Increased Frequency of Extreme Heat Waves over Texas Area Tied to the Amplification of Pacific Zonal Sea Surface Temperature Gradient

Extreme heat waves (EHWs) over Texas areas have been investigated using the reanalysis and five atmospheric general circulation model (AGCM) outputs. The Texas EHW day (EHWD) shows an increasing trend over the past three decades, which implies more frequent EHWs. The SVD analysis in North American EHWD and the Pacific SSTA reveals that the increasing frequency of Texas EHWs is significantly connected with the amplification of the Pacific zonal SST gradient (PZSSTG), which accounts for 47.8% of the total co-variance. There exist two Rossby wave trains related to the occurrences of Texas EHWs. One is triggered by the La Niña events, which propagates northeastward and results in anomalous anti-cyclones over the Texas area. The other originates from the western Pacific, which propagates eastward across the North Pacific, contributing to the Texas anti-cyclone anomaly. As a result, the induced sinking air and divergent water vapor fluxes reduce the Texas precipitation while increase the soil water evaporation, which leads to drier and hotter soil condition that favor the occurrences of EHWs. The amplification of PZSSTG is favorable for both the enhancement of western Pacific convections and the maintenance of central Pacific SST cooling, both of which would exacerbate the persistent droughts and EHWs over Texas area. In addition, all AGCMs could simulate the trends in Texas summer precipitation and surface temperature. The observed relationships between the winter PZSSTG and the following spring and summer Texas precipitation/temperature were also reproduced by these models, where the intensified PZSSTG tended to reduce the Texas precipitation while increase the surface temperature.