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DTSTAMP:20260410T025733Z
DESCRIPTION: \n\nStudent Seminar Series\n\nDepartment of Atmospheric & Ocea
 nic Sciences\n\npresents\n\na talk by\n\nMatthew HenryPhD candidate\n\nDec
 omposing the Drivers of Polar Amplification with a Single Column Model\n\n
 The Arctic amplification of surface temperature change is a common feature
  of both models and observations. The lapse rate feedback dominates the at
 tribution to forcings and feedbacks of polar surface warming under increas
 ed CO2. The surface temperature change attribution method based on top-of-
 atmosphere (TOA) energy budget changes assumes forcings and feedbacks lead
  to vertically uniform temperature changes\, and accounts for the deviatio
 n from vertically uniform warming by assigning it to the lapse rate feedba
 ck. Here\, we decompose the temperature change while accounting for the ve
 rtical structure of the temperature change contributions from each forcing
  and feedback. An idealized moist atmospheric General Circulation Model (G
 CM) with slab ocean boundary conditions\, no clouds or sea ice is forced w
 ith a quadrupling of CO2 concentrations with and without a polar surface h
 eat source. It is shown to have a polar amplified pattern of surface tempe
 rature change comparable to comprehensive GCM simulations. Then\, we use a
  single column model to decompose the tropical and polar temperature chang
 e from the idealized GCM into contributions from forcings and feedbacks ex
 cluding the temperature feedback\, by individually perturbing the CO2\, wa
 ter vapor and energy transport. The warming from increasing longwave absor
 bers (CO2 and water vapor) is bottom-heavy and accounts for most of the su
 rface warming in the absence of a surface heat source\, whereas the warmin
 g from atmospheric heat transport preferentially warms the mid and upper a
 tmosphere. The warming from CO2 alone is polar-amplified as tropical conve
 ction moves the warming maximum to the upper troposphere. Adding the `loca
 l' water vapor feedback preferentially warms the tropical surface temperat
 ure\, which cancels polar amplification. And\, adding the atmospheric ener
 gy transport and its implied water vapor change contributes to further pol
 ar amplification. The surface heat source\, which could represent oceanic 
 heat transport convergence or the surface albedo feedback\, increases pola
 r surface warming and is only partially compensated by a decrease in dry a
 tmospheric energy transport. While this decomposition is applied to an ide
 alized GCM\, we hope it can be generalized to a fully comprehensive GCM.\n
 \nWednesday Sep 25/ 2.30 PM/ Room 934 Burnside Hall\n\n \n\n \n\n \n
DTSTART:20190925T183000Z
DTEND:20190925T193000Z
LOCATION:Room 934\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue 
 Sherbrooke Ouest
SUMMARY:Decomposing the Drivers of Polar Amplification with a Single Column
  Model
URL:https://www.mcgill.ca/channels/channels/event/decomposing-drivers-polar
 -amplification-single-column-model-300649
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