M. Xu et al., Applications of the adjoint technique to short-range ensemble forecasting of mesoscale convective systems, M WEATH REV, 129(6), 2001, pp. 1395-1418
The feasibility of applying a mesoscale adjoint model to the creation of an
ensemble for short-range simulations of mesoscale convective systems (MCSs
) is explored. Because past studies show that forecasters routinely improve
upon numerical guidance and can identify mesoscale-sized areas of forecast
concern with a high level of skill, it is clear that forecasters have insi
ghts into the daily weather forecast problems that exceed what can be provi
ded by a numerical weather prediction model. Using an adjoint model, one co
uld develop a system in which a forecaster identifies the area of forecast
concern and then designs a set of rapidly produced sensitivity experiments
that evaluate the influence of key atmospheric parameters on the model fore
cast. The output from these sensitivity experiments is then used to create
ensemble members for a short-range operational ensemble forecast, which is
specifically designed to investigate the forecast concern of the day.
This adjoint ensemble approach is tested for the 48-h period beginning 1200
UTC 27 May 1985, in which a long-lived MCS developed underneath a large-sc
ale ridge. A mesoscale adjoint model is used to define the alterations to t
he model initial conditions necessary to evaluate the influences of key mes
oscale structures, which the authors believe have a large influence on late
r convective development in the model. Results indicate that the adjoint te
chnique is effective in creating the proper directional response in the mod
el simulation.
When compared to initial condition and model physics ensembles of this even
t, the adjoint ensemble produces more variance than the initial condition e
nsemble and almost as much variance as the model physics ensemble. However,
the values of the equitable threat score and the ranked probability score
are better for the adjoint ensemble between 6 and 24 h than for either of t
he other two ensembles. These results suggest that further exploration of e
nsembles that incorporate the experience and expertise possessed by forecas
ters is warranted.