1. Principal Investigator (Co-PI - Daniel Weber)
Funding Agency: National Science Foundation Grant #ATM-0350539
Title: A study of moist deep convection: Generation of multiple updrafts in association with mesoscale forcing
Summary: The proposed work seeks to investigate the interaction of moist deep convection with mesoscale processes via new methods of initiating convection. The intent of this work is to investigate more realistic forcing from mesoscale processes on time scales that are much longer than the convective time scale with the goal of capturing the interaction between mesoscale forcing and convection. Specifically, the project team will investigate and observe the effects of several key environmental factors on the updraft and convective regeneration cycle of numerically simulated convection. The project team will apply, within a three-dimensional numerical cloud model, two initiating mechanisms, a constant near surface heat source and a momentum flux source within a non-dimensional parameter range study. These methods provide a continuous source of vertical motion that is consistent with environmental conditions commonly observed with organized convection. The results will be used to further classify and understand isolated multicellular thunderstorms.
Amount: $430,000
Period: 7/15/04-7/14/07
2. Co-Principal Investigator (PI - Lance Leslie, Co-PI - Michael Richman)
Funding Agency: National Science Foundation Grant # ATM-050297
Title: Detecting synoptic-scale precursors of tornado outbreaks
Summary: Historically, synoptic-scale signals have played an elusive role in discriminating between tornado outbreak days and severe thunderstorm days without substantial tornadic activity.A question that needs to be answered is: "To what extent are tornado outbreaks attributable to processes on the synoptic-scale rather than on the mesoscale and smaller?" To explore this question, a series of numerical simulations are proposed that commence from smoothed, "synoptic-scale " initial conditions". These simulations will be run for lead-times of one to three days. The exclusion of mesoscale observational data is necessary to establish a baseline for determining the relationship between synoptic-scale signals and tornado outbreaks.
The MM5 and OU-HIRES numerical models both are extensively tested mesoscale numerical models. The models will be initialized using composite gridded fields from the NCEP/NCAR reanalysis data, which has a horizontal grid spacing of about 200 km. A family of such composites will be developed using Empirical Orthogonal Functions (EOF) that filter the data such that only the dominant synoptic-scale modes are retained. A range of meteorological covariates, including CAPE, low-level wind shear, storm-relative helicity, relative vorticity, and relative humidity, will be used as proxy variables for the occurrence of tornadoes. The covariates are necessary, as even the most sophisticated mesoscale models currently can predict supercell formation and motion but are incapable of explicitly predicting tornadoes, now and in the foreseeable future. Because we have no a priori hypotheses, we will investigate the spatial and temporal correlations between the simulated fields associated with tornado outbreak cases and cases involving primarily non-tornadic severe weather.
Statistical exploration of the outbreak and non-outbreak cases will enhance our physical understanding of the relationships between the synoptic environment and tornado outbreaks. A high statistical correlation between the outbreak and non-outbreak cases implies that even the most important tornado events, major tornado outbreaks, are controlled primarily at sub-synoptic scales. This finding has clear and profound implications for observing strategies, and for research programs: observation and prediction of major tornado outbreaks will depend almost exclusively on sub-synoptic-scale measurements. Alternatively, if we find low correlations, further study aimed at diagnosis of those processes that connect the synoptic scales to tornado outbreaks is likely to prove very fruitful.
Amount: $352,278
Period: 01/16/05-01/15/08
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