- Timestamp:
- 2012-04-25T12:51:18+02:00 (12 years ago)
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branches/2012/dev_r3337_NOCS10_ICB/DOC/TexFiles/Chapters/Chap_SBC.tex
r3342 r3368 866 866 %} 867 867 868 869 % ================================================================ 870 % Handling of icebergs 871 % ================================================================ 872 \section{ Handling of icebergs (ICB) } 873 \label{ICB_icebergs} 874 %------------------------------------------namberg---------------------------------------------------- 875 \namdisplay{namberg} 876 %------------------------------------------------------------------------------------------------------------- 877 878 Icebergs are modelled as lagrangian particles in NEMO. 879 Their physical behaviour is controlled by equations as described in \citet{Martin_Adcroft_OM10} ). 880 (Note that the authors kindly provided a copy of their code to act as a basis for implementation in NEMO.) 881 Icebergs are initially spawned into one of ten classes which have specific mass and thickness as described by 882 \np{rn\_initial\_mass} and \np{rn\_initial\_thickness}. 883 Each class has an associated scaling (\np{rn\_mass\_scaling}), which is an integer representing how many icebergs 884 of this class are being described as one lagrangian point (this reduces the numerical problem of tracking every single iceberg). 885 They are enabled by setting \np{ln\_icebergs}~=~true. 886 887 Two initialisation schemes are possible. 888 \begin{description} 889 \item[\np{nn\_test\_icebergs}~$>$~0] 890 In this scheme, the value of \np{nn\_test\_icebergs} represents the class of iceberg to generate 891 (so between 1 and 10), and \np{nn\_test\_icebergs} provides a lon/lat box in the domain at each 892 grid point of which an iceberg is generated at the beginning of the run. 893 (Note that this happens each time the timestep equals \np{nn\_nit000}.) 894 \np{nn\_test\_icebergs} is defined by four numbers in \np{nn\_test\_box} representing the corners 895 of the geographical box: lonmin,lonmax,latmin,latmax 896 \item[\np{nn\_test\_icebergs}~=~-1] 897 In this scheme the model reads a calving file supplied in the \np{sn\_icb} parameter. 898 This should be a file with a field on the configuration grid (typically ORCA) representing ice accumulation rate at each model point. 899 These should be ocean points adjacent to land where icebergs are known to calve. 900 Most points in this input grid are going to have value zero. 901 When the model runs, ice is accumulated at each grid point which has a non-zero source term. 902 At 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). 903 Note that this is the initial mass multiplied by the number each particle represents ($i.e.$ the scaling). 904 If there is enough ice, a new iceberg is spawned and the total available ice reduced accordingly. 905 \end{description} 906 907 Icebergs are influenced by wind, waves and currents, bottom melt and erosion. 908 The latter act to disintegrate the iceberg. This is either all melted freshwater, or 909 (if \np{rn\_bits\_erosion\_fraction}~$>$~0) into melt and additionally small ice bits 910 which are assumed to propagate with their larger parent and thus delay fluxing into the ocean. 911 Melt water (and other variables on the configuration grid) are written into the main NEMO model output files. 912 913 Extensive diagnostics can be produced. 914 Separate output files are maintained for human-readable iceberg information. 915 A separate file is produced for each processor (independent of \np{ln\_ctl}). 916 The amount of information is controlled by two integer parameters: 917 \begin{description} 918 \item[\np{nn\_verbose\_level}] takes a value between one and four and represents 919 an increasing number of points in the code at which variables are written, and an 920 increasing level of obscurity. 921 \item[\np{nn\_verbose\_write}] is the number of timesteps between writes 922 \end{description} 923 924 Iceberg trajectories can also be written out and this is enabled by setting \np{nn\_sample\_rate}~$>$~0. 925 A non-zero value represents how many timesteps between writes of information into the output file. 926 These output files are in NETCDF format. 927 When \key{mpp\_mpi} is defined, each output file contains only those icebergs in the corresponding processor, 928 so care is needed to recreate data for individual icebergs. 929 930 868 931 % ================================================================ 869 932 % Miscellanea options … … 1047 1110 1048 1111 % ------------------------------------------------------------------------------------------------------------- 1049 % Handling of icebergs1050 % -------------------------------------------------------------------------------------------------------------1051 \subsection{ Handling of icebergs (ICB) }1052 \label{ICB_icebergs}1053 %------------------------------------------namberg----------------------------------------------------1054 \namdisplay{namberg}1055 %-------------------------------------------------------------------------------------------------------------1056 1057 Icebergs are modelled as lagrangian particles in NEMO.1058 Their 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.)1060 Icebergs are initially spawned into one of ten classes which have specific mass and thickness as described by1061 \np{rn\_initial\_mass} and \np{rn\_initial\_thickness}.1062 Each class has an associated scaling (\np{rn\_mass\_scaling}), which is an integer representing how many icebergs1063 of this class are being described as one lagrangian point (this reduces the numerical problem of tracking every single iceberg).1064 They are enabled by setting \np{ln\_icebergs}~=~true.1065 1066 Two initialisation schemes are possible.1067 \begin{description}1068 \item[\np{nn\_test\_icebergs}~>~0]1069 In this scheme, the value of \np{nn\_test\_icebergs} represents the class of iceberg to generate (so between 1 and 10), and1070 \np{nn\_test\_icebergs} provides a lon/lat box in the domain at each grid point of which an iceberg is generated at the1071 beginning 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 geographical1073 box: lonmin,lonmax,latmin,latmax1074 \item[\np{nn\_test\_icebergs}~=~-1]1075 In this scheme the model reads a calving file supplied in the \np{sn\_icb} parameter.1076 This should be a file with a field on the configuration grid (typically ORCA) representing ice accumulation rate at each model point.1077 These should be ocean points adjacent to land where icebergs are known to calve.1078 Most points in this input grid are going to have value zero.1079 When the model runs, ice is accumulated at each grid point which has a non-zero source term.1080 At 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).1081 Note that this is the initial mass multiplied by the number each particle represents (i.e. the scaling).1082 If there is enough ice, a new iceberg is spawned and the total available ice reduced accordingly.1083 \end{description}1084 1085 Icebergs are influenced by wind, waves and currents, bottom melt and erosion.1086 The latter act to disintegrate the iceberg.1087 This is either all melted freshwater, or (if \np{rn\_bits\_erosion\_fraction}~>~0) into melt and additionally small ice bits1088 which are assumed to propagate with their larger parent and thus delay fluxing into the ocean.1089 Melt water (and other variables on the configuration grid) are written into the main NEMO model output files.1090 1091 Extensive diagnostics can be produced.1092 Separate output files are maintained for human-readable iceberg information.1093 A separate file is produced for each processor (independent of \np{ln\_ctl}).1094 The amount of information is controlled by two integer parameters:1095 \begin{description}1096 \item[\np{nn\_verbose\_level}] takes a value between one and four and represents an increasing number of points in the code1097 at which variables are written, and an increasing level of obscurity.1098 \item[\np{nn\_verbose\_level}] is the number of timesteps between writes1099 \end{description}1100 1101 Iceberg trajectories can also be written out and this is enabled by setting \np{nn\_sample\_rate}~>~0.1102 A non-zero value represents how many timesteps between writes of information into the output file.1103 These output files are in NETCDF format.1104 When \key{mpp\_mpi} is defined, each output file contains only those icebergs in the corresponding processor,1105 so care is needed to recreate data for individual icebergs.1106 1107 % -------------------------------------------------------------------------------------------------------------1108 1112 % Freshwater budget control 1109 1113 % -------------------------------------------------------------------------------------------------------------
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