MMM Seminar Series - On the Dynamical Mechanisms Governing El Niño–Southern Oscillation Irregularity

MMM Seminar Series - Thursday, January 17, 2019 - 3:30pm

Speaker: Judith Berner

Affiliation: National Center for Atmospheric Research (NCAR)

This talk will investigate the mechanisms by which short-timescale perturbations to atmospheric processes can affect interannual variability such as the El Niño-Southern Oscillation (ENSO). To this end a coupled simulation of NCAR's Community Climate System Model is compared to a simulation in which the model's atmospheric diabatic tendencies are perturbed at each time step using a Stochastically Perturbed Parameterized Tendencies scheme.

The simulation with stochastic parameterization compares better with 20th-century reanalysis in having lower inter-annual sea surface temperature (SST) variability and more irregular transitions between El Niño and La Niña states.  The broadening of the SST spectrum is consistent with a reduced decorrelation time scale of the ENSO eigenmode from 17 to 11 months, which is closer to 8 months as obtained in 20th-century reanalysis.

It will be shown that for the simple model of a linear damped oscillator, such a noise-induced stabilization and broadening of the spectrum is obtained when its frequency parameter is perturbed (i.e., a randomization of phases).

It will be discussed how these results can be used to inform next generation physical parameterization development. The seminar will close with a discussion of other areas where fast-slow interactions play a fundamental role and stochastic parameterization can add value to weather predictions and climate projections.

Refreshments: 3:15 PM

NCAR-Foothills Laboratory, 3450 Mitchell Lane, Bldg. 2, FL2-1022, Large Auditorium

 

Building:

Room Number: 
Large Auditorium, Room 1022

Type of event:

Will this event be webcast to the public by NCAR|UCAR?: 
Announcement Timing: 
Tuesday, December 18, 2018 to Thursday, January 17, 2019
Calendar Timing: 
Thursday, January 17, 2019 - 3:30pm to 4:30pm

Posted by Nancy Kerner at ext. 8946, nskerner@ucar.edu

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