83rd Annual

Wednesday, 12 February 2003: 9:00 AM
Comparisons of LDAR network height and density data with WSR-88D echo top and SCIT reflectivity data
Nicholas W. S. Demetriades, Vaisala-GAI Inc., Tucson, AZ; and R. L. Holle and M. J. Murphy
Poster PDF (519.4 kB)
WSR-88D reflectivity data and the algorithms used to help meteorologists interpret these data are extremely important in nowcasting. However, a number of inherent problems arise when tracking thunderstorm cells with three-dimensional reflectivity. These problems include: (1) detecting thunderstorm cells at close range from the radar, (2) misidentification of a newly developed cell in the path of a preexisting Storm Cell Identification and Tracking (SCIT) identified cell as the new location of that preexisting SCIT cell, (3) identifying and tracking cells in a complex multi-cellular thunderstorm environment, (4) SCIT echo top altitude trends that exaggerate or misidentify thunderstorm growth and decay, and (5) volume scans that take 5 minutes to complete. Lightning Detection and Ranging (LDAR) provides another three-dimensional thunderstorm dataset that has the potential to both complement and supplement WSR-88D reflectivities. It detects the breakdown of lightning in three-dimensions with high time and spatial resolution.

Vaisala-GAI has compared thunderstorm cell identification, tracking and altitude trends from the SCIT algorithm with lightning data provided by LDAR. Lightning density plots were used for cell identification and tracking and many different methods were employed for tracking lightning cell altitude trends. LDAR has been able to identify cells that produced severe weather that were too close to radar to be identified by SCIT. LDAR has also been able to identify and track thunderstorm cells more accurately in complex multi-cellular environments. Two major reasons for this are (1) LDAR's higher spatial resolution than WSR-88D, and (2) the range of LDAR density data allowing a linear scale to be used instead of the logarithmic reflectivity scale of WSR-88D. LDAR density data have shown great continuity when trying to track thunderstorm cells. In many cases, lightning altitude trends have provided a large improvement over SCIT echo top trends for tracking thunderstorms growth and decay. A number of thunderstorms that exhibited exaggerated growth and decay from echo tops were better represented by lightning altitude trends. The exaggerated trends were partially due to echo tops from cells moving between different vertical tilts of the radar beam, and partly due to storms approaching the radar and gradually being caught in the cone of silence. One such cell had a monotonically decreasing echo top during a time period when the updraft strength appeared to be increasing, as indicated by LDAR maximum altitudes rising from 13 to 15 km and dime-sized hail being produced. Finally, the continuous data stream provided by LDAR allowed lightning altitude trends to be tracked on smaller time scales than the 5-minute updates of WSR-88D. This provided a higher level of detail for both thunderstorm growth and decay.

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