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Influence of PDO and ENSO with Indian summer monsoon rainfall and its changing relationship before and after 1976 climate shift
Xavier, A.K.; Varikoden, H.; Babu, C.A.; Reshma, T. (2023). Influence of PDO and ENSO with Indian summer monsoon rainfall and its changing relationship before and after 1976 climate shift. Clim. Dyn. 61: 5465-5482. https://dx.doi.org/10.1007/s00382-023-06865-w
In: Climate Dynamics. Springer: Berlin; Heidelberg. ISSN 0930-7575; e-ISSN 1432-0894, meer
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| Author keywords |
Rainfall variability; Pacific decadal oscillation; El Nino Southern Oscillation; Climate shift; Circulation pattern |
| Auteurs | | Top |
- Xavier, A.K., meer
- Varikoden, H.
- Babu, C.A.
- Reshma, T.
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| Abstract |
In this study, we investigated the possible relation between the Indian summer monsoon and the combination of the different phases of Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO) before and after the climate shift in 1976. This study is carried out using IMD’s rainfall dataset, HadISST v1.1 dataset and twentieth century reanalysis dataset by comparing anomalies of the respective parameters from 1901 to 2020. It is found that when positive (negative) phases of PDO and El Niño (La Niña) co-occur, deficit (surplus) rainfall are likely to occur over entire India. The SST signatures of both the PDO and ENSO are showing their respective spatial structures. However, when negative (positive) PDO and El Niño (La Niña) co-occur, the signal is mixed and it is unlikely that either surplus or deficit rainfall conditions will occur over entire India, and the SST signatures are not capturing their proper spatial pattern. In other words, when ENSO and PDO are in (out of) phase they enhance (counteract) the conventional monsoon-ENSO relationship. After confirming the climate shift in 1976, study periods were further divided into pre and post climate shift periods based on Niño 3.4 index and PDO index and analysed their impact on the Indian summer monsoon rainfall. In the pre-shift example, in-phase conditions exhibit similar qualities to those described above. Rainfall patterns are more indicative of ENSO than PDO. In the post-shift situation, the positive anomaly of SST in the PDO and Niño region is significantly stronger than in the pre-shift phase. When compared to the pre-shift example, positive rainfall anomalies are amplified during positive PDO and El Niño, while negative PDO and La Niña show a weakening of positive rainfall anomalies. The out-of-phase condition has a balancing effect due to the counteracting impact, but with an increased positive anomaly of SST. In that combination, rainfall patterns with PDO characteristics rather than ENSO characteristics emerge. Circulation features at 850 hPa during the pre-shift and post shift periods show considerable changes as an indication of the climate shift. During the pre-shift of positive PDO and La Niña, convergence at low level enhances over Indian subcontinent and resulting enhanced rainfall; however, in the post shift period the strength of convergence reduces, and it leads to reduced rainfall. The patterns of stream function and velocity potential are also consistent with rainfall during the pre and post shift periods. |
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