Stratosphere Modeling
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One of the important missions of CCSR is to study atmospheric behaviors in the stratosphere. The stratosphere is characterized by stronger wave signals due to lower atmospheric density and stable stratification of the atmosphere. The wave signals are mainly generated in the troposphere and penetrate the stratosphere. The nonlinear effects of the stronger wave signals cause interesting phenomena. Further, there are some climate changes in the stratosphere, including the stratospheric ozone hole (not only the Antarctic but also the Arctic).
The Quasi-Biennial Oscillation (QBO) in the equatorial lower
stratosphere simulated in the CCSR climate model is presented in
Figure 1. This is the first realistic simulation in the climate model.
The figure shows that the simulated QBO is quantitatively similar to
the observed. There is a long history of efforts to get the QBO in the
general circulation model (GCM). However, all were unsuccessful until
recently, when our group succeeded.
Besides the equatorial lower stratospheric QBO, there are various
inter-annual variations in the stratosphere. These variations are
related to those in the troposphere. Figure 2 shows the mutual
interaction between the equatorial QBO and tropospheric motion. When
the equatorial QBO is easterly (westerly) phase, the polar night jet
in the northern hemispheric winter is weaker (stronger) than average.
The correlation is also connected to the westerly jet in the
troposphere. The climate effect of the stratosphere on the troposphere
is being studied.
[Figure 1]: Time-height cross section of zonally averaged zonal wind over the equator. Warm colors show westerly winds, and cold colors easterly winds.
[Figure 2]: Latitude-height cross section of the difference of zonally averaged zonal wind between the easterly phase and the westerly phase (Easterly-Westerly) of the equatorial QBO.
Chemistry and transport problems of minor constituents in the
atmosphere are also being studied. For example, we are studying the
ozone hole problem in the polar lower stratosphere using CCSR GCM. In
the model, there are many chemical species, including CH4 and N2O as
green gas species; Freon, NOX, HOX, ClOX, and polar stratospheric
clouds (PSC). These species are treated as prognostic variables in the
GCM and varies interactively modifying temperature fields through
radiative effects.
[Figure 3]: Global distribution of the calculated ClONO2 at the height of 50hPa in October.
Figure 4 shows a simulated ozone QBO in the GCM corresponding to the mean zonal wind QBO as shown in Figure 1. The behavior of ozone QBO is similar to the observed. This example shows a close relationship between atmospheric motion and chemical species.
[Figure 4]: Time-height section of a simulated ozone QBO in the GCM corresponding to the mean zonal wind QBO as shown in Fig. 1.
Figure 5 shows the model simulated total ozone distribution over the Antarctic in October. Including the polar stratospheric clouds in the chemical model, we are now developing the model to simulate the ozone hole in the polar lower stratosphere and to see the climate effects of the ozone hole.
[Figure 5]: Distribution of the calculated total ozone in October.
There are also mesoscale atmospheric motions in the stratosphere. These are phenomena of gravity wave activities due to atmospheric stratification in the stratosphere. Figure 6 shows gravity wave propagations into the stratosphere, generated around mid-latitude cyclones in the troposphere. The generation of the gravity waves around the mid-latitude cyclones is interesting because of the momentum balance of general circulation.
[Figure 6]: Time-height section of simulated meridional wind at 34N. The figure shows gravity wave propagation into the stratosphere, generated around mid-latitude cyclones in the troposphere.
Figure 7 shows the meridional distribution of global spectra of gravity waves, indicating relative intensity of gravity wave of each frequency. Global distribution by observation, such as in Figure 7, has not been composed yet. These are important results. The gravity waves make important contributions to the temperature and zonal wind structures in the troposphere and stratosphere. These dynamic problems are being considered.
[Figure 7]: Frequency-latitude distribution of gravity wave spectra around 25-30 km height level (lower stratosphere).
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