Contribution of changes in the leading climate variability modes to long-term trends in the diurnal temperature range during the Northern Hemisphere wintertime and its implication on the detection of regional climate trends

This study examines the contributions of four leading climate variability modes, including the AO, hemispheric PNA-like mode, PDO and AAO, to trends of the winter-season (Jan–Mar) diurnal temperature range (DTR) in observations at the global, hemispheric, sub-continental, and grid-box scales. During 1951 to 2000, variations in the these circulation patterns explain significant fractions of the DTR increase at all scales although the strength of these associations varies geographically. After removing the linearly congruent contribution of leading climate variability modes from the total wintertime DTR trends in the observation, statistically significant residual trends in DTR are still found at the global, hemispheric, and most sub-continental regions. Ensemble mean multi-model averaged DTR trends to major anthropogenic and natural forcing are significantly smaller than not only observed total DTR trends, but also residual trends at the these large scales.

The implication of changes in the leading climate variability modes on the detection of regional DTR trends is discussed. We compare observed DTR trends over the second half of the 20th century with those simulated in response to natural and anthropogenic climate forcings in a suite of six current coupled general circulation models. Control runs from these models are used to provide estimates of the internal variability of trends. We find that the detection of the regional response to combined anthropogenic and natural forcing is robust to the exclusion of trends related to changes of the four modes considered here.