Open AccessImpacts of parameterized orographic drag on the N orthern H emisphere winter circulation
Author(s) -
Sandu Irina,
Bechtold Peter,
Beljaars Anton,
Bozzo Alessio,
Pithan Felix,
Shepherd Theodore G.,
Zadra Ayrton
Publication year - 2016
Publication title -
journal of advances in modeling earth systems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.03
H-Index - 58
ISSN - 1942-2466
DOI - 10.1002/2015ms000564
Subject(s) - orographic lift , orography , stratosphere , atmospheric sciences , climatology , environmental science , troposphere , numerical weather prediction , drag , meteorology , atmospheric circulation , northern hemisphere , geology , precipitation , physics , mechanics
Abstract A recent intercomparison exercise proposed by the Working Group for Numerical Experimentation (WGNE) revealed that the parameterized, or unresolved, surface stress in weather forecast models is highly model‐dependent, especially over orography. Models of comparable resolution differ over land by as much as 20% in zonal mean total subgrid surface stress ( τ tot ). The way τ tot is partitioned between the different parameterizations is also model‐dependent. In this study, we simulated in a particular model an increase in τ tot comparable with the spread found in the WGNE intercomparison. This increase was simulated in two ways, namely by increasing independently the contributions to τ tot of the turbulent orographic form drag scheme (TOFD) and of the orographic low‐level blocking scheme (BLOCK). Increasing the parameterized orographic drag leads to significant changes in surface pressure, zonal wind and temperature in the Northern Hemisphere during winter both in 10 day weather forecasts and in seasonal integrations. However, the magnitude of these changes in circulation strongly depends on which scheme is modified. In 10 day forecasts, stronger changes are found when the TOFD stress is increased, while on seasonal time scales the effects are of comparable magnitude, although different in detail. At these time scales, the BLOCK scheme affects the lower stratosphere winds through changes in the resolved planetary waves which are associated with surface impacts, while the TOFD effects are mostly limited to the lower troposphere. The partitioning of τ tot between the two schemes appears to play an important role at all time scales.