18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Wednesday, 1 August 2001: 1:45 PM
Simple numerical simulations of convective lines with leading stratiform precipitation
Matthew D. Parker, Colorado State University, Fort Collins, CO; and R. H. Johnson
Poster PDF (1.3 MB)
As discussed by Parker and Johnson (2000), there exist three distinct modes of organization for midlatitude linear mesoscale convective systems: those with convective lines and trailing stratiform precipitation (TS), leading stratiform precipitation (LS), and parallel stratiform precipitation (PS). The dynamics of LS MCSs have yet to be elaborated. Parker et al. (2001) found that LS MCSs had unique lightning behavior among MCS archetypes, and continuing work suggests that LS MCSs may be fed by either lower tropospheric front-to-rear inflow or rear-to-front inflow. As well, while representing approximately 20% of the Parker and Johnson (2000) study population, LS MCSs are rarer than TS systems. In an effort to better understand the conditions necessary for the formation and maintenance of LS MCSs, as well as to better understand the feasibility and nature of a quasi-steady convective system in the LS configuration, the authors are currently performing idealized simulations of LS MCSs using the Advanced Regional Prediction System (ARPS).

In the numerical simulations, convection is initiated by inserting a mesoscale cold pool into a model environment defined by a typical pre-MCS thermodynamic sounding with a wind profile from archetypal LS MCSs. As in previously published modeling studies, the comparative strengths of the surface cold pool and the opposing low-level shear determine the rate at which a simulated convective system evolves toward a long-lived, rearward-sloping mesoscale updraft with attendant trailing stratiform precipitation. There exists in the model an optimal state in which upright convection above the nose of the cold pool is periodic, and the resultant system is quasi-steady, yet in which line-perpendicular storm-relative flow aloft advects hydrometeors toward the leading (inflow) side of the convective line. This structure has been the subject of some conjecture because inflowing air passes through pre-line precipitation before arriving at the system's convective line. The authors will present the kinematic structure of the MCS in this optimal simulation and the MCS's general effects on its environment, describing in particular the source of and modification to the system's inflowing air. Currently, the authors are also testing the simulated MCS's sensitivity to the wind and thermal profiles of the initial condition, and will comment on these results in their proposed presentation and extended pre-print abstract.

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