NCL Skew-T CAPE calculation

Hello,

I am working with the NCL Skew-T routine to plot NCEP/NCAR reanalysis
temperatures over the North Atlantic Ocean. The program is producing CAPE
values much too high for the environment (~3000-4000 J when my calculations
estimate 600-1200 J).

I noticed something on the Skew-T plots that might be part of the problem.
The CAPE curve is plotted along the pseudo-adiabat starting at the first
pressure level, not at the LFC. I am really puzzled, especially since the
NCL-calculated LCLs match the LCLs on my hand-plotted Skew-Ts (usually
between 925-960 hPa). Do I need to set another attribute or three in my
program, or in the original skewt_func.ncl code?

I have attached a sample text file (I don't have dewpoints for pressures
above the first level, so the remainder are filler values) and the resulting
plot in jpg and ps format. My version of routine skewt_2.ncl is included
below in this email.

I really appreciate any assistance. Please let me know if more information
is needed.

Rachel G Mauk
Masters Candidate
Atmospheric Sciences Program
The Ohio State University
1036 Derby Hall
154 N. Oval Mall
Columbus, OH 43210

;**************************************************
; skewt_new.ncl, based on skewt_2.ncl from NCL lib, ncl.ucar.edu
;**************************************************
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/skewt_func.ncl"
;**************************************************

 begin

; --- Read Data; no winds; set to _FillValue------------;
diri = "$NCARG_ROOT/textfiles/"
fili = "jose_2918_trial.txt"
nlvl = 12
ncol = 3
TestData = asciiread (diri+fili, (/nlvl,ncol/), "float")

p = TestData (:,0)
tc = TestData (:,1)
tcd = TestData (:,2)

z =
(/-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999./)
wspd =
(/-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999./)
wdir =
(/-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999.,-999./)

tcd@_FillValue = -999.
z@_FillValue = -999.
wspd@_FillValue = -999.
wdir@_FillValue = -999.

;*************************
; create plot
;*************************
  wks = gsn_open_wks ("ps", "skewt_jose_2918")

; --- Create background skew-T; plot sounding ---------------------
  skewtOpts = True
  skewtOpts@DrawColAreaFill = True ; default is False
  skewtOpts@tiMainString = "Jose 10/29/81 18Z; Filler Dewpoints"

  dataOpts = False ; set options
  dataOpts@colTemperature = "black"

  skewt_bkgd = skewT_BackGround (wks, skewtOpts)
  skewt_data = skewT_PlotData (wks, skewt_bkgd,
p,tc,tcd,z,wspd,wdir,dataOpts)
  draw (skewt_bkgd)
  draw (skewt_data)
  frame(wks)

 end

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• text/plain attachment: jose_2918_trial.txt

• application/postscript attachment: skewt_jose_2918.ps