| Atmospheric convection has a tendency organized on a hierarchy of scales ranging
from the mesoscale to the planetary scales, with the latter especially manifested
by the Madden–Julian oscillation. The present talk examines two major possible
mechanisms of self–organization identified in wider literature from a phenomenological
thermodynamic point of view by analysing a planetary-scale cloud–resolving model
simulation.
The first mechanism is self–organized criticality. A saturation tendency of precipitation
rate with the increasing column–integrated water, reminiscence of critical phenomena,
indicates self–organized criticality. The second is a self–regulation mechanism
that is known as homeostasis in biology. A thermodynamic argument suggests that
such self–regulation maintains the column–integrated water below a threshold by
increasing the precipitation rate. Previous analyses of both observational data as well as
cloud–resolving model (CRM) experiments give mixed results. A satellite data
analysis suggests self–organized criticality. Some observational data as well as CRM
experiments support homeostasis. Other analyses point to a combination of these two
interpretations.
In this study, a CRM experiment over a planetary–scale domain with a constant
sea–surface temperature is analyzed. This analysis shows that the relation between the
column–integrated total water and precipitation suggests self–organized criticality, whereas
the one between the column–integrated water vapor and precipitation suggests homeostasis.
The concurrent presence of these two mechanisms are further elaborated by detailed
statistical and budget analyses. These statistics are scale invariant, reflecting a spatial scaling
of precipitation processes.
These self–organization mechanisms are most likely be best theoretically understood by
the energy cycle of the convective systems consisting of the kinetic energy and the
cloud–work function. The author has already investigated the behavior of this cycle system
under a zero–dimensional configuration. Preliminary simulations of this cycle system over a
two–dimensional domain will be presented. |