GrADS Function: fndlvl

## fndlvl()

`fndlvl (expr, expr_to_find, lev1, lev2)`

Given two gridded variables, `expr` and `expr_to_find`, this function finds the first vertical level at which the `expr_to_find` value occurs in `expr`. `lev1` and `lev2` specify the range of levels over which to search. The result is a grid of pressure values.

### Usage Notes

1. The dimensions of `expr` and `expr_to_find` must match.

### Examples

1. This example finds the pressure levels of the 240 degree isotherm:

   `d fndlvl (t, const(t,240), lev=1000, lev=100)`

2. The `expr_to_find` doesn't have to be a constant; it can change with location. This example returns the pressure level of the tropopause, given the variable `'ttrop'` that contains the temperature at the tropopause:

   `d fndlvl (t, ttrop, lev=1000, lev=100)`

3. This example illustrates the limitations of `fndlvl`. It returns the level of the surface pressure variable `psfc` in the coordinate system of `lev`, a GrADS pre-defined variable.

   `d fndlvl (lev, psfc, lev=1000, lev=100)`

   The display should be exactly the same as `psfc` except in locations where `psfc` is greater than 1000 mb, the maximum value of `lev`.``