The potential impact of upper stratospheric measurements on sub-seasonal forecasts in the extra-tropics

This chapter examines the potential improvements in tropospheric weather
forecasts that might arise from an improved representation of the upper stratospheric
state. First, the chapter reviews current operational practice regarding observation of
the atmosphere and the relative paucity of observations in the altitude range 40 to
70km. Then we describe in detailed some idealised model calculations to quantify
the potential gain in skill available from improved monitoring in this region.
The idealised model experiments use a relaxation technique with the Hadley Centre
General Environment Model, to assess the potential gain in skill from improved
knowledge both the whole stratosphere and the upper stratosphere. At weather forecasting
time-scales (up to forecast day 30), improved knowledge of the stratosphere,
close to the onset of a sudden stratospheric warming, improves forecasts of the tropospheric
norther annular mode. Whole-stratosphere information significantly improved
average surface temperature anomalies over northern North America, whilst
upper-stratosphere information improved anomalies over Central Siberia. These results
suggest any new observational technique which can improve montioring of
the 40 to 70km region would likely benefit tropospheric forecast skill during winter
time.