Rm. Errico et al., Estimation of the error distributions of precipitation produced by convective parametrization schemes, Q J R METEO, 127(578), 2001, pp. 2495-2512
Citations number
27
Categorie Soggetti
Earth Sciences
Journal title
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
If a parametrization scheme for convective precipitation is to be used for
assimilating observations of precipitation using a statistically based tech
nique, then statistics of the errors produced by that scheme are required.
These are the errors produced by the scheme's formulation itself, not count
ing any errors in the scheme's input, Such errors are extremely difficult t
o estimate, but examination of differences produced by various suitable sch
emes can yield qualitative descriptions of such errors. Here, hourly accumu
lated convective precipitation fields produced from six different versions
of a short-term forecast model are compared. The versions have identical in
itial and boundary conditions, but vary in the schemes used for either the
convection or the planetary boundary layer, or both. The distribution of di
fferences, or differences in logarithms of accumulations, between correspon
ding precipitating grid points for pairs of forecasts are examined using a
simple binning technique. When the convection schemes differ, results revea
l that if either a log-normal or normal distribution is a better characteri
zation of the distributions, it is the log-normal one. The standard deviati
ons of these logarithmic distributions correspond to different schemes at i
dentical grid points producing values differing by factors of 2 or more. A
large proportion of grid points that have non-zero hourly accumulations usi
ng one model version may have no accumulation using another version, For mo
st pairs of forecasts examined, however, grid points having larger values o
f accumulation for one scheme tend to have a smaller fraction of values hav
ing no accumulation in the other scheme. These results suggest that the fin
ite probability that the model produces no precipitation when the correspon
ding, true atmospheric state does, should be considered in the statistical
description of the model errors and that, because of the large standard dev
iation of model errors as well as large possible errors of hourly precipita
tion observations, the quantitative usefulness of assimilating such observa
tions may be very limited.