Temporal trends in global sea surface temperature fronts

Sea surface temperature (SST) fronts, generally defined as regions of enhanced surface temperature gradient, are of broad interest in oceanography both because of the role that they play in the dynamics of the upper ocean and because of the large volume of data available from satellite-borne sensors with which they can be studied. Gradients in the background surface temperature, surface wind stress, and cloud cover likely play a role in establishing and maintaining SST fronts. Furthermore, each of these characteristics is thought to be affected by changes in global climate. The objective of this study is to determine to what extent the probability of finding SST fronts in satellite-derived SST has changed in the recent past. To this end, front probability was determined from the output of an edge detection algorithm applied to the 30-year (1981-2011) time series of Pathfinder v5.2 SST data. Based on approximately 1°x1° squares that are 90% or more clear, front probability has been found to increase globally at a very nearly linear rate of approximately 0.25 %/decade; i.e., over the 30-year period the mean probability of finding a front has increased from approximately 5.58% to 6.30%. However, the trend in front probability is not globally uniform so the study also included a determination of regional trends in front probability. Requiring broad temporal coverage in each 1°x1° square, to reduce the uncertainty associated with the trend estimates, resulted in dense coverage only in an approximately 750 km wide ‘coastal’ band. In this region, clusters of predominantly positive trends that were significantly larger, 0.6 to 0.8 %/decade, than the mean trend were observed; i.e., increases of 30 to 50% in the number of fronts over the past 30 years. The mean trend in the ‘coastal band’ is approximately 0.30%/decade, substantially higher than the global trend. This implies that the increase in front probability in coastal regions is significantly larger than in open ocean regions.

[1]  Raffaele Ferrari,et al.  A Frontal Challenge for Climate Models , 2011, Science.

[2]  M. Jeroen Molemaker,et al.  Balanced and unbalanced routes to dissipation in an equilibrated Eady flow , 2010, Journal of Fluid Mechanics.

[3]  Peter Cornillon,et al.  Modification of surface winds near ocean fronts: Effects of Gulf Stream rings on scatterometer (QuikSCAT, NSCAT) wind observations , 2006 .

[4]  T. Hara,et al.  Surface wind response to oceanic fronts , 2006 .

[5]  J. Le Fèvre,et al.  Aspects of the Biology of Frontal Systems , 1987 .

[6]  J. Norris.  Multidecadal Changes in Near-Global Cloud Cover and Estimated Cloud Cover Radiative Forcing , 2005 .

[7]  B. Samuels,et al.  Parameterization of mixed layer eddies. III: Implementation and impact in global ocean climate simulations , 2010 .

[8]  S. Solomon.  The Physical Science Basis : Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change , 2007 .

[9]  Peter Cornillon,et al.  Fronts in Large Marine Ecosystems , 2009 .

[10]  Alexander Ignatov,et al.  Equator crossing times for NOAA, ERS and EOS sun-synchronous satellites , 2004 .

[11]  Peter Cornillon,et al.  Air–sea interaction over ocean fronts and eddies , 2008 .

[12]  Peter Cornillon,et al.  Edge Detection Algorithm for SST Images , 1992 .

[13]  Hiroyasu Hasumi,et al.  Ocean modeling in an eddying regime , 2008 .

[14]  Craig M. Lee,et al.  Enhanced Turbulence and Energy Dissipation at Ocean Fronts , 2011, Science.

[15]  M. Enayatmehr,et al.  Global Climate Change and Intensification of Coastal Ocean Upwelling , 2015 .

[16]  Peter Cornillon,et al.  Satellite-derived sea surface temperature fronts on the continental shelf off the northeast U.S. coast , 1999 .

[17]  David I. Berry,et al.  A 20 year independent record of sea surface temperature for climate from Along‐Track Scanning Radiometers , 2012 .

[18]  Corinne Le Quéré,et al.  Climate Change 2013: The Physical Science Basis , 2013 .

[19]  A. Longhurst.  Ecological Geography of the Sea , 1998 .

[20]  Michael H. Freilich,et al.  Observations of coupling between surface wind stress and sea surface temperature in the Eastern Tropical Pacific , 2001 .

[21]  Amit Tandon,et al.  Submesoscale Processes and Dynamics , 2013 .

[22]  E. M. Acha,et al.  The relationship between marine fronts and fish diversity in the Patagonian Shelf Large Marine Ecosystem , 2009 .

[23]  Peter Cornillon,et al.  Multi-Image Edge Detection for SST Images , 1995 .

[24]  Donald B. Olson,et al.  Life on the edge : marine life and fronts , 1994 .

[25]  M. Saier,et al.  Climate Change, 2007 , 2007 .

[26]  William J. Emery,et al.  Data Analysis Methods in Physical Oceanography , 1998 .

[27]  J. Largier,et al.  Observations of increased wind‐driven coastal upwelling off central California , 2010 .

[28]  M. Kahru,et al.  Spatial and temporal statistics of sea surface temperature and chlorophyll fronts in the California Current , 2012 .

[29]  James C. McWilliams,et al.  Mesoscale to Submesoscale Transition in the California Current System. Part II: Frontal Processes , 2008 .

[30]  Xiaosu Xie,et al.  Atmospheric manifestation of tropical instability wave observed by QuikSCAT and tropical rain measuring mission , 2000 .

[31]  I. Young,et al.  Global Trends in Wind Speed and Wave Height , 2011, Science.

[32]  R. Evans,et al.  Overview of the NOAA/NASA advanced very high resolution radiometer Pathfinder algorithm for sea surface temperature and associated matchup database , 2001 .