WHOI PO
Christoph Renkl, WHOI - Intensification of Atmospheric Rivers by Marine Heatwaves: Multi-Scale Air-Sea Interaction and Downstream Effects on Coastal and Inland Climate
| Date |
Time |
Location |
| January 14th, 2025 |
3:05pm-4:05pm |
Clark 507 |
Title: Intensification of Atmospheric Rivers by Marine Heatwaves: Multi-Scale Air-Sea Interaction and Downstream Effects on Coastal and Inland Climate
Abstract: The climate along the US West Coast is profoundly affected by air-sea interactions, influencing moisture transport and valuable precipitation that play an important role in agricultural and water resource management efforts. On a basin scale, seasonal to interannual anomalies in the atmospheric circulation can create persistent sea surface temperature (SST) anomalies known as marine heatwaves (MHWs). These anomalous ocean conditions have direct impact on air-sea fluxes, thereby influencing synoptic-scale weather patterns including atmospheric rivers (ARs). Given the heat and moisture pickup by ARs from the oceans, these multi-scale MHW-AR interactions may also represent a potential mechanism for dissipation of MHWs. We examine diabatic multi-scale coupled air-sea interaction processes between persistent MHWs and synoptic-scale ARs, and evaluate their downstream effects on the coastal and inland climate.
Here, a comprehensive analysis based on observations and high-resolution, large-ensemble regional coupled model simulations is presented targeting a series of landfalling ARs that interacted with warm SST anomalies during the Northeast Pacific MHW event in winter 2014/2015. Sensitivity simulations are performed where the large-scale observed MHW is removed from the ocean component of the coupled model to quantify the diabatic modification of the AR moisture budgets. The results show that MHWs exert diabatic forcing of the lower troposphere via enhanced latent heat flux from the ocean to the atmosphere and an associated increase in evaporation. This ultimately creates a robust anomaly in moisture content leading to an amplification of AR intensity indicated by an earlier onset and prolonged duration of precipitation inland. Analysis of the moisture flux convergence suggests the increased mean moisture content to be the dominant driver. Implications of MHW dissipation arising from the diabatic interaction between ARs and MHW will be discussed.