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From the observed data (p,T,RH), the other thermodynamic variables are calculated using the hydrostatic equation and Bolton's conversion formula (1980) as follows. Here, all units are MKS, and each variable has its usual meaning:
es=611.2*exp(17.67*(t-273.15)/(t-29.65))
qsv=0.622*(es/p)
qv=0.622*(es/p)*RH
e=p*qv/0.622
tv=t*(1.+0.61*qv)
td=273.15+(243.5*alog(0.01*e)-440.8)/(19.48-alog(0.01*e))
tlcl=55.+ 1./(1./(t-55.)-alog(RH)/2840.)
theta=t*(100000./p)**(0.2854*(1.-0.28*qv))
thetav=theta*(1.+0.61*qv)
thetae=theta*exp((3.376/tlcl-0.00254)*1000.*qv*(1+0.81*qv))
LCL: 102.62*(t-tLCL)
Where:
| es: | saturation vapor pressure |
| qsv: | water vapor saturation specific humidity |
| qv: | water vapor specific humidity |
| e: | water vapor pressure |
| tv: | virtual temperature |
| td: | dew point temperature |
| tlcl: | temperature an air parcel wil have when it is saturated after dry adiabatic ascent. |
| theta: | potential temperature |
| thetae: | equivalent potential temperature |
| LCL: | lifting condensation level |
| p: | pressure |
| t: | temperature |
| td: | dew point temperature |
| RH: | relative humidity(0<RH<<) |
| Z: | geopotential height |
| ws: | wind speed |
| wd: | wind direction |
| u: | |
| u: | zonal wind speed |
| v: | meridional wind speed |
After these initial conversions, a Quality-Control Check was executed using a QC-program from Colorado State University which requires (p,Z,t,td,ws,wd) as input variables. In the QC procedure, a subjective decision was made to identify apparent problematic data points. In most EPIC sounding data, all the observations except RH (or td) seemed not to have any serious problems. For RH, abrupt spikes were frequently observed. By comparing with the preceding and succeeding sounding observation, and by comparing with the temperature observation, apparently problematic RH were filtered out. The QC procedure was focused on low altitude data points. In high altitude data above 500hPa, many spikes in RH were not filtered.
After the QC-procedure, we made a 10m-height regularily gridded, linearly interpolated sounding file with (p,Z,t,td,ws,wd). From these, we re-calculated various thermodynamic variables, such as (RH,lcl,tlcl,tv,....) using the same conversion formula. "-999.9" is assigned to all missing (either no observation or bad points) variables. The units of final output are as follows:
Z(m) zlcl(m) p(hPa) t(C) td(C) RH(%) tv(C) theta(C) thetav(C) thetae(C) tlcl(C) qv(g/kg) qsv(g/kg) ws(m/s) wd(deg) u(m/s) v(m/s)Reference:
Bolton, David, 1980: The Computation of Equivalent Potential Temperature. Monthly Weather Review, 108, 1046-1053.
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