5 research outputs found
The role of surface and advective heat and salt fluxes in the variability of North Sea temperature and salinity
Comparison of three regional coupled ocean atmosphere models for the North Sea under today‘s and future climate conditions (KLIWAS Schriftenreihe ; KLIWAS-27/2014)
On sea level change in the North Sea influenced by the North Atlantic Oscillation: local and remote steric effects
In this study, contributions of both local steric and remote baroclinic effects (i.e., steric variations external to the region of interest) to the inter-annual variability of winter sea level in the North Sea, with respect to the North Atlantic Oscillation (NAO), for the period of 1953–2010 are investigated. On inter-annual time scales in this period, the NAO is significantly correlated to sea level variations in the North Sea only in the winter months (December–March), while its correlation to sea temperature over much of the North Sea is only significant in January and February. The discrepancy in sea level between observations and barotropic tide and surge models forced by tides and local atmospheric forcing, i.e., local atmospheric pressure effects and winds, in the present study are found to be consistent with previous studies. In the North Sea, local thermosteric effects caused by thermal expansion play a minor role on winter-mean NAO related sea level variability compared with atmospheric forcing. This is particularly true in the southeastern North Sea where water depths are mostly less than 25 m. Our calculations demonstrate that the discrepancy can be mostly explained by remote baroclinic effects, which appear as water mass exchanges on the continental shelf and are therefore only apparent in ocean bottom pressure. In the North Sea, NAO related sea level variations seem to be a hybrid of barotropic and baroclinic processes. Hence, they can only be adequately modelled with three-dimensional baroclinic ocean models that include contributions of baroclinic effects and large-scale atmospheric forcing external to the region of interest
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Assessment of the Met Office Global Coupled model version 5 (GC5)configurations
GC5 is the latest global coupled configuration which is a combination of Global Atmosphere and Land
(GAL9) and Global Ocean and Sea Ice (GOSI9). GAL9 includes over 26 science tickets that cover
changes to almost all areas of global model science, including several enhancements to the 6A convection
scheme, latent heating in the gravity wave drag scheme, ‘fountain buster’ scheme which adds
improvements to advection conservation in conditions of near-grid-scale convergence, bimodal cloud
initiation and dust dependent ice-nucleation temperature. GOSI9 is built on the NEMO 4.0.4 ocean
model and a new sea ice model SI3. This includes a new equation of state (TEOS-10), 4th order tracer
advection, adaptive-implicit vertical advection and Southern Ocean tuning.
Important model improvements in global temperature and winds, subtropical jet, monsoon processes
over India and Maritime Continent and their diurnal cycle in convection were noted. Most aspects of
processes over Africa were also notably improved. Southern Ocean biases continue to reduce in GC5
as a result of the Southern Ocean package including the Antarctic Sea ice area. At NWP scales, significant
improvements in the tropical temperature at 850hPa and precipitation SEEPs score at all lead
times were achieved. In addition, the tropical cyclone track and intensity are significantly better in GC5
compared to GC4. There are aspects where the model has slightly degraded such as the MJO, Indian
Ocean SSTs and winds, biases over NE South America, western Pacific high in northern hemisphere
summer and European blocking in northern hemisphere summer. These degradations require more
detailed investigations. Degradations to NWP performance at higher resolution also need to be investigated
before operational implementation but will require minimal adjustments.
While the N216 GC5 model is acceptable for release as the physical model configuration, further
work is being undertaken in the climate science community to address the cold bias in GC5 N96ORCA1
configuration. The resulting GC5 configurations for a wider range of climate applications will be documented
in a separate paper.
Unlike previous configurations, with the aim of getting an early understanding of the impact of GC5,
tests were carried out on the UK convective-scale ensemble system, MOGREPS-UK. The results assessed
here show degradation in the skills of 10m-wind and clouds in Boreal summer, but improvements
in the spatial skill of the precipitation forecasts. The results also show a decrease in the ensemble
spread with GC5 along with a slight increase in error and this is being investigated