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