Thursday, January 22, 2009
Saturday, January 10, 2009
Arbiters of Energy
If there’s one thing atmospheric scientists have discovered about clouds in recent years it’s that they still have much to learn about them. Sure, scientists know what clouds look like, what they’re made of, and how and why they form and dissipate. But they are struggling to predict how clouds will change in the future. Specifically, how will their composition, structure, and extent change if the surface of our planet grows significantly warmer? Two teams of scientists surprised the Earth science community recently by publishing evidence that tropical atmospheric circulation patterns are more intense in the 1990s than the 1980s, thereby changing the structure and extent of clouds in the tropics (Wielicki, et al. 2002; Chen et al. 2002).
One indicator for how well scientists understand a given phenomenon of nature is how well they can predict it. It is inherently difficult to predict cloud behavior because there are so many variables that are constantly changing over time and space, and these variables influence one another (such as surface temperature and air temperature, wind currents, varying amounts of water vapor, abundance of aerosol particles, etc.). All meteorological models inevitably fail at some point due to the sheer complexity of the Earth’s system. In fact, chaos theory shows that weather will never be predictable with any significant accuracy for longer than 2 weeks, even with a nearly perfect model and nearly perfect input data. So missing a prediction of cloudiness on a given day is no big surprise. But climate is the average of many weather events, and may be predictable at longer time scales ranging from seasons to decades to centuries. Today, climate models are in an early development stage somewhat similar to the status of weather prediction 30 years ago. As a result, the recent observations of cloudiness changes from the 1980s to the 1990s are particularly useful tests of how well the models perform. So far, the climate observations and climate models don’t agree very well.
But why even bother with clouds? Why do we care about them?
Clouds are the arbiters the Earth’s energy budget. They are so plentiful and widespread, clouds cover up to 60 percent of our planet at any given time. They play a major role in governing how much sunlight reaches the surface, how much sunlight is reflected back up to space, how and where warmth is spread around the globe, and how much heat escapes from the surface and atmosphere back into space. In short, clouds are a key component of Earth’s climate system, and scientists cannot construct accurate global climate models until they gain a better understanding of cloud physics.
Clouds play a crucial role in regulating the balance of energy received by and emitted from the Earth, but scientists aren’t sure exactly what this role is. How much solar energy do different types of clouds reflect? How much heat do clouds trap? How will clouds change as humans change the Earth’s surface and atmosphere? New satellite instruments and controversial theories are motivating scientists to answer these questions.
Currently, scientists are focusing their attention on the tropics because, over the course of a year, the tropics receive more of the sun’s warmth than anywhere else on Earth. Air and ocean currents help spread this warmth toward the poles. Since the tropics are covered mostly by warm ocean water and since warmer water evaporates more readily, there is a direct relationship between higher sea surface temperatures and cloud formation. Certain types of clouds (i.e., marine stratocumulus) tend to cool the surface by reflecting sunlight, and certain types of clouds (i.e., cirrus) tend to warm the surface by allowing sunlight to pass through and then trapping the heat radiated by the surface. So there is a physical feedback loop between sea surface temperature and cloud formation in that each influences the other.
This understanding frames the importance of the original question: How will tropical clouds change if tropical sea surface temperatures warm significantly? One team of scientists recently proposed that the Earth has a built-in mechanism for changing the structure and distribution of certain types of clouds in the tropics to release more radiant energy into outer space as the surface warms (Lindzen et al. 2001). Dubbed the “Iris Hypothesis,” this theory generated considerable buzz among science and political circles alike because, if true, it would mean that the Earth’s climate system naturally counteracts global warming by allowing more heat to escape through the top of the atmosphere.
But when another team of scientists at NASA’s Langley Research Center (LaRC) plugged these satellite measurements into the same Iris Hypothesis model, they found a slight increase in surface temperatures (Lin et al. 2001). How can the same model produce two very different results? The answer, it turns out, is that all clouds are not created equal. The answer you get depends heavily on the type of cloud you assume in your model. Part one of this three-part series of articles on tropical clouds presents an overview of the Iris Hypothesis as well as the contrasting findings of the NASA LaRC Team.
A second science team examined the Iris Hypothesis in light of current understanding of general circulation patterns within the ocean and atmosphere. Led by Dennis Hartmann, a physicist within Washington University’s Department of Atmospheric Sciences, this second team had major disagreements with some of the key assumptions made by Lindzen’s team (Fu et al. 2001). Thus, when they repeated Lindzen’s model experiment, they arrived at significantly different findings. Moreover, based upon their own analysis of the data, they report that none of the shrinkage in cirrus clouds proposed by Lindzen is due to an increase in sea surface temperature (Hartmann and Michelsen 2002). Part two of this three part series of articles presents an overview of current research into oceanic and atmospheric circulation patterns around the globe and how factors outside of the tropics can influence cloud formations within the tropics (Lau et al. 1997).
Yet recent satellite remote sensing data suggest that the structure and amount of tropical clouds (located between 30°N and 30°S latitudes) has changed substantially from the 1980s to the 1990s, thereby influencing the Earth’s radiant energy budget (Wielicki et al. 2002). The evidence for the change in cloud patterns, according to another team of scientists led by Junye Chen at NASA’s Goddard Institute for Space Studies, points to an overall strengthening of tropical atmospheric circulation patterns through the 1990s (Chen et al. 2002). Could this be a signal that the climate system is changing? Or, is the change merely a short-term anomaly? The third article in this three-part series will explore in detail these new findings and discuss their implications within the context of global warming.
Monday, December 8, 2008
Introduction to meteorology and physical oceanography
Meteorology (from Greek μετέωρος, metéōros, "high in the sky"; and -λογία, -logia) is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting (in contrast with climatology). Meteorological phenomena are observable weather events which illuminate and are explained by the science of meteorology. Those events are bound by the variables that exist in Earth's atmosphere. They are temperature, air pressure, water vapor, and the gradients and interactions of each variable, and how they change in time. The majority of Earth's observed weather is located in the troposphere. [1] [2]
Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology compose the interdisciplinary field of hydrometeorology.
Interactions between Earth's atmosphere and the oceans are part of coupled ocean-atmosphere studies. Meteorology has application in many diverse fields such as the military, energy production, transport, agriculture and construction.
Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.
Physical oceanography is one of several sub-domains into which oceanography is divided; others include biological, chemical and geological oceanographies.
Dimensions of Ocean
The oceans are far deeper than the continents are tall; examination of the earth's hypsographic curve shows that the average elevation of Earth's landmasses is only 840 metres (2,800 ft), while the ocean's average depth is 3,800 metres (12,000 ft). Though this apparent discrepancy is great, for both land and sea, the respective extremes such as mountains and trenches are rare.[1]
Area, volume plus mean and maximum depths of oceans (excluding adjacent seas) Body Area (106km²) Volume (106km³) Mean depth (m) Maximum (m) Pacific Ocean 165.2 707.6 4282 -10911 Atlantic Ocean 82.4 323.6 3926 -8605 Indian Ocean 73.4 291.0 3963 -8047 Southern Ocean 20.3-7235 Arctic Ocean 14.1
1038
Caribbean Sea 2.8
-7686
--
supernova:1572
In 1572, a "new star" appeared in the sky which stunned astronomers and exploded ancient theories of the universe.
Now the supernova recorded by Tycho Brahe has been glimpsed again, by Max Planck Institute scientists.
They used telescopes in Hawaii and Spain to capture faint light echoes of the original explosion, reflected by interstellar dust.
This "fossil imprint" of Tycho's famous supernova is reported in Nature.
The study will help solve a 400-year-old mystery over the nature of the celestial event which captivated observers across the globe.
In early November 1572, the brilliant "new star" appeared in the constellation Cassiopeia, and was even visible during daylight.
Among those who marvelled was the great Danish astronomer Tycho Brahe, who recorded its precise position in his book, "Stella Nova".
His measurements revealed the "new star" was located far beyond the Moon - contradicting the Aristotelian tradition that such stars were unchangeable - which had dominated western thinking for nearly 2000 years.
This set the stage for the work of Kepler, Galileo, Newton and others.
Stella Nova
"The supernova of 1572 marked a milestone in the history of science," said Oliver Krause, of the Max Planck Institute for Astronomy, Germany.
"It ultimately led to the abandonment of the notion of the immutability of the heavens.
"But its classification has been controversial.
"The determination of the exact supernova type has not been possible, without spectroscopic information."
Based on historic records, Tycho's supernova [SN 1572] has traditionally been interpreted as a type Ia supernova.
Such supernovas are believed to occur when a white dwarf star undergoes a titanic, thermonuclear explosion.
Material from the star is ejected at up to 18,000 miles per second - or one-tenth of the speed of light.
The debris from Tycho's supernova has expanded over the last 400 years into a cloud of gas and dust with a diameter of more than 20 light years.
But the nature of the original explosive event which created this remnant has remained unresolved.
Cosmic flashbulb
To elucidate, Dr Krause and his team conducted a "post-mortem", by training their telescopes on faint light echoes from the original event.
A supernova explosion acts like a cosmic flashbulb - producing light that propagates in all directions.
The first direct light wave from the explosion swept past Earth in 1572, observed by Brahe.
But even today, further waves of light from the original explosion continue to reach Earth indirectly - reflected in the "mirror" of interstellar dust particles.
These "light echoes" contain a kind of "fossil imprint" of the original supernova, and are used by astronomers to "time travel" back to witness ancient cosmic events.
Dr Krause and his team were able to detect an optical spectrum of Tycho's supernova at near maximum brightness, using telescopes at the Calar Alto observatory, Spain, and at Mauna Kea, Hawaii.
"We find that it belongs to the majority class of normal type Ia supernovae," said Dr Krause.
"An exciting opportunity now would be to use other [light echoes] to construct a three-dimensional spectroscopic view of the explosion."
The new measurements may also shed light on important, unsolved questions about how type Ia supernovae arise.
In one model, a white dwarf star accumulates (accretes) material from a companion star until it reaches a critical mass and undergoes a thermonuclear explosion.
In another, the accretion occurs by the merging of two white dwarfs.
The proximity of Tycho - which lies in the Milky Way - makes it an ideal candidate for more detailed studies.
"The technique of observing light echoes from supernovae is a remarkable observational tool," said Dr Andrea Pastorello, of Queens University, Belfast.
"It will allow astrophysicists to characterise other supernova remnants in our galaxy and in nearby galaxies.
"This will hopefully clarify the relationship between supernova relics and their explosion mechanisms.
"Finally, it is likely that precise information about the frequency of the different supernova types in our galaxy and its surroundings will shed light on the star-formation history and chemical evolution of the local group of galaxies."
India & terror; what can we do?
Mumbai, India's financial capital, has been targeted before.
In March 1993, a series of car bombs were detonated at public landmarks across the city, including the stock exchange, killing 257 people.
Those attacks, in which the city's underworld played a key role, followed Hindu-Muslim violence in the city during December 1992 and January 1993. Working-class Muslims were the principal victims, often shot at point-blank range by members of the city's police force.
In July 2006, a series of bombs planted on Mumbai's commuter train network killed 183 people.
Other Indian cities have been regularly targeted as well, particularly Delhi, the capital.
In October 2005 bombs exploded in crowded Delhi markets on the eve of the festive day Diwali, the festival of lights. More than 60 people were killed.
Most recently, in July 2008, bombs exploded at a number of congested public locations in Ahmedabad, the capital of the western state of Gujarat.
 India's parliament was attacked in 2001, leaving nine people dead. |
Gujarat, one of India's most prosperous states, saw large-scale killings of Muslims in 2002 after an arson attack on a train in the state killed 59 Hindu nationalist activists.
More than 50 people were killed in the Ahmedabad bombings.
A previously unknown group, the Indian Mujahideen, claimed responsibility.
The Ahmedabad attacks were particularly vicious in that bombs were detonated outside the emergency facilities of city hospitals just as people injured in other explosions were being brought in by ambulances.
Frontal assault
So what is new about Mumbai, November 2008?
 |  It is tempting to label the attackers as 'crazies' - but such a dismissive appellation may be misplaced  Sumantra Bose  |
The obvious novelty is the use of frontal assault tactics instead of timed explosive devices.
This is new in the urban Indian context. There was one notable exception - an attack by a five-man squad armed with rifles and grenades on India's Parliament in New Delhi in December 2001.
The attackers were narrowly prevented by alert staff from gaining access to the building, where hundreds of parliamentarians and ministers were attending a session.
They were gunned down near the entrance by security personnel after an hour-long battle.
Nine guards and parliament stewards also died.
This attack led to the crisis of 2002 between India and Pakistan.
The Indian government blamed Pakistani religious radicals, and embarked on a major military build-up on the border with Pakistan, to which Pakistan responded with its own mobilisation.
The stand-off eventually wound down later in 2002 after months of tension and brinkmanship.
But frontal assaults, usually carried out by two-man teams firing semi-automatic rifles and lobbing grenades, were the favoured tactic of the insurgency in Indian-administered Kashmir between 1999 and 2003.
Fidayeen technique
Scores of such attacks were carried out by "fidayeen" (literally "death-defying") squads in Indian-administered Kashmir during that period.
 Ahmedabad saw rioting after the Gujarat killings in 2002 |
Most of the locations targeted were Indian military and police installations in the Kashmir Valley, particularly in the regional capital Srinagar.
But some attacks targeted civilians, especially in and around the Hindu-majority city of Jammu, in the southern part of Indian-administered Kashmir.
The perpetrators were not members of the main homegrown Kashmiri insurgent group, the Hizb-ul Mujahideen ("Warriors of the Faith").
The fidayeen technique - a rudimentary form of "shock and awe" warfare - was introduced into Kashmir by Pakistani radical organisations that entered the Kashmir insurgency from the mid-1990s onwards.
The large majority of fidayeen attacks in Kashmir were perpetrated by one such organisation, the Lashkar-e-Toiba, headquartered in Pakistan and founded and led by Pakistani religious radicals.
The Lashkar-e Toiba did over time recruit a handful of local Kashmiris as fidayeen cadre, but most of the attackers were Pakistani nationals who had crossed into Indian-administered Kashmir.
Fidayeen attacks have died down in Kashmir since India-Pakistan relations thawed from 2004 onward.
But the deployment of exactly the same tactic in central Mumbai shows that this technique has now found a new and even more dangerous theatre in which to operate.
Method
The tactic is thus not without precedent, but the mayhem in Mumbai may nonetheless mark a new chapter in the evolution of urban terrorism in India.
Bombs planted in markets and on commuter trains kill and maim working-class and middle-class Indians.
The gunmen who attacked two luxury hotels, and a fashionable cafe frequented by visiting Westerners, have brought the "war" - as they see it - to India's elite class, and to affluent Westerners living in or visiting India's most cosmopolitan city.
If reports that the gunmen specifically looked for American and British citizens to take hostage are true, it would suggest that this terrorist spectacular had little to do with the prejudice and discrimination many Muslims do encounter in India.
It is tempting to label the attackers as "crazies". But such a dismissive appellation may be misplaced.
It is more than likely that the masterminds are seasoned operatives and that the foot-soldiers, young as they may have been, had undergone rigorous training for months, perhaps years.
The attacks also show every sign of having been designed to maximise media attention on a global scale.
In other words, there is a method to the madness.
Wednesday, August 27, 2008
meteorology
Meteorology (from Greek: μετέωρον, metéōron, "high in the sky"; and λόγος, lógos, "knowledge") is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting (in contrast with climatology). Meteorological phenomena are observable weather events which illuminate and are explained by the science of meteorology. Those events are bound by the variables that exist in Earth's atmosphere. They are temperature, pressure, water vapor, and the gradients and interactions of each variable, and how they change in time. The majority of Earth's observed weather is located in the troposphere. [1] [2]
Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology compose the interdisciplinary field of hydrometeorology.
Interactions between Earth's atmosphere and the oceans are part of coupled ocean-atmosphere studies. Meteorology has application in many diverse fields such as the military, energy production, transport, agriculture and construction.
