Improving precipitation estimates from weather radar using quality control and correction techniques

Abstract

Errors and uncertainty in radar estimates of precipitation result both from errors in the basic measurement of reflectivity and from attempts to relate this to the precipitation falling at the ground. If radar data are to be used to their full potential, it is essential that effective measures are taken to mitigate these problems. The automatic processing of radar data that forms part of the UK Met. Office's Nimrod system addresses a number of specific sources of error. These include the identification and removal of spurious echoes resulting from anomalous propagation of the radar beam, errors resulting from variations in the vertical profile of reflectivity and radar sensitivity errors. Routine verification of the surface precipitation estimates has been undertaken, largely through comparison with rain gauge observations, over a range of timescales, which has allowed the benefits of the quality control and correction processes to be quantified. Although the improvement derived varies according to the dominant synoptic situation, an average reduction in the root‐mean‐square difference between gauge and radar data of 30% can be achieved. Copyright © 2000 Royal Meteorological Society

A high‐resolution radar experiment on the island of Jersey

“…The reflectivity was transformed to an estimate of rain rate using the Marshall and Palmer equation, that is, Z = 200R 1.6 (Marshall et al, 1955) which is valid for stratiform precipitation. This equation seems to work well for stratiform precipitation in the UK (Harrison et al, 2000), but variations in the general shape of the DSD may produce changes in the Z-R climatology. Without additional information on the shape of the DSD, it would be an additional source of discrepancy to choose a different Z-R relationship.…”

“…The radar usually scans at low elevation angles to obtain measurements close to the ground but echoes from nearby high elevation topography can be misinterpreted as heavy precipitation over that area (Cluckie and Rico-Ramirez, 2004). These echoes are called ground clutter and under standard beam propagation conditions their location is well defined and usually techniques such as a map of ground clutter are relatively successful in removing them (Harrison et al, 2000). However, occasionally the radar beam is bent towards the Earth's surface due to particular vertical temperature and humidity profiles, for example, when warm dry air overlays cooler more moist air (Collier, 1996).…”

Evaluation of the Plant–Craig stochastic convection scheme (v2.0) in the ensemble forecasting system MOGREPS-R (24 km) based on the Unified Model (v7.3)

“…A detailed validation was carried out against Nimrod radar rainfall data (Harrison et al, 2000;Smith et al, 2006). This observational data set is only available over the UK (as shown in Fig.…”

From Observations to Forecasts ‐ Part 13: The UK weather radar network – past, present and future

“…Figure 5 shows that the fractional error in hourly radar raingauge comparisons is typically a factor of two (Harrison et al, 2000). New radar technology being implemented over the next few years offers the hope of further progress (see below).…”