Das Wetter und der Klimawandel

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Hubble´s Expanding Universe

During 1922 and 1923 astronomer Edwin Hubble succeeded for the first time to identify single stars in the famous spiral nebula Andromeda, even visible with the naked eye. For this detection Hubble used world’s largest telescope at that time, the 2,5m Hooker Telescope at Mt. Wilson Observatory.

Andromeda Galaxy (M31) Source: Palomar Observatory

Several of these new-found stars were Cepheids, large and bright stars, pulsating and thus varying luminosity. Typical Cepheids pulsate with periods from a few days through to months. There is a quite relationship between cycle duration and absolute luminosity of these variable stars. As longer the period as higher the luminosity.

That is why cepheids are workable standard candles for cosmic distance measurements. It is merely necesssary to calibrate the distance of the cepheids with other techniques like geometric parallax (difference in the apparent position of an object viewed along two different lines of sight against a much more distant background) and spectroscopic parallax (comparing the luminosity of main sequence stars in Hertzsprung-Russel-Diagrams).

Edwin Hubble (1889-1953) and 2,5m (100 inch) Hooker-Teleskope at Mt.Wilson Observatory Source: Wikipedia, www.astro.caltech.edu/

Using the period-luminosity-relationship of Cepheids in Andromeda, Hubble calculated a distance of nearly one million light years (ly), too much this nebula could be a part of the Milky Way. And Hubble even undervalued Andomeda´s distance due to calibration errors. Today`s reading ist about more than two million light years (ly).

Previously most astronomers took the view that Milky Way and universe were the same. But in fact, our Milky Way was only one galaxy among many galaxies in the universe. Hubble had found the ultimate proof and from then on the world became much larger than before.

Hubble also devised a system for classifying galaxies according to their optical appearance  in a diagram, resembling a tuning fork ,  also known as the Hubble sequence.

Hubble´s Tuning-Fork-Diagram for classification of galaxies. Source: Wikipedia

In the following years Hubble searched out a direct proportionality of the galaxies’ distances with redshifts in their spectra. This redshift is a consequence of the Doppler effect and hence a clear evidence for a flight of galaxies away from the Milky Way.  The received frequency of a moving light source increases during approach (blueshift), remains constant at the moment of passing by, and decreases during recession (redshift). stretched. At first electromagnetical waves are compressed due to approach,  afterwards they are stretched due to recession. Accordingly direct proportionality of galaxies’ distances with redshifts also means a direct proportionality of galaxies’ distances with the galaxies’ escape velocity.

Hubble´s Law Source: Edwin Hubble (www.pnas.org/)

The redshift of almost galaxies does not mean that Milky Way is centre of the universe. Universe acts like a proving yeast dough of a plum cake before baking. From the viewpoint of every raisin all the other raisins are going away as faster as longer the distance between raisins are. That´s because the dough itself is expanding.

In almost the same manner the space between galaxies expands, leading to an expansion of the whole universe. This discovery of Hubble was a complete surprise at that time.  In place of a stable and eternal Universe there was an  evolving universe with it´s own history, leading to big bang theory.

Next up Hubble wanted to know, if universe is open or closed.

In other words: Does the entire universe have enough matter and energy to stop it´s own expansion by gravitational force, warping space to a closed (four-dimensional) space-time bubble? Or will expansion last to all eternity, leading to an open universe?

Hubble tried to solve the problem by counting the galaxies as a function of their distance. He assumed in average a relationship between luminosity and distance of galaxies. If the nummber of galaxies increased overproportional with their distance, the space should have a positive curvature, leading to a closed universe and vice versa.

A two-dimensional analogy for better understanding: A spherical surface has a positive curvature, a riding saddle (hyperboloide) has a negative curvature and a flagstone is flat.

Jens Christian Heuer

Sources: Lonely Hearts of the Cosmos: The Story of the Scientific Quest for the Secret of the Universe, Dennis Overbye, Wikipedia

Full Disk Earth on 27th May, 2012

On May 27th 2012 european weather satellite MeteoSat took a nice picture of full disk earth displaying some intersting weather action. Meteosat circles Earth in a geostationary orbit (36.000 km altitude) delivering daily current views frome same fixed position above surface of the planet.

Jetstream and dynamical weather systems: A band of cloud across Northern Atlantic (from Greenland to Scandinavia) indicates behaviour of jetstream, driven by gradient in air-temperature (and gradient in air pressure arising thereby, respectively) between polar regions and mid latitudes.

Jetstream is crucial to weather forecast:

Like the vortexes in a raging river high and low pressure systems – weather-determining in mid latitudes – arise from turbulences in jetstream and are moved by flow of jetstream after that.

Weather on 27th May, 2012, 16:00 UTC . Innertropical Convergence Zone, the deserts of Subtropical High Pressure Belt and the weather systems (cyclones and anticyclones) of the mid – latidudes are easily dercernable. Natural Color RGB images makes use of three solar channels: red, green and blue. In this color scheme vegetation appears greenish because of its large reflectance in the green beam channel compared to the red and blue beam channels. Water clouds with small droplets have large reflectance at all three channels and hence appear whitish, while snow and ice clouds appears cyan because ice strongly absorbs in red. Bare ground appears brown because of the larger reflectance in the red beam channel than at the blue one, and the ocean appears black because of the low reflectance in all three channels. Source: Meteosat, EUMETSAT

The two vortexes over middle Northern Atlantic, one of them in the southwest of British Isles, another one further westward, are cut-off  lows. They have separated from jetstream some time ago, triggered by a large blocking high pressure system widespread over parts of Northern, Western and Central Europe and German Sea. Blocking highs occur if the flow of  jetstream slows down or even breaks so that a moving high pressure systeme comes to a deadlock. The two Cut-off lows over middle Northern Atlantic are following a pathway southward blocking high.

Inside high pressure systems (anticyclones), spinning arount clockwise, air sinks and nearly all clouds decay, because water in the condensed form tends to evaporate into water vapor. Thus high pressure systems lead to fair weather at most times.

Inside low pressure systems (cyclones), spinning around counterclockwise, air rises and cools, so that water vapor condenses, forming clouds made of tiny water droplets or ice crystals. Latent heat (thermal energy of condensation) released thereby, powers cloud formation for her part by warming the rising air. Low pressure systems imply bad weather with rainfall an thunderstorms many a time. 

Tropical-subtropical Hadley-Circulation:  Away from almost cloud-free subtropical belt of high pressure systems air flows to equator going along surface. These tradewinds are turning westward due to Earth´s rotation. Throughout the region of equator there´s a buildup of low pressure, called Innertropical Convergence Zone (ITCZ). Heated by the sun, equatorial air rises and cools, forcing whatever water vapor it holds to condense into clouds. The ascended air moves poleward, turning eastward by Earth´s rotation soon after. As moving poleward, air flow comes closer to the axis of earth’s rotation. That´s why it goes faster, often forming a subtropical jetstream that rotates more rapidly than the Earth itself. In addition air descends closing the circulation in this way. This so called Hadley-Circulation is breaking up in a row of cloud-rich convective cells around the whole planet Earth.

Jens Christian Heuer

Scientific Award for Michael Mann

From 22. – 27. April 2012 General Assembly of European Geosciences Union (EGU) takes place in Vienna. During this meeting climate scientist Michael E. Mann received the Oeschger-Medal for his research! Hans Oeschger (1927) was a Swiss scientist, famous because of his ice core research. Together with Willi Dansgaard he discovered a series of abrupt climate changes (Dansgaard-Oeschger Events) during the last glacial period by analysis of Greenland ice cores. Also he measured first the glacial-interglacial change of atmospheric CO2 encased in ice core´s tiny air bubbles.

Prof. Michael E. Mann holding a tree grate with tree rings Source: Homepage Michael E. Mann

Michael E. Mann came to be known for his “hockeystick”-curve. This curve was the result of a reconstruction of average temperatures last millenium-round on northern hemisphere, published by Mann and his colleagues in 1999 (M.E.Mann,R.S.Bradley, M.K.Hughes: „Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations“, Geophysical Research Letters, 1999) It was really a pioneering feat!

The team of scientists used proxy data from tree rings, corals and ice cores on the one hand and instrumental temprature data on the other hand such as it was. The „hockeystick” demonstrated at first how extraordinary (human-made) global warming during 20th century really was! For that reason all climate skeptics dislike this curve up to the present day.

The Hockeystick-Curve. The graph resembles a hockeystick in shape: with a long part of curve declining slightly as the shaft and with a short part of curve upturning suddenly as the blade.   Source: Mann, Bradley und Hughes 1999

Assembling and evaluation of all data for “hockeystick” happened in a very sophisticated way. The proxy-data, mainly tree rings extending to 1980 were validated by instrumental data back to 1854, occasional to 18th century yet. Long proxy record and shorter instrumental record overlapped a good way. Using only instrumental data from time intervall 1902 to 1980 for calibration of proxy data, Mann and his collegues were able to use leftover intervall from 1854 to 1901 (and the rare earlier instrumental data from 18th century) to verify this calibration. Calibration and validation of proxy data  worked accurately, meaning that „hockeystick“ is correct in this regard.

CO2 is a greenhouse gas but it also acts as a fertilizer, especially for trees in high elevations. More CO2 let tree ring width and tree ring density (of summerly late wood) mimic an additional rise in temperature that does not really exist. Thus the tree ring data were readjusted.

Above: Records of two tree ring data series (ITRDB Millenial, North American Treeline), which diverged from 19th century on due to influence of CO2. ITRDB Millenial includes trees in high elevations much sensitive to dunging effect of CO2. Below: Variations in atmospheric CO2 and residual between the two data series, used for readjustment. Source: Mann, Bradley und Hughes, 1999 

Two examples how carefully Mann and his team had gone about it! All that and then some you can read in original paper, downloadable on Mann´s homepage (see sources below). It´s worth it! Michael E. Mann was also a lead author of 3rd. IPCC-Report about global warming in 2001. Again and again some climate sceptics tried to discredit Mann scientifically and also personally. Fortunately they failed yet.  I hope it stays that way!

Jens Christian Heuer

Sources: European Geosciences Union (EGU) , Homepage Michael E. Mann

Global Warming, Arctic Amplification and Extreme Weather

A brand-new paper from Jennifer A. Francis and Stephen J. Vavrus „Evidence linking Arctic amplification to extreme weather in mid-latitudes“, (GEOPHYSICAL RESEARCH LETTERS, VOL. 39, 2012)
sheds new light on the issue of extreme weather events due to global warming!
The two scientists found evidence that enhanced Arctic warming relative to mid latitudes (Arctic amplification, AA) leads to prolonged extreme weather events, like droughts, heat waves (such as in Russia, summer 2010!), heavy rain and cold spells (remember persistent chilly conditions in recent winters!).

Arctic Amplification means enhanced arctic warming relative to mid latitudes due to a sort of inverse Ice-Albedo-Feedback. Decreasing bright, highly reflective sea ice is replaced by dark open water, absorbing sunlight strongly. Open water also releases a lot of moisture and latent heat in artctic atmosphere.
Due to the fact that jetstream is driven by gradient in air-temperature (and gradient in air pressure arising thereby, respectively) between polar regions and mid latitudes, jetstream slows down and becomes wavier.

Seasonal anomalies in 1000-500 hPa thicknesses (m) north of 40°N during 2000–2010 relative to 1970–1999: (a) autumn (OND), (b) winter (JFM), (c) spring (AMJ), and (d) summer (JAS). White asterisks indicate significance with chance level p < 0.05. 1000-500 hPa thickness reveals aerial vertical thermal expansion by means of distance between 1000 hPa- and 500 hPa isobaric surface. Source: Francis and Vavrus, 2012

As a result high and low pressure systems moved by jetstream slow down, too.
These weather systems arise from turbulence in jetstream like the vortexes of a raging river do.

A wavy jetstream results in cold spells via wave troughs (in reverse warm spells via wave crests, respectively), whereas high air moisture makes possible  a lot of snow.

Finally a nice animation of the jetstream of northern hemisphere from NASA/Goddard Space Flight Center (Scientific Visualization Studio):

Jens Christian Heuer

A Satellite Picture explaining our Weather

The European weather satellite Meteosat, circles the Earth on a geostationary orbit (36.000 km altitude) providing daily current views of our planet. On this color infrared recording of  November 22th 2011, you can see some important phenomena of global weather patterns.  

Dynamical Weather Systems: Weather on earth-like planets is driven by temperature differences between equator and poles, caused by different sun´s irradiance. In mid – latitudes, where warm tropical and cool polar air masses encounter each other, gradient of temperature (and thereby gradient of pressure) is sufficient to generate a high altitude air current (called tropospheric polar jetstream) on both hemispheres, turning eastward under influence of earth’s rotation.

Breaking a critical speed limit, the jetstream forms Rossby waves with troughs and ridges(wave peaks). A lot of shear forces emerge. The waves break and roll up to vortices. These are the high pressure und low pressure systems, enabled to intermix the warm tropical and cool polar air masses.

The high pressure vortices (anticyclones) are spinning downward and clockwise (counterclockwise) on northern (southern) hemisphere, whereas the low pressure vortices (cyclones) are spinning upward and counterclockwise (clockwise) on northern (southern) hemisphere.

Weather at November 22th, 2011, 12:00 UTC . The ITCZ, the deserts in the Subtropical High Presure Belt and the Low Pressure Systems (Cyclones) of the mid – latidudes are easily dercernable. Natural Color RGB images makes use of three solar channels: red, green and blue. In this color scheme vegetation appears greenish because of its large reflectance in the green beam channel compared to the red and blue beam channels. Water clouds with small droplets have large reflectance at all three channels and hence appear whitish, while snow and ice clouds appears cyan because ice strongly absorbs in red. Bare ground appears brown because of the larger reflectance in the red beam channel than at the blue one, and the ocean appears black because of the low reflectance in all three channels. Source: Meteosat, EUMETSAT

Inside low pressure systems the air rises and cools, so that water vapor condenses, forming clouds made of tiny water droplets or ice crystals (bad weather). Latent heat (thermal energy of condensation) thereby released powers cloud formation on her part warming the rising air.

Inside high pressure systems the air sinks and clouds decay, because water in the condensed form tends to evaporate into water vapor (fair weather).

Cyclones derive their energy not only from the jetstream, but also from latent heat liberated during formation of clouds. In turn they transmitted back a portion of their energy to jetstream.

The pathways of cyclones are affected by the behaviour of the jetstream.But sometimes the high air current slow down or breaks actually, so that the cyclones are able to seperate from jetstream. These cut off lows move slowly and won’t exit a region until they are captured by a trough of a new jetstream, which meanwhile has usually formed.

Low Pressure Systeme (Cyclone) Source: Bjerknes (1922)

Tropical Hadley – Circulation: Away from this areas of high pressure the air masses move equatorially along the surface (tradewinds), where´s a buildup of low pressure (Innertropical Convergence Zone, ITCZ) : These tradewinds turn westward due to earth´s  rotation. Heated by the sun,  equatorial air rises and cools, forcing whatever water vapor it holds to condense into clouds. The ascended air moves poleward , but it is turned eastward by the earth´s rotation. As moving  polewards, the air current contracts closer to the axis of earth’s rotation. So it must spin faster, creating subtropical jetstreams that rotate more rapidly than the Earth itself..In parts however, the air descends in the belt of subtropical pressure, closing the air circulation. This so called Hadley-Circulation.partions in a row of convective cells around the whole planet.

Stratosphere and Polar Vortex: The stratosphere is the next layer of atmosphere above the troposphere, in which most weather processes play. The stratosphere contains little water vapor, but larger quantities of ozone, protecting life by absorption of dangerous solar ultraviolet radiation. Therefore the stratosphere is much warmer than the upper troposphere.

If the stratosphere over the poles is cold enough during the polar night, a polar vortex forms due to a sufficient gradient of temperature to build up an eastward stratospheric jetstream, which is a propulsion engine of tropospheric polar jetstream (see above).

A strong polar vortex favors a poleward, zonal circulation (along the lines of latitude), a weak, often divided polar vortex, however, favors a meridional circulation with pronounced troughs and ridges (along the lines of longitude).

Jens Christian Heuer

Schlagwörter-Wolke