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CR prepress abstract   -  DOI: https://doi.org/10.3354/cr01702

South Pacific Tropical Upper Tropospheric Trough: variability and impact on the French Polynesian climate

Victoire Laurent, Keitapu Maamaatuaiahutapu*, Marania Hopuare, Patrick Varney, Pascal Ortega

*Corresponding author:

ABSTRACT: The South Pacific Tropical Upper Tropospheric Trough (TUTT) is an elongated trough that appears in summer monthly averaged maps of the upper tropospheric flow over the ocean. We provide the first comprehensive description of the South Pacific TUTT and analyze its impact on the regional climate with 42 years (1979-2020) of monthly data from ERA5, radiosonde, rain, keraunic data, and lightning flash rate from OTD-LIS (Optical Transient Detector-Lightning Imaging Sensor). The data confirm the presence of the TUTT along a southeast-northwest axis from November to May. Located between 100 to 400 hPa, the TUTT is a cold-core with a relative vorticity minimum and negative geopotential anomaly. Divergent, ascending flow with high relative humidity is found south and west of the TUTT axis and convergent, descending flow with low relative humidity is observed north and east of the TUTT axis. The TUTT’s seasonal and long term impacts on the local and regional climate is dependent on its location and its strength. The existence of the TUTT in the South Pacific is strongly dependent on the El Niño Southern Oscillation (ENSO) phases: stronger during a strong negative ENSO phase, it disappears from French Polynesia during a strong positive ENSO phase. Genesis of tropical disturbances east of 180 °W is possible only if the TUTT is located east of 120 °W. The environmental conditions associated with the TUTT, lightning and rainfall data from three sites in French Polynesia show that lightning flash rates are higher during a negative ENSO phase than during a positive ENSO phase.