Julia Windmiller - The moist and dry tropics - Is the tropical atmosphere bistable?

Event type: 
24 April 2020
4.00pm - 5.00pm

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Dr. Julia Windmiller
Max Planck Institute of Meteorology, Hamburg
Climate Change Research Centre

Atmospheric humidity plays an important role for the radiative properties of the atmosphere and the formation of deep convection. In this presentation, Julia will focus on a peculiarity of the vertically integrated humidity content of the tropical atmosphere, namely its tendency to be either moist or dry. This tendency can, for example, be inferred from the bimodal frequency distribution of column integrated humidity. Interestingly, idealized simulations of the tropical atmosphere suggest that this bimodality does not exist because of any external forcing but because of processes which lead to a moistening of already moist regions and a drying of already dry regions. This indicates that the tropical atmosphere is bistable with respect to humidity perturbations. In addition to discussing a method to diagnose this bistability in reanalysis data and in idealized simulations, I will also discuss possible implications for the spatial evolution of the humidity field. In particular, I suggest that the humidity field tends to minimize the boundary length between the moist and dry regions. In the absence of any disturbing processes, that evolution may be represented analogous to surface tension.

Brief Biography: Julia Windmiller is a PostDoc at the Max Planck Institute of Meteorology in Hamburg where she studies tropical convection. Julia holds a Master’s degree from the Ludwig-Maximilians University in Munich, and she received her PhD from the Meteorological Institute Munich.