Jun 22, 2018

Increased Frequency of Summer Extreme Heat Waves over Texas Area Tied to the Amplification of Pacific Zonal SST Gradient

Kaiqiang Deng
AMS Journal of Climate
  • Investigates summer extreme heat waves (EHWs) and their trend over the Texas area
  • Uses observations and atmospheric general circulation model (AGCM) outpu
  • Finds there is a positive linear trend in Texas EHW days for the period 1979–2015
  • Finds that the upward trend in Texas EHWs is found to be significantly associated with the tropical Pacific zonal SST gradient (PZSSTG)—this is in addition to the interannual variability linked to ENSO conditions
  • States the amplification of PZSSTG leads to both enhanced convection in the western Pacific and suppressed convection in the central-eastern Pacific (i.e., La Niña–like pattern), both of which can induce anomalous anticyclones over the Texas area through two distinct planetary wave trains in the antecedent spring
  • States that, as a result, anomalously sinking motions and divergent water vapor flux appear over the Texas area, which reduce precipitation and increase downward solar radiation, leading to dry and hot soil that favors the occurrence of Texas summer EHWs
  • All AGCMs using observed SSTs as boundary conditions were able to simulate the observed decreasing trend in Texas summer precipitation and the observed increasing trend in Texas summer surface air temperature
  • Finds that the observed relationships between winter PZSSTG and the following spring–summer Texas precipitation/temperature were also reproduced by these models, where the intensified PZSSTG tended to reduce the Texas precipitation while increasing the surface air temperature