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<p>Intraseasonal variability strongly influences East African climate, yet its impact on near-surface temperature has received limited attention compared to rainfall. This study examines intraseasonal variability of 2&#xa0;m temperature (T2m) over Tanzania during the October–December (OND) season using daily NCEP/DOE Reanalysis 2 data for 1990–2020. A 10–30-day Butterworth filter isolates the quasi-biweekly oscillation (QBWO) signal. Results show that warm QBWO phases are characterized by low-level divergence and enhanced northeasterly anomalies, with an overlying mid- and upper-tropospheric ridge centered on East Africa. Cold phases exhibit the opposite structure, marked by convergence, southerly flow, and a barotropic trough aloft. Correlation and wave-activity flux diagnostics reveal equatorward-propagating Rossby wave trains from the Southern Hemisphere midlatitudes that converge over Tanzania, providing a dynamical pathway linking extratropical variability to local intraseasonal temperature swings. ENSO further modulates these teleconnections: El Niño strengthens and organizes the wave trains, producing larger and more coherent T2m anomalies, whereas La Niña shifts the wave axis poleward and weakens the signal. These findings provide the first targeted evidence that Southern Hemisphere Rossby wave activity influences quasi-biweekly temperature extremes in Tanzania, highlighting a physical mechanism with potential to enhance sub-seasonal forecast skill in East Africa.</p>

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Quasi-biweekly oscillations and midlatitude wave-train modulation of intraseasonal temperature variability over Tanzania during OND

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  • 发表日期：

    2025年11月25日

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  • Godfrey Thomas Assenga,
  • Daudi Mikidadi Ndabagenga

摘要

Intraseasonal variability strongly influences East African climate, yet its impact on near-surface temperature has received limited attention compared to rainfall. This study examines intraseasonal variability of 2 m temperature (T2m) over Tanzania during the October–December (OND) season using daily NCEP/DOE Reanalysis 2 data for 1990–2020. A 10–30-day Butterworth filter isolates the quasi-biweekly oscillation (QBWO) signal. Results show that warm QBWO phases are characterized by low-level divergence and enhanced northeasterly anomalies, with an overlying mid- and upper-tropospheric ridge centered on East Africa. Cold phases exhibit the opposite structure, marked by convergence, southerly flow, and a barotropic trough aloft. Correlation and wave-activity flux diagnostics reveal equatorward-propagating Rossby wave trains from the Southern Hemisphere midlatitudes that converge over Tanzania, providing a dynamical pathway linking extratropical variability to local intraseasonal temperature swings. ENSO further modulates these teleconnections: El Niño strengthens and organizes the wave trains, producing larger and more coherent T2m anomalies, whereas La Niña shifts the wave axis poleward and weakens the signal. These findings provide the first targeted evidence that Southern Hemisphere Rossby wave activity influences quasi-biweekly temperature extremes in Tanzania, highlighting a physical mechanism with potential to enhance sub-seasonal forecast skill in East Africa.