Characteristics of ENSO-Associated Southeast US Daily Temperature Range Frequencies

Daily temperature ranges (DTRs) in the Southeast United States have a wide distribution of magnitudes; patterns in this distribution are observed on both spatial and temporal scales. Rapid or intense changes in daily temperatures can create heat/cold stress on animals or tax a power grid; therefore, an accurate prediction of these climate-driven fluctuations could be helpful for agricultural, livestock, and energy industries. It is hypothesized that in addition to seasonal and annual distributions, DTR frequencies vary with respect to the climatological phase of El Niño-Southern Oscillation (ENSO). It is well documented that ENSO has climate impacts in the Southeast US (e.g., Ropelewski and Halpert 1986). El Niño phase is typically associated with warm and wet winters whereas La Niña phase is typically associated with cool and dry winters. Maximum and minimum temperatures (Lim and Schubert 2011) and extreme mean temperatures (Gershunov and Barnett 1998, Higgins et al. 2001) are known to be specifically influenced by ENSO in the winter. Monthly averaged DTRs have been shown to vary in the winter with respect to ENSO (Mote 1996). The purpose of this study is to determine the relationship between high-resolution daily DTRs and ENSO and make the information available to stakeholders for application purposes. A 62-year record of quality-controlled observations collected from 290 stations of the National Weather Service's Cooperative Observing Network is used for analysis. Histograms are created to evaluate the distributions (all-year and ENSO-separated) for the 290 stations and all four seasons. To make the analysis manageable, the authors develop a new metric, identified as conditional ratios in this study. These conditional ratios enable us to directly compare ENSO phases and perform spatial and statistical analyses. A tool more relevant to stakeholders, exceedance probability graphs, is created. Results show that high DTRs are significantly associated with La Niña events whereas low DTRs are significantly associated with El Niño events. The response is stronger during spring than winter.