XCS seminar: Michael Byrne (St Andrews) Daily temperature distributions over a range of climate states

 

Here we use an idealised GCM to explore temperature distributions over a range of climate states. Climate is varied by scaling the longwave optical thickness. Slab-ocean aquaplanet simulations are performed along with simulations using a meridional-band land configuration and a simple bucket model for hydrology. The behaviours of the daily temperature distributions over this suite of simulations are investigated. The responses of extreme temperatures (i.e., high percentiles of daily near-surface temperature) to climate warming contrast strongly over tropical land and ocean. Over land, warming is amplified for hot days relative to the average day. But over ocean, hot days generally warm less than the average day, implying a tightening of the temperature distribution.

 

The contrasting responses of tropical temperature distributions over land and ocean are interpreted using a theory based on convective quasi-equilibrium. In the limit of constant relative humidity, the theory predicts that warming of extremes relative to the average temperature depends on the climatological specific humidity on hot days. Over land, warming is amplified for hot days because they are dry relative to the average day. But over ocean, warming is muted for hot days because they are relatively moist. Extensions of the theory to understand the sensitivity of extratropical summertime temperature distributions to climate change are discussed.