Changeset 3342

2012-04-02T15:41:34+02:00 (9 years ago)

NEMO branch dev_r3337_NOCS10_ICB: add documentation for iceberg code

1 added
1 edited


  • branches/2012/dev_r3337_NOCS10_ICB/DOC/TexFiles/Chapters/Chap_SBC.tex

    r3294 r3342  
    11% ================================================================ 
    2 % Chapter Ñ Surface Boundary Condition (SBC)  
    3 % ================================================================ 
    4 \chapter{Surface Boundary Condition (SBC) } 
     2% Chapter Ñ Surface Boundary Condition (SBC, ICB)  
     3% ================================================================ 
     4\chapter{Surface Boundary Condition (SBC, ICB) } 
    5656Next the scheme for interpolation on the fly is described. 
    5757Finally, the different options that further modify the fluxes applied to the ocean are discussed. 
     58One of these is modification by icebergs (see \S\ref{ICB_icebergs}), which act as drifting sources of fresh water. 
    10451046the expense of having more idle CICE processors in areas where there is no sea ice. 
     1048% ------------------------------------------------------------------------------------------------------------- 
     1049%        Handling of icebergs 
     1050% ------------------------------------------------------------------------------------------------------------- 
     1051\subsection{ Handling of icebergs (ICB) } 
     1057Icebergs are modelled as lagrangian particles in NEMO. 
     1058Their physical behaviour is controlled by equations as described in Martin and Adcroft (2010). 
     1059(Note that the authors kindly provided a copy of their code to act as a basis for implementation in NEMO.) 
     1060Icebergs are initially spawned into one of ten classes which have specific mass and thickness as described by 
     1061\np{rn\_initial\_mass} and \np{rn\_initial\_thickness}. 
     1062Each class has an associated scaling (\np{rn\_mass\_scaling}), which is an integer representing how many icebergs  
     1063of this class are being described as one lagrangian point (this reduces the numerical problem of tracking every single iceberg). 
     1064They are enabled by setting \np{ln\_icebergs}~=~true. 
     1066Two initialisation schemes are possible. 
     1069In this scheme, the value of \np{nn\_test\_icebergs} represents the class of iceberg to generate (so between 1 and 10), and  
     1070\np{nn\_test\_icebergs} provides a lon/lat box in the domain at each grid point of which an iceberg is generated at the  
     1071beginning of the run. (Note that this happens each time the timestep equals \np{nn\_nit000}.) 
     1072\np{nn\_test\_icebergs} is defined by four numbers in \np{nn\_test\_box} representing the corners of the geographical 
     1073box: lonmin,lonmax,latmin,latmax 
     1075In this scheme the model reads a calving file supplied in the \np{sn\_icb} parameter. 
     1076This should be a file with a field on the configuration grid (typically ORCA) representing ice accumulation rate at each model point.  
     1077These should be ocean points adjacent to land where icebergs are known to calve. 
     1078Most points in this input grid are going to have value zero. 
     1079When the model runs, ice is accumulated at each grid point which has a non-zero source term. 
     1080At each time step, a test is performed to see if there is enough ice mass to calve an iceberg of each class in order (1 to 10). 
     1081Note that this is the initial mass multiplied by the number each particle represents (i.e. the scaling). 
     1082If there is enough ice, a new iceberg is spawned and the total available ice reduced accordingly. 
     1085Icebergs are influenced by wind, waves and currents, bottom melt and erosion. 
     1086The latter act to disintegrate the iceberg. 
     1087This is either all melted freshwater, or (if \np{rn\_bits\_erosion\_fraction}~>~0) into melt and additionally small ice bits 
     1088which are assumed to propagate with their larger parent and thus delay fluxing into the ocean. 
     1089Melt water (and other variables on the configuration grid) are written into the main NEMO model output files. 
     1091Extensive diagnostics can be produced. 
     1092Separate output files are maintained for human-readable iceberg information. 
     1093A separate file is produced for each processor (independent of \np{ln\_ctl}). 
     1094The amount of information is controlled by two integer parameters: 
     1096\item[\np{nn\_verbose\_level}]  takes a value between one and four and represents an increasing number of points in the code 
     1097at which variables are written, and an increasing level of obscurity. 
     1098\item[\np{nn\_verbose\_level}] is the number of timesteps between writes 
     1101Iceberg trajectories can also be written out and this is enabled by setting \np{nn\_sample\_rate}~>~0. 
     1102A non-zero value represents how many timesteps between writes of information into the output file. 
     1103These output files are in NETCDF format. 
     1104When \key{mpp\_mpi} is defined, each output file contains only those icebergs in the corresponding processor, 
     1105so care is needed to recreate data for individual icebergs. 
    10481107% ------------------------------------------------------------------------------------------------------------- 
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