Séminaire
The high-latitude vertical structure of temperature is poorly understood, yet is an important factor in the polar amplification of climate change. To better understand the high-latitude lapse rate and its sensitivity to various forcings, we explore two perspectives on the high-latitude temperature structure.
The first is the Lagrangian perspective of Arctic air formation. We prescribe the initial sounding of the atmosphere representing an air column starting over the ocean, then allow the air mass to evolve for two weeks in the absence of any solar heating, representing the movement of the air column over a high-latitude continent. Using a single-column model, we find that a low-cloud feedback slows cooling of the surface and amplifies continental warming, increasing the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature.
The second is the Eulerian perspective of radiative-advective equilibrium. High latitude temperature profiles are generally stable to convection, with frequent surface-based inversions, especially in winter. Such profiles result from the stabilizing influences of
advective heat flux convergence and atmospheric solar absorption, which dominate over the destabilizing influences of surface solar absorption and subsurface heating. We formulate an analytical model that represents the dominant balance between advective heating and radiative cooling, and discuss how climate feedbacks in this state depend on the type of forcing.
Speaker’s website:
http://people.fas.harvard.edu/~timothywcronin/
marie-pierre.lefebvre@lmd.jussieu.fr