Advances in Research on Atmospheric Energy Propagation and the Interactions between Different Latitudes

Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes.To better understand such atmospheric teleconnection,several theories of wave energy propagation are reviewed in this paper：（1） great circle theory,which reveals the characteristics of Rossby waves propagating in the spherical atmosphere;（2） westerly duct theory,which suggests a ＂corridor＂ through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere;（3） energy accumulation-wave emanation theory,which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes;（4） equatorial wave expansion theory,which further explains the physical mechanisms involved in the interaction between the tropics and extratropics;and（5） meridional basic flow theory,which argues that stationary waves can propagate across the tropical easterlies under certain conditions.In addition,the progress made in diagnosing wave-flow interaction,particularly for Rossby waves,inertial-gravity waves,and Kelvin waves,is also reviewed.The meridional propagation of atmospheric energy exhibits significant annual and interannual variations,closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs,amongst others.

Long-Term Trend in Potential Vorticity Intrusion Events over the Pacific Ocean： Role of Global Mean Temperature Rise

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 reaualysis datasets. The fre- quency 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-dccadal timescalc, 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 wanning related global mean temperuate rise. When the interan- nual variability of ENSO is removed from the intrusion time series, the long-term trend in PV intrusions due to ex- ternal 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 ana- lysis 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 lung-term increase in PV intrusion fre- quency over the Pacific Ocean.