What is the Ultimate Limit of Weather Predictability?
Fuqing Zhang
Penn State
9 Mar, Noon, in 2155
Abstract:
Through extremely high-resolution global ensemble experiments with
state-of-the-science global numerical weather prediction models from
ECMWF and US NOAA, this study investigates the ultimate predictability
limit of day-to-day weather phenomena such as midlatitude winter storms
and summer monsoonal rainstorms. Results suggest such a limit may
indeed exist that is intrinsic to the underlying dynamical system and
instabilities even if the forecast model and the initial conditions are
nearly perfect. Currently, the practical predictability limit of
midlatitude instantaneous weather is around 10 days; reducing
initial-condition error by an order of magnitude will extend the
deterministic forecast lead times of day-to-day weather by up to 3-5
days, with much shorter room for improving prediction of small-scale
severe weather phenomena like thunderstorms. Achieving this additional
predictability limit can have enormous socioeconomic benefits but
requires coordinated efforts by the entire community to design better
numerical weather models, to improve observations, and to make better
use of observations with advanced data assimilation and computing
techniques. In essence, predictability of daily weather may be
intrinsically limited to about 2 weeks but can be extended by as much
as 3-5 days beyond the current-day limit.