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Transects and Cross Sections

The calculation of a lat/lon transect involves the following steps:
  1. Determine the two lat/lon pairs that define the ends of the transect
  2. Calculate the great circle path between the two lat/lon pairs using gc_latlon
  3. If your data is not rectilinear, then interpolate it a rectilinear grid
  4. Interpolate the input grid to the great circle using linint2_points

A simple example of drawing only a straight line and great circle path is availble. See the polyline Example 14

trans_1.ncl: Calculates and plots a transect and also plots the transect location on a separate plot.

The data is on a rectilinear grid, so no regridding is necessary before calling linint2_points to interpolate values to an arbitrary lat/lon line.

asr_5.ncl: Draw a vertical cross section at an arbitary longitude position (indicated by the blue line). This data is on a curvilinear grid, which means each point is represented by a unique lat,lon pair. Thus, when plotting the X axis, this example labels both lat and lon values at each tickmark location.
narr_5.ncl: The NARR data is on a curvilinear grid. This script uses an ESMF generated weight file (see ESMF example 30) to first regrid the NARR curvilinear grid to a rectilinear grid. Then three cross sections are plotted: (a) pressure x longitude; (b) pressure x latitude; and (c) pressure x user_specified_set_of_points.

For this example the user specified latitude/longitude locations lie along a great circle path between two user specified locations (see gc_latlon). They could be latitude/longitude locations along a (say) cold front.

cloudsat_1.ncl This example shows three kinds of cross sections of data on a rectilinear grid:

  1. Average "CloudSat Radar Reflectivity" over the period 200606-200612 at user specified levels.

  2. Radar reflectivity in the vertical at user specified (lat,lon) locations.

  3. User-specified cross sections. This uses linint2_points_Wrap to interpolate to a series of arbitrary points. The gc_latlon function is used to generate the points on a great circle path.