Key Observations and Physics that Coupled El Nino Southern Oscillation (ENSO) Models Often Do Not Model Well.

Abstract:

The following key ENSO observations are often not well modeled. This presentation will offer explanations for the discrepancies.

(i) The raw monthly anomaly of the observed model El Niño index Niño3.4 is strongly persistent from about July to the following January (the observed correlation of long time series is typically 0.85) but not persistent from January to the following July (observed correlation about 0.03).

(ii) During El Niño (La Niña) the fundamental physical cause of this persistence is the eastward (westward) growing displacement of the equatorial edge of the Western Pacific Warm Pool and attendant anomalous westerly (easterly) wind and deep atmospheric convection anomalies during July to November. Typically this equatorial zonal movement ends when the monthly anomalous deep atmospheric convection and attendant zonal wind anomalies follow the overhead sun and warmer water south of the equator in the southern hemisphere summer (December to February). But how does this relate to the known ability of the equatorial warm water volume to overcome the persistence barrier?

(iii) In the tropics deep convective precipitation anomalies cancel out tightly when averaged around the earth between two tropical latitudes (e.g., 10 deg. S to 10 deg. N). For example negative OLR anomalies (indicative of positive anomalous deep convection) are cancelled by positive ones (indicative of anomalous drying). This is fundamental to understanding tropical teleconnections. Why is the cancellation so precise in a latitude band?