EESS Spring Seminar Series - Allison Steiner, Associate Professor, Atmospheric, Oceanic and Space Sciences, University of Michigan
EESS Spring Seminar Series - Allison Steiner, Assoc Professor, Atmospheric, Oceanic and Space Sciences, University of Michigan, "The surface forcing of atmospheric aerosols: From local observations to regional circulation", Abstract: The role of aerosols on land surface processes in observations and models is investigated from the local to the regional scale. We evaluate the local effect of atmospheric aerosols on observed sensible and latent heat fluxes from six FLUXNET sites and find that aerosol optical depth (AOD) greater than 0.5 reduces sensible and latent heat fluxes by about 10-30%, with some variations in partitioning by ecosystem. While this local effect is relatively small, a stronger aerosol-land surface feedback is simulated through the regional circulation. Decadal-length simulations with a regional climate model (the ICTP RegCM) at 25km resolution with and without anthropogenic aerosols reduces the top of the atmosphere (TOA) forcing by about 4-8 W m-2. This reduction in forcing is matched at the surface with greater magnitude, yet does not cause any significant change in surface air temperatures co-located with aerosol forcing. However, the southern Great Plains demonstrate a cooling of up to 0.5 K in response to a weakening of the GPLLJ circulation. This feature is robust across multiple summers and several model members with variable emission inventories. We hypothesize that the weakening of the GPLLJ is triggered by black carbon warming over the central US, thereby reducing the east-west geopotential gradient that drives the GPLJJ and altering convective precipitation patterns in the region.