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Oceanic alternating zonal jets at depth have been detected ubiquitously in observations and ocean general circulation models (GCMs). Such oceanic jets are generally considered as being generated by purely oceanic processes. Here we explore a possible air‐sea interaction induced by surface signatures of the deep zonal jets using an eddy‐permitting coupled atmosphere‐ocean GCM (CGCM). The 23‐year CGCM integration reproduces bands of latitudinally‐narrow alternating jets in the Southeast Pacific. They extend from the sea surface to well below the main thermocline and are embedded in the large‐scale westward‐flowing South Equatorial Current, the latter mostly confined above the thermocline. These jets generate fine‐scale sea surface temperature (SST) anomalies through the advection of zonal temperature gradients. The atmospheric boundary layer appears to respond thermally to this fine‐scale SST field, which induces fine‐scale wind stress anomaly through atmospheric pressure adjustment, as indicated by a good spatial correlation between the SST Laplacian field and the fine‐scale wind stress curl. A Sverdrup calculation on the wind stress field of the CGCM predicts fine‐scale zonal currents driven by the meridional gradient of the fine‐scale wind stress curl. The positions of these Sverdrup currents are generally coincident with those of the original zonal jets and the Sverdrup prediction explains roughly half of the amplitudes of the jets. While the original cause of the deep zonal jets simulated in our CGCM is unidentified, this analysis suggests that there is likely a positive air‐sea feedback: the jets generate fine‐scale wind stress curl that reinforces themselves through the Sverdrup dynamics. Key Points Oceanic deep zonal jets are examined using a high‐resolution coupled GCM Vertically coherent oceanic zonal jets generate fine‐scale SST anomaly SST‐induced wind stress curl reinforces the oceanic jets, a positive feedback

In August 2002, many parts of central Europe were affected by heavy precipitation and ooding caused by a cut-off cyclone. This study shows that this cyclone developed as a result of the propagation of a Rossby wave packet. The wave-packet propagation along the relatively weak sub-tropical jet was accompanied by wave-breaking and re-emission in the subtropics. In particular, there was an interaction between the Rossby wave packet and a precipitation band along the east coast of North America associated with tropical storm Cristobal. This interaction had a signicant inuence upon the formation of the European cut-off low. Results from numerical simulations from two different initial conditions are investigated to study this interaction. Downstream inuences from tropical storm Cristobal upon the development of this cyclone and associated ooding precipitation are conrmed by sensitivity analysis using ensemble forecasts. It is concluded from analysis and simulations that poor forecast skills of tropical storm Cristobal affected the predictability of the European cut-off low. [PUBLICATION ABSTRACTION]

High-resolution simulations of the atmospheric and oceanic general circulations on the Earth Simulator are briefly introduced to a wider research and educational community. Some early results have been published and are reviewed in this article. The high-resolution simulations may have more information in certain aspects than observations while the simulations need to be validated. On the other hand, high-resolution observations in which uncertainties are unavoidable are now available. Possible close collaboration between observational and simulation research is proposed.

A conservative semi-Lagrangian scheme with rational function for interpolation is implemented in spherical geometry and tested in an atmospheric general circulation model (AGCM). The new scheme, different from the conventional semi-Lagrangian method, is conservative and oscillation free. By introducing polar mixing and a time split computation of divergence, the scheme can compute advection transport correctly over the polar regions. Idealized advection tests with various velocity fields were carried out to demonstrate numerical accuracy and conservation in comparison with the spectral schemes. The impact of the advection computation on water vapor circulation in an AGCM is also investigated with numerical simulations on the Earth Simulator. Both pure advection tests and general circulation experiments show that the presented scheme is effective in improving the tracer transport property and the precipitation field in comparison with the leapfrog-spectral method.

Following the development of an atmospheric general circulation model that runs very efficiently on the Earth Simulator, three meso-scale resolving global 10-km mesh simulations were performed. Three meso-scale phenomena were chosen as simulation and research targets: They were the typhoon genesis, wintertime cyclogenesis and Baiu-Meiyu frontal zone. A brief summary of these results is given in this paper. Generally speaking, the results are realistic, and the figures of precipitation fields from the simulations may look like synthesized pictures from artificial satellites. The results are very encouraging and suggest the usefulness of such ultra-high resolution global simulations for studies on, for example, interaction between large-scale circulation and meso-scale disturbances. Also rationales for this kind of simulations are discussed.