Abstract The teleconnection mechanisms associated with midlatitude climate dipoles are of high interest because of their potential broad impacts on ecological patterns and processes. A prominent example attracting increasing research interest is a summer (June–August) North American dipole (NAD), which drives continental-scale bird irruptions in the boreal forest (semiperiodic movements of large numbers of individual birds). Here, the NAD is objectively defined as a second principal component of 500-hPa geopotential height and is linked to two mechanisms: 1) Rossby waves associated with Madden–Julian oscillation (MJO) convection and 2) a pan-Pacific stationary Rossby wave triggered by East Asian monsoonal convection. The MJO mechanism relates to anomalously frequent occurrence of MJO phase 1 or 6, which are captured by the leading principal component of daily summer MJO phases (PC M1 ; accounting for 46% of the phase variance). In “nonuniform” MJO summers, defined as |PC M1 | > 0.5, anomalously frequent phase 1 triggers positive NAD, and anomalously frequent phase 6 triggers negative NAD, yielding the correlation r (NAD, PC M1 ) = 0.55, p < 0.01. During “uniform” MJO summers, defined as |PC M1 | ≤ 0.5, the effect of East Asian precipitation anomalies P EA becomes apparent, and r (NAD, P EA ) = 0.49, p < 0.01. The impacts of P EA are largely masked during nonuniform MJO summers, meaning this subset of summers lacks a significant correlation between the NAD and P EA . Our interpretation is that uniformly distributed MJO allows monsoonal convection over the midlatitudes to modulate the NAD, whereas tropical convection anomalies associated with anomalously frequent MJO phases 1 and 6 overwhelm the extratropical teleconnection.
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Atmospheric Modeling Study on Convection-Triggered Teleconnections Driving the Summer North American Dipole
The summer North American dipole (NAD) is a pattern of climate variability linked to variations in boreal forest seed production and migration of seed-eating birds. This is a modeling investigation of two teleconnections identified as drivers of the NAD in prior observational work: 1) tropically sourced atmospheric Rossby waves associated with anomalies in the phase distribution of the Madden–Julian oscillation (MJO) (i.e., phases 1 and 6 are anomalously prominent), and 2) a pan-Pacific atmospheric Rossby wave linked to East Asian monsoonal (EAM) convection. Sea surface temperature (SST) boundary forcing experiments were conducted with the Community Earth System Model 2 (CESM2) to trigger convection patterns that align with those observed during EAM and nonuniform phase distributions of MJO. For the EAM case, an El Niño–like SST dipole pattern combined with cool southern Japan SST forcing produced a convection and jet stream shift anomaly over East Asia and the northern Pacific with a positive NAD pattern downstream over North America, similar to the observed pattern when precipitation over East Asia (
- NSF-PAR ID:
- 10461906
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 36
- Issue:
- 19
- ISSN:
- 0894-8755
- Format(s):
- Medium: X Size: p. 6991-7003
- Size(s):
- ["p. 6991-7003"]
- Sponsoring Org:
- National Science Foundation
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