Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Rossby wave breaking and transient eddy forcing during Euro-Atlantic circulation regimes

TitleRossby wave breaking and transient eddy forcing during Euro-Atlantic circulation regimes
Publication TypeJournal Article
Year of Publication2017
AuthorsSwenson, Erik T., and Straus David M.
JournalJournal of the Atmospheric Sciences
Volume74
Number6
Abstract / Summary

The occurrence of boreal winter Rossby wave breaking (RWB) along with the quantitative role of synoptic transient eddy momentum and heat fluxes directly associated with RWB are examined during the development of Euro-Atlantic circulation regimes using the ERA Interim Reanalysis. Results are compared to those from seasonal re-forecasts made using the Integrated Forecast System model of ECWMF coupled to the NEMO ocean model. The development of both Scandinavian Blocking and the Atlantic Ridge is directly coincident with anticyclonic wave breaking (AWB); however, the associated transient eddy fluxes do not contribute to (in fact, oppose) ridge growth, as indicated by the local Eliasson-Palm (EP) flux divergence. Evidently other factors drive development, and it appears that wave breaking assists more with ridge decay. The growth of the North Atlantic Oscillation (NAO) in its positive phase is independent of RWB in the western Atlantic, but strongly linked to AWB further downstream. During AWB, the Equator-ward flux of cold air at upper levels contributes to a westerly tendency just as much the pole-ward flux of momentum. The growth of the negative phase of the NAO is almost entirely related to cyclonic wave breaking (CWB), during which Equator-ward momentum flux dominates at jet level, yet low-level heat fluxes dominate below. The re-forecasts yield realistic frequencies of CWB and AWB during different regimes, as well as realistic estimates of their roles during development. However, a slightly weaker role of RWB is simulated, generally consistent with a weaker anomalous circulation.

URLhttp://dx.doi.org/10.1175/JAS-D-16-0263.1
DOI10.1175/JAS-D-16-0263.1
Journal: Journal of the Atmospheric Sciences
Year of Publication: 2017
Volume: 74
Number: 6
Publication Date: 03/2017

The occurrence of boreal winter Rossby wave breaking (RWB) along with the quantitative role of synoptic transient eddy momentum and heat fluxes directly associated with RWB are examined during the development of Euro-Atlantic circulation regimes using the ERA Interim Reanalysis. Results are compared to those from seasonal re-forecasts made using the Integrated Forecast System model of ECWMF coupled to the NEMO ocean model. The development of both Scandinavian Blocking and the Atlantic Ridge is directly coincident with anticyclonic wave breaking (AWB); however, the associated transient eddy fluxes do not contribute to (in fact, oppose) ridge growth, as indicated by the local Eliasson-Palm (EP) flux divergence. Evidently other factors drive development, and it appears that wave breaking assists more with ridge decay. The growth of the North Atlantic Oscillation (NAO) in its positive phase is independent of RWB in the western Atlantic, but strongly linked to AWB further downstream. During AWB, the Equator-ward flux of cold air at upper levels contributes to a westerly tendency just as much the pole-ward flux of momentum. The growth of the negative phase of the NAO is almost entirely related to cyclonic wave breaking (CWB), during which Equator-ward momentum flux dominates at jet level, yet low-level heat fluxes dominate below. The re-forecasts yield realistic frequencies of CWB and AWB during different regimes, as well as realistic estimates of their roles during development. However, a slightly weaker role of RWB is simulated, generally consistent with a weaker anomalous circulation.

DOI: 10.1175/JAS-D-16-0263.1
Citation:
Swenson, ET, and DM Straus.  2017.  "Rossby wave breaking and transient eddy forcing during Euro-Atlantic circulation regimes."  Journal of the Atmospheric Sciences 74(6).  https://doi.org/10.1175/JAS-D-16-0263.1.