Brightband Delineation and Dual-Pol VPR Corrections for QPE Improvements in MRMS

Radar-based quantitative precipitation estimation (QPE) in the Multi-Radar Multi-Sensor (MRMS) system is derived from the reflectivity field when the radar observations are within or above the melting layer. To reduce errors associated with the bright band or when the radar beam overshoots precipitation at further ranges from the radar, an apparent vertical profile of reflectivity (AVPR) correction was implemented. This AVPR correction is derived from the reflectivity profile only, and assumes that the bright band structure is predominantly isotropic. However, this isotropic AVPR correction becomes less effective in instances of non-isotropic bright band structure due to underlying terrain influences or by variable vertical motions, or when the meting layer low enough such that the full bright band structure cannot be observed.

Using dual-polarization variables, a more accurate detection of the bright band areal extent and melting layer top and bottom heights can be obtained. This information can be used to implement a radially-dependent AVPR model which can better correct reflectivity in instances of non-isotropic bright bands. This algorithm was tested on multiple cases across the CONUS with varying bright band intensities, structures, and melting layer heights. The radially-dependent AVPR correction provided a more accurate delineation of bright band areas and a more effective reduction in QPE errors within and above the bright band than the prior isotropic AVPR correction, especially for precipitation events with low melting layers or with strong variability of vertical motions.