Investigating Wintertime North Pacific Jet Variability and Disturbance-Driven Rainfall over Hawai'i Using the Self-Organizing Map (SOM).
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| Title: | Investigating Wintertime North Pacific Jet Variability and Disturbance-Driven Rainfall over Hawai'i Using the Self-Organizing Map (SOM). |
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| Authors: | Fandrich, Katrina M.1 (AUTHOR) kfandrich@albany.edu, Timm, Oliver1 (AUTHOR), Giambelluca, Thomas W.2,3 (AUTHOR) |
| Source: | Journal of Climate. Dec2025, Vol. 38 Issue 23, p7001-7017. 17p. |
| Subjects: | Jet streams, Rainfall, El Niño, Modes of variability (Climatology), Self-organizing maps, Climate change |
| Geographic Terms: | North Pacific Ocean |
| Abstract: | Interannual rainfall variability in Hawai'i is strongly influenced by the large-scale circulation over the North Pacific, natural modes of climate variability [e.g., Pacific–North American (PNA) and El Niño–Southern Oscillation (ENSO)], and wintertime rainfall disturbances (e.g., Kona lows and cold fronts). In this study, the self-organizing map (SOM) was applied to investigate the relationship between the large-scale circulation over the North Pacific and its relationship to natural climate modes and wintertime rainfall disturbances in Hawai'i. The SOM was trained with daily 250-hPa zonal wind anomalies from the fifth generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5). Results indicate that a zonally retracted jet is associated with the negative PNA/ENSO phase and above-normal rainfall across Hawai'i, while a zonally extended jet is associated with the positive PNA/ENSO phase and below-normal rainfall across Hawai'i. Further, to investigate future changes in the variability of the large-scale circulation, 250-hPa wind data from 21 CMIP6 models were projected onto the ERA5-trained SOM. The ensemble-mean wind changes (future–historical) suggest that overall, the jet will experience general poleward shift in a future climate. The SOM node frequency changes provide a more complex description of how the North Pacific jet (NPJ) is projected to change in a future climate. Our results suggest that a zonally retracted jet will become more frequent in a future climate (2071–2100), which could lead to increased frequencies in Kona lows and increases in wet season rainfall. In contrast, our results also suggest that a zonally extended jet will become more frequent in a future climate, which could lead to decreased Kona low activity and decreases in wet season rainfall. Overall, the results suggest increased variability in a future climate and highlight the complexity and uncertainty of the future NPJ changes, making it difficult to explain the ensemble-mean NPJ changes with a single physical mechanism. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| Abstract: | Interannual rainfall variability in Hawai'i is strongly influenced by the large-scale circulation over the North Pacific, natural modes of climate variability [e.g., Pacific–North American (PNA) and El Niño–Southern Oscillation (ENSO)], and wintertime rainfall disturbances (e.g., Kona lows and cold fronts). In this study, the self-organizing map (SOM) was applied to investigate the relationship between the large-scale circulation over the North Pacific and its relationship to natural climate modes and wintertime rainfall disturbances in Hawai'i. The SOM was trained with daily 250-hPa zonal wind anomalies from the fifth generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5). Results indicate that a zonally retracted jet is associated with the negative PNA/ENSO phase and above-normal rainfall across Hawai'i, while a zonally extended jet is associated with the positive PNA/ENSO phase and below-normal rainfall across Hawai'i. Further, to investigate future changes in the variability of the large-scale circulation, 250-hPa wind data from 21 CMIP6 models were projected onto the ERA5-trained SOM. The ensemble-mean wind changes (future–historical) suggest that overall, the jet will experience general poleward shift in a future climate. The SOM node frequency changes provide a more complex description of how the North Pacific jet (NPJ) is projected to change in a future climate. Our results suggest that a zonally retracted jet will become more frequent in a future climate (2071–2100), which could lead to increased frequencies in Kona lows and increases in wet season rainfall. In contrast, our results also suggest that a zonally extended jet will become more frequent in a future climate, which could lead to decreased Kona low activity and decreases in wet season rainfall. Overall, the results suggest increased variability in a future climate and highlight the complexity and uncertainty of the future NPJ changes, making it difficult to explain the ensemble-mean NPJ changes with a single physical mechanism. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 08948755 |
| DOI: | 10.1175/JCLI-D-24-0422.1 |
