The Impact of Background ENSO and NAO Conditions and Anomalies on the Modeled Response to Pinatubo-Sized Volcanic Forcing
Strong, strato-volcanic eruptions are a substantial, intermittent source of natural climate variability. Background atmospheric and oceanic conditions such as El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) also naturally impact climate on regular time scales. We examine...
| Main Authors: | , , |
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| Format: | Text |
| Language: | English |
| Published: |
2023
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/acp-2023-54 https://acp.copernicus.org/preprints/acp-2023-54/ |
| Summary: | Strong, strato-volcanic eruptions are a substantial, intermittent source of natural climate variability. Background atmospheric and oceanic conditions such as El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) also naturally impact climate on regular time scales. We examine how background conditions of ENSO and NAO impact the climate's response to a Pinatubo-type eruption using a large (81-member) ensemble of model simulations in GISS Model E2.1-G. Simulations are sampled from possible background conditions under the protocol of the coordinated CMIP6 Volcanic Model Intercomparison Project (VolMIP) – where aerosol forcing with time, latitude, and height. We analyze paired paired anomalous variation (perturbed - control) to understand changes in global and regional climate responses under positive, negative, and neutral ENSO and NAO conditions. In particular, we find that for paired anomalies there is a high probability of strong (~1.5 °C) post-eruptive winter warming for negative NAO ensembles with analysis coincident with decreased lower stratospheric temperature at the poles, decreased geopotential height, and strengthening of the stratospheric polar vortex. Historical anomalies (relative to climatology) show no mean warming and suggest that strength of this response is impacted by control conditions. Again using paired anomalies, we also observe that positive and negative ENSO ensembles relax the ENSO anomaly in the first post-eruptive Boreal Winter while neutral-phase ensembles are variable and show no clear response. In general, paired anomalies give insight into the evolution of the climate response to volcanic forcing, but are significantly impacted by background climate conditions present in control conditions. |
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