Note: The confusing sentence in the abstract below is easier to understand if broken down into the 2 components:
1. Several daily maximum EHEs [Extreme Heat Events] near the 1930’s led to 1930-2010 trends of daily maximum EHEs [Extreme Heat Events] decreasing.
2. Several daily (minimum) EHEs [Extreme Heat Events] near the (2000’s) led to 1930-2010 trends of daily (minimum) EHEs [Extreme Heat Events] (increasing).
Journal of Applied Meteorology and Climatology 2013 ; e-View
Evan M. Oswald1 and Richard B. Rood
The USHCN-daily version 1 dataset was integrated with the homogenized USHCN-monthly version 2.0 dataset to create daily data for trend analysis. Time series and estimated trends in multiple characteristics of EHEs (e.g. number, total days, mean duration, etc) were calculated as were the continental means and spatial maps. The differences between EHEs based on daily maximum temperatures, minimum temperatures and both minimum and maximum temperatures were explored. In order to focus on warming and cooling periods the trends were also estimated separately over the first half and second half of the study period (1930-2010).
The results indicated the trends for different EHE characteristics were coherent (e.g. temporally correlated, similar spatial pattern of trends). Maps indicated negative trends in the interior of the CONUS [continental United States] and positive trends in coastal and southern areas. Continental scale increases between 1970 and 2010 were mostly offset by the decreases between 1930 and 1970. Several daily maximum (minimum) EHEs near the 1930’s (2000’s) led to 1930-2010 trends of daily maximum (minimum) EHEs decreasing (increasing). Lastly, the results suggest linear trends depend on which daily temperature extreme is required to exceed the threshold.