A Theory of Summertime Temperature Variability

Abstract

A new theory of temperature variability presents fluctuations of near-surface temperature on timescales ranging from one day to one month as outgrowths of solar radiation and precipitation forcing and the coupling between the surface energy and moisture budgets. After a introductory chapter, we develop a diagnostic model of monthly average summertime temperature variability that uses observations of monthly solar radiation and precipitation to describe the pattern of summertime temperature variance across the extratropics. In the third chapter, we use this model to understand the projections of temperature variance projected by global climate models driven by increasing CO$_2$ emissions. The fourth chapter presents a treatment of heat waves, individual extremely hot days, and the way temperature distributions depend on the timescale of averaging. Summertime temperature variability is seen to be crucially dependent on a nonlinear feedback between soil moisture and temperature via the vapor pressure deficit - this non-linear feedback and the slowly evolving soil moisture timescale ensures that hot months contain an inordinate number of extremely hot days, which are shown to be filigree adorning the low-frequency precipitation-induced temperature variability.