A Divergence-Form Wave-Induced Pressure Inherent in the Extension of the Eliassen–Palm Theory to a Three-Dimensional Framework for All Waves at All Latitudes

Classical theory concerning theEliassen–Palmrelation is extended in this study to allowfor a unified treatment of midlatitude inertia–gravity waves (MIGWs), midlatitude Rossby waves (MRWs), and equatorial waves (EQWs). A conservation equation for what the authors call the impulse-bolus (IB) pseudomomentum is useful, because it is applicable to ageostrophic waves, and the associated three-dimensional flux is parallel to the direction of the group velocity of MRWs. The equation has previously been derived in an isentropic coordinate system or a shallow-water model. The authors make an explicit comparison of prognostic equations for the IB pseudomomentum vector and the classical energy-based (CE) pseudomomentum vector, assuming inviscid linear waves in a sufficiently weak mean flow, to provide a basis for the former quantity to be used in an Eulerian time-mean (EM) framework. The authors investigate what makes the three-dimensional fluxes in the IB and CE pseudomomentum equations look in different directions. It is found that the two fluxes are linked by a gauge transformation, previously unmentioned, associated with a divergence-form wave-induced pressure L. The quantity L vanishes for MIGWs and becomes nonzero for MRWs and EQWs, and it may be estimated using the virial theorem. Concerning the effect of waves on the mean flow, L represents an additional effect in the pressure gradient term of both (the three-dimensional versions of) the transformed EM momentum equations and the merged form of the EMmomentumequations, the latter of which is associated with the nonacceleration theorem

Disparate Midlatitude Responses to the Eastern Pacific El Niño

To investigate the disparate influences of the eastern Pacific (EP) El Niño on the winter climate in the Far East, we conducted composite analyses using long-term reanalysis datasets. Our analysis shows that the western Pacific (WP) pattern dominates in the warm winter (typical) composite and the Pacific–North American (PNA) pattern dominates in the non-warm winter (atypical) composite. In the warm winter case, the amplitudes of the negative sea surface temperature (SST) anomalies in the western Pacific Ocean are large whereas in the non-warm winter case, these amplitudes are small. In addition, the Indian Ocean basin warming occurs following the Indian Ocean dipole mode, as seen in the warm winter composite. We investigated the dynamical mechanisms responsible for the disparate midlatitude responses to the EP El Niño by focusing on Rossby wave sources and propagation. These SST anomalies modulate the Walker and Hadley circulations and the convective activity in the western Pacific Ocean. Upper-tropospheric divergences at the midlatitudes due to the anomalous Hadley circulation result in different teleconnection patterns. In the warm winter composite, the anticyclonic anomaly in the southern part of the WP pattern is created by the upstream negative Rossby wave source, while the other cyclonic anomaly is reinforced by the northward Rossby wave propagation. The cyclonic second and fourth centers of action of the PNA pattern are created by the positive Rossby wave sources. Furthermore, the equatorial SST gradient near the date line is found be a good precursor of the winter climate in the Far East

Coherent amplification of the Okhotsk high, Korean trough, and northwestern Pacific subtropical high during heavy rainfall over Japan in August 2021

Abstract In August 2021, rain front stagnation in Japan resulted in prolonged and disastrous rainfall across the entire country. During the heavy rainfall period, the large-scale atmospheric field over the East Asian–western North Pacific region was characterized by meridional tripolar circulation anomalies: the Okhotsk high (OH), the trough over the Korean Peninsula (Korean trough), and the northwestern Pacific subtropical high (NWPSH). Simultaneously, tropical convective activity was enhanced over the eastern Indian Ocean and suppressed over the tropical western–central Pacific. This study investigates the dynamic mechanism of linkage of the extratropical tripolar anomalies and the effects of tropical convective modulation using a reanalysis dataset, a cutoff low detection scheme, the potential vorticity inversion method, and numerical experiments. Upper-tropospheric blocking over eastern Siberia connected to the surface OH is conducive to the stagnation of synoptic depressions, including cutoff lows and troughs, over the Korean Peninsula, contributing to the development and maintenance of the quasi-stationary Korean trough. Rossby waves emanating from the Korean trough excite an anticyclonic anomaly over the northwestern Pacific. This upper-level anomalous anticyclone acts to enhance the surface NWPSH through zonal heat transport, accompanied by a northward tilting structure with height. Simultaneously, the tropical intraseasonal oscillation is amplified over the Indo–western Pacific Ocean sector under the negative-phase Indian Ocean dipole and multi-year La Niña conditions. The combination of enhanced convection over the eastern Indian Ocean and suppressed convection across the tropical western–central Pacific reinforces the NWPSH. The anomalous circulation associated with the extratropical tripolar pattern and concurrent tropical heat forcing causes more moisture transport, convergence, and anomalous ascent, which contribute to heavy rainfall in Japan. These results suggest that the dynamically correlated amplification of tropical and extratropical circulation anomalies plays a crucial role in precipitation variability in East Asia