Merge pull request #590 from cbegeman/add-bsf-function

Port barotropic streamfunction from MPAS-Analysis

Author: xylar

conda_package/docs/api.rst

@@ -225,6 +225,8 @@ Ocean Tools
    depth.compute_depth
    depth.compute_zmid
 
+   compute_barotropic_streamfunction
+
 .. currentmodule:: mpas_tools.ocean.inject_bathymetry
 
 .. autosummary::

conda_package/docs/index.rst

@@ -50,6 +50,7 @@ analyzing simulations, and in other MPAS-related workflows.
    ocean/coastline_alteration
    ocean/moc
    ocean/depth
+   ocean/streamfunction
    ocean/visualization
 
 .. toctree::

conda_package/docs/ocean/streamfunction.rst

@@ -0,0 +1,14 @@
+.. _ocean_streamfunction:
+
+Computing streamfunctions
+=========================
+
+Computing the barotropic streamfunction
+---------------------------------------
+
+The function :py:func:`mpas_tools.ocean.compute_barotropic_streamfunction()`
+computes the barotproic streamfunction at vertices on the MPAS-Ocean grid.
+The function takes a dataset containing an MPAS-Ocean mesh and another with
+``normalVelocity`` and ``layerThickness`` variables (possibly with a
+``timeMonthly_avg_`` prefix).  The streamfunction is computed only over the
+range of (positive-down) depths provided and at the given time index.

conda_package/mpas_tools/ocean/__init__.py

@@ -1,7 +1,16 @@
-from mpas_tools.ocean.build_mesh import build_spherical_mesh, \
-    build_planar_mesh
+from mpas_tools.ocean.build_mesh import (
+    build_spherical_mesh,
+    build_planar_mesh,
+)
+from mpas_tools.ocean.barotropic_streamfunction import (
+    compute_barotropic_streamfunction,
+)
 from mpas_tools.ocean.inject_bathymetry import inject_bathymetry
-from mpas_tools.ocean.inject_meshDensity import inject_meshDensity_from_file, \
-    inject_spherical_meshDensity, inject_planar_meshDensity
-from mpas_tools.ocean.inject_preserve_floodplain import \
-    inject_preserve_floodplain
+from mpas_tools.ocean.inject_meshDensity import (
+    inject_meshDensity_from_file,
+    inject_spherical_meshDensity,
+    inject_planar_meshDensity,
+)
+from mpas_tools.ocean.inject_preserve_floodplain import (
+    inject_preserve_floodplain,
+)

conda_package/mpas_tools/ocean/barotropic_streamfunction.py

@@ -0,0 +1,158 @@
+import xarray as xr
+import numpy as np
+import scipy.sparse
+import scipy.sparse.linalg
+
+import logging
+import sys
+from mpas_tools.ocean.depth import compute_zmid
+
+
+def compute_barotropic_streamfunction(ds_mesh, ds, logger=None,
+                                      min_depth=-5., max_depth=1.e4,
+                                      prefix='timeMonthly_avg_',
+                                      time_index=0):
+    """
+    Compute barotropic streamfunction. Returns BSF in Sv on vertices.
+
+    Parameters
+    ----------
+    ds_mesh : ``xarray.Dataset``
+        A dataset containing MPAS mesh variables
+
+    ds : ``xarray.Dataset``
+        A dataset containing MPAS output variables ``normalVelocity`` and
+        ``layerThickness`` (possibly with a ``prefix``)
+
+    logger : ``logging.Logger``, optional
+        A logger for the output if not stdout
+
+    min_depth : float, optional
+        The minimum depth (positive down) to compute transport over
+
+    max_depth : float, optional
+        The maximum depth (positive down) to compute transport over
+
+    prefix : str, optional
+        The prefix on the ``normalVelocity`` and ``layerThickness`` variables
+
+    time_index : int, optional
+        The time at which to index ``ds`` (if it has ``Time`` as a dimension)
+    """
+
+    useStdout = logger is None
+    if useStdout:
+        logger = logging.getLogger()
+        logger.addHandler(logging.StreamHandler(sys.stdout))
+        logger.setLevel(logging.INFO)
+
+    inner_edges, transport = _compute_transport(
+        ds_mesh, ds, min_depth=min_depth, max_depth=max_depth, prefix=prefix,
+        time_index=time_index)
+    logger.info('transport computed.')
+
+    nvertices = ds_mesh.sizes['nVertices']
+
+    cells_on_vertex = ds_mesh.cellsOnVertex - 1
+    vertices_on_edge = ds_mesh.verticesOnEdge - 1
+    is_boundary_cov = cells_on_vertex == -1
+    boundary_vertices = np.logical_or(is_boundary_cov.isel(vertexDegree=0),
+                                      is_boundary_cov.isel(vertexDegree=1))
+    boundary_vertices = np.logical_or(boundary_vertices,
+                                      is_boundary_cov.isel(vertexDegree=2))
+
+    # convert from boolean mask to indices
+    boundary_vertices = np.flatnonzero(boundary_vertices.values)
+
+    n_boundary_vertices = len(boundary_vertices)
+    n_inner_edges = len(inner_edges)
+
+    indices = np.zeros((2, 2 * n_inner_edges + n_boundary_vertices), dtype=int)
+    data = np.zeros(2 * n_inner_edges + n_boundary_vertices, dtype=float)
+
+    # The difference between the streamfunction at vertices on an inner
+    # edge should be equal to the transport
+    v0 = vertices_on_edge.isel(nEdges=inner_edges, TWO=0).values
+    v1 = vertices_on_edge.isel(nEdges=inner_edges, TWO=1).values
+
+    ind = np.arange(n_inner_edges)
+    indices[0, 2 * ind] = ind
+    indices[1, 2 * ind] = v1
+    data[2 * ind] = 1.
+
+    indices[0, 2 * ind + 1] = ind
+    indices[1, 2 * ind + 1] = v0
+    data[2 * ind + 1] = -1.
+
+    # the streamfunction should be zero at all boundary vertices
+    ind = np.arange(n_boundary_vertices)
+    indices[0, 2 * n_inner_edges + ind] = n_inner_edges + ind
+    indices[1, 2 * n_inner_edges + ind] = boundary_vertices
+    data[2 * n_inner_edges + ind] = 1.
+
+    rhs = np.zeros(n_inner_edges + n_boundary_vertices, dtype=float)
+
+    # convert to Sv
+    ind = np.arange(n_inner_edges)
+    rhs[ind] = 1e-6 * transport
+
+    ind = np.arange(n_boundary_vertices)
+    rhs[n_inner_edges + ind] = 0.
+
+    matrix = scipy.sparse.csr_matrix(
+        (data, indices),
+        shape=(n_inner_edges + n_boundary_vertices, nvertices))
+
+    solution = scipy.sparse.linalg.lsqr(matrix, rhs)
+    bsf_vertex = xr.DataArray(-solution[0],
+                              dims=('nVertices',))
+
+    return bsf_vertex
+
+def _compute_transport(ds_mesh, ds, min_depth, max_depth, prefix,
+                       time_index):
+
+    cells_on_edge = ds_mesh.cellsOnEdge - 1
+    inner_edges = np.logical_and(cells_on_edge.isel(TWO=0) >= 0,
+                                 cells_on_edge.isel(TWO=1) >= 0)
+
+    if 'Time' in ds.dims:
+        ds = ds.isel(Time=time_index)
+
+    # convert from boolean mask to indices
+    inner_edges = np.flatnonzero(inner_edges.values)
+
+    cell0 = cells_on_edge.isel(nEdges=inner_edges, TWO=0)
+    cell1 = cells_on_edge.isel(nEdges=inner_edges, TWO=1)
+
+    normal_velocity = \
+        ds[f'{prefix}normalVelocity'].isel(nEdges=inner_edges)
+    layer_thickness = ds[f'{prefix}layerThickness']
+    layer_thickness_edge = 0.5 * (layer_thickness.isel(nCells=cell0) +
+                                  layer_thickness.isel(nCells=cell1))
+
+    n_vert_levels = ds.sizes['nVertLevels']
+
+    vert_index = xr.DataArray.from_dict(
+        {'dims': ('nVertLevels',), 'data': np.arange(n_vert_levels)})
+    mask_bottom = (vert_index < ds_mesh.maxLevelCell).T
+    mask_bottom_edge = 0.5 * (mask_bottom.isel(nCells=cell0) +
+                              mask_bottom.isel(nCells=cell1))
+
+    if 'zMid' not in ds.keys():
+        z_mid = compute_zmid(ds_mesh.bottomDepth, ds_mesh.maxLevelCell,
+                             ds_mesh.layerThickness)
+    else:
+        z_mid = ds.zMid
+    z_mid_edge = 0.5 * (z_mid.isel(nCells=cell0) +
+                        z_mid.isel(nCells=cell1))
+
+    mask = np.logical_and(np.logical_and(z_mid_edge >= -max_depth,
+                                         z_mid_edge <= -min_depth),
+                          mask_bottom_edge)
+    normal_velocity = normal_velocity.where(mask)
+    layer_thickness_edge = layer_thickness_edge.where(mask)
+    transport = ds_mesh.dvEdge[inner_edges] * \
+        (layer_thickness_edge * normal_velocity).sum(dim='nVertLevels')
+
+    return inner_edges, transport

conda_package/mpas_tools/ocean/depth.py

@@ -37,7 +37,7 @@ def compute_depth(refBottomDepth):
     depth_bnds[0, 0] = 0.
     depth_bnds[1:, 0] = refBottomDepth[0:-1]
     depth_bnds[:, 1] = refBottomDepth
-    depth = 0.5*(depth_bnds[:, 0] + depth_bnds[:, 1])
+    depth = 0.5 * (depth_bnds[:, 0] + depth_bnds[:, 1])
 
     return depth, depth_bnds
 
@@ -82,11 +82,11 @@ def compute_zmid(bottomDepth, maxLevelCell, layerThickness,
 
     thicknessSum = layerThickness.sum(dim=depth_dim)
     thicknessCumSum = layerThickness.cumsum(dim=depth_dim)
-    zSurface = -bottomDepth+thicknessSum
+    zSurface = -bottomDepth + thicknessSum
 
     zLayerBot = zSurface - thicknessCumSum
 
-    zMid = zLayerBot + 0.5*layerThickness
+    zMid = zLayerBot + 0.5 * layerThickness
 
     zMid = zMid.where(vertIndex < maxLevelCell)
     if 'Time' in zMid.dims:
@@ -150,8 +150,7 @@ def add_depth(inFileName, outFileName, coordFileName=None):
     history = '{}: {}'.format(time, ' '.join(sys.argv))
 
     if 'history' in ds.attrs:
-        ds.attrs['history'] = '{}\n{}'.format(history,
-                                              ds.attrs['history'])
+        ds.attrs['history'] = f'{history}\n{ds.attrs["history"]}'
     else:
         ds.attrs['history'] = history
 
@@ -229,8 +228,7 @@ def add_zmid(inFileName, outFileName, coordFileName=None):
     history = '{}: {}'.format(time, ' '.join(sys.argv))
 
     if 'history' in ds.attrs:
-        ds.attrs['history'] = '{}\n{}'.format(history,
-                                              ds.attrs['history'])
+        ds.attrs['history'] = f'{history}\n{ds.attrs["history"]}'
     else:
         ds.attrs['history'] = history
 
@@ -288,8 +286,8 @@ def write_time_varying_zmid(inFileName, outFileName, coordFileName=None,
 
     dsIn = xarray.open_dataset(inFileName)
     dsIn = dsIn.rename({'nVertLevels': 'depth'})
-    inVarName = '{}layerThickness'.format(prefix)
-    outVarName = '{}zMid'.format(prefix)
+    inVarName = f'{prefix}layerThickness'
+    outVarName = f'{prefix}zMid'
     layerThickness = dsIn[inVarName]
 
     zMid = compute_zmid(dsCoord.bottomDepth, dsCoord.maxLevelCell,