Observations
There are many atmospheric variables which can
be used to provide observations of Walker-type circulation cells. Here we
examine, vertically integrated atmospheric heating and vertical velocities;
but it should be mentioned that observations of precipitation, Outgoing Longwave
Radiation (OLR), velocity potential, and lower- and upper-level divergence
and divergent winds, are also good indicatiors for Walker-type circulations.
All of the data used here is from the NCER/NCAR Reanalysis (http://cdc.noaa.gov/)
.
Column Heating: The
dynamics of Walker-type cells consists of atmospheric
warming columns (convection) coupling with cooling columns (subsidence).
Time averaged observations of vertically integrated heating show this phenomena
for July, Figure 6.
Figure 6. Vertically integrated
diabatic heating, provided by the NOAA-CIRES
Climate Diagnostics Center, Boulder, CO, website located at http://cdc.noaa.gov/.
Vertical Velocity: If we look at observations of the vertially
integrated vertical velocity (omega), (Figure 7)
we see the same spatial structure of flow as above.
Figure 7. JJA vertically integrated
omega contours in 0.01 Pa/s, overlayed with 200mb rotational wind field and
divergent vector winds. Blue
omega contours correspond with rising air and red contours with sinking air.
To examine the closed behavior of atmospheric Walker-type cells,
we look at their meridonally or zonally averaged form and use our mass conservation laws. Using the same omega data,
below we show the MMC (Figure 8), where omega
has been zonally averaged around the globe. We can also depict a Mean
Zonal Circulation (MZC) by averaging meridionally over the area of interest,
here from [50S-50N] (Figure 9). Upon analyzing the
mass conservation balances associated with the MMC&
MZC, one can find that Walker-type circulations
are indeed closed
.
Figure 8. Zonally averaged
[0-360] omega and divergence depict the MMC along with mass conservation
laws.
Figure 9. Meridionally
averaged [50S-50N] omega
and divergence depict the MZC along with mass conservation laws.