ENSO and Volcanic Contributions to GMSL Estimated from the NCAR LE. John Fasullo and Steve Nerem NCAR/CU

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1 ENSO and Volcanic Contributions to GMSL Estimated from the NCAR LE John Fasullo and Steve Nerem NCAR/CU

2 Background Sea level is mainly influenced on interannual timescales by changes in terrestrial water storage (TWS), ocean heat content (OHC), and atmospheric precipitable water (PW). PW OHC TWS

3 Background Sea level exhibits both a trend and interannual variability. The data record exhibits consistent qualitative behavior ( El Niño La Niña) but with large inter-event variability. Why? Data error? What is typical? Why isn t an acceleration evident? (3.4 mm/yr pre-2003 vs 2.8 mm/yr post-2003) What would be the impact of a volcanic eruption? mm El Niño de-trended La Niña

4 Key Points Given that our understanding provided by short records (ARGO/GRACE) is limited, models can provide essential insight. The Large Ensemble shows that: 1. OHC, TWS, and PW variability all make important contributions to ENSO-related GMSL variability. Typical variations 0.5 mm K -1 [ is a highly unusual event, 1 in 75 yrs]. Signif background noise. 2. Volcanic contributions to GMSL can be large and prolonged. Unlike ENSO, they are characterized by compensation between OHC and TWS/PW anomalies. 3. Pinatubo s influence on GMSL in the 1990 s is likely sufficient to explain recent observed decadal variability in sea level rise.

5 CESM1-CAM5 Validation ENSO Teleconnections CESM1-CAM5 Control GPCC v7 Precipitation teleconnections are largely reasonable (except in N/Eq Africa) Continent-mean correlations (r) and regressions (m) agree well (except NA, Afr).

6 CESM1-CAM5 Validation ENSO / Response to Pinatubo ENSO has too much power in the 3-10 year band. (address this by normalization) Radiative response to volcanic events agree well with estimates from Allan et al ERBS outages in late 1993, early 1998, 1999

7 Methods POP is a fixed volume ocean GMSL is invariant Contributing terms are estimated including: 1) OHC GMSL influence estimated with Church s conversion (5 mm = 3x10 22 J) 2) TWS = SOILLIQ+SOILICE + WT + H2OSNO + H2OCAN + VOLR 3) PW = TMQ El Niño is identified for events where the objective Niño index > 2C; La Niña for 1.7C Forced component removed (ensemble mean). Results in 500+ events.

8 El Niño 524 events (~1/decade) GMSL at onset, at peak GMSL Composite El Niño Event (524 events) GMSL due largely to OHC but also TWS as SST As El Niño peaks, rapid OHC accompanies a PW GMSL As El Niño transitions to La Niña, GMSL steadies Ts, PW offsets TWS PW-mm/K K/K J/K TWS-mm/K 1 2 Niño 3.4 OHC -TWS -PW -1 Year -2 Year -1 Year +1 Year +2 0 GMSL (mm/k) GMSL (mm/k) -0.5

9 La Niña 506 events (~1/decade) GMSL/OHC steady at onset PW balance TWS As La Niña peaks, rapid OHC PW and TWS GMSL (recovers)

10 El Niño: Regional Features SA and AUS dominate TWS SA has peak value, AUS has greatest low frequency power OHC is characterized by a major and rapid decrease in the Pacific compensated somewhat by other basins (as obs in Mayer et al. 2015)

11 Background Methods ENSO Volcanic Contributions La Niña: Regional Features SA and AUS transition from drought to flood during La Niña - AUS continues to evidence low frequency power (per Fasullo et al. 2013) OHC is characterized by a major and rapid increase in the Pacific, compensated somewhat by other basins.

12 Volcanic Influences During Pinatubo (and other eruptions) GMSL due to OHC TWS and PW offset GMSL Timescale of GMSL recovery >> Timescale of Forcing Suggests anom 6 mm rise in the early altimeter era adj. trend pre 2003 post 2003

13 Variability in GMSL during ENSO results from several contributors: changes in OHC, TWS, and PW. [~0.5 mm/k*] Large background variability exists (not tightly controlled by ENSO) OHC/TWS/PW also play a key role during volcanic eruptions with TWS and PW reducing the OHC-driven GMSL Volcanic events influence GMSL on decadal and longer timescales and likely play a key role in observed decadal variability. Pinatubo explains recent decadal variability. *caveat: CESM ENSO teleconnections to Africa / NA

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