The energy cycle of ENSO

Hanke, Tyler J

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https://hdl.handle.net/2142/127279 Copy

Description

Title

The energy cycle of ENSO

Author(s)

Hanke, Tyler J

Issue Date

2024-12-09

Director of Research (if dissertation) or Advisor (if thesis)

Proistosescu, Cristian

Committee Member(s)

• Raghuraman, Shiv P
• Wang, Zhuo

Department of Study

Climate Meteorology & Atm Sci

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• El Nino
• ENSO
• Radiative Feedbacks
• Climate Sensitivity
• Pattern Effect

Abstract

The spatial pattern of warming in sea surface temperatures (SSTs) can have major impacts on Earth’s top-of-atmosphere (TOA) energy budget, a phenomenon known in recent research as the “pattern effect”. Much of this pattern effect has been attributed to variability in low cloud radiative effect (CRE), and previous studies have shown that ENSO variability in CRE could inform long-term cloud radiative feedbacks. While ENSO teleconnections and predictability have been extensively researched for decades, ENSO-induced variability in atmospheric radiation has not been fully characterized. Here I use ENSO as an emergent constraint on the pattern effect. We find strong linear relationships between modeled ENSO feedbacks and their respective pattern effects, especially for net CRE. Observed ENSO feedbacks lie within the middle of the model ensemble and suggest a pattern effect magnitude of 1.00 ± 0.35 W /m2/K when calculated relative to preindustrial conditions. Model-simulated pattern effects also exhibit similar spatial distributions as the pattern diversity of ENSO, hinting at similar physics governing the two phenomena. Additionally, I add to previous studies of the ENSO-radiation relationship by exploring the impact of the ENSO cycle and pattern diversity on observed top-of-atmosphere (TOA) radiation. I find that both eastern Pacific (EP) and central Pacific (CP) ENSO SST patterns have associated all-sky radiation patterns that are dominated by low-cloud radiative effect (CRE) anomalies that are primarily driven by EIS CRE, with regional contributions by SST CRE, EIS CRE, and Tadv CRE. Clear-sky radiation anomalies do not contribute as significantly to the net radiative response patterns because they are driven by a negative Planck+lapse-rate feedback that is partially compensated by a positive longwave water vapor feedback. This competition between clear-sky feedbacks results in little contribution to the total radiative response patterns. These findings suggest that ENSO provides a potential emergent constraint on model pattern effect uncertainty, demonstrates the influence of ENSO pattern diversity on the drivers of the ENSO SST-radiation relationship, and depicts the first-order importance of ENSO pattern diversity in setting TOA radiation anomalies.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127279

Copyright and License Information

Copyright 2024 Tyler Hanke

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