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Structure of an Evolving Hailstorm, Part II: Thermodynamic Structure and Airflow in the Near Environment

J. C. FankhauserNational Center for Atmospheric Research, Boulder, Colo. 80303

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Abstract

A diverse set of mesoscale observations collected in the National Hail Research Experiment in connection with an evolving Colorado hailstorm is analyzed to determine the kinematic and thermodynamic structure of the near environmental and subcloud regimes. The analysis centers on multi–level aircraft measurements in the inflow sector and on mesoscale observations at the surface and aloft. Although considerable evolution was observed in overall radar echo development patterns, changes in one of the many storms detected occurred in a systematic and periodic manner. The instantaneous structure of the subcloud inflow into this storm is emphasized in the present work.

Surface and aircraft data substantiate the following characteristics. Inflow air approached the front of the storm, originating from a very shallow layer (≤5 m) near the ground and at a considerable distance (≥20 km) upstream in the relative wind direction. Inflow air rose unmixed to at least cloud base, feeding the main updraft which was inclined upward in a direction opposite to the storm movement. Discrete inflow–updraft branches were found to be supporting coexisting cells in varying stages of development. These had lateral widths of 6–8 km and were separated by regions of weak subsidence. Downdraft air approached the storm from the right flank at mid-cloud level and at least a portion descended unmixed the ground in the strongest downdrafts.

Abstract

A diverse set of mesoscale observations collected in the National Hail Research Experiment in connection with an evolving Colorado hailstorm is analyzed to determine the kinematic and thermodynamic structure of the near environmental and subcloud regimes. The analysis centers on multi–level aircraft measurements in the inflow sector and on mesoscale observations at the surface and aloft. Although considerable evolution was observed in overall radar echo development patterns, changes in one of the many storms detected occurred in a systematic and periodic manner. The instantaneous structure of the subcloud inflow into this storm is emphasized in the present work.

Surface and aircraft data substantiate the following characteristics. Inflow air approached the front of the storm, originating from a very shallow layer (≤5 m) near the ground and at a considerable distance (≥20 km) upstream in the relative wind direction. Inflow air rose unmixed to at least cloud base, feeding the main updraft which was inclined upward in a direction opposite to the storm movement. Discrete inflow–updraft branches were found to be supporting coexisting cells in varying stages of development. These had lateral widths of 6–8 km and were separated by regions of weak subsidence. Downdraft air approached the storm from the right flank at mid-cloud level and at least a portion descended unmixed the ground in the strongest downdrafts.

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