ESRL/PSL Seminar Series

Global-scale convective aggregation and the Madden-Julian oscillation.

Nathan Arnold
Colorado State University

Abstract


The Madden-Julian Oscillation is the dominant mode of tropical intraseasonal variability, but its dynamics remain poorly understood. In the first half of this talk I will argue that the MJO is a large scale consequence of a tendency for convection to self-aggregate. Simulations with a super-parameterized model of a non-rotating atmosphere with globally uniform boundary conditions show that convection self-organizes into large (~4000km) clusters surrounded by dry regions. A moist static energy budget indicates this aggregation is driven by diabatic feedbacks, particularly cloud-longwave interaction. When rotation is restored the model simulates a robust MJO, and mechanism denial experiments confirm the importance of longwave heating to both aggregation and the MJO. Non-rotating simulations using a conventional model with a weak MJO show a much weaker tendency to aggregate.

The second half of the talk will consider the MJO response to global warming. Two sets of warming experiments with super-parameterized models show large increases in MJO activity in response to increased SST. Moist static energy budgets suggest the stronger MJO is driven by vertical MSE advection, which becomes increasingly destabilizing at high temperatures. The change in advection is due to a steepening of the mean vertical MSE profile in the lower troposphere, a thermodynamic consequence of warming.


1D-403
Tuesday, Mar 4
2:00pm
Seminar Coordinator: barbara.s.herrli@noaa.gov


SECURITY: If you are coming from outside the NOAA campus, you must stop at the Visitor Center to obtain a vistor badge. Please allow 10 extra minutes for this procedure. If you are a foreign national coming from outside the NOAA campus, please email the seminar coordinator at least 48 hours prior to the seminar to provide information required for security purposes.

Past seminars: 1996-2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | 2014