[gradsusr] column water vapor from specific humidity: using vint with hybrid height coordinates

[Katrina Hales-Garcia]

Hi All,
I need to calculate column water vapor from specific humidity.  The way I have done this in the past is to use the grads function vint (just as in the example in the documentation).  However, now I am using a data set that has a hybrid height coordinate with units in 'm' rather than pressure levels in 'mb'.  Is there a way to use the vint function when the z levels aren't in mb?  

If the vint function does not fit the situation, I was also looking into doing the integral layer by layer, but I am stuck on how to get the pressure information from the hybrid height coordinate.  If anyone has some insights on these I would much appreciate it! 

I've attached the file information (clipped from ncdump) with the vertical layer info of the data set (netcdf format, CMIP5 data, in this case: HadGEM2-ES model).

With Thanks,
Katrina

--------------------------------------------
netcdf hus_6hrLev_HadGEM2-ES_rcp45_r1i1p1_202512010600-202603010000 {
dimensions:
        time = UNLIMITED ; // (360 currently)
        lev = 38 ;
        lat = 145 ;
        lon = 192 ;
        bnds = 2 ;
variables:
        double time(time) ;
                time:units = "days since 1859-12-01" ;
                time:calendar = "360_day" ;
                time:axis = "T" ;
                time:long_name = "time" ;
                time:standard_name = "time" ;
        double lev(lev) ;
                lev:bounds = "lev_bnds" ;
                lev:units = "m" ;
                lev:axis = "Z" ;
                lev:positive = "up" ;
                lev:long_name = "hybrid height coordinate" ;
                lev:standard_name = "atmosphere_hybrid_height_coordinate" ;
                lev:formula = "z(k,j,i) = a(k) + b(k)*orog(j,i)" ;
                lev:formula_terms = "a: lev b: b orog: orog" ;
        double lev_bnds(lev, bnds) ;
                lev_bnds:formula = "z(k,j,i) = a(k) + b(k)*orog(j,i)" ;
                lev_bnds:standard_name = "atmosphere_hybrid_height_coordinate" ;
                lev_bnds:units = "m" ;
                lev_bnds:formula_terms = "a: lev_bnds b: b_bnds orog: orog" ;
        double b(lev) ;
                b:long_name = "vertical coordinate formula term: b(k)" ;
        float orog(lat, lon) ;

.....

 lev = 20.000337600708, 80.001350402832, 179.999114990234, 320.00146484375, 
    500.000579833984, 720.000366210938, 980.000854492188, 1279.998046875, 
    1619.99987792969, 1999.99841308594, 2420.00170898438, 2880.00146484375, 
    3379.99829101562, 3919.99951171875, 4500.00146484375, 5120, 
    5779.99951171875, 6479.99951171875, 7220, 8000.00146484375, 8820, 
    9679.9990234375, 10579.998046875, 11519.998046875, 12499.9990234375, 
    13520.0009765625, 14580.7998046875, 15694.6396484375, 16875.310546875, 
    18138.626953125, 19503.009765625, 20990.1875, 22626.08203125, 
    24458.28515625, 26583.640625, 29219.080078125, 32908.69140625, 
    39254.83203125 ;

 lev_bnds =
  0, 49.9988822937012,
  49.9988822937012, 130.000228881836,
  130.000228881836, 249.998336791992,
  249.998336791992, 410.001037597656,
  410.001037597656, 610.00048828125,
  610.00048828125, 850.000610351562,
  850.000610351562, 1130.00146484375,
  1130.00146484375, 1449.9990234375,
  1449.9990234375, 1810.00109863281,
  1810.00109863281, 2210,
  2210, 2649.99951171875,
  2649.99951171875, 3129.99975585938,
  3129.99975585938, 3650.00073242188,
  3650.00073242188, 4209.99853515625,
  4209.99853515625, 4810.0009765625,
  4810.0009765625, 5450,
  5450, 6129.99951171875,
  6129.99951171875, 6850,
  6850, 7610.0009765625,
  7610.0009765625, 8409.9990234375,
  8409.9990234375, 9250.0009765625,
  9250.0009765625, 10130,
  10130, 11050,
  11050, 12010.0009765625,
  12010.0009765625, 13010.001953125,
  13010.001953125, 14050.400390625,
  14050.400390625, 15137.7197265625,
  15137.7197265625, 16284.9736328125,
  16284.9736328125, 17506.96875,
  17506.96875, 18820.8203125,
  18820.8203125, 20246.599609375,
  20246.599609375, 21808.13671875,
  21808.13671875, 23542.18359375,
  23542.18359375, 25520.9609375,
  25520.9609375, 27901.357421875,
  27901.357421875, 31063.888671875,
  31063.888671875, 36081.76171875,
  36081.76171875, 42427.90234375 ;

 b = 0.99771648645401, 0.990881502628326, 0.979542553424835, 0.9637770652771, 
    0.943695485591888, 0.919438362121582, 0.891178011894226, 
    0.859118342399597, 0.823493480682373, 0.784570515155792, 
    0.742646217346191, 0.698050200939178, 0.651142716407776, 
    0.602314412593842, 0.55198872089386, 0.500619947910309, 0.44869339466095, 
    0.39672577381134, 0.34526526927948, 0.294891387224197, 0.24621507525444, 
    0.199878215789795, 0.156554222106934, 0.116947874426842, 
    0.0817952379584312, 0.0518637150526047, 0.0279368180781603, 
    0.0107164792716503, 0.00130179093685001, 0, 0, 0, 0, 0, 0, 0, 0, 0 ;

 orog =
  2801.479, 2801.479, 2801.479, 2801.479, 2801.479, 2801.479, 2801.479, 
....

---------------------------------------------


------------------------------------------------------------------
Katrina Hales-Garcia
UCLA Department of Atmospheric and Oceanic Sciences
7235 Math Sciences Bld.
Los Angeles CA  90095-1565
hales at atmos.ucla.edu
------------------------------------------------------------------

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