Long-term trend in potential vorticity intrusion events over the Pacific Ocean: Role of global mean temperature rise
- 16 Downloads
In this study, we examine a long-term increasing trend in subtropical potential vorticity (PV) intrusion events over the Pacific Ocean in relation to the global mean temperature rise, based on multiple reanalysis datasets. The frequency of the PV intrusions is closely related to the upper-tropospheric equatorial westerly duct and the subtropical jet (STJ). An overall strengthening of the westerly duct and weakening of the STJ are found to be driven by the warming-induced strengthening of Walker circulation and regional changes in Hadley circulation on multi-decadal timescale, leading to an increase in the PV intrusion frequency over the tropics. The results are robust in all datasets. The multi-decadal strengthening in the Pacific Walker circulation is consistent with the global mean temperature rise. In this way, the PV intrusions are correlated with the warming related global mean temperuate rise. When the interannual variability of ENSO is removed from the intrusion time series, the long-term trend in PV intrusions due to external forcing associated with anthropogenic warming (global mean temperature rise) becomes clearer. The link between the global mean temperature rise and intrusion frequency is further verified by performing a correlation analysis between the two. The significant (> 95%) correlation coefficient is 0.85, 0.94, 0.84, 0.83, and 0.84 for ERA-40, ERA-Interim, NCEP-NCAR, JRA-55, and JRA-25, respectively. This unequivocally indicates that the global mean temperature rise can explain around 69%–88% of the variance related to the long-term increase in PV intrusion frequency over the Pacific Ocean.
Key wordspotential vorticity (PV) intrusion Pacific Ocean westerly duct subtropical jet Walker circulation global warming
Unable to display preview. Download preview PDF.
- L’Heureux, M. L., S. Lee, and B. Lyon, 2013: Recent multidecadal strengthening of the Walker circulation across the tropical Pacific. Nat. Climate Change, 3, 571–576.Google Scholar
- Roeckner, E., G. Bäuml, L. Bonaventura, et al., 2003: The Atmospheric General Circulation model ECHAM5. Part I: Model Description. Report No. 349, Hamburg, Germany, Max-Planck-Institut für Meteorologie.Google Scholar
- Wang, C., 2005: ENSO, Atlantic climate variability, and the Walker and Hadley circulations. The Hadley Circulation: Present, Past and Future. Diaz, H. F., and R. S. Bradley, Eds. Dordrecht, Springer, 173–202.Google Scholar
- Waugh, D. W., R. A. Plumb, and L. M. Polvani, 1994: Nonlinear, barotropic response to a localized topographic forcing: Formation of a " tropical surf zone” and its effect on interhemispheric propagation. J. Atmos. Sci., 51, 1401–1416, doi: 10.1175/1520-0469(1994)051<1401:NBRTAL>2.0.CO;2.CrossRefGoogle Scholar