Tuesday, 9 January 2018: 3:15 PM
Salon F (Hilton) (Austin, Texas)
Climate teleconnections play an important role in modulating seasonal tropical cyclone (TC) activity around the globe. The El Niño–Southern Oscillation (ENSO) is a major source of seasonal TC predictability in both local and remote ocean basins. Unusually warm eastern-central equatorial Pacific
sea surface temperature (SST) during El Niño tends to enhance eastern and central North Pacific (ECNP) TCs and suppress Atlantic TCs. This study investigates the teleconnection in the opposite direction, i.e., the influence of Atlantic SST variability on Pacific TC activity, using observational analysis and high resolution (27 km) tropical channel model (TCM) simulations. Observations from 1950 to 2015 indicate that seasonal ECNP TC activity is remotely suppressed by the positive Atlantic Meridional Mode (AMM) phase, which is characterized by warm northern and cool southern tropical Atlantic SST anomalies, and vice versa during the negative AMM phase. A large ensemble of TCM simulations forced with idealized AMM and ENSO SST patterns supports these conclusions and reveals that the mean response in ECNP TC activity is sufficiently large compared to internal atmospheric variability to gain significant seasonal TC predictability from skillful AMM predictions.
The mechanism by which Atlantic SST influences ECNP TCs is in many ways analogous to the Walker Circulation response associated with the ENSO-Atlantic TC teleconnection. Both ENSO and AMM modify the favorability for ECNP and Atlantic TCs largely through vertical wind shear. In addition, the responses in eastern Pacific and tropical Atlantic TC activity, vertical velocity, and upper and lower tropospheric zonal wind are similar between the positive AMM and La Niña, and between the negative AMM and El Niño. However, the western North Pacific circulation response is different between the AMM and ENSO. This work highlights the importance of considering the competing influences of modes of tropical Atlantic and Pacific SST variability in seasonal predictions and climate projections of North Pacific TC activity.
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