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   

Weather Situation September,14th 2012

Full Earth September, 14th 2012, 11.00 UTC Sourece: EUMETSAT

General Synopsis of North Atlantic and Europe: A Cut-Off Low over Mediterranian has detached from Jetstream further north. Mediterranian Cut-Off Low looks really beautiful! Jetstream at the North is decernible as a band of cloud.

Usually the pathways of low pressure weather systems are strongly controlled by current of the Jetstream. But sometimes the Jetstream  slows down or even breaks, so that weather systems can detach (Cut-Off). After that they move independently until they decay or are captured by a trough of a new established Jetstream.

Low pressure systems on Northern Hemisphere are spinning anticlockwise due to Coriolis force. Inside the system air is rising and cooling. If air-moisture is sufficient condensing water vapor starts to form clouds, made of tiny water droplets (or tiny ice crystals in higher altitudes). It might rain or snow. Bad Weather!

For comparison the model calculation chart for windspeed and Jetstream in the higher troposphere:

Windspeed and Jetstream in the higher Troposphere. Source: www.netweather.tv

The mathematic circulation model shows almost perfect all features of reality!

Jens Christian Heuer

New MeteoSat

First Picture of MeteoSat 3rd Generation. Full Earth from geosationary orbit. Source ESA

MeteoSat Weather satellites 3rd Generation are stabilized by three gyrating momentum-wheels orientated to the three directions in space. The precursor MeteoSats, 1rd and 2rd generation were stabilized by their own spin. With the new three-axle stabilization the instruments of weather satellite are pointed to Earth more exactly and for a longer time, most likely even to the end of orbit time.

MeteoSat 3rd Generation have a Flexible Combined Imager for visible and infrared channels (inclusive some additional ones) with better spatial resolution compared to old weather satellites.

Jens Christian Heuer

Jetstream


Nice Animation of a Jetstream Source: NASA – GISS

Jetstreams are driven by atmospherical differences in temperature and thus in air pressure. There are horizontal gradients in air-temperature of atmosphere, for example between polar regions and mid latitudes, but there are also vertical gradients leading to convection and to cloud formation if air moisture is sufficient.

A Jetstream forms Rossby waves, troughs and ridges traveling streamwise and also eddies, the weather-making high and low pressure systems. These eddies arise from turbulences in jetstream like the vortexes of a raging river do.

Jens Christian Heuer

A nice animation: