Talk by Jan Haerter – Københavns Universitet

Talk by Jan Haerter

Title: Convective organization and precipitation - two sides of the same medal

Abstract: Convective clouds have long been one of the key uncertainties in climate projections and they have traditionally been hard to incorporate explicitly in numerical simulations of the global climate due to their small ("sub-grid") spatial extent (few km). It has therefore remained unclear, how increasing global temperatures might affect the radiative properties, lifetime or precipitation produced by these clouds. To make matters more complicated, it has recently been discovered and confirmed, that convective-type clouds produce extreme precipitation with intensities exceeding the Clausius-Clapeyron rate of increase as temperatures rise - hence ruling out equilibrium thermodynamics as a null model. Indeed, observations have long shown that convective clouds have complex dynamics, with convective cells interacting: The outflow from decaying cells can often bring about new events in the vicinity, under certain conditions leading to larger scale structures, such as mesoscale convective systems. 

Through recent high-resolution numerical simulations, we have shown that these clouds not only interact, but the interaction has direct consequences for precipitation intensities and extremes. Precipitation and organization may hence be two sides of the same medal, with the two feeding back on one-another. Bringing temperature back into the picture, we look for "universal" features, both of precipitation intensity and organization, that are invariant under modification of the temperature boundary conditions.