Mesoscale Convective Systems in Weakly Forced Large-Scale Environments. Part II: Generation of a Mesoscale Initial Condition

David J. Stensrud NOAA/ERL/National Severe Storms Laboratory, Norman, Oklahoma

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J. Michael Fritsch Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Abstract

A series of five mesoscale convective systems (MCSs) developed within a weakly forced large-scale environment on 11 and 12 May 1982. Two of these systems had a large component of motion against the midtroposphoric flow and propagated in a direction nearly opposite to that of the traveling upper-level disturbances. This description of the evolution of convection is very different from traditional ones in which convection develops and moves more or less in phase with traveling upper-level disturbances. Observations indicate that the initiation and evolution of convection are tied to mesoscale features that are not well observed by the conventional observing network, making the structure of the model initial condition a potentially crucial factor in the success or failure of any subsequent numerical simulation.

It is found that the initial conditions created using the conventional initialization procedure of The Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model do not include several of the mesoscale-sized features observed at 1200 UTC 11 May 1982, 9 h before the development of the first MCS. This is attributed to the lack of observed data with mesoscale resolution, and, therefore, likely is a deficiency in most initialization procedures in use today. Although it is true that new operational observing systems, such as the WSR-88D radar and the 404-MHz radar wind profilers, provide more detailed information, the data density on the mesoscale remains subcritical. A methodology to include mesoscale features, based upon using subjective interpretations of all the available observations, is developed. 11 is found that the mesoscale initial condition created using this subjective approach produces a more reasonable representation of the observed mesoscale features in comparison with the conventionally produced initial condition.

Abstract

A series of five mesoscale convective systems (MCSs) developed within a weakly forced large-scale environment on 11 and 12 May 1982. Two of these systems had a large component of motion against the midtroposphoric flow and propagated in a direction nearly opposite to that of the traveling upper-level disturbances. This description of the evolution of convection is very different from traditional ones in which convection develops and moves more or less in phase with traveling upper-level disturbances. Observations indicate that the initiation and evolution of convection are tied to mesoscale features that are not well observed by the conventional observing network, making the structure of the model initial condition a potentially crucial factor in the success or failure of any subsequent numerical simulation.

It is found that the initial conditions created using the conventional initialization procedure of The Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model do not include several of the mesoscale-sized features observed at 1200 UTC 11 May 1982, 9 h before the development of the first MCS. This is attributed to the lack of observed data with mesoscale resolution, and, therefore, likely is a deficiency in most initialization procedures in use today. Although it is true that new operational observing systems, such as the WSR-88D radar and the 404-MHz radar wind profilers, provide more detailed information, the data density on the mesoscale remains subcritical. A methodology to include mesoscale features, based upon using subjective interpretations of all the available observations, is developed. 11 is found that the mesoscale initial condition created using this subjective approach produces a more reasonable representation of the observed mesoscale features in comparison with the conventionally produced initial condition.

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