El Niño-Southern Oscillation (ENSO) can effectively modulate global tropical cyclone (TC) activity, but the role TCs may play in determining ENSO characteristics remains unclear. Here we investigate the impact of TC winds on ENSO using a suite of Earth system model experiments where we insert TC winds, extracted from a TC-permitting high-resolution simulation, into a low-resolution model configuration with nearly no intrinsic TCs. The presence of TC winds in the model increases ENSO power and shifts ENSO frequency closer to what we observe. TCs lead to an increase of strong-to-extreme El Niño events seen in observations and not simulated in the low-resolution model without intrinsic TCs, mainly through enhanced zonal advection feedback and thermocline feedback. Our results indicate that TCs play a fundamental role in producing the ENSO characteristics we experience today in the climate system and point to two-way climatological interaction between TCs and ENSO.
This study verified in a fully coupled comprehensive Earth system model that the TCs are active participants in ENSO dynamics. We show that the added TC winds can shift ENSO frequency, improve ENSO phase-locking, and enhance El Niño strength, bringing all in closer agreement with observations. Additionally, we find that the integrated TC wind power correlates with the strong El Niño. TCs' impact on El Niño is manifested in the warmer eastern equatorial Pacific SST, eastward-propagating thermocline deepening, and enhanced eastward wind stress and surface current -- these TC-induced climatological changes are essential to El Niño dynamics through enhanced thermocline feedback and zonal advection feedback. In addition, the experiment uses TCs winds extracted from the high-resolution TC-permitting model to mimic the model behavior where the impact of the models' self-generated TCs is implicitly included. Our findings about TCs' climatological role in shaping ENSO characteristics, therefore, have important implications for understanding not only the role TCs play in general in the climate system but also the uncertainties of the simulated ENSO characteristics in the high-resolution models in current and future climate.
It is well accepted that ENSO can influence global TC activity by altering large-scale conditions. TCs, as transient yet powerful weather events, can cause strong air-sea interactions over the tropical ocean that may consequently influence the climate mean state. Here we show how TCs could be essential to the characteristics of ENSO using a suite of Earth system model experiments where we insert TC winds, extracted from a high-resolution model simulation, into a low-resolution model simulation with nearly no intrinsic TCs. The added TC winds in the model increase ENSO power and shift ENSO frequency closer to the observations. TCs lead to an increase of strong-to-extreme El Niño events seen in observations and not simulated in the low-resolution model without intrinsic TCs. Our results indicate that TCs play a fundamental role in producing the ENSO characteristics we experience today in the climate system and point to a previously unidentified two-way climatological interaction between TCs and ENSO.