bottomdocumentation
bottomreturns the lowermost finite values in a 3D matrix. This function is useful for getting the seafloor temperature or atmospheric surface temperature in the presence of topography.
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Syntax
Zb = bottom(Z) [Zb,ind] = bottom(Z)
Description
Zb = bottom(Z)returns a 2D matrix containing the lowermost finite values in the 3D matrixZ.
[Zb,ind] = bottom(Z)also returns 2D matrix ind which contains the indices along the third dimension ofZcorresponding to the lowermost finite values inZ.
Example: Drake Passage
这个例子使用了一些网格海洋温度data from the Southern Ocean Database (described below). Begin by loading the example data:
loadsodb_examplewhos% displays the names and sizes of variables
Name Size Bytes Class Attributes d 44x1 352 double lat 1x61 488 double lon 1x91 728 double ptm 61x91x44 1953952 double readme 1x79 158 char
The 61x91x44 matrixptmcontains potential temperatures at latitudeslat, longitudeslon, and depthsd. Here's the potential temperature at the deepest depth,d(44)
imagescn(lon,lat,ptm(:,:,44)) cmoceanthermalcb = colorbar; ylabel(cb,'potential temperature (\circC)') xlabel'longitude'ylabel'latitude'
That's not much information! That's because throughout most of the domain the seafloor is shallower thand(44)= 5500 m deep, so we just get NaN values wherever the the 5500 m layer is deeper than the bathymetry.
So instead, plot the lowermost finite values with thebottomfunction:
figure imagescn(lon,lat,bottom(ptm)) cmoceanthermalcaxis([-2 12]) cb = colorbar; ylabel(cb,'bottom temperature (\circC)') xlabel'longitude'ylabel'latitude'
Since we have a depth arraydand indicesindcorresponding to the deepest finite values at each grid cell, we can get a 2D grid of bottom depths simply from d(ind). Add them to the map as contours:
% Get bottom temperature and corresponding indices:[T_bot,ind] = bottom(ptm);% Make a 2D bottom depth matrix:D = d(ind);% Overlay bathymetry contours:holdoncontour(lon,lat,D,0:1000:5500,'k')% Underlay a silly-looking earth image:h = earthimage; uistack(h,'bottom');
On a mildly interesting note, the bottom temperature seems to have some relationship to the bottom depth. Compare the two in profile like this:
figure plot(T_bot(:),D(:),'.') axistightij% flips y directionboxoffxlabel'bottom temperature \circC'ylabel'bottom depth (m)'
How the sodb_example data were acquired
The sodb_example.mat data come from the Southern Ocean Database and were saved usingAntarctic Mapping Tools for Matlab(Greene et al., 2017) via the following code:
lon = -180:2:0; lat = -75:0.5:-45; [Lon,Lat] = meshgrid(lon,lat); [ptm,d] = sodb_interp('ptm',Lat,Lon); readme = 'potential temperature data from the Southern Ocean Database (Orsi and Whitorth)'; save('sodb_example.mat','lat','lon','ptm','d','readme');
Author Info
This function is part of theClimate Data Toolbox for Matlab. The function and supporting documentation were written by Chad A. Greene of the University of Texas at Austin.