Recent and future modulation of the annual cycle

Abstract

This study investigates changes to the annual temperature cycle in both observed records and output from a coupled ocean-atmosphere global climate model. Using least-squares harmonic analysis, changes to the observed annual harmonic (for the time period 1856-1998), in addition to the climatology, are compared with 9 simulations from the HadCM2 model. The first simulation is a 1400 yr control integration, whilst the remainder are from 2 ensembles representing (1) increases in CO 2 concentrations and (2) a combination of CO 2 and sulphate aerosol increases. Observed and simulated climatologies are generally comparable, although large amplitude and phase discrepancies exist over northern North America and high-latitude oceans, respectively. The agreement may be partly artificial over the oceans due to the use of flux adjustments to maintain a realistic sea-surface temperature field. Observed northern hemisphere amplitude decreases during the 20th century agree well with simulated changes, although there are some regional differences; observed changes to the southern hemisphere amplitude are insignificant. The sign of northern hemisphere phase changes are opposite in the 2 data sets. The nature of these results is unchanged after consideration is given to the varying spatial coverage of the observed data set, by means of applying a frozen grid mask to both observed and simulated data. These findings are consistent with previous studies, though we extend them by updating the observed record, by using ensembles to better define the climate change signal, and by considering the direct effects of sulphate aerosols. For a given warming, the inclusion of aerosols results in an enhanced amplitude decrease within the northern hemisphere, related to the summertime maximum of the direct sulphate cooling effect.KEY WORDS: Annual temperature cycle · Greenhouse gas · Sulphate aerosols · Climate change · Phase · AmplitudeResale or republication not permitted without written consent of the publisher

Projected changes in thermal seasons and the growing season in Finland

“…This is in reasonable agreement with the analysis of the annual cycle of the hemispheric mean temperature by Wallace and Osborn (2002); as a response to greenhouse gas forcing, they reported a minor delay of 1-3 days in the phase of the cycle by 2100.…”

Changes in the phase of the annual cycle of surface temperature

“…First, the models that have been used to evaluate phase and amplitude variability have used seasonal heat and freshwater flux adjustments to match the mean annual cycle, which may artificially stabilize the modelled annual cycle. Second, and more troubling, Northern Hemisphere phase trends predicted by models forced with twentieth-century anthropogenic forcing are in the opposite direction to the observed trend 2,3 . Modelled Northern Hemisphere amplitude trends also disagree with observations when compared using a temporally fixed network 3 .…”

“…Second, and more troubling, Northern Hemisphere phase trends predicted by models forced with twentieth-century anthropogenic forcing are in the opposite direction to the observed trend 2,3 . Modelled Northern Hemisphere amplitude trends also disagree with observations when compared using a temporally fixed network 3 .…”

The complex dynamics of the seasonal component of USA's surface temperature

“…Unlike the external solar forcing, which is almost constant from year to year, there is no guarantee that climatic seasons have to be the same each year. Actually seasonal variations cause more than 90% of the variance of a temperature record and represent one of the basic examples of the complex atmospheric response to external forcing (Thomson, 1995(Thomson, , 1997Mann and Park, 1996;Wallace and Osborn, 2002;Jones et al, 2003;Stine et al, 2009).…”