Contributions of Different Combinations of the IPO and AMO to Recent Changes in Winter East Asian Jets

Abstract Recent concurrent shifts of the East Asian polar-front jet (EAPJ) and the East Asian subtropical jet (EASJ) in the boreal winter have raised concerns, since they could result in severe weather events over East Asia. However, the possible mechanisms are not fully understood. In this study, the roles of the interdecadal Pacific oscillation (IPO) and the Atlantic multidecadal oscillation (AMO) are investigated by analyzing reanalysis data and model simulations. Results show that combinations of opposite phases of the IPO and AMO can result in significant shifts of the two jets during 1920–2014. This relationship is particularly evident during 1999–2014 and 1979–98 in the reanalysis data. A combination of a negative phase of the IPO (−IPO) and a positive phase of the AMO (+AMO) since the late 1990s has enhanced the meridional temperature gradient and the Eady growth rate and thus westerlies over the region between the two jets, but weakened them to the south and north of the region, thereby contributing to the equatorward and poleward shifts of the EAPJ and EASJ, respectively. Atmospheric model simulations are further used to investigate the relative contribution of −IPO and +AMO to the jet shifts. The model simulations show that the combination of −IPO and +AMO favors the recent jet changes more than the individual −IPO or +AMO. Under a concurrent −IPO and +AMO, the meridional eddy transport of zonal momentum and sensitive heat strengthens, and more mean available potential energy converts to the eddy available potential energy over the region between the two jets, which enhances westerly winds there.

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Contributions of Different Combinations of the IPO and AMO to the Concurrent Variations of Summer East Asian Jets

Journal of Climate ◽

10.1175/jcli-d-19-0366.1 ◽

2020 ◽

Vol 33 (18) ◽

pp. 7967-7982

Author(s):

Xiucheng Xiao ◽

Danqing Huang ◽

Ben Yang ◽

Jian Zhu ◽

Peiwen Yan ◽

...

Keyword(s):

East Asia ◽

East Asian ◽

Active Regions ◽

Atlantic Multidecadal Oscillation ◽

Atmospheric Model ◽

Polar Front ◽

Reanalysis Data ◽

Boreal Winter ◽

Multilinear Regression ◽

The North

ABSTRACTHuang et al. recently reported that opposite phases of the interdecadal Pacific oscillation (IPO) and the Atlantic multidecadal oscillation (AMO) can affect the shift of the East Asian polar front jet (EAPJ) and the East Asian subtropical jet (EASJ) in the boreal winter. To give a full image of the relationship among the IPO, AMO, and concurrent variation of jets throughout the whole year, this study investigates the changes in summer jets response to the combinations of the IPO and AMO, and mostly focuses on the quantitative analysis in the role of the IPO and AMO. Both of the diagnostic analysis and atmospheric model simulations confirm that combinations of the negative phase of the IPO (“−IPO”) and the positive phase of the AMO (“+AMO”) can significantly enhance the EAPJ and reduce the EASJ in the summer, via the meridional temperature gradient and the Eady growth rate, and vice versa in the “+IPO −AMO” combination. The reanalysis data show that this relationship is particularly evident between the periods of 1999–2014 and 1979–98. Based on the simulations, the multilinear regression has indicated that −IPO plays a more important role than +AMO, particularly for the reduced EASJ. We have further revealed two pathways of the stationary Rossby wave activity anomaly, eastward from the North Atlantic to East Asia along 60°N and westward from the North Pacific to East Asia along 40°N. The two activities are associated with anomalous anticyclone along the active regions between EAPJ and EASJ, and therefore affect the jet variations.

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Warm Season Rainfall Variability over the U.S. Great Plains in Observations, NCEP and ERA-40 Reanalyses, and NCAR and NASA Atmospheric Model Simulations

Journal of Climate ◽

10.1175/jcli3343.1 ◽

2005 ◽

Vol 18 (11) ◽

pp. 1808-1830 ◽

Cited By ~ 105

Author(s):

Alfredo Ruiz-Barradas ◽

Sumant Nigam

Keyword(s):

Great Plains ◽

Rainfall Variability ◽

Warm Season ◽

Moisture Flux ◽

Atmospheric Model ◽

Precipitation Variability ◽

Reanalysis Data ◽

Ncep Reanalysis ◽

Model Simulations ◽

Precipitation Estimates

Abstract Interannual variability of Great Plains precipitation in the warm season months is analyzed using gridded observations, satellite-based precipitation estimates, NCEP reanalysis data and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data, and the half-century-long NCAR Community Atmosphere Model (CAM3.0, version 3.0) and the National Aeronautics and Space Administration (NASA) Seasonal-to-Intraseasonal Prediction Project (NSIPP) atmospheric model simulations. Regional hydroclimate is the focus because of its immense societal impact and because the involved variability mechanisms are not well understood. The Great Plains precipitation variability is represented rather differently, and only quasi realistically, in the reanalyses. NCEP has larger amplitude but less traction with observations in comparison with ERA-40. Model simulations exhibit more realistic amplitudes, which are between those of NCEP and ERA-40. The simulated variability is however uncorrelated with observations in both models, with monthly correlations smaller than 0.10 in all cases. An assessment of the regional atmosphere water balance is revealing: Stationary moisture flux convergence accounts for most of the Great Plains variability in ERA-40, but not in the NCEP reanalysis and model simulations; convergent fluxes generate less than half of the precipitation in the latter, while local evaporation does the rest in models. Phenomenal evaporation in the models—up to 4 times larger than the highest observationally constrained estimate (NCEP’s)—provides the bulk of the moisture for Great Plains precipitation variability; thus, precipitation recycling is very efficient in both models, perhaps too efficient. Remote water sources contribute substantially to Great Plains hydroclimate variability in nature via fluxes. Getting the interaction pathways right is presently challenging for the models.

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Impacto de um mecanismo de disparo da convecção na precipitação simulada com o modelo regional BRAMS sobre a bacia amazônica durante a estação chuvosa de 1999

Revista Brasileira de Meteorologia ◽

10.1590/0102-778620140039 ◽

2015 ◽

Vol 30 (2) ◽

pp. 145-157 ◽

Cited By ~ 1

Author(s):

Cláudio Moisés Santos e Silva ◽

Saulo Ribeiro de Freitas

Keyword(s):

Potential Energy ◽

Atmospheric Model ◽

Available Potential Energy ◽

Regional Atmospheric Model ◽

De Se

O objetivo deste artigo é mostrar o impacto da implementação de uma função de disparo da convecção na parametrização convectiva de Grell e Devenyi, contida no modelo atmosférico regional BRAMS (Brazilian developments on Regional Atmospheric Model). Para verificar o ciclo de precipitação foi usado um conjunto de dados do período chuvoso de 1999 no âmbito do projetoLarge scale Biosphere-Atmosphere Experiment in Amazonia(LBA). A nova função de disparo de convecção é acoplada aos fluxos de calor sensível e latente à superfície. Além disso, possui a vantagem de considerar a média dos primeiros 60 hPa da troposfera para caracterizar a ascenção pseudo adiabática da parcela. Assim, a parcela em ascenção apresenta redução daConvective Available Potential Energy (CAPE), o modelo acumula menos CAPE nas primeiras horas do dia e com isso, o máximo de precipitação é atrasado (embora dependa da região analisada). Um aspecto negativo foi que a precipitação sobre a Cordilheira dos Andes aumentou relativamente à versão original. Conclui-se que o esquema apresenta vantagens e desvantagens e que faz-se necessário avaliar outras parametrizações do modelo, principalmente a troca de energia e massa na interface solo-vegetação-atmosfera a fim de se obter resultados mais realísticos da precipitação sobe a Amazônia.

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