MSGID: 1:317/3 649e5a66   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Significant decline of snow cover in the Northern hemisphere over the   
   last half century    
    Snow cover plays a major role in global energy balance, continental   
   thermal stability, and regional temperatures    
      
     Date:   
         June 29, 2023   
     Source:   
         University of California - Santa Cruz   
     Summary:   
         A new study that uses rigorous mathematical models and statistical   
         methods and finds declining snow cover in many parts of the northern   
         hemisphere over the last half century.   
      
      
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   FULL STORY   
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   In the face of the ongoing climate crisis, scientists from many fields   
   are directing their expertise at understanding how different climate   
   systems have changed and will continue to do so as climate change   
   progresses. Robert Lund, professor and department chair of statistics   
   at the UC Santa Cruz Baskin School of Engineering, collaborated on a new   
   study that uses rigorous mathematical models and statistical methods and   
   finds declining snow cover in many parts of the northern hemisphere over   
   the last half century.   
      
   Understanding snow cover trends is important because of the role that   
   snow plays in the global energy balance. Snow's high albedo -- the   
   ability to reflect light -- and insulating characteristics affects   
   surface temperatures on a regional scale and thermal stability on a   
   continent-wide scale.   
      
   In the new study published in the Journal of Hydrometeorology,researchers   
   analyzed snow cover data gathered from weekly satellite flyovers between   
   1967 (when satellites became more common) and 2021, which was divided into   
   grid sections for analysis. Of the grids that researchers determined had   
   reliable data, they found that snow cover is declining in nearly twice   
   as many grids as it is advancing.   
      
   "In the Arctic regions, snow is going away more often than not -- I think   
   climatologists sort of suspected this," Lund said. "But it's also going   
   away at the southern boundaries of the continents."  In a study that took   
   about four years to complete, the researchers show that snow presence   
   in the Arctic and southern latitudes of the Northern hemisphere is   
   generally decreasing, while some areas such as Eastern Canada are seeing   
   an increase in snow cover. This could be due to increasing temperatures   
   in areas that are typically very cold but still below freezing, allowing   
   the atmosphere to hold more water, which then falls as snow.   
      
   Lund believes this is the first truly dependable analysis of snow cover   
   trends in the Northern hemisphere due to the rigor of the researchers'   
   statistical methods. It is often challenging for non-statisticians   
   to extract trends from this type of satellite data, which comes as a   
   sequence of 0s or 1s to indicate if snow was present during a certain   
   week. The researchers also had to take correlation into account when   
   looking at trends, as the presence of snow cover one week greatly affects   
   the likelihood of snow cover the following week. These two factors were   
   taken into account with a Markov chain based model. Accurate uncertainty   
   estimates of the trends could be computed from the model. The researchers   
   found hundreds of grids where snow cover was declining with at least   
   97.5% certainty.   
      
   However, they also found that some of the satellite data gathered in   
   mountainous regions was unreliable, showing no snow in the winter and   
   several weeks of snow in the winter. This was likely due to a flaw in   
   the algorithm that processed the satellite data to determine if snow   
   was present or not.   
      
   "The reason this study took a lot of work is because the satellite data is   
   so doggone poor," Lund said. "Whatever the meteorologists did to estimate   
   snow from the pictures in some of the mountainous regions just didn't   
   work, so we had to take all the grids in the Northern hemisphere, and   
   figure out whether the data was even trustworthy or not."  By determining   
   which satellite data is unreliable, this study can serve as a resource   
   to the scientific community who also may want to evaluate this snow   
   cover data for their research.   
      
   Lund collaborated on this study with UCSC Ph.D. candidate Jiajie Kong,   
   Assistant Professor of Math and Statistics at the University of North   
   Florida Yisu Jia, Professor of Meteorology and Climatology at Mississippi   
   State University Jamie Dyer, Associate Professor of Statistics at   
   Mississippi State University Jonathan Woody, and Professor of Statistics   
   and Operations Research at the University of North Carolina at Chapel   
   Hill J. S. Marron. This research was supported by funding from the   
   National Science Foundation.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Snow_and_Avalanches # Climate # Severe_Weather #   
                   Storms # Weather # Geography # Atmosphere # Global_Warming   
       * RELATED_TERMS   
             o Climate_model o Coriolis_effect o   
             Atmospheric_dispersion_modeling o Sea_level o Taiga o Snow o   
             Computer_simulation o Avalanche   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_California_-_Santa_Cruz. Original written by Emily   
   Cerf. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Yisu Jia, Robert Lund, Jiajie Kong, Jamie Dyer, Jonathan Woody,   
      J. S.   
      
         Marron. Trends in Northern Hemispheric Snow Presence. Journal of   
         Hydrometeorology, 2023; 24 (6): 1137 DOI: 10.1175/JHM-D-22-0182.1   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230629193256.htm   
      
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