ALBERT

Beschreibung: ABSTRACT During 2009, the Met Office implemented a new surface observing system, the Meteorological Monitoring System (MMS). We report the results of a comparison of screen temperature as measured by MMS, and the Semi-Automatic Meteorological Observing System (SAMOS), the most widely used of the systems which MMS replaces. In each system, temperature was measured at 1-min resolution using 100 Ω platinum resistance thermometers. Comparison of MMS and SAMOS temperatures in separate Stevenson screens revealed acceptably small mean temperature differences (0.05 °C); however, MMS temperatures tended to be 0.3–0.5 °C higher than SAMOS temperatures during conditions of strong solar radiation, with extreme differences of up to 0.8 °C. Such differences were largely absent when MMS and SAMOS temperatures were measured from within the same screen, suggesting that differences in the immediate environment of each screen may have been responsible. However, even within the same screen, a diurnal cycle in the (SAMOS–MMS) temperature differences of amplitude (peak-to-peak) ∼0.04–0.06 °C was observed, which was likely due to the effects of low-angle solar radiation. Additional testing using a third, independent temperature unit revealed a slight temperature dependency in the SAMOS measurements; extrapolation of the results suggests differences of 0.2–0.3 °C between SAMOS and MMS temperatures at ambient temperatures 〉30 °C (MMS warmer). Overall, however, the differences between SAMOS and MMS temperatures were small, being well within World Meteorological Organization (WMO) accuracy limits for mean and extreme temperatures. The results therefore demonstrate that any step change in climatological temperature records associated with the introduction of MMS may be considered negligible.

Beschreibung: ABSTRACT We investigated which landscape and climate-related data (including information on hydrological source of flow) were statistically significant predictors of channel wetted width (WW) across a sizeable (2200 km 2 ) region of the UK. This was conducted specifically when flow was less than mean daily flow (MDF) and where channels are in a near natural state. Orthorectified air photos at 25 cm spatial resolution were used to measure WW, with the magnitude of the errors in these measurements quantified. We used flow information from local gauging stations to ensure that channels were below MDF for the days on which the air photos were captured. The root mean squared difference between the field and air photo measurements of WW ( n  = 28sites) was small (0.14 m) in comparison to median WW (3.07 m). We created points along sections of channels visible in air photos and used a terrain model to create drainage catchments for these points and computed their catchment area (CA). We selected a subset of points ( n  = 472) and measured their WW from air photos, and computed landscape-related data for each of their catchments (mean slope, mean annual rainfall, land cover type, elevation) and also mean BFIHOST, a quantitative index relating to hydrological source of flow. We used a linear mixed model to predict WW by including the landscape data (including CA 0.5 ) as fixed effects, plus a spatial covariance function estimated by residual maximum likelihood (REML) to determine unbiased estimates of the predictors. There was no evidence for retaining the spatial covariance function. With the exception of land cover, all the predictors were statistically significant and accounted for 76% of the variance of WW. When CA 0.5 alone was used as a predictor it captured 54% of the variance. The vast majority of this difference was due to inclusion of an interaction between CA and hydrological source of flow (BFIHOST). As catchment area increases, those channels with larger mean catchment BFIHOST values (greater proportion of baseflow contribution) have narrower WW by comparison to those with smaller mean BFIHOST for the same CA. Improved predictions of channel WW (based on our findings) could be used in channel restoration. This article is protected by copyright. All rights reserved.