Title: Seasonal cycle of surface temperature: insights from simple models
Speaker: Joshua Duffield (Imperial)
Abstract: From the perspective of the annual harmonic, the role of surface heat capacity in controlling the seasonal cycle of surface temperature is readily apparent: a larger heat capacity leads to a greater lag (i.e., the time delay between peak incoming solar radiation and the hottest day of the year), as well as a reduced seasonal amplitude (i.e., the difference between summer and winter temperatures). Over the ocean, changes in heat capacity in response to global warming can therefore drive opposing amplitude trends. At high latitudes, sea-ice melt increases heat capacity and reduces seasonal amplitude, whereas elsewhere, a reduction in mixed-layer depth associated with increased stratification decreases heat capacity and increases seasonal amplitude. Over land, the response of the seasonal cycle to warming and the underlying physical mechanisms are less certain. Here, we use single-column model simulations to investigate this response, with particular attention to the expected decrease in seasonal amplitude resulting from increased atmospheric heat capacity under warming.