Numerical Studies on Time Variations of the Troposphere-Stratosphere Coupled System.

Abstract

Interannual variation is a year-to-year variation which is defined as a deviation from the climatolog-ical annual cycle of a meteorological quantity. It can be caused by a variation of an external forcing of the atmospheric circulation system, or can be generated internally within the system. On the other hand, intraseasonal variation is a low-frequency variation within a season, and it is basically considered to be a result of internal processes which may exist even under constant external conditions. In this article, some observational facts on the intraseasonal and interannual variations of the polar stratosphere are presented, and the use of a hierarchy of numerical models to understand the strato-spheric variations is reviewed systematically. Numerical models can be roughly divided into three classes based on their complexity; simple low-order models, medium mechanistic circulation models, and complex general circulation models. In order to understand the stratospheric variations, a hierarchy of stratosphere-only models have been used under an assumption of ''slave stratospheric-variations'' or ''independent stratospheric-variations''. Parameter sweep experiment, in which many trials of computations in parameter space are done by sweeping the value of a control parameter, is a powerful method to understand complex behavior in the models. Recently, however, the importance of the coupled variability of the troposphere and the stratosphere was pointed out for the intraseasonal and interannual variations. In addition to numerical studies with simple or complex models, we have done some parameter sweep experiments with three-dimensional mechanistic circulation models to understand the troposphere-stratosphere coupled variability. All the effects of external forcings that might cause interannual variations can be excluded in the numerical experiments to focus only on internally generated variations within the coupled system. The obtained intraseasonal and interannual variations have some similar characteristics of the real atmosphere in some realistic parameter ranges. Roles of the interannual variations of the external forcings are discussed , which might be significant even if the amplitude is small.

Middle atmosphere response to the solar cycle in irradiance and ionizing particle precipitation

“…The Brewer-Dobson circulation change has three layers between 50 • and 80 • N with increased strength below 25 km, weakening between 25 and 40 km and an increase above only to 75 • N. However, the Brewer-Dobson circulation change is not statistically significant. This highlights the limitations of using the Student-t test for the atmosphere, which has non-Gaussian statistics (e.g., Yoden et al, 2002). Presumably there is a unique meridional circulation change associated with the zonal wind change.…”

Changes in Frequency of Major Stratospheric Sudden Warmings with El Niño/Southern Oscillation and Quasi-Biennial Oscillation

“…The extratropical stratosphere is affected by several external factors (e.g., Yoden et al 2002). This study focuses on changes of the Northern winter stratosphere with El Niño/Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO).…”

“…We do not take account of effects of other factors such as the solar cycle, volcanic eruptions, extratrop-ical SST anomalies, global warming, and so on, which will also affect the Northern extratropical stratosphere (e.g., Yoden et al 2002). In particular, the combination of the QBO and solar cycle is known to induce nonlinear changes of the Northern polar vortex (e.g., Baldwin et al 2001;Anstey and Shepherd 2014).…”

A Minimal Model of QBO-Like Oscillation in a Stratosphere-Troposphere Coupled System under a Radiative-Moist Convective Quasi-Equilibrium State

“…In a laboratory analogue of the QBO, a standing internal gravity wave was forced mechanically at the bottom boundary (Plumb and McEwan 1978) or at the top (Otobe et al 1998) of an annulus of salt-stratified water. The separation is a theoretical idealization under an assumption of "independent stratospheric variations" in stratosphere-only models (Yoden et al 2002).…”

“…Dynamical coupling between them in the extra-tropics has drawn much attention over recent years (see, e.g., Yoden et al 2002), whereas relatively little attention has been paid to the coupling in the tropics, in particular, to the downward influence of the stratosphere to the troposphere. Only a few observational studies have shown some evidence of the downward influence of the stratospheric QBO.…”