Land surface air temperature diurnal range over high northern latitudes

Global warming is quantified based on daily maximum and minimum temperatures with their difference representing the diurnal range (DTR). Here we analyze the Climate Research Unit (CRU) monthly averaged daily maximum and minimum land surface air temperature data and our newly-developed CRU/MERRA (reanalysis) merged hourly temperature data from 1979 to 2009. We find that the January mean DTR over high northern latitudes is unrealistically large and inappropriate in representing the monthly averaged hourly temperature diurnal cycle (whose amplitude is DTRh); instead it primarily reflects the movement of lower-frequency synoptic weather systems. The DTR trends in November, December, and January north of 40N are negative, also contradicting the near-zero trends of DTRh. This calls for the revision of previous observational and modeling studies on monthly temperature diurnal range and its trends over high northern latitudes. Future studies (e.g., climate model evaluations) should also be based on DTRh rather than monthly DTR.