;+
;
; .. _d2m_to_q2m_erai.pro:
;
; ===================
; d2m_to_q2m_erai.pro
; ===================
;
;     .. graphviz::
;
;        digraph d2m_to_q2m_erai {
;           graph [
;           rankdir="LR",
;           ]
;           file_d2m [shape=ellipse,fontname=Courier,label="/Volumes/PRAVEEN/TropFlux/input_uncor/erai_d2m_19890101_20091231_oafluxgrid.nc"];
;           file_t2m [shape=ellipse,fontname=Courier,label="/Volumes/PRAVEEN/TropFlux/input_uncor/erai_t2m_19890101_20091231_oafluxgrid.nc"];
;           file_msl [shape=ellipse,fontname=Courier,label="/Volumes/PRAVEEN/TropFlux/input_uncor/erai_msl_19890101_20091231_oafluxgrid.nc"];

;           file_q2m [shape=ellipse,fontname=Courier,label="/Volumes/PRAVEEN/TropFlux/input_uncor/q2m_erai_19890101_20091231_oafluxgrid.nc"];
;
;           d2m_to_q2m_erai [shape=box,
;           fontname=Courier,
;           color=blue,
;           URL="http://forge.ipsl.jussieu.fr/tropflux/browser/trunk/src/d2m_to_q2m_erai.pro",
;           label="${PROJECT}/src/d2m_to_q2m_erai.pro"];
;           {file_d2m file_t2m file_msl} -> {d2m_to_q2m_erai} -> {file_q2m}
;        }
;
; SEE ALSO
; ========
;
; :func:`rh_to_spechum`
; :func:`initncdf <saxo:initncdf>`
; :func:`read_ncdf <saxo:read_ncdf>`
; :func:`julday <saxo:julday>`
; :func:`ncdf_quickwrite <saxo:ncdf_quickwrite>`
;
; EXAMPLES
; ========
;
; ::
;
;  IDL> d2m_to_q2m_erai
;
; TODO
; ====
;
; hard coded directory - usage of ${PROJECT_ID}
;
; coding rules
;
; EVOLUTIONS
; ==========
;
; - fplod 20101215T162933Z aedon.locean-ipsl.upmc.fr (Darwin)
;
;   * graph correction
;
; - fplod 20101215T093141Z aedon.locean-ipsl.upmc.fr (Darwin)
;
;   * add graph in header
;
; - fplod 20101214T093615Z aedon.locean-ipsl.upmc.fr (Darwin)
;
;   * minimal header
;
; - pbk 2008
;
;   * creation
;
;-
pro d2m_to_q2m_erai
@common
;; reading erai dew point temperature
d1=19881001 & d2=20101231

file='/Volumes/PRAVEEN/TropFlux/input_uncor/erai_d2m_19890101_20091231_oafluxgrid.nc'
initncdf, file
td=read_ncdf("d2m", d1,d2, file=file,/nostr)

;; reading erai air temperature
file='/Volumes/PRAVEEN/TropFlux/input_uncor/erai_t2m_19890101_20091231_oafluxgrid.nc'
initncdf, file
t=read_ncdf("t2m", d1,d2, file=file,/nostr)
tt=time &jpt=n_elements(time)
help, t, td

;;since the t2m and d2m are already in K, no need for conversion

e=es0*exp((25.e5/461.5)*((1/273.15)-(1/td)))
es=es0*exp((25.e5/461.5)*((1/273.15)-(1/t)))

rh=(e/es)*100

;; conversion of relative humidity to sp. humidity
;; Ref.1 -  Gill, Appendix 4,
;; Ref.2 - http://efdl.cims.nyu.edu/project_aomip/forcing_data/atmosphere/humidity.html

t=t-273.15

file='/Volumes/PRAVEEN/TropFlux/input_uncor/erai_msl_19890101_20091231_oafluxgrid.nc'
initncdf, file
P=read_ncdf("msl", d1, d2, file=file,/nostr)
help, P
q2m=rh_to_spechum(rh,t,P)

;;writing field
ncfile='!/Volumes/PRAVEEN/TropFlux/input_uncor/q2m_erai_19890101_20091231_oafluxgrid.nc'
time=timegen(7670, units='days', start=julday(1,1,1989)) & jpt=n_elements(time)
cda0=string(jul2date(time(0)),format='(i8.8)')
cda1=string(jul2date(time(jpt-1)),format='(i8.8)')


tt=time-julday(1,1,1950,00,00,00)
xlon=reform(glamt(*,0) ) & ylat=reform(gphit(0,*))
valmask=1.e20

lon_attr={units:'degrees_east',long_name:'Longitude'}
lat_attr={units:'degrees_north',long_name:'Latitude'}
q2m_attr={units:'kg/kg',missing_value:valmask,long_name:'Surface specific humidity at 2m ',short_name:'q2m',axis:'TYX'}
time_attr={units:'days since 1950-01-01 00:00:00',long_name:'Time axis',time_origin:' 1950-JAN-01 00:00:00'}
globattr={source:'Surface specific humidity at 2m calculated from dew point temperature',timerange:cda0+' - '+cda1}

ncfields = 'q2m[longitude,latitude,time]=q2m:q2m_attr; ' $
                      + 'longitude[]=xlon:lon_attr; ' $
                      + 'latitude[]=ylat:lat_attr; ' $
                      + 'tt[*time]=tt:time_attr ' $
                      + ' @ globattr'

@ncdf_quickwrite
return
end