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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A new Asian/North American teleconnection linking clustered extreme precipitation from Indian to Canada
Three consecutive precipitation extremes emerged in November 2021, including India-Sri Lanka flooding, East Asian blizzard, and Canadian floods. Why the catastrophic events occurred successively and whether they will become more frequent as global warming continues are unknown. Here we show they are organized by an intraseasonal Asian/North American (ANA) teleconnection consisting of two cross-Pacific wave trains fortified by dipolar diabatic heating anomalies (“wet India-dry Philippines”). The dipolar heating anomaly is shaped by multi-scale interaction between a quasi-stationary Madden-Julian Oscillation (MJO) episode and a rapidly developed La Niña over the tropical Asian monsoon region. Numerical experiments suggest that the off-equatorial heating dipole can generate the ANA pattern resembling observations, distinct from the equatorial MJO-induced teleconnection and the La Niña-induced Pacific/North American teleconnection. Philippine cooling stimulates the circum-Pacific wave train, while Indian heating produces the eastward-propagating subtropical wave train. These wave trains persistently steered cross-Pacific atmospheric rivers channeling warm-moisture-laden air to the extratropics. We suggest that the ANA teleconnection could be a new route by which multi-scale interaction between the La Niña and quasi-stationary MJO over the tropical Asian monsoon affects extratropical East Asia and North America. This work provides a unique perspective on understanding the origins of increasing collisions of extremes worldwide within a short time as the global climate warms.
more » « less- NSF-PAR ID:
- 10380146
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- npj Climate and Atmospheric Science
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2397-3722
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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