Almost a year ago a powerful hurricane Sandy hit New York and its area. Although long past, it still intrigues scientists. Recently, they completed its fully detailed computer reconstruction.
Sandy attacked during the night of 29 October last year. She came from the Atlantic Ocean and entered the land from the south of New York. Along with her came hurricane winds and several-meter high waves which crashed on the shore. The damages were enormous. Tens of thousands of homes went under water, the subway and road tunnels were flooded, 150 people died, many thousands were found without shelter. Material damages suffered in USA because of Sandy were estimated for a total of USD 65 billion. Only Katrina was worse when in 2005 she flooded New Orleans, killing over one and half thousand people and causing damages up to USD 120 billion.
Sandy made a mess and then disappeared, melting away in the upper troposphere, while the scientists started wondering why was she so violent. As usual, the researchers looked at mathematical models, this time those allowing for the examination of the whims of hurricanes. Such models are, of course, only computer programmes and they do not completely represent the reality, but if there is a large number of observation data and a good computing machine it is possible to reconstruct the past with a close approximation.
It was possible with Sandy which was recently revived, this time only on the computer. The journey of the hurricane from the moment when it was born on the Caribbean sea till the moment it crashed into the north-western part of the USA can be watched on the You Tube Channel of the National Canter for Atmospheric Research: http://www.youtube.com/user/ncarucar.
Photo 1. 3D map of potential temperature inside Sandy (in Kelvin’s). Relatively cold air (blue and violet) wraps itself around the eye, and next it moves up, collecting energy and warming itself with condensing steam, next clouds and rain are created (yellow and red). Source: Mel Shapiro/UCAR
We especially recommend the visualisation no. 5, showing the manner in which the large whirlpool wandering through the northern Atlantic, instead of moving further to the north and gradually losing force, begun grabbing, pulling and sucking in with its powerful arms the relatively cold air from many miles away. Then it warmed the air and pumped it to the height of dozen or so kilometres, up to the upper line of the troposphere. It was in that moment when this atmospheric “mega vacuum” gathered force and made a 90 degree turn into the left and set off towards the land. This was the unique characteristic of the hurricane - when it was entering the land it was simultaneously a hurricane and a great low-pressure area with weather fronts. If Sandy was only the former, she would have a smaller diameter. If she was only the latter she would not be so powerful.
The creators of the simulation claim that it is the best reconstruction of a hurricane’s path and the phenomena occurring inside. It was accomplished thanks to joined efforts of the atmosphere researchers and programmers. The former – and those were Tom Galarneau and Mel Shapiro from National Center of Atmospheric Research in Boulder, Colorado (USA) – contributed a detailed observation data concerning Sandy and their own knowledge about hurricanes. The former – Peter Johnsen from Cray Inc. and Mark Straka from the National Center for Supercomputing Applications computing unit in Urbana-Champaign, Illinois (USA) – took care about the "details", namely increasing the accuracy of the model.
Photo 2. Sandy’s path in October 2012. The line shows the location of the hurricane’s eye. Blue indicates the stages of weakening of the element, yellow and cream colour – the periods when her force was growing. Sandy rolled first through Jamaica, Cuba and the Bahamas and later on she weakened. Not for long. The next day she suddenly gathered force and shortly after turned in the direction of New York. Just before her entrance onto the land her qualification as a hurricane (circle) was changed into an extra tropical cyclone (triangle). Source: wikimedia commons/cyclonebiskit
The joined efforts were impressive. Sandy was chopped into 4 billion points with 500 m spaces between, and later on a programme simulating the behaviour of the hurricane second after second, was launched. This was taken care of by Blue Waters - one of the fastest electronic brains in the world, constructed by the Cray Company and launched last year in the aforementioned facility in Urbana-Champaign, where it occupies a hall of 2000 m2. Using just a fraction of this supercomputer’s power several simulations of Sandy’s journey were made, of which each one lasted 58 hours! For almost a year the scientists prepared and conducted the experiment as well as the elaborated its results.