Method to estimate radar echo top height. This technique uses a volume scan to determine the maximum elevation angle at which a certain reflectivity threshold is exceeded. This is based upon the work of Lakshmanan et al. (2013).
Instead of simply finding the highest elevation angle within a volume, or a virtual volume where reflectivity exceeds some threshold, the modified algorithm is as follows:
- Find the maximum elevation angle (θb) where reflectivity (Zb) exceeds the echo-top reflectivity threshold.
- If θb is not the highest elevation scan in the virtual volume, obtain the reflectivity value (Za) at the next higher elevation angle (θa). Then, the echo-top height is given by the height of the radar beam at an elevation angle:
where ZT is the threshold value (e.g., 0 dBZ, 18 dBZ) used to compute the echo top.
- If θb is the highest elevation scan available, set . This condition is met far away from the radar if higher-elevation scans have shorter ranges than a base “surveillance” scan and very close to the radar if the highest-elevation scan does not sample the top of the cloud. Under these circumstances, θT is set to be the top of the beam containing dBZ ≥ ZT; that is, the traditional echo-top algorithm is followed when there are no data available from a higher-elevation scan.
This module requires numpy and numba.
1. Lakshmanan, V., Hondl, K., Potvin, C. K. & Preignitz, D. An Improved Method for Estimating Radar Echo-Top Height. Weather Forecast. 28, 481–488 (2013).