## 3 Results
### Influence of Measurement Strategies and Instrument Metrologies
An additional study comparing MRR with the Theis LPM found persistently higher RR for the Theis LPM, and a lower concentration of droplets with \(D\) < 2 mm in the Theis LPM [150]. This feature of a negative bias in the concentration of smaller droplets measured by the ground-based gradiometer relative to the MRR is also seen in the Norway data presented here (Figure 7). Comparison of 1 min RR and mean DSD conditionally sampled for three RR based on four years of data from the OTT Parsivel\({}^{2}\) disrometer, video disrometer and an impact disrometer operating at the US SGP site further illustrate the key importance of metrology in dictating the implied hydroclimate and, by association, LEE potential (Figure 16, Tables 2 and 3). The probability of precipitation computed using a RR threshold of 0 mmhr\({}^{-1}\) for all periods when all three disrdometers were operating show good closure between the 2D video disrdometers and the impact disrometer, and both show a higher \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Reference**} & \multirow{2}{*}{**Instruments Considered**} & \multicolumn{2}{c}{**Comparison of Accumulated**} & \multirow{2}{*}{**Comparison of DSD**} \\  & & **Precipitation (acc. PPT) or Rainfall** & & \\  & & **Rates (RR)** & & \\ \hline [PERSON] et al. [145] & PWS100, Theis LPM, & All underestimated of acc. PPT v & & \\  & Parsivel\({}^{1}\) & weighing rain gauge & & \\ \hline [PERSON] et al. [147] & Theis, Parsivel\({}^{1}\) & & & \\ \hline [PERSON] et al. [148] & Impact, 2 DVD, Parsivel\({}^{1}\) & Negative bias in acc PPT in Parsivel\({}^{1}\) & Differences in DSD and total number concentration (2 DVD and Parsivel\({}^{1}\)) \\ \hline [PERSON] et al. [149] & Theis LPM and Parsivel\({}^{2}\) & & & \\ \[PERSON] [PERSON] et al. [146] & Theis LPM and tipping & Large differences (18\%) in seasonal & \\  & & & acc PPT from 5 different Theis LPM & \\  & & bucket rain gauges & & \\  & & & \\  & & & \\  & & & \\  & & & \\ \hline [PERSON] et al. [43] & Theis LPM, 2 DVD & Theis LPM negative bias in RR & \\ \hline [PERSON] et al. [151] & 2 DVD, Parsivel\({}^{1}\) & RR consistently higher from Parsivel\({}^{1}\) & Parsivel\({}^{1}\) higher droplet counts, 2 DVD & higher conc. of \(D\) > 4 mm \\ \hline [PERSON] et al. [30] & 2 DVD, MRR & & MRR higher conc for \(D\) < 1 mm than \\  & & & ground-based gradiometers \\ \hline [PERSON] et al. [152] & Parsivel\({}^{1}\), MRR & Lower RR from MRR & MRR higher conc for \(D\) < 1 mm, Parsivel\({}^{1}\) & \\  & & & higher conc for \(D\) > 2 mm \\ \hline [PERSON] et al. [150] & Theis LPM, MRR & RR MAE = 3 mm/hr between instruments, MRR RR lower than & \\  & & Theis LPM & \\  & & & \\  & & & \\ \hline  & & RR higher from Parsivel\({}^{2}\) by 10\% v. & \\  & & 2 DVD and 37\% v. impact (0.1 mm/hr & \\  & & to define wet minute). Difference & Impact disrometer lower conc of \\  & & decreases with use of 1 mm/hr to & \\  & & define a wet minute, but increase for a & \\  & & threshold of 10 mm/hr & \\ \hline Current study: coastal & & & MRR higher conc than Parsivel\({}^{2}\) \\  & Norway & MRR, Parsivel\({}^{2}\) & & for \(D\) < 1 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of some previous closure experiments for different disrdometers, and new findings from the current analysis. precipitation frequency than the OTT Parsivel\({}^{2}\) (Table 2). This finding may be partly attributable to differences in the diameter range to which the disdrometers are sensitive. Specifically, as mentioned above, the smallest size channel (centered at a \(D\)\(\sim\)0.062 mm) from the OTT Parsivel\({}^{2}\) has zero reports of droplets and the second channel centered at \(D\)\(\sim\)0.187 mm has very few reported droplets. Thus, the OTT Parsivel\({}^{2}\) has a functional observational range beginning at \(D\)\(\sim\)0.22 mm which is above the smallest diameter reported by the video disdrometer, though not the impact disdrometer.