Stratospheric Multiple Equilibria and Seasonal Variations

Wakata, Yoshinobu; Uryu, Michiya

doi:10.2151/jmsj1965.65.1_27

Cited by 11 publications

(4 citation statements)

References 19 publications

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“…Much simple height-only b-channel models have also been used to understand the nature of seasonal and interannual variations (e.g., Wakata and Uryu 1987;Plumb 1989;Yoden 1990). Yoden (1990) performed an experiment by varying dU R =dz in the HM model periodically with an annual component for various values of h B , but obtained only periodic annual response, or seasonal variation.…”

Section: Use Of Stratosphere-only Modelsmentioning

confidence: 99%

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

Yoden

Taguchi

Naito

2002

Journal of the Meteorological Society of Japan

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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.

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Section: Use Of Stratosphere-only Modelsmentioning

confidence: 99%

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

Yoden

Taguchi

Naito

2002

Journal of the Meteorological Society of Japan

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“…In an effort to include a more realistic troposphere, we incorporate a lower boundary at the surface where both the mean wind and wave components are internally determined. The boundary condition we use was first developed by Tung [1983] and has been used by Robinson [1985], Wakata and Uryu [1987], and Yoden [1987] in their quasi‐geostrophic β‐plane model studies.…”

Section: Model Descriptionmentioning

confidence: 99%

A mechanistic model of the northern annular mode

Eichelberger

Holton

2002

J. Geophys. Res.

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[1] The northern annular mode (NAM) is the leading mode of variability in the Northern Hemisphere. The NAM consists of a meridional dipole of the zonal mean zonal wind that extends into the stratosphere during the winter season. During the high-index state of the NAM, high-latitude westerly winds are stronger than normal, leading to a stronger and colder polar vortex. Over the past few decades, observations show a trend toward higher NAM index values. To investigate whether this trend is a result of natural variability or is related to greenhouse warming, a mechanistic model is developed that provides a simple analogue of the NAM. The model represents the interaction between the zonally symmetric flow and planetary waves for two meridional modes of variation. Greenhouse warming is specified in the model by varying the radiative equilibrium meridional temperature gradient. Variations in the second meridional mode qualitatively resemble those of the observed NAM. Model runs that correspond to larger greenhouse gas concentrations yield on average higher NAM index values.

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“…The existence of the two distinct circulation regimes having a strong or weak polar night jet is more clearly seen in a one-dimensional mechanistic model [Holton and Mass, 1976;Chao, 1985]. In fact, two stable steady state solutions are found for this one-dimensional mechanistic model with winter conditions, while there is only one in summer [Yoden, 1987;Wakata and Uryu, 1987]. With a more realistic three-dimensional model, the bifurcation property of modes is still observed from fall to winter, although it becomes somewhat fuzzy [O'Sullivan and Dunkerton, 1994].…”

Section: A Characteristic Variation Of Time Coefficients Of the Eofmentioning

confidence: 99%

On the origin and nature of the interannual variability of the winter stratospheric circulation in the northern hemisphere

Kodera¹

1995

J. Geophys. Res.

128

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During the northern hemisphere winter, the stratospheric circulation exhibits quite large interannual variability. In the present study, the nature and origin of the interannual variation in the winter stratosphere is studied with two different approaches: one is composite analysis assuming a priori four possible causes: solar activity, equatorial quasi‐biennial oscillation (QBO), volcanic aerosols, and unknown cause producing trends, while the other is an extended empirical orthogonal function analysis (E‐EOF). The results of composite analysis show that in November, anomalous zonal‐mean zonal winds and meridional temperature gradients are found in accordance with the assumed forcings in different regions in the stratosphere. As winter progresses, however, anomalous patterns in zonal wind become similar by forming a dipole‐type pattern and extend down into the troposphere. The common features of the evolution of the anomalies during the winter can be well explained by the first mode of the E‐EOF. The results of the present study suggest that interannual variability in the winter stratosphere in the northern hemisphere can be considered an internal mode of variability triggered by changes in forcing, such as solar activity, equatorial QBO, and volcanic aerosols. Although overall features of the evolution of zonal‐mean zonal wind associated with trends are similar, the cause of the trends is still undetermined.

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Stratospheric Multiple Equilibria and Seasonal Variations

Cited by 11 publications

References 19 publications

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

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

A mechanistic model of the northern annular mode

On the origin and nature of the interannual variability of the winter stratospheric circulation in the northern hemisphere

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