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<p>This study explores the role of atmospheric waves, including the Madden-Julian Oscillation (MJO) and convectively coupled equatorial waves (Kelvin, equatorial Rossby (ER) and Mixed Rossby-Gravity (MRG) along with tropical depressions (TD) collectively considered as MT wave) in influencing extreme temperature events over Sri Lanka from 1979 to 2020. Daily maximum temperature (Tmax) and minimum temperature (Tmin) from very high-resolution Indian Monsoon Data Assimilation and Analysis (IMDAA) reanalysis is used to find the extreme temperature events over Sri Lanka based on the percentiles. Using daily outgoing longwave radiation (OLR) data from NOAA, the study investigates wave activity during dry and wet phases and their link to extreme temperature events over Sri Lanka. Results show that dry phases significantly amplify extreme temperature events by suppressing convection, reducing cloud cover and enhancing solar radiation. Based on monthly climatology, March-May emerges as the most heat-prone period with northern Sri Lanka recording Tmax values above 34&#xa0;°C, while December-February corresponds to lower temperature extremes. The ER wave exhibits the strongest influence, producing higher Tmax and lower Tmin anomalies compared to other wave types. Spatial patterns highlight that the dry phases of ER waves and MJO cause widespread warming, whereas Kelvin and MT waves have more localized effects. The Tmin increases significantly during wet phases. In addition, the Excess Heat Factor (EHF) also attains its highest values during the dry phases of ER waves, favors intensified heat-wave conditions. Whereas, the frequency of EHF exceedance is greatest during the dry phases of the MJO, particularly over northern and eastern regions of Sri Lanka, indicating enhanced likelihood of extreme heat events in this region. The wave filtered zonal and meridional winds at 850&#xa0;hPa modulate these extremes. Overall, the results highlight the key role of atmospheric wave dynamics in temperature variability and underscore the need to integrate wave-related metrics into regional climate models for improved prediction and mitigation strategies in Sri Lanka. Keywords: Madden Julian Oscillation, Convectively Coupled Equatorial Waves; Excess heat factor; Extreme heat events; IMDAA reanalysis</p>

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Role of equatorial waves in modulating extreme temperature events over Sri Lanka

  • 期刊论文

  • 发表日期：

    2026年3月21日

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  • Bibhuti Sharan Keshav,
  • Mohan T. S.,
  • Raghavendra Ashrit

摘要

This study explores the role of atmospheric waves, including the Madden-Julian Oscillation (MJO) and convectively coupled equatorial waves (Kelvin, equatorial Rossby (ER) and Mixed Rossby-Gravity (MRG) along with tropical depressions (TD) collectively considered as MT wave) in influencing extreme temperature events over Sri Lanka from 1979 to 2020. Daily maximum temperature (Tmax) and minimum temperature (Tmin) from very high-resolution Indian Monsoon Data Assimilation and Analysis (IMDAA) reanalysis is used to find the extreme temperature events over Sri Lanka based on the percentiles. Using daily outgoing longwave radiation (OLR) data from NOAA, the study investigates wave activity during dry and wet phases and their link to extreme temperature events over Sri Lanka. Results show that dry phases significantly amplify extreme temperature events by suppressing convection, reducing cloud cover and enhancing solar radiation. Based on monthly climatology, March-May emerges as the most heat-prone period with northern Sri Lanka recording Tmax values above 34 °C, while December-February corresponds to lower temperature extremes. The ER wave exhibits the strongest influence, producing higher Tmax and lower Tmin anomalies compared to other wave types. Spatial patterns highlight that the dry phases of ER waves and MJO cause widespread warming, whereas Kelvin and MT waves have more localized effects. The Tmin increases significantly during wet phases. In addition, the Excess Heat Factor (EHF) also attains its highest values during the dry phases of ER waves, favors intensified heat-wave conditions. Whereas, the frequency of EHF exceedance is greatest during the dry phases of the MJO, particularly over northern and eastern regions of Sri Lanka, indicating enhanced likelihood of extreme heat events in this region. The wave filtered zonal and meridional winds at 850 hPa modulate these extremes. Overall, the results highlight the key role of atmospheric wave dynamics in temperature variability and underscore the need to integrate wave-related metrics into regional climate models for improved prediction and mitigation strategies in Sri Lanka. Keywords: Madden Julian Oscillation, Convectively Coupled Equatorial Waves; Excess heat factor; Extreme heat events; IMDAA reanalysis