Cumhuriyet Science Journal

Abstract

Precipitable Water (PW) data
of NCEP/NCAR Reanalysis Project (NNRP) model is evaluated by comparing to
radiosonde data obtained from 8 locations of Turkey for the years between 2015
and 2017. Two methods are utilized to extract NNRP data for the observation
locations. In the first method, the nearest NNRP grid point to the radiosonde
locations is selected. The second method is the application of bilinear
interpolation method on NNRP data to include the weighted effects of
corresponding grid locations related with the observation sites. Both NNRP and
radiosonde data have 12 h interval for the times 0000 Z and 1200 Z. PW output
of NNRP model is compared to observations by means of graphical evaluation of
time series, error analyses (Mean Absolute Error (MAE), Root Mean Square Error
(RMSE), and Root Mean Squared Error (nRMSE)), goodness of fit tests (Cp and
PBIAS), and probability density functions (PDF). Error analyses of most of the
observation locations indicate that bilinear interpolation method is better
than utilizing the nearest grid value data which is not obtained by applying
any interpolation technique. Error analyses indicate that nRMSEs of NNRP data
for PW analyses are less than 10% for 6 locations of Turkey (Ankara,
Diyarbakir, Erzurum, Isparta, Istanbul, and Izmir) if it is assumed that the
observations have no errors for the years between 2015 and 2017. nRMSEs of the
other 2 coastal locations (Adana and Samsun) are the same as 13.8% and this may
indicate that local moisture sources of these locations are greater than mesoscale
moisture fields, since NNRP data may not capture local effects well due to its
spatial resolution. Comparisons of probability density functions (PDF) of these
data sets show that NNRP model may not be successful in capturing extreme
values.