A key to the mesoscale Quantitative Precipitation Forecast (QPF) problem
is our lack of understanding of the definitive processes and mechanisms
responsible for the wide range of observed modes and evolution of precipitating
systems. At the National Severe Storms Laboratory (NSSL), we continue to
study the entire life cycle of summertime precipitation, from convective
initiation through the lifetime and demise of mesoscale convective systems.
Such a large effort is necessarily composed of a wide range of linked efforts,
including modeling, theoretical, and field studies, with synthesizing analyses.
TIMEx will be a series of field programs and analyses designed to answer
specific questions concerning convective initiation.
One of the fundamental issues in precipitation forecasting is the timing
and location of the initiation of convection, or, in many cases, the failure
of initiation. Clearly, any precipitation forecast will fail completely
if initiation is forecast and fails to occur, and vice versa. Further,
quantitative errors are strongly dependent on errors in the location and
time of initiation. For example, recent work on seabreeze, terrain-induced
convergence band, and dryline case studies shows the strong dependence
of convection initiation upon:
- the trajectories that parcels follow while rising from the ground
toward the level of free convection;
- the amount of mixing that occurs along these plumes of moisture;
- the low-level temperature and humidity stratification.
In turn, the foregoing depend on the shear profile and variations in
the vertical motion field associated with boundaries. None of these processes
are adequately understood, and appear to be misrepresented in mesoscale
models in the presence of weak larger-scale forcing.
The focus for TIMEx is ONLY convective initiation; other possible focii
are (or will be) addressed in related (or subsequent) efforts.
Following the example of VORTEX, testable hypotheses are being refined and
debated among a group of Principal Investigators, whose membership is determined
by said debate. Initial meetings and related discussion have prompted evolution
in plans and approaches (see “History”), according to the observations required
to test the hypotheses. Some hypotheses can be tested with existing systems,
and detailed experiment plans, designed specifically to evaluate the hypotheses,
can be developed and discussed at the discretion of the PIs. As these plans
mature, they will become the basis for the development of proposals to appropriate
funding agencies. Other hypotheses require the development of new or improved
observing systems. The PIs who need these new systems are working directly
and indirectly to support such development, and their plans and efforts
will be posted here.
There is no over-arching funding available to support this observational
and analysis effort. All activities will be contingent on the acquisition
of sufficient resources. All PIs will be expected to provide/obtain their
own support to participate, and are expected to contribute some level
of resources toward related group efforts.