, and a wealth of other metadata that could not be realistically obtained in any other fashion.


BBC Video: How solar storms create Northern Lights

24 May 2013:

The Weather Network

National Hurricane Center: Beware of the storm surge

The Canadian Press

Friday, May 24, 2013, 2:18 PM –

During a hurricane, the storm surge poses the greatest threat to life and land, yet many people dont even know what it means.

Simply put, storm surge is the abnormal rise of sea water. Predicting it is far more complicated and explaining it is tricky, too, as forecasters at the National Hurricane Center in the U.S. discovered, again, during a review of Superstorm Sandy.

File photo

File photo

This hurricane season, forecasters hope to offer easy-to-understand colour-coded maps and they are changing the way they talk to emergency officials, the media and the public.
Scientists by their very nature use very sophisticated language, technical language, said Jamie Rhome, leader of the hurricane centres storm surge team. It turns out that nobody else understands what were talking about. So once we figured that out, we started using more plain language.
Forecasts during Sandy were exceptionally accurate, but often confusing. Perhaps because so many things contribute to storm surge: intensity, pressure, forward speed, size, where it makes landfall and other factors.
Most people believe storm surge is a wall of water, similar to a tsunami, but its actually just sea water being pushed toward the shore by winds. It can happen quickly and move kilometres inland, flooding areas not accustomed to being inundated with sea water.
Large death tolls have been blamed storm surge. At least 1,500 people died during Hurricane Katrina either directly or indirectly because of storm surge, the hurricane centre said.
To better explain the danger, forecasters talked to focus groups consisting of local and state officials, law enforcement and hospital associations and other people from Maine to New Orleans. One thing they found out is that when they talk about storm surge, they should say height instead of depth when explaining how water levels might change.
We were using depth, thinking this was very clear. It turns out that nobody else does, Rhome said. Theyre waiting for height, how high it is, and I would never have guessed in a million years that one word — one word — makes a difference in how people interpret something.
Forecasters also will try to stress that the storm surge isnt just from the ocean and can come from other bodies of water such as sounds, bays and lakes, sometimes well inland.
The hurricane centre also plans to show people where to expect storm surge with high resolution, colour-coded maps, much like a radar map on the local news showing rain and severe weather. If they cant post the maps on the hurricane centres website this storm season, which begins June 1, the plan is to have the maps ready in 2014. theweathernetwork

Beaufort Wind Scale

Saffir-Simpson Hurricane Wind Scale

The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a hurricane’s sustained wind speed. This scale estimates potential property damage. Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for significant loss of life and damage. Category 1 and 2 storms are still dangerous, however, and require preventative measures. In the western North Pacific, the term “super typhoon” is used for tropical cyclones with sustained winds exceeding 150 mph.

Category Sustained Winds Types of Damage Due to Hurricane Winds
1 74-95 mph
64-82 kt
119-153 km/h
Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.
2 96-110 mph
83-95 kt
154-177 km/h
Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.
111-129 mph
96-112 kt
178-208 km/h
Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.
130-156 mph
113-136 kt
209-251 km/h
Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
157 mph or higher
137 kt or higher
252 km/h or higher
Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
Conceptual animation illustrates the wind damage associated with increasing hurricane intensity – courtesy of The COMET Program

More Information

If you have trouble viewing linked files, obtain a free viewer for the file format:

Tropical Cyclone Classification Guide



20 July 2013: U.S. and U.K. heat waves caused by new extreme weather pattern

The extremely cold temperatures from last winter and the current stifling heat waves blanketing the U.S. and U.K. are caused by what may be an increasingly common type of weather formation called a blocking high.

25 July 2013:

Meteorology: Rivers in air could boost flooding 2507132055z (Link)

Noctilucent Clouds

From Wikipedia, the free encyclopedia
Noctilucent cloud
Noctilucent clouds over Kuresoo bog, Viljandimaa, Estonia

Noctilucent clouds over Kuresoo bog, Viljandimaa, Estonia
Abbreviation NLC/PMC
Altitude 76,000 to 85,000 m
(250,000 to 280,000 ft)
Classification Other
Precipitation cloud? No

Night clouds or noctilucent clouds are tenuous cloud-like phenomena that are the ragged-edge of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. Noctilucent roughly means night shining in Latin. They are most commonly observed in the summer months at latitudes between 50 and 70 north and south of the equator. They can only be observed when the Sun is below the horizon.

They are the highest clouds in Earths atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometres (47 to 53 mi). They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earths shadow. Noctilucent clouds are not fully understood and are a recently-discovered meteorological phenomenon; there is no record of their observation before 1885.

Noctilucent clouds can form only under very restrictive conditions; their occurrence can be used as a sensitive guide to changes in the upper atmosphere. They are a relatively recent classification. The occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent. It is theorized that this increase is connected to climate change.



Night clouds or noctilucent clouds are composed of tiny crystals of water ice up to 100nm in diameter[1] and exist at a height of about 76 to 85 km (47 to 53 mi),[2] higher than any other clouds in Earths atmosphere.[3] Clouds in the Earths lower atmosphere form when water collects on particles, but mesospheric clouds may form directly from water vapour[4] in addition to forming on dust particles.[5]

The sources of both the dust and the water vapour in the upper atmosphere are not known with certainty. The dust is believed to come from micrometeors, although particulates from volcanoes and dust from the troposphere are also possibilities. The moisture could be lifted through gaps in the tropopause, as well as forming from the reaction of methane with hydroxyl radicals in the stratosphere.[6]

The exhaust from Space Shuttles, which was almost entirely water vapour after the detachment of the Solid Rocket Booster at a height of about 46km, was found to generate minuscule individual clouds. About half of the vapour was released into the thermosphere, usually at altitudes of 103 to 114 km (64 to 71 mi).[7]

This exhaust can be transported to the Arctic region in little over a day, although the exact mechanism of this very high-speed transport is unknown. As the water migrates northward, it falls from the thermosphere down into the colder mesosphere, which occupies the region of the atmosphere just below.[8] Although this mechanism is the cause of individual noctilucent clouds, it is not thought to be a major contributor to the phenomenon as a whole.[6]

As the mesosphere contains very little moisture, approximately one hundred millionth that of air from the Sahara desert,[9] and is extremely thin, the ice crystals can only form at temperatures below about −120 C (−184F).[6] This means that noctilucent clouds form predominantly during summer when, counterintuitively, the mesosphere is coldest,[10] therefore they cant be observed (even if they are present) inside the Polar circles because the Sun is never low enough under the horizon at this season at these latitudes.[11] Noctilucent clouds form mostly near the polar regions,[5] because the mesosphere is coldest there.[11] Clouds in the southern hemisphere are about 1km (0.62mi) higher than those in the northern hemisphere.[5]

Ultraviolet radiation from the Sun breaks water molecules apart, reducing the amount of water available to form noctilucent clouds. The radiation is known to vary cyclically with the solar cycle and satellites have been tracking the decrease in brightness of the clouds with the increase of ultraviolet radiation for the last two solar cycles. It has been found that changes in the clouds follow changes in the intensity of ultraviolet rays by about a year, but the reason for this long lag is not yet known.[12]

Noctilucent clouds are known to exhibit high radar reflectivity,[10] in a frequency range of 50MHz to 1.3GHz.[13] This behaviour is not well understood but a Caltech professor, Paul Bellan, has proposed a possible explanation: that the ice grains become coated with a thin metal film composed of sodium and iron, which makes the cloud far more reflective to radar,[10] although this explanation remains controversial.[14] Sodium and iron atoms are stripped from incoming micrometeors and settle into a layer just above the altitude of noctilucent clouds, and measurements have shown that these elements are severely depleted when the clouds are present. Other experiments have demonstrated that, at the extremely cold temperatures of a noctilucent cloud, sodium vapour can rapidly be deposited onto an ice surface.[15]

Discovery and investigation

Noctilucent clouds over Bargerveen, Drenthe, Netherlands

Noctilucent clouds are first known to have been observed in 1885, two years after the 1883 eruption of Krakatoa.[5][16] It remains unclear whether their appearance had anything to do with the volcano eruption, or whether their discovery was due to more people observing the spectacular sunsets caused by the volcanic debris in the atmosphere. Studies have shown that noctilucent clouds are not caused solely by volcanic activity, although dust and water vapour could be injected into the upper atmosphere by eruptions and contribute to their formation.[11] Scientists at the time assumed the clouds were another manifestation of volcanic ash, but after the ash had settled out of the atmosphere, the noctilucent clouds persisted.[9] Finally, the theory that the clouds were composed of volcanic dust was disproved by Malzev in 1926.[16] In the years following their discovery the clouds were studied extensively by Otto Jesse of Germany, who was the first to photograph them, in 1887, and seems to have been the one to coin the term noctilucent cloud,[17] which means night-shining cloud.[1] His notes provide evidence that noctilucent clouds first appeared in 1885. He had been doing detailed observations of the unusual sunsets caused by the Krakatoa eruption the previous year and firmly believed that, if the clouds had been visible then, he would undoubtedly have noticed them.[18] Systematic photographic observations of the clouds were organized in 1887 by Jesse, Foerster, and Stolze and, after that year, continuous observations were carried out at the Berlin Observatory.[19] During this research the height of the clouds was first determined, via triangulation.[20] The project was discontinued in 1896.

In the decades after Otto Jesses death in 1901, there were few new insights into the nature of noctilucent clouds. Wegeners conjecture, that they were composed of water ice, was later shown to be correct.[21] Study was limited to ground-based observations and scientists had very little knowledge of the mesosphere until the 1960s, when direct rocket measurements began. These showed for the first time that the occurrence of the clouds coincided with very low temperatures in the mesosphere.[22]

Noctilucent clouds were first detected from space by an instrument on the OGO-6 satellite in 1972. The OGO-6 observations of a bright scattering layer over the polar caps were identified as poleward extensions of these clouds.[23] A later satellite, the Solar Mesosphere Explorer, mapped the distribution of the clouds between 1981 and 1986 with its ultraviolet spectrometer.[23] The clouds were detected with a lidar in 1995 at Utah State University, even when they were not visible with the naked eye.[24] The first physical confirmation that water ice is indeed the primary component of noctilucent clouds came from the HALOE instrument on the Upper Atmosphere Research Satellite in 2001.[25]

In 2001 the Swedish Odin satellite performed spectral analyses on the clouds, and produced daily global maps that revealed large patterns in their distribution.[26]

On April 25, 2007, the AIM satellite (Aeronomy of Ice in the Mesosphere) was launched.[27] It is the first satellite dedicated to studying noctilucent clouds,[28] and made its first observations on May 25, 2007.[29] Images taken by the satellite show shapes in the clouds that are similar to shapes in tropospheric clouds, hinting at similarities in their dynamics.[1]

On August 28, 2006, scientists with the Mars Express mission announced that they found clouds of carbon dioxide crystals over Mars that extended up to 100km (62mi) above the surface of the planet. They are the highest clouds discovered over the surface of a planet. Like noctilucent clouds on Earth, they can only be observed when the Sun is below the horizon.[30]

Research published in the journal Geophysical Research Letters in June 2009 suggests that noctilucent clouds observed following the Tunguska Event are evidence that the impact was caused by a comet.[31][32]

The United States Naval Research Laboratory (NRL) and the United States Department of Defense Space Test Program (STP) conducted the Charged Aerosol Release Experiment (CARE) on September 19, 2009, using exhaust particles from a Black Brant XII suborbital sounding rocket launched from NASAs Wallops Flight Facility to create an artificial noctilucent cloud. The cloud was to be observed over a period of weeks or months by ground instruments and the Spatial Heterodyne IMager for MEsospheric Radicals (SHIMMER) instrument on the NRL/STP STPSat-1 spacecraft.[33] The rockets exhaust plume was observed and reported to news organizations in the United States from New Jersey to Massachusetts.[34]


Noctilucent clouds are generally colourless or pale blue,[35] although occasionally other colours including red and green occur.[36] The characteristic blue colour comes from absorption by ozone in the path of the sunlight illuminating the noctilucent cloud.[37] They can appear as featureless bands,[35] but frequently show distinctive patterns such as streaks, wave-like undulations, and whirls.[38] They are considered a beautiful natural phenomenon.[39] Noctilucent clouds may be confused with cirrus clouds, but appear sharper under magnification.[35] Those caused by rocket exhausts tend to show colours other than silver or blue,[36] because of iridescence caused by the uniform size of the water droplets produced.[40]

Noctilucent clouds photographed by the crew of the ISS

Noctilucent clouds may be seen by observers at a latitude of 50 to 65.[41] They seldom occur at lower latitudes (although there have been sightings as far south as Utah, Italy, and Paris),[35][42] and closer to the poles it does not get dark enough for the clouds to become visible.[43] They occur during summer, from mid-May to mid-August in the northern hemisphere and between mid-November and mid-February in the southern hemisphere.[35] They are very faint and tenuous, and may only be observed in twilight around sunrise and sunset when the clouds of the lower atmosphere are in shadow, but the noctilucent cloud is illuminated by the Sun.[43] They are best seen when the Sun is between 6 and 16 below the horizon.[44] Although noctilucent clouds occur in both hemispheres, they have been observed thousands of times in the northern hemisphere, but fewer than 100 times in the southern. Southern hemisphere noctilucent clouds are fainter and occur less frequently; additionally the southern hemisphere has a lower population and less land area from which to make observations.[11][45]

The clouds may show a large variety of different patterns and forms. An identification scheme was developed by Fogle in 1970 that classified five different forms. These classifications have since been modified and subdivided.[46]

They may be studied from the ground, from space, and directly by sounding rocket. Also, some noctilucent clouds are made of smaller crystals, 30nm or less, which are invisible to observers on the ground because they do not scatter enough light.[1]

Connection to climate change

There is evidence that the relatively recent appearance of noctilucent clouds, and their gradual increase, may be linked to climate change.[47] The author of this study, atmospheric scientist Gary Thomas of the Laboratory for Atmospheric and Space Physics at the University of Colorado has pointed out[1] that the first sightings coincide with both Krakatoa and the nascent Industrial Revolution, and they have become more widespread and frequent throughout the twentieth century, including an uptick between 1964 and 1986. The connecting of global warming and noctilucent clouds however, remains controversial.[1] Gary Thomas may have penned his paper after Wilfried Schrder, who might hold the distinction of being the first to explain noctilucent clouds as indicators for atmospheric processes (Gerlands Beitrge zur Geophysik, 1971, Meteorologische Rundschau 19681970.[48]

Climate models predict that increased greenhouse gas emissions cause a cooling of the mesosphere, which would lead to more frequent and widespread occurrences of noctilucent clouds.[45] A competing theory is that larger methane emissions from intensive farming activities produce more water vapour in the upper atmosphere.[11] Methane concentrations have more than doubled in the past 100 years.[2]

Tromp et al. also controversially, suggest that a transition to a hydrogen economy, and this resulting in an increases of the free hydrogen concentration of the atmosphere by 1 ppm, would increase the number of noctilucent clouds.[49]

See also

Video credit: TheDaveWalker)

Published on Jun 9, 2013

Astonishing display over Blackrod.
The display lasted all night, it was amazing.
254 shots, 15 seconds each, taken between midnight and 3AM.


Animated map of global wind conditions

(Image via

This mesmerizing Earth Wind Map (Click here) showcases real-time or near real-time, data on global wind conditions in the form of snaking neon lines. Breezes are represented by thin strands of green lines, strong winds with long streaks of yellow, while the most violent currents are shown in red.

The Earth Wind Map gathers weather data from the Global Forecast System at the National Center for Environmental Prediction, a NOAA initiative. The script then translates the data into a user friendly interactive animation.


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