Mechanisms for a PNA-Like Teleconnection Pattern in Response to the MJO

Abstract

Kinematic mechanisms of the Pacific–North America (PNA)-like teleconnection pattern induced by the Madden–Julian oscillation (MJO) is examined using an atmospheric general circulation model (GCM) and a barotropic Rossby wave theory. Observation shows that a negative PNA-like teleconnection pattern emerges in response to MJO phase-2 forcing with enhanced (suppressed) convection located over the Indian (western Pacific) Ocean. The GCM simulations show that both forcing anomalies contribute to creating the PNA-like pattern. Indian Ocean forcing induces two major Rossby wave source (RWS) regions: a negative region around southern Asia and a positive region over the western North Pacific (WNP). The negative RWS to the north of the enhanced convection in the Indian Ocean arises from southerly MJO-induced divergent wind crossing the Asian jet. Unexpectedly, another significant RWS region develops over the WNP owing to refracted northerly divergent wind. A ray-tracing method demonstrates three different ways of wave propagation emanating from the RWS to the PNA region: 1) direct arclike propagation from the negative RWS to the PNA region occurs in the longest waves, 2) shorter waves are displaced first downstream by the jet waveguide effect and then emanate at the jet exit to the PNA region, and 3) waves with zonal wavenumbers 1 and 2 exhibit canonical wave propagation from the positive RWS at the jet exit to the PNA region. On the other hand, the positive RWS induced by western Pacific forcing shows similar characteristics to feature 3 described above, with some relaxation such that much shorter waves also contribute to the formation of the southern cells.

The Seasonality and Regionality of MJO Impacts on North American Temperature

“…Figure b shows that MJO teleconnections to the extratropics are strongest in the winter (DJF) for Alaska and New England. This is consistent with previous work; these are both centers of action of the Pacific‐North America pattern, a quasi‐stationary feature of the local large‐scale circulation that is tied to the MJO (Goss & Feldstein, ; Mori & Watanabe, ; Seo et al, ), and most active during the winter months (Barnston & Livezey, ). However, other regions show significant peaks in MJO covariability outside of DJF.…”

Future Changes of Subseasonal Precipitation Variability in North America During Winter Under Global Warming

“…It is found that the subseasonal precipitation variability is consistently increased over the mid-to-high latitudes with intensified swing between wet and dry extremes, but the subseasonal precipitation variability declines in Mexico with weakened extremes. In certain MJO phases, the prediction skill for subseasonal atmospheric circulation in the North Pacific is significant (Becker et al, 2011;Seo & Lee, 2017;Tseng et al, 2018). With the help of a moisture budget decomposition framework, we explore the mechanisms that lead to changes in subseasonal precipitation variability.…”

“…Many studies revealed that the convection associated with the MJO can act as diabatic heating source and modify the precipitation and circulation along the west coast of North America by exciting Rossby waves and modulating atmospheric rivers and storm-track activity (e.g., Baggett et al, 2017;Guan et al, 2012;Guan & Waliser, 2015;Jones, 2000;Lau et al, 2012;Mundhenk et al, 2018;Zheng et al, 2018). In certain MJO phases, the prediction skill for subseasonal atmospheric circulation in the North Pacific is significant (Becker et al, 2011;Seo & Lee, 2017;Tseng et al, 2018). As the MJO is projected to become more active under global warming (e.g., Jones & Carvalho, 2011;Liu, 2013;Slingo et al, 1999;Subramanian et al, 2014), whether the subseasonal precipitation changes in the North America are related to changes in the remote MJO forcing and how such changes may influence predictability of subseasonal variability deserve further studies.…”

Effects of Moisture Initialization on MJO and its Teleconnection Prediction in BCC Subseasonal Coupled Model

“…In addition to tropics, MJO could also significantly alter extratropical climate anomalies through modulating teleconnections, such as the North Atlantic Oscillation (NAO; Cassou, 2008) and the Pacific-North American (PNA) patterns (Henderson et al, 2017;Seo & Lee, 2017). In addition to tropics, MJO could also significantly alter extratropical climate anomalies through modulating teleconnections, such as the North Atlantic Oscillation (NAO; Cassou, 2008) and the Pacific-North American (PNA) patterns (Henderson et al, 2017;Seo & Lee, 2017).…”