Hurricane Sandy

Hurricane Sandy, awesome vortex off the East Coast interacting with Jetstream in mid latitudes. Source: GEOS 13, NOAA

Hurricane Sandy has developped to the “Storm of the Century” causing damages by wind and flooding at Eastern U.S. never seen before! People have died sad to say.

Sandy started as an ordinary tropical depression (low) in Atlantic like many other. In hurricane season if temperatures of water surface are high enough  – sufficient vertical difference in temperature and sufficient latent heat to boost cloud formation – convective thunderstorm clouds self-assemble to an upward vortex hundreds of kilometers in diameter. The process is triggered by disturbances (pile-ups, convergences) within African Easterly Jet flowing in lower troposphere, driven by differences in temperature between burning hot subtropical desert areas and tropical rain forest, clearly cooler by comparison. Often there is an cloud-free eye inside the upward vortex, an area of sinking and warming air leading to cloud dispersal. Contrary to extratropical lows in mid latitudes hurricanes have no frontal systems. Extratropical lows are driven by horizontal differences in temperature, originated from disturbances within (air divergences) and moved by mid latitude Jetstream flowing in upper troposphere.

Hurricane Sandy grew to a superstorm after moving northward and then meeting with the mid-latitude Jetstream, wavy out of the common.  Hurricane was affected by  a trough in wavy Jetstream and guided to East Coast.  A slightly meandering Jetstream would have swept it out to sea! Furthermore Sandy got much energy from Jetstream.

Maybe there is a link to climate change:  Melting polar sea ice reduces albedo so that rays of the Sun are better absorbed leading to an extra warming of the Arctic.  Hence differences in temperature between Arctic and mid latitudes lessen and thereof driven Jetstream becomes weaker and more wavy.

Jens Christian Heuer   


Greenish Clouds on Jupiter

Unusual greenish clouds in equatorial region of planet Jupiter. Source: Lunar Captures

Green clouds on Jupiter. Really not a usual color for clouds neither on Jovian like gas giants nor on terrestrial planets!
A crazy idea: Maybe it´s chlorophyll?! Free-floating colonies of algae-like lifeforms in temperated Jovian atmosphere layers performing a sort of photosynthesis.

Jupiter ist a veritable weather planet. Jetstreams, high and low pressure systems, clouds of all kinds, thunderstorms, rain and snow (ammonia but also water in temperated layers).

Jovian weather is primary driven by internal heat, but only secondary by the Sun, leading to vertical and horizontal differences in temperature. Remember: Distance to Sun is many times greater compared to Earth.
Jens Christian Heuer

Another New Hockeystick!

Two temperature reconstructions: 2000 years backward (left), 500 years backward (right) using proxy and also instrumental data (1880-1960) for calibration. Source: Christiansen and Ljunqvist, Climate of the Past, 2012.

Christiansen (Danish Meteorological Institute, Copenhagen) and Ljunqvist (Stockholm University) have published a two millennia (o-2000 AD) and a five centurys (1500-2000 AD) temperature reconstruction for extra-tropical Northern Hemisphere (The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability, Climate of the Past, 8-2012)! The two scientists used diverse proxys (tree ring widht and density, ice-cores, (varved) lake sediments and speleothems, widespread on Northern Hemisphere) and also instrumental data for calibration. As reconstruction based on a variety of proxys it is eminently reliable and thus comparable to hockeystick, the pioneering Millenia temperature reconstruction of Michael Mann and colleagues (The Hockeystick – A Milestone in Climate Science )!

Like the previous ones the new reconstruction shows a long term cooling trend and a strong natural variability in temperature. Long term cooling trend is caused by decreasing angle of Earth´s axial tilt leading to a cooler world in the long run. Cooler summers, less melting of snow. Balmier winters, increased evaporation of water, more snow. Extending Polar ice sheets are reflecting more sunlight thus cooling down planet Earth.

Natural variability of climate due to variations in solar irridiance and changing ocean currents seems to be stronger than usually estimated.
A big surprise: In Medieval Warm Period (MWP) a Global Warming came up like nowadays! However, current warming started from a subjacent level compared to MWP due to long term cooling trend.
But in the 1930th temperatures on Northern Hemisphere reached almost the same level as today, too. That´s even a result of instrumental data alone!
Jens Christian Heuer

A New Hockeystick

Temperature reconstruction of last 2000 years with tree ring proxys and instrumental data.  Source Esper et al. (Nature Climate Change, March 2012)

In March 2012 Jan Esper (Department of Geography, Johannes Gutenberg-University, Mainz, Germany) and his collegues published a paper about a Two Millennia Reconstruction of Temperatures on Northern Hemisphere (Esper J, Frank DC, Timonen M, Zorita E, Wilson RJS, Luterbacher J, Holzkämper S, Fischer N, Wagner S, Nievergelt D, Büntgen U (2012) Orbital forcing of tree-ring data. Nature Climate Change).

Esper et al. used proxys (tree ring data from North Scandinavian Pines) and also instrumental data for calibration. Measuring the maximal latewood density with x-rays (MXD), they used a more reliable method than often used tree ring width.

The results were a little surprise: There is a long term cooling trend caused by orbital forcing like in other temperature reconstructions, too. But there is also a strong natural variability in temperature, in all likelihood a consequence of changes in Solar irradiation and fluctuating ocean currents. Warming during Medieval Warm Period (MWP) and Roman Climate Optimum (RCO) were almost the same as present-day!

Long term cooling by orbital forcing refers to decreasing angle of Earth´s axial tilt leading to a cooler world in the long run. Cooler summers, less melting of snow. Balmier winters, increased evaporation of water, more snow. Extending Polar ice sheets are reflecting more sunlight thus cooling down planet Earth.

Jens Christian Heuer