scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
The role of gravity wave effects and stratospheric sudden warmings in modelling solar
signal propagation
Cnossen Ingrid 1 , Lu Hua 1 , Bell Christopher 2 , Gray Lesley 2
1 British Antarctic Survey, 2 University of Reading
We used a troposphere-stratosphere model of intermediate complexity to study the
atmospheric response to an idealized solar forcing in the subtropical upper stratosphere in
early winter. Our analysis focuses on the poleward and downward propagation of the solar
signal in the northern hemisphere, and we investigate two conditions that could influence this
propagation: 1) the type of representation of gravity wave effects in the model, and 2) the
presence or absence of Stratospheric Sudden Warming (SSW) events. Two sets of simulations
were performed: one with a traditional Rayleigh friction representation of gravity wave
effects (RF), and another with a Holton-Lindzen-type gravity wave scheme (GWS). Both
control simulations produce similar climatologies, but substantially different distributions of
SSW events, with the GWS distribution being most realistic. For the same forcing in the
subtropical upper stratosphere, larger and longer-lasting responses, which propagated further
poleward and downward, were obtained when the gravity wave scheme was used. The GWS
version of the model thus has a higher sensitivity to external forcing than the RF version.
When years with SSWs during early winter are excluded, the GWS results show an enhanced
signal in the troposphere, which appears to be not directly connected to signals in the
stratosphere, while signals appear to propagate more directly into the troposphere when
examining SSW years only. This suggests that different mechanisms of tropospherestratosphere
coupling are active during disturbed (with SSW) and undisturbed (without SSW)
conditions.