Polar Vertical Profile of Reflectivity - Warning Decision Training Division (WDTD)
Polar Vertical Profile of Reflectivity
Short DescriptionThe Polar Vertical Profile of Reflectivity (Polar VPR) product is derived from a full volume scan of quality-controlled base reflectivity. Its use is for bright band identification and identifying radars that are observing tropical rain in their domains.
Primary UsersNone. Primarily used as input to other algorithms (such as the Tropical Rain Identification) and products (such as the Height of Bright Band Top/Bottom).
Input SourcesRadar Reflectivity
Spatial resolution: one profile at each radar site
Temporal resolution: 5 minutes (per volume scan)
The MRMS Polar Vertical Profile of Reflectivity (VPR) includes six individual vertical profiles of reflectivity:
- Instantaneous global polar VPR
- Instantaneous convective polar VPR
- Instantaneous stratiform polar VPR
- Hourly mean global polar VPR
- Hourly mean convective polar VPR
- Hourly mean stratiform polar VPR
First, after the reflectivity has been quality controlled to remove non-precipitation echoes, volume scan pixels are classified as either convective or stratiform. In each region, the reflectivities are interpolated to predefined height fields and the mean at each level is computed. This will give the instantaneous VPR for a volume scan, for each the convective, stratiform, and combination (“global”) regions. The instantaneous VPRs are generated every 5 minutes from a full volume scan of quality-controlled base reflectivities. The hourly mean products for a given time are a running average of the corresponding instantaneous VPRs over the previous 60 minutes.
It is important to note that, unlike the Tilt Apparent VPR, the Polar VPR is NOT used for reflectivity adjustments. It used within criteria for the Tropical Rain Identification and Height of BB Top/Bottom.
The procedure for calculating them is described below:
- Quality control the base reflectivity from the current volume scan, in order to remove non-precipitation echoes, using the method described in the Dual Polarization Quality Control Algorithm (dpQC) documentation.
- Classify the QC’ed reflectivity as either convective or stratiform using the Convective/Stratiform Precipitation Separation (CSPS) algorithm.
- At this point, all calculations are completed separately for convective and stratiform bins. Therefore, only stratiform bins contribute to the stratiform VPR, and only convective bins for the convective VPR.
- Linearly interpolate reflectivities from the radar spherical coordinates onto the predefined height fields, only between the ranges of 20-80 km (to assure high vertical resolution).
- The height levels are 200 m apart, beginning at 500 m above radar level and ending at 20,000 m above radar level.
- Compute the mean reflectivity at each predefined height level (in dBZ) for each the convective and stratiform groups, and then for the combination of the two (“global”).
- Only the layers that pass certain thresholds of reflectivity (10 dBZ) and numbers of reflectivity observations (10) are used in the VPR; otherwise, a linear interpolation is done between the surrounding layers.
- This will give the three instantaneous polar VPRs for a volume scan. See Figure 1 for an example of each.
- For each the instantaneous convective, stratiform, and global polar VPRs, find the average of each type over the previous 60 minutes. a. This will give the three hourly mean polar VPRs.
Zhang, Jian, Carrie Langston, and Kenneth Howard. "Brightband identification based on vertical profiles of reflectivity from the WSR-88D." Journal of Atmospheric and Oceanic Technology 25.10 (2008): 1859-1872.
Zhang, J., K. Howard, S. Vasiloff, C. Langston, et al., 2011: National Mosaic and multi-sensor QPE (NMQ) system: description, results and future plans. Bull. Amer. Met. Soc., 92, 1321-1338.