Dr. Ben Kirtman, University of Miami - CIMAS - "The role of air-sea coupling in SubX"

This talk examines the role of air-sea coupling in the SubX forecasts from two perspectives. First, we examine how current dynamical prediction systems forecast individual MJO events that occurred during the Dynamics of the MJO (DYNAMO) field campaign and the effects of ocean-atmospheric coupling on the forecasts of these events. Previous studies have shown the apparent need for active coupling in models to produce a realistic MJO, while others only need atmospheric dynamics. Past work on the DYNAMO MJO events has demonstrated that the October event (MJO1) did not need ocean-atmospheric coupling (an “uncoupled” event) for maintenance and propagation and the November event (MJO2) needed ocean-atmospheric coupling (a “coupled” event). We group the SubX models into a coupled ensemble and an uncoupled ensemble to examine the effects of ocean-coupling on the forecasts of these two events. Second, we examine the evolution of local air-sea feedbacks in mid--latitude region western boundary currents, and how these feedbacks are affected by resolution.

Dr. Carl Schreck, North Carolina State - "Sources of tropical subseasonal skill in CFSv2"

This study applies Fourier filtering to a combination of rainfall estimates from TRMM and forecasts from the CFSv2. The combined data are filtered for low-frequency (LF, ≥120 days) variability, the MJO, and convectively coupled equatorial waves. The filtering provides insight into the sources of skill for the CFSv2. The LF filter, which encapsulates persistent anomalies generally corresponding with SSTs, has the largest contribution to forecast skill beyond week 2. Variability within the equatorial Pacific is dominated by its response to ENSO, such that both the unfiltered and the LF-filtered forecasts are skillful over the Pacific through the entire 45-day CFSv2 forecast. In fact, the LF forecasts in that region are more skillful than the unfiltered forecasts or any combination of the filters. Verifying filtered against unfiltered observations shows that subseasonal variability has very little opportunity to contribute to skill over the equatorial Pacific. Any subseasonal variability produced by the model is actually detracting from the skill there. The MJO primarily contributes to CFSv2 skill over the Indian Ocean, particularly during March–May and MJO phases 2–5. However, the model misses opportunities for the MJO to contribute to skill in other regions. Convectively coupled equatorial Rossby waves contribute to skill over the Indian Ocean during December–February and the Atlantic Ocean during September¬–November. Convectively coupled Kelvin waves show limited potential skill for predicting weekly averaged rainfall anomalies since they explain a relatively small percent of the observed variability.