**The linkage of tropical/extratropical coupling with the
stratosphere-troposphere coupling: A global mass circulation view in the
isentropic coordinate**

**Ming Cai**, Department of Meteorology, Florida State University

Using the NCAR/NCEP reanalysis in the isentropic coordinate, we here
present evidence suggesting that the out-of-phase relationships of
temperature anomalies both between the low and high latitudes and
between the stratosphere and troposphere are intimately related to the
meridional and downward propagation of anomalies of both signs. The
temperature anomalies propagate poleward and downward above the
tropopause and propagate equatorward below the tropopause. The
characteristic time scale for anomalies of one polarity to propagate
from the equator to the pole (or the half period of the complete cycle)
is about 40-70 days. The relatively slow meridional propagation helps to
explain the well-known seesaw oscillatory pattern between low and high
latitudes found in monthly data. The equatorward propagation in the
troposphere is synchronized with the poleward propagation of the
stratospheric temperature anomalies of the opposite sign in both low and
high latitudes, responsible for the out-of-phase relation between the
stratospheric and tropospheric temperature anomalies in the polar
region. Accompanied with warm (cold) anomalies is a successive levelling
(steepening) of isentropic surfaces propagating poleward and downward.
The zonal wind anomalies follow the poleward and downward propagating
temperature anomalies of the opposite sign.

A global mass circulation paradigm is proposed to qualitatively explain
the simultaneous meridional and downward propagation of circulation
anomalies that appears responsible for the annular mode variability. The
global mass circulation paradigm also relates the
stratosphere-troposphere coupling in the extratropics to heating
anomalies in the tropics via the tropical-extratropical coupling in the
stratosphere. When the mass circulation is weaker, the isentropic
surfaces in the extratropical stratosphere (troposphere) are steeply
(gently) sloped, corresponding to the positive phase of the annular
mode. The cold air mass is effectively imprisoned within the polar cap
when the mass circulation is weaker, responsible for warm surface
temperature anomalies prevailing in the extratropics. Meantime, the
weaker mass circulation also implies a temporary reduction of air mass
supply over the polar cap, leading to a negative surface pressure
anomaly. The warm anomalies brought by the stronger mass circulation
cause a lowering of isentropic surfaces in the polar stratosphere,
resulting in more gently sloped isentropic surfaces in the extratropical
stratosphere. This corresponds to the negative phase of the annular mode
in which the meridional temperature gradient in the extratropical
stratosphere is weaker accompanied with a weakened polar jet and a
falling of the tropopause. The stronger warm air branch of the mass
circulation aloft requires a strengthening of the compensating
equatorward advancement of the surface air mass, causing massive cold
air outbreaks in the extratropics. The more air mass aloft brought by
the stronger mass circulation contributes to a rising of the surface
pressure over the polar cap till the surface cold air moves out. This
explains why the surface pressure anomalies in high latitudes are
positive during the negative phase of the annular mode.