What's to Blame for Wild Weather? "La Nada"   
       
   Such sheets of fire, such bursts of horrid thunder,   
   Such groans of roaring wind and rain,   
   I never Remember to have heard; man's nature cannot carry   
   The affliction nor the fear... from Shakespeare's Tragedy of King Lear   
       
   June 21, 2011: Record snowfall, killer tornadoes, devastating floods: There's   
   no doubt about it. Since Dec. 2010, the weather in the USA has been positively   
   wild. But why?   
       
   Some recent news reports have attributed the phenomenon to an extreme "La   
   Ni¤a," a band of cold water stretching across the Pacific Ocean with global   
   repercussions for climate and weather. But NASA climatologist Bill Patzert   
   names a different suspect: "La Nada."     
   "La Ni¤a was strong in December," he says. "But back in January it pulled a   
   disappearing act and left us with nothing - La Nada - to constrain the jet   
   stream. Like an unruly teenager, the jet stream took advantage of the newfound   
   freedom--and the results were disastrous."   
       
   La Ni¤a and El Ni¤o are opposite extremes of a great Pacific oscillation.   
   Every 2 to 7 years, surface waters across the equatorial Pacific warm up (El   
   Ni¤o) and then they cool down again (La Ni¤a). Each condition has its own   
   distinct effects on weather.   
   [...]   
   The blue and purple band in this satellite image of the Pacific Ocean traces   
   the cool waters of the La Ni¤a phenomenon in December 2010. (from Ocean   
   Surface Topography Mission (OSTM)/Jason-2 satellite, Credit: NASA JPL)   
       
   The winter of 2010 began with La Ni¤a conditions taking hold. A "normal" La   
   Ni¤a would have pushed the jet stream northward, pushing cold arctic air (one   
   of the ingredients of severe weather) away from the lower US. But this La Ni¤a   
   petered out quickly, and no El Ni¤o rose up to replace it. The jet stream was   
   free to misbehave.   
       
   "By mid-January 2011, La Ni¤a weakened rapidly and by mid-February it was   
   adios La Ni¤a, allowing the jet stream to meander wildly around the US.   
   Consequently the weather pattern became dominated by strong outbreaks of   
   frigid polar air, producing blizzards across the West, Upper Midwest, and   
   northeast US."1   
       
   The situation lingered into spring -- and things got ugly. Russell Schneider,   
   Director of the NOAA-NWS Storm Prediction Center, explains:   
       
   "First, very strong winds out of the south carrying warm, moist air from the   
   Gulf of Mexico met cold jet stream winds racing in from the west. Stacking   
   these two air masses on top of each other created the degree of instability   
   that fuels intense thunderstorms."   
       
   Extreme contrasts in wind speeds and directions of the upper and lower   
   atmosphere transformed ordinary thunderstorms into long-lived rotating   
   supercells capable of producing violent tornadoes.2   
       
   In Patzert's words, "The jet stream -- on steroids -- acted as an atmospheric   
   mix master, causing tornadoes to explode across Dixie and Tornado Alleys, and   
   even into Massachusetts."   
   [...]   
   This satellite image, taken in April 2011, reveals La Ni¤a's rapid exit from   
   the equator near the US coast. The cool (false-color blue) water was gone by   
   early spring. (from Ocean Surface Topography Mission (OSTM)/Jason-2 satellite,   
   Credit: NASA JPL)   
       
   All this because of a flaky La Ni¤a?   
       
   "La Ni¤a and El Ni¤o affect the atmosphere's energy balance because they   
   determine the location of warm water in the Pacific, and that in turn   
   determines where huge clusters of tropical thunderstorms form," explains   
   Schneider. "These storms are the main energy source from the tropics   
   influencing the large scale pattern of the jet stream that flows through the   
   US."   
       
   In agreement with Patzert, he notes that the very strong and active jet stream   
   across the lower US in April "may have been related to the weakening La Ni¤a   
   conditions observed over the tropical Pacific."   
       
   And of course there's this million dollar question: "Does any research point   
   to climate change as a cause of this wild weather?"   
       
   "Global warming is certainly happening," asserts Patzert, "but we can't   
   discount global warming or blame it for the 2011 tornado season. We just don't   
   know ... Yet."3   
       
   What will happen next? And please don't say, "La Nada."   
       
   Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   End Notes   
   (1) Other atmospheric factors also contributed to the inflow of frigid polar   
   air, says Patzert. One of the most significant was a weakening in the   
   whirlpool motion of the air around the North Pole. As a result of this   
   weakening, more cold air flowed away from the pole and down toward the states.   
   Climatologists call this an "arctic oscillation."   
       
   (2) Imagine a paddle wheel oriented like a Ferris wheel and placed in winds   
   that that are much stronger at the top than at the bottom. The wheel will spin   
   in the direction of the strong winds above. This spring, these strong, turning   
   winds led to ongoing rotation of the supercells themselves. So we ended up   
   with intense rotation and updraft close to Earth's surface -- conditions ripe   
   for strong tornadoes.   
       
   (3) On May 26, 2011, Patzert posted a comment about this topic on Andrew   
   Revkin's The New York Times' DOT EARTH Blog, "Demography, Design, Atom Bombs   
   and Tornado Deaths." See comment 6 at this URL.   
       
   http://dotearth.blogs.nytimes.com/2011/05/26/demography-design-and-tornado-de   
   aths/?ref=science   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.62   
    * Origin: NCS BBS (1:3828/7)