Seasonality

What does the turning of the seasons teach us about climate?

• Building on our earlier work, Karen McKinnon showed that its possible to constrain climate sensitivity using both the phase and amplitude of the seasonal cycle 2024.
• Karen McKinnon led up a study on explaining the phase and amplitude structure of extra-tropical seasonality. This structure turned out to be representable as the integrated influence of land and ocean heat exchanges on the mixing of air parcels that climatologically populate a given grid box (2013). Following up on this work, Karen showed that the basic structure of the response to the seasonal cycle also provides insight into the rate of adjustment observed in response to increasing greenhouse gases (2014).
• The annual cycle in surface temperature is generally larger than the temperature change between glacial and interglacial climates, and even small changes in seasonality can have large consequences. Zan Stine showed that the annual cycle on land has been trending earlier over the last fifty years (2009). More recently, we found that these trends in seasonality almost entirely result from variations in the Northern Annular Mode and Pacific/North-American patterns of atmospheric variability (2012).
• Variations in Earth's orbital configuration act primarily through modifying the seasonal cycle of insolation (e.g., 2006), suggesting that the seasonal response may be a good analog for constraining the response to orbital variations. One application of this concept was with respect to the importance of Eastern Equatorial Pacific cooling for the initiation of Northern Hemisphere glaciation. Working with Peter Molnar, we fit relationships between ENSO and North American temperature as well as the seasonal cycles of insolation and temperature in North America to gage the importance of Eastern Equatorial cooling relative to changes in obliquity for determining the onset of North American glaciation (2007).
• An approximate power-law scaling of temperature variations with frequency exists between monthly and centennial timescales, and the slope of this power law is proportional to the amplitude of the annual cycle (2006). Why does this structure across timescales arise? Presumably it tells us something about the nonlinear coupling between seasonal and other varations.

References

• McKinnon and Huybers, Inferring Northern Hemisphere continental warming patterns from the amplitude and phase of the seasonal cycle in surface temperature, Journal of Climate, 37(2), 2024. link
• McKinnon and Huybers On using the seasonal cycle to interpret extratropical temperature changes since 1950, Geophysical Research Letters, 2014. pdf
• McKinnon, Stine and Huybers The spatial structure of the annual cycle in surface temperature: amplitude, phase, and Lagrangian history, Journal of Climate, 2013. pdf
• Stine and Huybers Changes in the seasonal cycle of temperature and atmospheric circulation, Journal of Climate, 2012. pdf
• Stine, Huybers and Fung Changes in the phase of the annual cycle of surface temperature , Nature, 2009. pdf and supplemental information
• Huybers, Early Pleistocene glacial cycles and the integrated summer insolation forcing, Science, 2006. pdf, supporting online material, and insolation values and code posted at NCDC
• Huybers and Molnar, Tropical cooling and the onset of North American glaciation, Climate of the Past, 2007. pdf
• Huybers and Curry, Links between annual, Milankovitch, and continuum temperature variability, Nature, 2006. pdf and supplemental material