Stationary Wave Interference and its Relation to Tropical Convection and Climate Extremes Steven Feldstein, Michael Goss, and Sukyoung Lee The Pennsylvania State University 2015 AGU Fall Meeting, San Francisco, December 18, 2015

Questions: 1. What is the relationship between interference and tropical convection and how does it impact the extratropical circulation, including weather/climate extremes? 2. What is the relative impact of different centers of tropical convection on the extratropical circulation? Methods: Composites, Idealized Numerical Model Data: ERA-Interim Reanalysis, NOAA OLR, NSICD sea ice Stationary wave index (SWI): Defined as the projection of the daily 300-hPa streamfunction onto the 300-hPa climatological stationary eddies.

Evolution of 300-hPa streamfunction Positive SWI daysNegative SWI days

Evolution of outgoing longwave radiation Positive SWI daysNegative SWI days Enhanced convection

Evolution of Surface Air Temperature Positive SWI daysNegative SWI days

Time evolution: OLR  SWI  sea ice  stratospheric polar vortex  AO (for k=1)

Surface Air Temperature: Constructive interference with and without Warm Pool convection Western Pacific OLR < -0.5 Western Pacific -0.5 < OLR < 0.5 Western Pacific OLR > 0.5

Surface Air Temperature: Destructive interference with and without Warm Pool convection Western Pacific OLR < -0.5 Western Pacific -0.5 < OLR < 0.5 Western Pacific OLR > 0.5

Question: What is the extratropical response to individual tropical convection anomalies?

Convective heating anomalies

Anomalous 0.3σ Geopotential Height (7-10 days) MJO Phase 1El Nino

Anomalous 0.3σ Geopotential Height (7-10 days) MJO Phase 5La Nina

CONCLUSIONS Interference and changes in Warm Pool (WP) tropical convection: Enhanced convection  constructive interference  warming of the Arctic & melting of sea ice  deceleration of the stratospheric polar vortex  excitation of the negative AO Warm and cold extreme events take place in different regions in the Northern Hemisphere depending upon the presence of interference and the strengths and signs of WP tropical convection. Extratropical response to tropical convection, including climate extremes, may depend upon the competing influences of warm pool (WP) and central Pacific (CP) convection.

Time evolution: OLR  SWI  sea ice  stratospheric polar vortex  AO (for k=1)

Summary of impact of sea ice

Arctic Sea-Ice Concentration evolution Positive SWI daysNegative SWI days Reduced Sea ice